wterl/c_src/wterl.c

/*
 * wterl: an Erlang NIF for WiredTiger
 *
 * Copyright (c) 2012-2013 Basho Technologies, Inc. All Rights Reserved.
 *
 * This file is provided to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 */
#include "erl_nif.h"
#include "erl_driver.h"

#include <stdio.h>
#include <string.h>
#include <errno.h>

#ifdef DEBUG
#include <stdio.h>
#include <stdarg.h>
#define dprint(s, ...) do {                                             \
    fprintf(stderr, s, ##__VA_ARGS__);                                  \
    fprintf(stderr, "\r\n");                                            \
    fflush(stderr);                                                     \
    } while(0);
#else
#  define dprint(s, ...) {}
#endif

#ifndef UNUSED
#define UNUSED(v) ((void)(v))
#endif

#include "wiredtiger.h"
#include "async_nif.h"
#include "khash.h"

#ifdef WTERL_STATS
#include "stats.h"
#endif

#if (ASYNC_NIF_MAX_WORKERS > 32768)
#error "WterlCtx cache won't work properly with > 32,768 workers."
#endif

static ErlNifResourceType *wterl_conn_RESOURCE;
static ErlNifResourceType *wterl_cursor_RESOURCE;

/* Generators for named, type-specific hash table functions. */
KHASH_MAP_INIT_STR(uri, unsigned int);  // URI -> number of cursors(URI)

    union {
        unsigned int hash[];
        struct {
            unsigned int:02 nest;  // cuckoo's nest choosen on hash collision
            unsigned int:15 off;   // bitpop((bmp & (1 << off) - 1) & bmp)
            unsigned int:10 depth;
        } nests;
    } cuckoo;


typedef struct {
    WT_SESSION *session;
    WT_CURSOR  *cursor;
} WterlCtx;

typedef struct {
    WT_CONNECTION *conn;
    const char *session_config;
    ErlNifMutex *contexts_mutex;
    unsigned int num_contexts;
    WterlCtx **contexts; // TODO: free this
} WterlConnHandle;

typedef struct {
    WT_CURSOR *cursor;
    WT_SESSION *session;
} WterlCursorHandle;

/* WiredTiger object names*/
typedef char Uri[128];

/* Atoms (initialized in on_load) */
static ERL_NIF_TERM ATOM_ERROR;
static ERL_NIF_TERM ATOM_OK;
static ERL_NIF_TERM ATOM_NOT_FOUND;
static ERL_NIF_TERM ATOM_FIRST;
static ERL_NIF_TERM ATOM_LAST;
static ERL_NIF_TERM ATOM_MESSAGE;
static ERL_NIF_TERM ATOM_PROGRESS;
static ERL_NIF_TERM ATOM_WTERL_VSN;
static ERL_NIF_TERM ATOM_WIREDTIGER_VSN;
static ERL_NIF_TERM ATOM_MSG_PID;

struct wterl_event_handlers {
    WT_EVENT_HANDLER handlers;
    ErlNifEnv *msg_env_error;
    ErlNifMutex *error_mutex;
    ErlNifEnv *msg_env_message;
    ErlNifMutex *message_mutex;
    ErlNifEnv *msg_env_progress;
    ErlNifMutex *progress_mutex;
    ErlNifPid to_pid;
};

/* Generators for 'conns' a named, type-specific hash table functions. */
KHASH_MAP_INIT_PTR(conns, WterlConnHandle*);

struct wterl_priv_data {
    void *async_nif_priv; // Note: must be first element in struct
    ErlNifMutex *conns_mutex;
    khash_t(conns) *conns;
    struct wterl_event_handlers eh;
    char wterl_vsn[512];
    char wiredtiger_vsn[512];
};

/* Global init for async_nif. */
ASYNC_NIF_INIT(wterl);


/**
 * Callback to handle error messages.
 *
 * Deliver error messages into Erlang to be logged via loger:error()
 * or on failure, write message to stderr.
 *
 * error    a WiredTiger, C99 or POSIX error code, which can
 *          be converted to a string using wiredtiger_strerror()
 * message  an error string
 * ->       0 on success, a non-zero return may cause the WiredTiger
 *          function posting the event to fail, and may even cause
 *          operation or library failure.
 */
int
__wterl_error_handler(WT_EVENT_HANDLER *handler, int error, const char *message)
{
    struct wterl_event_handlers *eh = (struct wterl_event_handlers *)handler;
    ErlNifEnv *msg_env;
    ErlNifPid *to_pid;
    int rc = 0;

    enif_mutex_lock(eh->error_mutex);
    msg_env = eh->msg_env_error;
    to_pid = &eh->to_pid;
    if (msg_env) {
        ERL_NIF_TERM msg =
            enif_make_tuple2(msg_env, ATOM_ERROR,
                 enif_make_tuple2(msg_env,
                      enif_make_atom(msg_env, erl_errno_id(error)),
                      enif_make_string(msg_env, message, ERL_NIF_LATIN1)));
        enif_clear_env(msg_env);
        if (!enif_send(NULL, to_pid, msg_env, msg))
           fprintf(stderr, "[%d] %s\n", error, message);
    } else {
        rc = (fprintf(stderr, "[%d] %s\n", error, message) >= 0 ? 0 : EIO);
    }
    enif_mutex_unlock(eh->error_mutex);
    return rc;
}

/**
 * Callback to handle informational messages.
 *
 * Deliver informational messages into Erlang to be logged via loger:info()
 * or on failure, write message to stdout.
 *
 * message  an informational string
 * ->       0 on success, a non-zero return may cause the WiredTiger
 *          function posting the event to fail, and may even cause
 *          operation or library failure.
 */
int
__wterl_message_handler(WT_EVENT_HANDLER *handler, const char *message)
{
    struct wterl_event_handlers *eh = (struct wterl_event_handlers *)handler;
    ErlNifEnv *msg_env;
    ErlNifPid *to_pid;
    int rc = 0;

    enif_mutex_lock(eh->message_mutex);
    msg_env = eh->msg_env_message;
    to_pid = &eh->to_pid;
    if (msg_env) {
        ERL_NIF_TERM msg =
            enif_make_tuple2(msg_env, ATOM_MESSAGE,
                 enif_make_string(msg_env, message, ERL_NIF_LATIN1));
        enif_clear_env(msg_env);
        if (!enif_send(NULL, to_pid, msg_env, msg))
            fprintf(stderr, "%s\n", message);
    } else {
        rc = (printf("%s\n", message) >= 0 ? 0 : EIO);
    }
    enif_mutex_unlock(eh->message_mutex);
    return rc;
}

/**
 * Callback to handle progress messages.
 *
 * Deliver progress messages into Erlang to be logged via loger:info()
 * or on failure, written message to stdout.
 *
 * operation    a string representation of the operation
 * counter      a progress counter [0..100]
 * ->       0 on success, a non-zero return may cause the WiredTiger
 *          function posting the event to fail, and may even cause
 *          operation or library failure.
 */
int
__wterl_progress_handler(WT_EVENT_HANDLER *handler, const char *operation, uint64_t counter)
{
    struct wterl_event_handlers *eh = (struct wterl_event_handlers *)handler;
    ErlNifEnv *msg_env;
    ErlNifPid *to_pid;
    int rc = 0;

    enif_mutex_lock(eh->progress_mutex);
    msg_env = eh->msg_env_progress;
    to_pid = &eh->to_pid;
    if (msg_env) {
        ERL_NIF_TERM msg =
            enif_make_tuple2(msg_env, ATOM_PROGRESS,
                 enif_make_tuple2(msg_env,
                      enif_make_string(msg_env, operation, ERL_NIF_LATIN1),
                      enif_make_int64(msg_env, counter)));
        enif_clear_env(msg_env);
        if (!enif_send(NULL, to_pid, msg_env, msg))
            fprintf(stderr, "[%ld] %s\n", counter, operation);
    } else {
        rc = (printf("[%ld] %s\n", counter, operation) >= 0 ? 0 : EIO);
    }
    enif_mutex_unlock(eh->progress_mutex);
    return rc;
}

