expose nextAvailableLSN for lsn-free pages

src/stasis/logger/inMemoryLog.c

@@ -2,6 +2,9 @@
 #include <stasis/latches.h>
 #include <string.h>
 #include <assert.h>
+/**
+   @todo remove static fields from inMemoryLog
+*/
 static rwl * flushedLSN_lock;
 static lsn_t nextAvailableLSN;
 static lsn_t globalOffset;
@@ -9,6 +12,15 @@ static rwl * globalOffset_lock;
 static LogEntry ** buffer;
 static lsn_t bufferLen;
 
+static lsn_t nextAvailableLSN_InMemoryLog(stasis_log_t * log) {
+  writelock(flushedLSN_lock,0);
+  writelock(globalOffset_lock,0);
+  lsn_t ret = nextAvailableLSN;
+  unlock(globalOffset_lock);
+  unlock(flushedLSN_lock);
+  return ret;
+}
+
 static int writeLogEntry_InMemoryLog(stasis_log_t * log, LogEntry *e) {
   writelock(flushedLSN_lock, 0);
   lsn_t bufferOffset;
@@ -136,6 +148,7 @@ stasis_log_t* open_InMemoryLog() {
     readLSNEntry_InMemoryLog, // read_entry
     nextEntry_InMemoryLog,// next_entry
     flushedLSN_InMemoryLog, // first_unstable_lsn
+    nextAvailableLSN_InMemoryLog, // next_available_lsn
     syncLog_InMemoryLog, // force_tail
     truncateLog_InMemoryLog, // truncate
     firstLogEntry_InMemoryLog,// truncation_point

src/stasis/logger/safeWrites.c

@@ -299,7 +299,6 @@ static inline lsn_t log_crc_next_lsn(stasis_log_t* log, lsn_t ret) {
     LSN encountered so far to the end of the log.
 
 */
-
 static int writeLogEntryUnlocked(stasis_log_t* log, LogEntry * e) {
 
   stasis_log_safe_writes_state* sw = log->impl;
@@ -426,6 +425,14 @@ static void syncLog_LogWriter(stasis_log_t * log,
   writeunlock(sw->flushedLSN_latch);
 }
 
+static lsn_t nextAvailableLSN_LogWriter(stasis_log_t * log) {
+  stasis_log_safe_writes_state* sw = log->impl;
+  pthread_mutex_lock(&sw->nextAvailableLSN_mutex);
+  lsn_t ret = sw->nextAvailableLSN;
+  pthread_mutex_unlock(&sw->nextAvailableLSN_mutex);
+  return ret;
+}
+
 static lsn_t flushedLSN_LogWriter(stasis_log_t* log,
                                   stasis_log_force_mode_t mode) {
   stasis_log_safe_writes_state* sw = log->impl;
@@ -746,6 +753,7 @@ stasis_log_t* stasis_log_safe_writes_open(const char * filename,
     readLSNEntry_LogWriter, // read_entry
     nextEntry_LogWriter,// next_entry
     flushedLSN_LogWriter, // first_unstable_lsn
+    nextAvailableLSN_LogWriter, // newt_available_lsn
     syncLog_LogWriter, // force_tail
     truncateLog_LogWriter, // truncate
     firstLogEntry_LogWriter,// truncation_point

stasis/logger/logger2.h

@@ -132,7 +132,13 @@ struct stasis_log_t {
   */
   lsn_t (*first_unstable_lsn)(struct stasis_log_t* log,
                               stasis_log_force_mode_t mode);
-
+  /**
+     This function returns the LSN of the next log entry passed to
+     write_entry.  This shouldn't be used to determine which entry a
+     particular call will assign; rather it is used to provide a lower
+     bound on the LSN of newly-loaded LSN-free pages.
+  */
+  lsn_t (*next_available_lsn)(struct stasis_log_t* log);
   /**
      Force any enqueued, unwritten entries to disk
   */

test/stasis/check_logWriter.c

@@ -85,9 +85,13 @@ static void setup_log() {
     rid.slot = 0;
     rid.size = sizeof(unsigned long);
 
+    lsn_t test = stasis_log_file->next_available_lsn(stasis_log_file);
+
     stasis_log_file->write_entry(stasis_log_file,e);
     prevLSN = e->LSN;
 
+    assert(test <= e->LSN);
+
     if(first) { 
       first = 0;
       firstLSN = prevLSN;