/**
 * Open a WT_SESSION for the thread context 'ctx' to use, also init the
 * shared cursor hash table.
 *
 * Note: always call within enif_mutex_lock/unlock(conn_handle->contexts_mutex)
 */
static int
__init_session_and_cursor_cache(WterlConnHandle *conn_handle, WterlCtx *ctx)
{
    /* Create a context for this worker thread to reuse. */
    WT_CONNECTION *conn = conn_handle->conn;
    int rc = conn->open_session(conn, NULL, conn_handle->session_config, &ctx->session);
    if (rc != 0) {
        ctx->session = NULL;
        return rc;
    }

    ctx->cursors = kh_init(cursors);
    if (!ctx->cursors) {
        ctx->session->close(ctx->session, NULL);
        ctx->session = NULL;
        return ENOMEM;
    }

    return 0;
}

/**
 * Close all sessions and all cursors open on any objects.
 *
 * Note: always call within enif_mutex_lock/unlock(conn_handle->contexts_mutex)
 */
void
__close_all_sessions(WterlConnHandle *conn_handle)
{
    int i;

    for (i = 0; i < ASYNC_NIF_MAX_WORKERS; i++) {
        WterlCtx *ctx = &conn_handle->contexts[i];
        if (ctx->session != NULL) {
            WT_SESSION *session = ctx->session;
            khash_t(cursors) *h = ctx->cursors;
            khiter_t itr;
            for (itr = kh_begin(h); itr != kh_end(h); ++itr) {
                if (kh_exist(h, itr)) {
                    WT_CURSOR *cursor = kh_val(h, itr);
                    char *key = (char *)kh_key(h, itr);
                    cursor->close(cursor);
                    kh_del(cursors, h, itr);
                    enif_free(key);
                    kh_value(h, itr) = NULL;
                }
            }
            kh_destroy(cursors, h);
            session->close(session, NULL);
            ctx->session = NULL;
        }
    }
}

/**
 * Close cursors open on 'uri' object.
 *
 * Note: always call within enif_mutex_lock/unlock(conn_handle->contexts_mutex)
 */
void
__close_cursors_on(WterlConnHandle *conn_handle, const char *uri)
{
    int i;

    for (i = 0; i < ASYNC_NIF_MAX_WORKERS; i++) {
        WterlCtx *ctx = &conn_handle->contexts[i];
        if (ctx->session != NULL) {
            khash_t(cursors) *h = ctx->cursors;
            khiter_t itr = kh_get(cursors, h, (char *)uri);
            if (itr != kh_end(h)) {
                WT_CURSOR *cursor = kh_value(h, itr);
                char *key = (char *)kh_key(h, itr);
                cursor->close(cursor);
                kh_del(cursors, h, itr);
                enif_free(key);
                kh_value(h, itr) = NULL;
            }
        }
    }
}

/**
 * A string hash function.
 *
 * A basic hash function for strings of characters used during the
 * affinity association.
 *
 * s    a NULL terminated set of bytes to be hashed
 * ->   an integer hash encoding of the bytes
 */
static inline unsigned int
__str_hash_func(const char *s)
{
    unsigned int h = (unsigned int)*s;
    if (h) for (++s ; *s; ++s) h = (h << 5) - h + (unsigned int)*s;
    return h;
}

/**
 * Get a reusable cursor that was opened for a particular worker within its
 * session.
 */
static int
__retain_ctx(WterlConnHandle *conn_handle, const char *uri, WterlCtx **ctx)
{
    /* Check to see if we have a cursor open for this uri and if so reuse it. */
    WterlCtx *ctx = &conn_handle->contexts[worker_id];
    khash_t(cursors) *h = NULL;
    khiter_t itr;
    int rc;
    unsigned int h = __str_hash_func(uri); // TODO: add config at some point

    if (ctx->session == NULL) {
        enif_mutex_lock(conn_handle->contexts_mutex);
        rc = __init_session_and_cursor_cache(conn_handle, ctx);
        enif_mutex_unlock(conn_handle->contexts_mutex);
        if (rc != 0)
            return rc;
    }

    h = ctx->cursors;
    itr = kh_get(cursors, h, (char *)uri);
    if (itr != kh_end(h)) {
        // key exists in hash table, retrieve it
        *cursor = (WT_CURSOR*)kh_value(h, itr);
    } else {
        // key does not exist in hash table, create and insert one
        enif_mutex_lock(conn_handle->contexts_mutex);
        WT_SESSION *session = conn_handle->contexts[worker_id].session;
        rc = session->open_cursor(session, uri, NULL, "overwrite,raw", cursor);
        if (rc != 0) {
            enif_mutex_unlock(conn_handle->contexts_mutex);
            return rc;
        }

        char *key = enif_alloc(sizeof(Uri));
        if (!key) {
            session->close(session, NULL);
            enif_mutex_unlock(conn_handle->contexts_mutex);
            return ENOMEM;
        }
        memcpy(key, uri, 128);
        int itr_status;
        itr = kh_put(cursors, h, key, &itr_status);
        kh_value(h, itr) = *cursor;
        enif_mutex_unlock(conn_handle->contexts_mutex);
    }
    return 0;
}

static void
__release_ctx(WterlConnHandle *conn_handle, const char *uri, WterlCtx *ctx)
{
    UNUSED(conn_handle);
    UNUSED(worker_id);
    UNUSED(uri);
    cursor->reset(cursor);
}

/**
 * Convenience function to generate {error, {errno, Reason}} or 'not_found'
 * Erlang terms to return to callers.
 *
 * env    NIF environment
 * rc     code returned by WiredTiger
 */
static ERL_NIF_TERM
__strerror_term(ErlNifEnv* env, int rc)
{
    if (rc == WT_NOTFOUND) {
        return ATOM_NOT_FOUND;
    } else {
        /* We return the errno value as well as the message here because the
           error message provided by strerror() for differ across platforms
           and/or may be localized to any given language (i18n).  Use the errno
           atom rather than the message when matching in Erlang.  You've been
           warned. */
        return enif_make_tuple2(env, ATOM_ERROR,
                                enif_make_tuple2(env,
                                                 enif_make_atom(env, erl_errno_id(rc)),
                                                 enif_make_string(env, wiredtiger_strerror(rc), ERL_NIF_LATIN1)));
    }
}

/**
 * Opens a WiredTiger WT_CONNECTION object.
 *
 * argv[0]    path to directory for the database files
 * argv[1]    WiredTiger connection config string as an Erlang binary
 * argv[2]    WiredTiger session config string as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_conn_open,
  { // struct

    ERL_NIF_TERM config;
    ERL_NIF_TERM session_config;
    char homedir[4096];
    struct wterl_priv_data *priv;
  },
  { // pre

    if (!(argc == 3 &&
          (enif_get_string(env, argv[0], args->homedir, sizeof args->homedir, ERL_NIF_LATIN1) > 0) &&
          enif_is_binary(env, argv[1]) &&
          enif_is_binary(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->config = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[1]);
    args->session_config = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);

    args->priv = (struct wterl_priv_data *)enif_priv_data(env);
  },
  { // work

    WT_CONNECTION *conn;
    ErlNifBinary config;
    ErlNifBinary session_config;

    if (!enif_inspect_binary(env, args->config, &config)) {
        ASYNC_NIF_REPLY(enif_make_badarg(env));
        return;
    }
    if (!enif_inspect_binary(env, args->session_config, &session_config)) {
        ASYNC_NIF_REPLY(enif_make_badarg(env));
        return;
    }

    int rc = wiredtiger_open(args->homedir,
                             (WT_EVENT_HANDLER*)&args->priv->eh.handlers,
                             config.data[0] != 0 ? (const char*)config.data : NULL,
                             &conn);
    if (rc == 0) {
      WterlConnHandle *conn_handle = enif_alloc_resource(wterl_conn_RESOURCE, sizeof(WterlConnHandle));
      if (!conn_handle) {
          ASYNC_NIF_REPLY(__strerror_term(env, ENOMEM));
          return;
      }
      if (session_config.size > 1) {
          char *sc = enif_alloc(session_config.size);
          if (!sc) {
              enif_release_resource(conn_handle);
              ASYNC_NIF_REPLY(__strerror_term(env, ENOMEM));
              return;
          }
          memcpy(sc, session_config.data, session_config.size);

          conn_handle->session_config = (const char *)sc;
      } else {
          conn_handle->session_config = NULL;
      }
      conn_handle->contexts_mutex = enif_mutex_create(NULL);
      enif_mutex_lock(conn_handle->contexts_mutex);
      conn_handle->conn = conn;
      memset(conn_handle->contexts, 0, sizeof(WterlCtx) * ASYNC_NIF_MAX_WORKERS);
      ERL_NIF_TERM result = enif_make_resource(env, conn_handle);

      /* Keep track of open connections so as to free when unload/reload/etc.
         are called. */
      khash_t(conns) *h;
      enif_mutex_lock(args->priv->conns_mutex);
      h = args->priv->conns;
      int itr_status = 0;
      khiter_t itr = kh_put(conns, h, conn, &itr_status);
      if (itr_status != 0) // 0 indicates the key exists already
          kh_value(h, itr) = conn_handle;
      enif_mutex_unlock(args->priv->conns_mutex);

      enif_release_resource(conn_handle);
      enif_mutex_unlock(conn_handle->contexts_mutex);
      ASYNC_NIF_REPLY(enif_make_tuple2(env, ATOM_OK, result));
    }
    else
    {
      ASYNC_NIF_REPLY(__strerror_term(env, rc));
    }
  },
  { // post

  });

/**
 * Closes a WiredTiger WT_CONNECTION object.
 *
 * argv[0]    WterlConnHandle resource
 */
ASYNC_NIF_DECL(
  wterl_conn_close,
  { // struct

    WterlConnHandle* conn_handle;
    struct wterl_priv_data *priv;
  },
  { // pre

    if (!(argc == 1 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    enif_keep_resource((void*)args->conn_handle);

    args->priv = (struct wterl_priv_data *)enif_priv_data(env);
  },
  { // work

    /* Free up the shared sessions and cursors. */
    enif_mutex_lock(args->conn_handle->contexts_mutex);
    __close_all_sessions(args->conn_handle);
    if (args->conn_handle->session_config) {
        enif_free((char *)args->conn_handle->session_config);
        args->conn_handle->session_config = NULL;
    }
    WT_CONNECTION* conn = args->conn_handle->conn;
    int rc = conn->close(conn, NULL);

    /* Connection is closed, remove it so we don't free on unload/reload/etc. */
    khash_t(conns) *h;
    enif_mutex_lock(args->priv->conns_mutex);
    h = args->priv->conns;
    khiter_t itr;
    itr = kh_get(conns, h, conn);
    if (itr != kh_end(h)) {
        /* key exists in table (as expected) delete it */
        kh_del(conns, h, itr);
        kh_value(h, itr) = NULL;
    }
    enif_mutex_unlock(args->priv->conns_mutex);
    enif_mutex_unlock(args->conn_handle->contexts_mutex);
    enif_mutex_destroy(args->conn_handle->contexts_mutex);
    memset(args->conn_handle, 0, sizeof(WterlConnHandle));

    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });

/**
 * Create a WiredTiger table, column group, index or file.
 *
 * We create, use and discard a WT_SESSION here because table creation is not
 * too performance sensitive.
 *
 * argv[0]    WterlConnHandle resource
 * argv[1]    object name URI string
 * argv[2]    config string as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_create,
  { // struct

    WterlConnHandle *conn_handle;
    Uri uri;
    ERL_NIF_TERM config;
  },
  { // pre

    if (!(argc == 3 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle) &&
          (enif_get_string(env, argv[1], args->uri, sizeof args->uri, ERL_NIF_LATIN1) > 0) &&
          enif_is_binary(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->config = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
    enif_keep_resource((void*)args->conn_handle);
  },
  { // work

    ErlNifBinary config;
    if (!enif_inspect_binary(env, args->config, &config)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }

    /* We create, use and discard a WT_SESSION here because a) we don't need a
       cursor and b) we don't anticipate doing this operation frequently enough
       to impact performance. */
    WT_CONNECTION *conn = args->conn_handle->conn;
    WT_SESSION *session = NULL;
    int rc = conn->open_session(conn, NULL, args->conn_handle->session_config, &session);
    if (rc != 0) {
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }

    rc = session->create(session, args->uri, (const char*)config.data);
    (void)session->close(session, NULL);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });

/**
 * Drop (remove) a WiredTiger table, column group, index or file.
 *
 * argv[0]    WterlConnHandle resource
 * argv[1]    object name URI string
 * argv[2]    config string as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_drop,
  { // struct

    Uri uri;
    ERL_NIF_TERM config;
    WterlConnHandle *conn_handle;
  },
  { // pre

    if (!(argc == 3 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle) &&
          (enif_get_string(env, argv[1], args->uri, sizeof args->uri, ERL_NIF_LATIN1) > 0) &&
          enif_is_binary(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->config = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
    enif_keep_resource((void*)args->conn_handle);
  },
  { // work

    /* This call requires that there be no open cursors referencing the object. */
    enif_mutex_lock(args->conn_handle->contexts_mutex);
    __close_cursors_on(args->conn_handle, args->uri);

    ErlNifBinary config;
    if (!enif_inspect_binary(env, args->config, &config)) {
      enif_mutex_unlock(args->conn_handle->contexts_mutex);
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }

    /* We create, use and discard a WT_SESSION here because a) we don't need a
       cursor and b) we don't anticipate doing this operation frequently enough
       to impact performance. */
    WT_CONNECTION *conn = args->conn_handle->conn;
    WT_SESSION *session = NULL;
    int rc = conn->open_session(conn, NULL, args->conn_handle->session_config, &session);
    if (rc != 0) {
        enif_mutex_unlock(args->conn_handle->contexts_mutex);
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }
    /* Note: we locked the context mutex and called __close_cursors_on()
       earlier so that we are sure that before we call into WiredTiger we have
       first closed all open cursors referencing this object.  Failure to do
       this will result in EBUSY(16) "Device or resource busy". */
    rc = session->drop(session, args->uri, (const char*)config.data);
    (void)session->close(session, NULL);
    enif_mutex_unlock(args->conn_handle->contexts_mutex);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });

/**
 * Rename a WiredTiger table, column group, index or file.
 *
 * argv[0]    WterlConnHandle resource
 * argv[1]    old object name URI string
 * argv[2]    new object name URI string
 * argv[3]    config string as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_rename,
  { // struct

    Uri oldname;
    Uri newname;
    ERL_NIF_TERM config;
    WterlConnHandle *conn_handle;
  },
  { // pre

    if (!(argc == 4 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle) &&
          (enif_get_string(env, argv[1], args->oldname, sizeof args->oldname, ERL_NIF_LATIN1) > 0) &&
          (enif_get_string(env, argv[2], args->newname, sizeof args->newname, ERL_NIF_LATIN1) > 0) &&
          enif_is_binary(env, argv[3]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->config = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[3]);
    enif_keep_resource((void*)args->conn_handle);
  },
  { // work

    /* This call requires that there be no open cursors referencing the object. */
    enif_mutex_lock(args->conn_handle->contexts_mutex);
    __close_cursors_on(args->conn_handle, args->oldname);

    ErlNifBinary config;
    if (!enif_inspect_binary(env, args->config, &config)) {
      enif_mutex_unlock(args->conn_handle->contexts_mutex);
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }

    /* We create, use and discard a WT_SESSION here because a) we don't need a
       cursor and b) we don't anticipate doing this operation frequently enough
       to impact performance. */
    WT_CONNECTION *conn = args->conn_handle->conn;
    WT_SESSION *session = NULL;
    int rc = conn->open_session(conn, NULL, args->conn_handle->session_config, &session);
    if (rc != 0) {
      enif_mutex_unlock(args->conn_handle->contexts_mutex);
      ASYNC_NIF_REPLY(__strerror_term(env, rc));
      return;
    }

    /* Note: we locked the context mutex and called __close_cursors_on()
       earlier so that we are sure that before we call into WiredTiger we have
       first closed all open cursors referencing this object.  Failure to do
       this will result in EBUSY(16) "Device or resource busy". */
    rc = session->rename(session, args->oldname, args->newname, (const char*)config.data);
    (void)session->close(session, NULL);
    enif_mutex_unlock(args->conn_handle->contexts_mutex);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });


/**
 * Salvage rebuilds the file, or files of which a table is comprised,
 * discarding any corrupted file blocks.  Use this as a fallback if
 * an attempt to open a WiredTiger database object fails.
 *
 * argv[0]    WterlConnHandle resource
 * argv[1]    object name URI string
 * argv[2]    config string as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_salvage,
  { // struct

    WterlConnHandle *conn_handle;
    Uri uri;
    ERL_NIF_TERM config;
  },
  { // pre

    if (!(argc == 3 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle) &&
          (enif_get_string(env, argv[1], args->uri, sizeof args->uri, ERL_NIF_LATIN1) > 0) &&
          enif_is_binary(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->config = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
    enif_keep_resource((void*)args->conn_handle);
  },
  { // work

    /* This call requires that there be no open cursors referencing the object. */
    enif_mutex_lock(args->conn_handle->contexts_mutex);
    __close_cursors_on(args->conn_handle, args->uri);

    ErlNifBinary config;
    if (!enif_inspect_binary(env, args->config, &config)) {
      enif_mutex_unlock(args->conn_handle->contexts_mutex);
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }

    /* We create, use and discard a WT_SESSION here because a) we don't need a
       cursor and b) we don't anticipate doing this operation frequently enough
       to impact performance. */
    WT_CONNECTION *conn = args->conn_handle->conn;
    WT_SESSION *session = NULL;
    int rc = conn->open_session(conn, NULL, args->conn_handle->session_config, &session);
    if (rc != 0) {
      enif_mutex_unlock(args->conn_handle->contexts_mutex);
      ASYNC_NIF_REPLY(__strerror_term(env, rc));
      return;
    }

    rc = session->salvage(session, args->uri, (const char*)config.data);
    (void)session->close(session, NULL);
    enif_mutex_unlock(args->conn_handle->contexts_mutex);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });

/**
 * Checkpoint writes a transactionally consistent snapshot of a database or set
 * of objects specified.
 *
 * argv[0]    WterlConnHandle resource
 * argv[1]    config string as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_checkpoint,
  { // struct

    WterlConnHandle *conn_handle;
    ERL_NIF_TERM config;
  },
  { // pre

    if (!(argc == 2 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle) &&
          enif_is_binary(env, argv[1]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->config = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[1]);
    enif_keep_resource((void*)args->conn_handle);
  },
  { // work

    ErlNifBinary config;
    if (!enif_inspect_binary(env, args->config, &config)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }
    WT_CONNECTION *conn = args->conn_handle->conn;
    WT_SESSION *session = NULL;
    int rc = conn->open_session(conn, NULL, args->conn_handle->session_config, &session);
    if (rc != 0) {
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }
    rc = session->checkpoint(session, (const char*)config.data);
    (void)session->close(session, NULL);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });

/**
 * Truncate a file, table or cursor range.
 *
 * argv[0]    WterlConnHandle resource
 * argv[1]    object name URI string
 * argv[2]    start key as an Erlang binary
 * argv[3]    stop key as an Erlang binary
 * argv[4]    config string as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_truncate,
  { // struct

    WterlConnHandle *conn_handle;
    Uri uri;
    int from_first;
    int to_last;
    ERL_NIF_TERM start;
    ERL_NIF_TERM stop;
    ERL_NIF_TERM config;
  },
  { // pre

    if (!(argc == 5 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle) &&
          (enif_get_string(env, argv[1], args->uri, sizeof args->uri, ERL_NIF_LATIN1) > 0) &&
          enif_is_binary(env, argv[4]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    if (enif_is_binary(env, argv[2])) {
        args->from_first = 0;
        args->start = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
    } else if (enif_is_atom(env, argv[2])) { // TODO && argv[2] == ATOM_FIRST) {
        args->from_first = 1;
        args->start = 0;
    } else {
        ASYNC_NIF_RETURN_BADARG();
    }
    if (enif_is_binary(env, argv[3])) {
        args->to_last = 0;
        args->stop = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[3]);
    } else if (enif_is_atom(env, argv[3])) { // TODO && argv[3] == ATOM_LAST) {
        args->to_last = 1;
        args->stop = 0;
    } else {
        ASYNC_NIF_RETURN_BADARG();
    }
    args->config = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[4]);
    enif_keep_resource((void*)args->conn_handle);
    affinity = args->uri;
  },
  { // work

    /* This call requires that there be no open cursors referencing the object. */
    enif_mutex_lock(args->conn_handle->contexts_mutex);
    __close_cursors_on(args->conn_handle, args->uri);

    ErlNifBinary config;
    if (!enif_inspect_binary(env, args->config, &config)) {
      enif_mutex_unlock(args->conn_handle->contexts_mutex);
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }

    /* Note: we locked the context mutex and called __close_cursors_on()
       earlier so that we are sure that before we call into WiredTiger we have
       first closed all open cursors referencing this object.  Failure to do
       this will result in EBUSY(16) "Device or resource busy". */
    WT_CONNECTION *conn = args->conn_handle->conn;
    WT_SESSION *session = NULL;
    int rc = conn->open_session(conn, NULL, args->conn_handle->session_config, &session);
    if (rc != 0) {
        enif_mutex_unlock(args->conn_handle->contexts_mutex);
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }

    ErlNifBinary start_key;
    ErlNifBinary stop_key;
    WT_CURSOR *start = NULL;
    WT_CURSOR *stop = NULL;

    /* The truncate method should be passed either a URI or start/stop cursors,
       but not both.  So we simply open cursors no matter what to avoid the
       mess. */
    if (!args->from_first) {
        if (!enif_inspect_binary(env, args->start, &start_key)) {
            enif_mutex_unlock(args->conn_handle->contexts_mutex);
            ASYNC_NIF_REPLY(enif_make_badarg(env));
            return;
        }
    }
    rc = session->open_cursor(session, args->uri, NULL, "raw", &start);
    if (rc != 0) {
        session->close(session, NULL);
        enif_mutex_unlock(args->conn_handle->contexts_mutex);
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }
    /* Position the start cursor at the first record or the specified record. */
    if (args->from_first) {
        rc = start->next(start);
        if (rc != 0) {
            start->close(start);
            session->close(session, NULL);
            enif_mutex_unlock(args->conn_handle->contexts_mutex);
            ASYNC_NIF_REPLY(__strerror_term(env, rc));
            return;
        }
    } else {
        WT_ITEM item_start;
        item_start.data = start_key.data;
        item_start.size = start_key.size;
        start->set_key(start, item_start);
    }

    if (!args->to_last) {
        if (!enif_inspect_binary(env, args->stop, &stop_key)) {
            start->close(start);
            session->close(session, NULL);
            enif_mutex_unlock(args->conn_handle->contexts_mutex);
            ASYNC_NIF_REPLY(enif_make_badarg(env));
            return;
        }
    }
    rc = session->open_cursor(session, args->uri, NULL, "raw", &stop);
    if (rc != 0) {
        start->close(start);
        session->close(session, NULL);
        enif_mutex_unlock(args->conn_handle->contexts_mutex);
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }
    /* Position the stop cursor at the last record or the specified record. */
    if (args->to_last) {
        rc = stop->prev(stop);
        if (rc != 0) {
            start->close(start);
            stop->close(stop);
            session->close(session, NULL);
            enif_mutex_unlock(args->conn_handle->contexts_mutex);
            ASYNC_NIF_REPLY(__strerror_term(env, rc));
            return;
        }
    } else {
        WT_ITEM item_stop;
        item_stop.data = stop_key.data;
        item_stop.size = stop_key.size;
        stop->set_key(stop, item_stop);
    }

    /* Always pass NULL for URI here because we always specify the range with the
       start and stop cursors which were opened referencing that URI. */
    rc = session->truncate(session, NULL, start, stop, (const char*)config.data);

    start->close(start);
    stop->close(stop);
    session->close(session, NULL);
    enif_mutex_unlock(args->conn_handle->contexts_mutex);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });

/**
 * Upgrade upgrades a file or table, if upgrade is required.
 *
 * argv[0]    WterlConnHandle resource
 * argv[1]    object name URI string
 * argv[2]    config string as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_upgrade,
  { // struct

    WterlConnHandle *conn_handle;
    Uri uri;
    ERL_NIF_TERM config;
  },
  { // pre

    if (!(argc == 3 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle) &&
          (enif_get_string(env, argv[1], args->uri, sizeof args->uri, ERL_NIF_LATIN1) > 0) &&
          enif_is_binary(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->config = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
    enif_keep_resource((void*)args->conn_handle);
  },
  { // work

    /* This call requires that there be no open cursors referencing the object. */
    enif_mutex_lock(args->conn_handle->contexts_mutex);
    __close_cursors_on(args->conn_handle, args->uri);

    ErlNifBinary config;
    if (!enif_inspect_binary(env, args->config, &config)) {
      enif_mutex_unlock(args->conn_handle->contexts_mutex);
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }

    /* We create, use and discard a WT_SESSION here because a) we don't need a
       cursor and b) we don't anticipate doing this operation frequently enough
       to impact performance. */
    WT_CONNECTION *conn = args->conn_handle->conn;
    WT_SESSION *session = NULL;
    int rc = conn->open_session(conn, NULL, args->conn_handle->session_config, &session);
    if (rc != 0) {
        enif_mutex_unlock(args->conn_handle->contexts_mutex);
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }

    rc = session->upgrade(session, args->uri, (const char*)config.data);
    (void)session->close(session, NULL);
    enif_mutex_unlock(args->conn_handle->contexts_mutex);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });

/**
 * Verify reports if a file, or the files of which a table is comprised, have
 * been corrupted.
 *
 * argv[0]    WterlConnHandle resource
 * argv[1]    object name URI string
 * argv[2]    config string as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_verify,
  { // struct

    WterlConnHandle *conn_handle;
    Uri uri;
    ERL_NIF_TERM config;
  },
  { // pre

    if (!(argc == 3 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle) &&
          (enif_get_string(env, argv[1], args->uri, sizeof args->uri, ERL_NIF_LATIN1) > 0) &&
          enif_is_binary(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->config = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
    enif_keep_resource((void*)args->conn_handle);
  },
  { // work

    /* This call requires that there be no open cursors referencing the object. */
    enif_mutex_lock(args->conn_handle->contexts_mutex);
    __close_all_sessions(args->conn_handle);

    ErlNifBinary config;
    if (!enif_inspect_binary(env, args->config, &config)) {
      enif_mutex_unlock(args->conn_handle->contexts_mutex);
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }

    /* We create, use and discard a WT_SESSION here because a) we don't need a
       cursor and b) we don't anticipate doing this operation frequently enough
       to impact performance. */
    WT_CONNECTION *conn = args->conn_handle->conn;
    WT_SESSION *session = NULL;
    int rc = conn->open_session(conn, NULL, args->conn_handle->session_config, &session);
    if (rc != 0) {
        enif_mutex_unlock(args->conn_handle->contexts_mutex);
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }

    rc = session->verify(session, args->uri, (const char*)config.data);
    (void)session->close(session, NULL);
    enif_mutex_unlock(args->conn_handle->contexts_mutex);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });

/**
 * Delete a key's value from the specified table or index.
 *
 * argv[0]    WterlConnHandle resource
 * argv[1]    object name URI string
 * argv[2]    key as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_delete,
  { // struct

    WterlConnHandle *conn_handle;
    Uri uri;
    ERL_NIF_TERM key;
  },
  { // pre

    if (!(argc == 3 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle) &&
          (enif_get_string(env, argv[1], args->uri, sizeof args->uri, ERL_NIF_LATIN1) > 0) &&
          enif_is_binary(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->key = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
    enif_keep_resource((void*)args->conn_handle);
    affinity = args->uri;
  },
  { // work

    ErlNifBinary key;
    if (!enif_inspect_binary(env, args->key, &key)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }

    WterlCtx *ctx = NULL;
    WT_CURSOR *cursor = NULL;
    int rc = __retain_ctx(args->conn_handle, args->uri, &ctx);
    if (rc != 0) {
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }
    cursor = ctx->cursor;

    WT_ITEM item_key;
    item_key.data = key.data;
    item_key.size = key.size;
    cursor->set_key(cursor, &item_key);
    rc = cursor->remove(cursor);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
    __release_ctx(args->conn_handle, args->uri, cursor);
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });

/**
 * Get the value for the key's value from the specified table or index.
 *
 * argv[0]    WterlConnHandle resource
 * argv[1]    object name URI string
 * argv[2]    key as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_get,
  { // struct

    WterlConnHandle *conn_handle;
    Uri uri;
    ERL_NIF_TERM key;
  },
  { // pre

    if (!(argc == 3 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle) &&
          (enif_get_string(env, argv[1], args->uri, sizeof args->uri, ERL_NIF_LATIN1) > 0) &&
          enif_is_binary(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->key = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
    enif_keep_resource((void*)args->conn_handle);
    affinity = args->uri;
  },
  { // work

    ErlNifBinary key;
    if (!enif_inspect_binary(env, args->key, &key)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }

    WterlCtx *ctx = NULL
    WT_CURSOR *cursor = NULL;
    int rc = __retain_ctx(args->conn_handle, args->uri, &ctx);
    if (rc != 0) {
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }
    cursor = ctx->cursor;

    WT_ITEM item_key;
    WT_ITEM item_value;
    item_key.data = key.data;
    item_key.size = key.size;
    cursor->set_key(cursor, &item_key);
    rc = cursor->search(cursor);
    if (rc != 0) {
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }

    rc = cursor->get_value(cursor, &item_value);
    if (rc != 0) {
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }
    ERL_NIF_TERM value;
    unsigned char *bin = enif_make_new_binary(env, item_value.size, &value);
    memcpy(bin, item_value.data, item_value.size);
    ASYNC_NIF_REPLY(enif_make_tuple2(env, ATOM_OK, value));
    __release_ctx(args->conn_handle, args->uri, ctx);
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });

/**
 * Store a value for the key's value from the specified table or index.
 *
 * argv[0]    WterlConnHandle resource
 * argv[1]    object name URI string
 * argv[2]    key as an Erlang binary
 * argv[3]    value as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_put,
  { // struct

    WterlConnHandle *conn_handle;
    Uri uri;
    ERL_NIF_TERM key;
    ERL_NIF_TERM value;
  },
  { // pre

    if (!(argc == 4 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle) &&
          (enif_get_string(env, argv[1], args->uri, sizeof args->uri, ERL_NIF_LATIN1) > 0) &&
          enif_is_binary(env, argv[2]) &&
          enif_is_binary(env, argv[3]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->key = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
    args->value = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[3]);
    enif_keep_resource((void*)args->conn_handle);
    affinity = args->uri;
  },
  { // work

    ErlNifBinary key;
    ErlNifBinary value;
    if (!enif_inspect_binary(env, args->key, &key)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }
    if (!enif_inspect_binary(env, args->value, &value)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }

    WterlCtx *ctx = NULL;
    WT_CURSOR *cursor = NULL;
    int rc = __retain_ctx(args->conn_handle, args->uri, &ctx);
    if (rc != 0) {
        ASYNC_NIF_REPLY(__strerror_term(env, rc));
        return;
    }
    cursor = ctx->cursors;

    WT_ITEM item_key;
    WT_ITEM item_value;
    item_key.data = key.data;
    item_key.size = key.size;
    cursor->set_key(cursor, &item_key);
    item_value.data = value.data;
    item_value.size = value.size;
    cursor->set_value(cursor, &item_value);
    rc = cursor->insert(cursor);
    __release_ctx(args->conn_handle, args->uri, ctx);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });

/**
 * Open a cursor on a table or index.
 *
 * argv[0]    WterlConnHandle resource
 * argv[1]    object name URI string
 * argv[2]    config string as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_cursor_open,
  { // struct

    WterlConnHandle *conn_handle;
    Uri uri;
    ERL_NIF_TERM config;
  },
  { // pre

    if (!(argc == 3 &&
          enif_get_resource(env, argv[0], wterl_conn_RESOURCE, (void**)&args->conn_handle) &&
          (enif_get_string(env, argv[1], args->uri, sizeof args->uri, ERL_NIF_LATIN1) > 0) &&
          enif_is_binary(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->config = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
    enif_keep_resource((void*)args->conn_handle);
    affinity = args->uri;
  },
  { // work

    ErlNifBinary config;
    if (!enif_inspect_binary(env, args->config, &config)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }

    /* We create a separate session here to ensure that operations are thread safe. */
    WT_CONNECTION *conn = args->conn_handle->conn;
    WT_SESSION *session = NULL;
    int rc = conn->open_session(conn, NULL, args->conn_handle->session_config, &session);
    if (rc != 0) {
      ASYNC_NIF_REPLY(__strerror_term(env, rc));
      return;
    }

    WT_CURSOR* cursor;
    rc = session->open_cursor(session, args->uri, NULL, (config.data[0] != 0) ? (char *)config.data : "overwrite,raw", &cursor);
    if (rc != 0) {
      session->close(session, NULL);
      ASYNC_NIF_REPLY(__strerror_term(env, rc));
      return;
    }

    WterlCursorHandle* cursor_handle = enif_alloc_resource(wterl_cursor_RESOURCE, sizeof(WterlCursorHandle));
    if (!cursor_handle) {
      cursor->close(cursor);
      session->close(session, NULL);
      ASYNC_NIF_REPLY(__strerror_term(env, ENOMEM));
      return;
    }
    cursor_handle->session = session;
    cursor_handle->cursor = cursor;
    ERL_NIF_TERM result = enif_make_resource(env, cursor_handle);
    enif_release_resource(cursor_handle);
    ASYNC_NIF_REPLY(enif_make_tuple2(env, ATOM_OK, result));
  },
  { // post

    enif_release_resource((void*)args->conn_handle);
  });

/**
 * Close a cursor releasing resources it held.
 *
 * argv[0]    WterlCursorHandle resource
 */
ASYNC_NIF_DECL(
  wterl_cursor_close,
  { // struct

    WterlCursorHandle *cursor_handle;
  },
  { // pre

    if (!(argc == 1 &&
          enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    /* Note: session->close() will cause all open cursors in the session to be
       closed first, so we don't have explicitly to do that here.

       WT_CURSOR *cursor = args->cursor_handle->cursor;
       rc = cursor->close(cursor);
     */
    WT_SESSION *session = args->cursor_handle->session;
    int rc = session->close(session, NULL);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });

static ERL_NIF_TERM
__cursor_key_ret(ErlNifEnv *env, WT_CURSOR *cursor, int rc)
{
    if (rc == 0) {
        WT_ITEM item_key;
        rc = cursor->get_key(cursor, &item_key);
        if (rc == 0) {
            ERL_NIF_TERM key;
            memcpy(enif_make_new_binary(env, item_key.size, &key), item_key.data, item_key.size);
            return enif_make_tuple2(env, ATOM_OK, key);
        }
    }
    return __strerror_term(env, rc);
}

static ERL_NIF_TERM
__cursor_kv_ret(ErlNifEnv *env, WT_CURSOR *cursor, int rc)
{
    if (rc == 0) {
        WT_ITEM item_key, item_value;
        rc = cursor->get_key(cursor, &item_key);
        if (rc == 0) {
            rc = cursor->get_value(cursor, &item_value);
            if (rc == 0) {
                ERL_NIF_TERM key, value;
                memcpy(enif_make_new_binary(env, item_key.size, &key), item_key.data, item_key.size);
                memcpy(enif_make_new_binary(env, item_value.size, &value), item_value.data, item_value.size);
                return enif_make_tuple3(env, ATOM_OK, key, value);
            }
        }
    }
    return __strerror_term(env, rc);
}

static ERL_NIF_TERM
__cursor_value_ret(ErlNifEnv* env, WT_CURSOR *cursor, int rc)
{
    if (rc == 0) {
        WT_ITEM item_value;
        rc = cursor->get_value(cursor, &item_value);
        if (rc == 0) {
            ERL_NIF_TERM value;
            memcpy(enif_make_new_binary(env, item_value.size, &value), item_value.data, item_value.size);
            return enif_make_tuple2(env, ATOM_OK, value);
        }
    }
    return __strerror_term(env, rc);
}

/**
 * Use a cursor to fetch the next key/value pair from the table or index.
 *
 * argv[0]    WterlCursorHandle resource
 */
ASYNC_NIF_DECL(
  wterl_cursor_next,
  { // struct

    WterlCursorHandle *cursor_handle;
  },
  { // pre

    if (!(argc == 1 &&
          enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    WT_CURSOR* cursor = args->cursor_handle->cursor;
    ASYNC_NIF_REPLY(__cursor_kv_ret(env, cursor, cursor->next(cursor)));
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });

/**
 * Use a cursor to fetch the next key from the table or index.
 *
 * argv[0]    WterlCursorHandle resource
 */
ASYNC_NIF_DECL(
  wterl_cursor_next_key,
  { // struct

    WterlCursorHandle *cursor_handle;
  },
  { // pre

    if (!(enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    WT_CURSOR* cursor = args->cursor_handle->cursor;
    ASYNC_NIF_REPLY(__cursor_key_ret(env, cursor, cursor->next(cursor)));
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });

/**
 * Use a cursor to fetch the next value from the table or index.
 *
 * argv[0]    WterlCursorHandle resource
 */
ASYNC_NIF_DECL(
  wterl_cursor_next_value,
  { // struct

    WterlCursorHandle *cursor_handle;
  },
  { // pre

    if (!(argc == 1 &&
          enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    WT_CURSOR* cursor = args->cursor_handle->cursor;
    ASYNC_NIF_REPLY(__cursor_value_ret(env, cursor, cursor->next(cursor)));
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });

/**
 * Use a cursor to fetch the previous key/value pair from the table or index.
 *
 * argv[0]    WterlCursorHandle resource
 */
ASYNC_NIF_DECL(
  wterl_cursor_prev,
  { // struct

    WterlCursorHandle *cursor_handle;
  },
  { // pre

    if (!(argc == 1 &&
          enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    WT_CURSOR* cursor = args->cursor_handle->cursor;
    ASYNC_NIF_REPLY(__cursor_kv_ret(env, cursor, cursor->prev(cursor)));
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });

/**
 * Use a cursor to fetch the previous key from the table or index.
 *
 * argv[0]    WterlCursorHandle resource
 */
ASYNC_NIF_DECL(
  wterl_cursor_prev_key,
  { // struct

    WterlCursorHandle *cursor_handle;
  },
  { // pre

    if (!(argc == 1 &&
          enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    WT_CURSOR* cursor = args->cursor_handle->cursor;
    ASYNC_NIF_REPLY(__cursor_key_ret(env, cursor, cursor->prev(cursor)));
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });

/**
 * Use a cursor to fetch the previous value from the table or index.
 *
 * argv[0]    WterlCursorHandle resource
 */
ASYNC_NIF_DECL(
  wterl_cursor_prev_value,
  { // struct

    WterlCursorHandle *cursor_handle;
  },
  { // pre

    if (!(argc == 1 &&
          enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    WT_CURSOR* cursor = args->cursor_handle->cursor;
    ASYNC_NIF_REPLY(__cursor_value_ret(env, cursor, cursor->prev(cursor)));
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });

/**
 * Position the cursor at the record matching the key.
 *
 * argv[0]    WterlCursorHandle resource
 * argv[1]    key as an Erlang binary
 * argv[2]    boolean, when false the cursor will be reset
 */
ASYNC_NIF_DECL(
  wterl_cursor_search,
  { // struct

    WterlCursorHandle *cursor_handle;
    ERL_NIF_TERM key;
    int scanning;
  },
  { // pre

    static ERL_NIF_TERM ATOM_TRUE = 0;
    if (ATOM_TRUE == 0)
        enif_make_atom(env, "true");

    if (!(argc == 3 &&
          enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle) &&
          enif_is_binary(env, argv[1]) &&
          enif_is_atom(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->key = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[1]);
    args->scanning = (enif_is_identical(argv[2], ATOM_TRUE)) ? 1 : 0;
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    WT_CURSOR* cursor = args->cursor_handle->cursor;
    ErlNifBinary key;
    if (!enif_inspect_binary(env, args->key, &key)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }

    WT_ITEM item_key;
    item_key.data = key.data;
    item_key.size = key.size;
    cursor->set_key(cursor, &item_key);

    ERL_NIF_TERM reply = __cursor_value_ret(env, cursor, cursor->search(cursor));
    if (!args->scanning)
      (void)cursor->reset(cursor);
    ASYNC_NIF_REPLY(reply);
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });

/**
 * Position the cursor at the record matching the key if it exists, or a record
 * that would be adjacent.
 *
 * argv[0]    WterlCursorHandle resource
 * argv[1]    key as an Erlang binary
 * argv[2]    boolean, when false the cursor will be reset
 */
ASYNC_NIF_DECL(
  wterl_cursor_search_near,
  { // struct

    WterlCursorHandle *cursor_handle;
    ERL_NIF_TERM key;
    int scanning;
  },
  { // pre

    static ERL_NIF_TERM ATOM_TRUE = 0;
    if (ATOM_TRUE == 0)
        enif_make_atom(env, "true");

    if (!(argc == 3 &&
          enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle) &&
          enif_is_binary(env, argv[1]) &&
          enif_is_atom(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->key = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[1]);
    args->scanning = (enif_is_identical(argv[2], ATOM_TRUE)) ? 1 : 0;
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    WT_CURSOR* cursor = args->cursor_handle->cursor;
    ErlNifBinary key;
    if (!enif_inspect_binary(env, args->key, &key)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }
    WT_ITEM item_key;
    int exact = 0;

    item_key.data = key.data;
    item_key.size = key.size;
    cursor->set_key(cursor, &item_key);

    int rc = cursor->search_near(cursor, &exact);
    if (rc != 0) {
      (void)cursor->reset(cursor);
      ASYNC_NIF_REPLY(__strerror_term(env, rc));
      return;
    }

    if (!args->scanning)
        (void)cursor->reset(cursor);

    if (exact == 0) {
      /* an exact match */
      ASYNC_NIF_REPLY(enif_make_tuple2(env, ATOM_OK, enif_make_atom(env, "match")));
    } else if (exact < 0) {
      /* cursor now positioned at the next smaller key */
      ASYNC_NIF_REPLY(enif_make_tuple2(env, ATOM_OK, enif_make_atom(env, "lt")));
    } else if (exact > 0) {
      /* cursor now positioned at the next larger key */
      ASYNC_NIF_REPLY(enif_make_tuple2(env, ATOM_OK, enif_make_atom(env, "gt")));
    }
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });

/**
 * Reset the position of the cursor.
 *
 * Any resources held by the cursor are released, and the cursor's key and
 * position are no longer valid. A subsequent iteration with wterl_cursor_next
 * will move to the first record, or with wterl_cursor_prev will move to the
 * last record.
 *
 * argv[0]    WterlCursorHandle resource
 */
ASYNC_NIF_DECL(
  wterl_cursor_reset,
  { // struct

    WterlCursorHandle *cursor_handle;
  },
  { // pre

    if (!(argc == 1 &&
          enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    WT_CURSOR* cursor = args->cursor_handle->cursor;
    int rc = cursor->reset(cursor);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });

/**
 * Insert, or overwrite, a record using a cursor.
 *
 * argv[0]    WterlCursorHandle resource
 * argv[1]    key as an Erlang binary
 * argv[2]    value as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_cursor_insert,
  { // struct

    WterlCursorHandle *cursor_handle;
    ERL_NIF_TERM key;
    ERL_NIF_TERM value;
    int rc;
  },
  { // pre

    if (!(argc == 3 &&
          enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle) &&
          enif_is_binary(env, argv[1]) &&
          enif_is_binary(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->key = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[1]);
    args->value = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    WT_CURSOR* cursor = args->cursor_handle->cursor;
    ErlNifBinary key;
    ErlNifBinary value;
    if (!enif_inspect_binary(env, args->key, &key)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }
    if (!enif_inspect_binary(env, args->value, &value)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }
    WT_ITEM item_key;
    WT_ITEM item_value;

    item_key.data = key.data;
    item_key.size = key.size;
    cursor->set_key(cursor, &item_key);
    item_value.data = value.data;
    item_value.size = value.size;
    cursor->set_value(cursor, &item_value);
    int rc = cursor->insert(cursor);
    if (rc == 0)
        rc = cursor->reset(cursor);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });

/**
 * Update an existing record using a cursor.
 *
 * argv[0]    WterlCursorHandle resource
 * argv[1]    key as an Erlang binary
 * argv[2]    value as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_cursor_update,
  { // struct

    WterlCursorHandle *cursor_handle;
    ERL_NIF_TERM key;
    ERL_NIF_TERM value;
    int rc;
  },
  { // pre

    if (!(argc == 3 &&
          enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle) &&
          enif_is_binary(env, argv[1]) &&
          enif_is_binary(env, argv[2]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->key = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[1]);
    args->value = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[2]);
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    WT_CURSOR* cursor = args->cursor_handle->cursor;
    ErlNifBinary key;
    ErlNifBinary value;
    if (!enif_inspect_binary(env, args->key, &key)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }
    if (!enif_inspect_binary(env, args->value, &value)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }
    WT_ITEM item_key;
    WT_ITEM item_value;

    item_key.data = key.data;
    item_key.size = key.size;
    cursor->set_key(cursor, &item_key);
    item_value.data = value.data;
    item_value.size = value.size;
    cursor->set_value(cursor, &item_value);
    int rc = cursor->update(cursor);
    if (rc == 0)
        rc = cursor->reset(cursor);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });

/**
 * Remove a record using a cursor.
 *
 * argv[0]    WterlCursorHandle resource
 * argv[1]    key as an Erlang binary
 */
ASYNC_NIF_DECL(
  wterl_cursor_remove,
  { // struct

    WterlCursorHandle *cursor_handle;
    ERL_NIF_TERM key;
    int rc;
  },
  { // pre

    if (!(argc == 2 &&
          enif_get_resource(env, argv[0], wterl_cursor_RESOURCE, (void**)&args->cursor_handle) &&
          enif_is_binary(env, argv[1]))) {
      ASYNC_NIF_RETURN_BADARG();
    }
    args->key = enif_make_copy(ASYNC_NIF_WORK_ENV, argv[1]);
    enif_keep_resource((void*)args->cursor_handle);
  },
  { // work

    WT_CURSOR* cursor = args->cursor_handle->cursor;
    ErlNifBinary key;
    if (!enif_inspect_binary(env, args->key, &key)) {
      ASYNC_NIF_REPLY(enif_make_badarg(env));
      return;
    }
    WT_ITEM item_key;

    item_key.data = key.data;
    item_key.size = key.size;
    cursor->set_key(cursor, &item_key);
    int rc = cursor->remove(cursor);
    if (rc == 0)
        rc = cursor->reset(cursor);
    ASYNC_NIF_REPLY(rc == 0 ? ATOM_OK : __strerror_term(env, rc));
  },
  { // post

    enif_release_resource((void*)args->cursor_handle);
  });


/**
 * Called by wterl_event_handler to set the pid for message delivery.
 */
static ERL_NIF_TERM
wterl_set_event_handler_pid(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
{
  struct wterl_priv_data *priv = enif_priv_data(env);
  struct wterl_event_handlers *eh = &priv->eh;

  if (!(argc == 1 && enif_is_pid(env, argv[0]))) {
      return enif_make_badarg(env);
  }
  if (enif_get_local_pid(env, argv[0], &eh->to_pid)) {
    if (!eh->msg_env_message)
      eh->msg_env_message = enif_alloc_env(); // TOOD: if (!eh->msg_env) { return ENOMEM; }
    if (!eh->msg_env_error)
      eh->msg_env_error = enif_alloc_env();
    if (!eh->msg_env_progress)
      eh->msg_env_progress = enif_alloc_env();

    eh->handlers.handle_error = __wterl_error_handler;
    eh->handlers.handle_message = __wterl_message_handler;
    eh->handlers.handle_progress = __wterl_progress_handler;
  } else {
    memset(&eh->to_pid, 0, sizeof(ErlNifPid));
  }
  return ATOM_OK;
}


/**
 * Called as this driver is loaded by the Erlang BEAM runtime triggered by the
 * module's on_load directive.
 *
 * env        the NIF environment
 * priv_data  used to hold the state for this NIF rather than global variables
 * load_info  an Erlang term, in this case a list with two two-tuples of the
 *            form: [{wterl, ""}, {wiredtiger, ""}] where the strings contain
 *            the git hash of the last commit for this code.  This is used
 *            to determin if a rolling upgrade is possible or not.
 */
static int
on_load(ErlNifEnv *env, void **priv_data, ERL_NIF_TERM load_info)
{
    int arity;
    ERL_NIF_TERM head, tail;
    const ERL_NIF_TERM* option;
    ErlNifResourceFlags flags = ERL_NIF_RT_CREATE | ERL_NIF_RT_TAKEOVER;
    wterl_conn_RESOURCE = enif_open_resource_type(env, NULL, "wterl_conn_resource",
                                                  NULL, flags, NULL);
    wterl_cursor_RESOURCE = enif_open_resource_type(env, NULL, "wterl_cursor_resource",
                                                    NULL, flags, NULL);

    ATOM_ERROR = enif_make_atom(env, "error");
    ATOM_OK = enif_make_atom(env, "ok");
    ATOM_NOT_FOUND = enif_make_atom(env, "not_found");
    ATOM_FIRST = enif_make_atom(env, "first");
    ATOM_LAST = enif_make_atom(env, "last");
    ATOM_MESSAGE = enif_make_atom(env, "message");
    ATOM_PROGRESS = enif_make_atom(env, "progress");
    ATOM_WTERL_VSN = enif_make_atom(env, "wterl_vsn");
    ATOM_WIREDTIGER_VSN = enif_make_atom(env, "wiredtiger_vsn");
    ATOM_MSG_PID = enif_make_atom(env, "message_pid");

    struct wterl_priv_data *priv = enif_alloc(sizeof(struct wterl_priv_data));
    if (!priv)
        return ENOMEM;
    memset(priv, 0, sizeof(struct wterl_priv_data));

    priv->conns_mutex = enif_mutex_create(NULL);
    priv->conns = kh_init(conns);
    if (!priv->conns) {
        enif_mutex_destroy(priv->conns_mutex);
        enif_free(priv);
        return ENOMEM;
    }

    struct wterl_event_handlers *eh = &priv->eh;
    eh->error_mutex = enif_mutex_create(NULL);
    eh->message_mutex = enif_mutex_create(NULL);
    eh->progress_mutex = enif_mutex_create(NULL);

    /* Process the load_info array of tuples, we expect:
       [{wterl_vsn, "a version string"},
        {wiredtiger_vsn, "a version string"}]. */
    while (enif_get_list_cell(env, load_info, &head, &tail)) {
      if (enif_get_tuple(env, head, &arity, &option)) {
        if (arity == 2) {
          if (enif_is_identical(option[0], ATOM_WTERL_VSN)) {
            enif_get_string(env, option[1], priv->wterl_vsn, sizeof(priv->wterl_vsn), ERL_NIF_LATIN1);
          } else if (enif_is_identical(option[0], ATOM_WIREDTIGER_VSN)) {
            enif_get_string(env, option[1], priv->wiredtiger_vsn, sizeof(priv->wiredtiger_vsn), ERL_NIF_LATIN1);
          }
        }
      }
      load_info = tail;
    }

    /* Note: !!! the first element of our priv_data struct *must* be the
       pointer to the async_nif's private data which we set here. */
    ASYNC_NIF_LOAD(wterl, priv->async_nif_priv);
    if (!priv->async_nif_priv) {
        kh_destroy(conns, priv->conns);
        enif_mutex_destroy(priv->conns_mutex);
        enif_free(priv);
        return ENOMEM;
    }
    *priv_data = priv;

    char msg[1024];
    snprintf(msg, 1024, "NIF on_load complete (wterl version: %s, wiredtiger version: %s)", priv->wterl_vsn, priv->wiredtiger_vsn);
    __wterl_message_handler((WT_EVENT_HANDLER *)&priv->eh, msg);
    return 0;
}

static int
on_reload(ErlNifEnv *env, void **priv_data, ERL_NIF_TERM load_info)
{
    UNUSED(env);
    UNUSED(priv_data);
    UNUSED(load_info);
    return 0; // TODO: implement
}

static void
on_unload(ErlNifEnv *env, void *priv_data)
{
    unsigned int i;
    struct wterl_priv_data *priv = (struct wterl_priv_data *)priv_data;
    khash_t(conns) *h;
    khiter_t itr_conns;
    WterlConnHandle *conn_handle;

    enif_mutex_lock(priv->conns_mutex);
    h = priv->conns;

    for (itr_conns = kh_begin(h); itr_conns != kh_end(h); ++itr_conns) {
      if (kh_exist(h, itr_conns)) {
        conn_handle = kh_val(h, itr_conns);
        if (conn_handle) {
          enif_mutex_lock(conn_handle->contexts_mutex);
          enif_free((void*)conn_handle->session_config);
          for (i = 0; i < ASYNC_NIF_MAX_WORKERS; i++) {
            WterlCtx *ctx = &conn_handle->contexts[i];
            if (ctx->session != NULL) {
              WT_SESSION *session = ctx->session;
              khash_t(cursors) *h = ctx->cursors;
              khiter_t itr_cursors;
              for (itr_cursors = kh_begin(h); itr_cursors != kh_end(h); ++itr_cursors) {
                if (kh_exist(h, itr_cursors)) {
                  WT_CURSOR *cursor = kh_val(h, itr_cursors);
                  char *key = (char *)kh_key(h, itr_cursors);
                  cursor->close(cursor);
                  kh_del(cursors, h, itr_cursors);
                  enif_free(key);
                  kh_value(h, itr_cursors) = NULL;
                }
              }
              kh_destroy(cursors, h);
              session->close(session, NULL);
            }
          }
        }

        /* This would have closed all cursors and sessions for us
           but we do that explicitly above. */
        conn_handle->conn->close(conn_handle->conn, NULL);
      }
    }

    /* Continue to hold the context mutex while unloading the async_nif
       to prevent new work from coming in while shutting down. */
    ASYNC_NIF_UNLOAD(wterl, env, priv->async_nif_priv);

    for (itr_conns = kh_begin(h); itr_conns != kh_end(h); ++itr_conns) {
      if (kh_exist(h, itr_conns)) {
        conn_handle = kh_val(h, itr_conns);
        if (conn_handle) {
          enif_mutex_unlock(conn_handle->contexts_mutex);
          enif_mutex_destroy(conn_handle->contexts_mutex);
        }
      }
    }

    /* At this point all WiredTiger state and threads are free'd/stopped so there
       is no chance that the event handler functions will be called so we can
       be sure that there won't be a race on eh.msg_env in the callback functions. */
    struct wterl_event_handlers *eh = &priv->eh;
    enif_mutex_destroy(eh->error_mutex);
    enif_mutex_destroy(eh->message_mutex);
    enif_mutex_destroy(eh->progress_mutex);
    if (eh->msg_env_message)
        enif_free_env(eh->msg_env_message);
    if (eh->msg_env_error)
        enif_free_env(eh->msg_env_error);
    if (eh->msg_env_progress)
        enif_free_env(eh->msg_env_progress);

    kh_destroy(conns, h);
    enif_mutex_unlock(priv->conns_mutex);
    enif_mutex_destroy(priv->conns_mutex);
    enif_free(priv);
}

static int
on_upgrade(ErlNifEnv *env, void **priv_data, void **old_priv_data, ERL_NIF_TERM load_info)
{
    UNUSED(priv_data);
    UNUSED(old_priv_data);
    UNUSED(load_info);
    ASYNC_NIF_UPGRADE(wterl, env); // TODO: implement
    return 0;
}

static ErlNifFunc nif_funcs[] =
{
    {"checkpoint_nif", 3, wterl_checkpoint},
    {"conn_close_nif", 2, wterl_conn_close},
    {"conn_open_nif", 4, wterl_conn_open},
    {"create_nif", 4, wterl_create},
    {"delete_nif", 4, wterl_delete},
    {"drop_nif", 4, wterl_drop},
    {"get_nif", 4, wterl_get},
    {"put_nif", 5, wterl_put},
    {"rename_nif", 5, wterl_rename},
    {"salvage_nif", 4, wterl_salvage},
    // TODO: {"txn_begin", 3, wterl_txn_begin},
    // TODO: {"txn_commit", 3, wterl_txn_commit},
    // TODO: {"txn_abort", 3, wterl_txn_abort},
    {"truncate_nif", 6, wterl_truncate},
    {"upgrade_nif", 4, wterl_upgrade},
    {"verify_nif", 4, wterl_verify},
    // TODO: {"cursor_get_key_nif", 2, wterl_cursor_get_key},
    // TODO: {"cursor_get_value_nif", 2, wterl_cursor_get_value},
    // TODO: {"cursor_get_nif", 2, wterl_cursor_get},
    // TODO: {"cursor_set_key_nif", 2, wterl_cursor_set_key},
    // TODO: {"cursor_set_value_nif", 2, wterl_cursor_set_value},
    // TODO: {"cursor_set_nif", 2, wterl_cursor_set},
    {"cursor_close_nif", 2, wterl_cursor_close},
    {"cursor_insert_nif", 4, wterl_cursor_insert},
    {"cursor_next_key_nif", 2, wterl_cursor_next_key},
    {"cursor_next_nif", 2, wterl_cursor_next},
    {"cursor_next_value_nif", 2, wterl_cursor_next_value},
    {"cursor_open_nif", 4, wterl_cursor_open},
    {"cursor_prev_key_nif", 2, wterl_cursor_prev_key},
    {"cursor_prev_nif", 2, wterl_cursor_prev},
    {"cursor_prev_value_nif", 2, wterl_cursor_prev_value},
    {"cursor_remove_nif", 3, wterl_cursor_remove},
    {"cursor_reset_nif", 2, wterl_cursor_reset},
    {"cursor_search_near_nif", 4, wterl_cursor_search_near},
    {"cursor_search_nif", 4, wterl_cursor_search},
    {"cursor_update_nif", 4, wterl_cursor_update},
    {"set_event_handler_pid", 1, wterl_set_event_handler_pid},
};

ERL_NIF_INIT(wterl, nif_funcs, &on_load, &on_reload, &on_upgrade, &on_unload);