add latch-free slotted pages, and a bug-fix in page.c

src/stasis/CMakeLists.txt

@@ -24,6 +24,7 @@ ADD_LIBRARY(stasis crc32.c redblack.c tsearchcompat.c lhtable.c concurrentHash.c
                    page/raw.c
                    page/lsnFree.c
                    page/segment.c
+                   page/latchFree/lfSlotted.c
                    compensations.c
                    operations/pageOperations.c
                    operations/decrement.c operations/increment.c

src/stasis/page.c

@@ -77,6 +77,7 @@ terms specified in this license.
 #include <stasis/page/slotted.h>
 #include <stasis/page/fixed.h>
 #include <stasis/page/uninitialized.h>
+#include <stasis/page/latchFree/lfSlotted.h>
 #include <stasis/operations/arrayList.h>
 #include <stasis/bufferPool.h>
 #include <stasis/truncation.h>
@@ -120,6 +121,7 @@ void stasis_page_init(stasis_dirty_page_table_t * dpt) {
   stasis_page_impl_register(lsmRootImpl());
   stasis_page_impl_register(slottedLsnFreeImpl());
   stasis_page_impl_register(segmentImpl());
+  stasis_page_impl_register(stasis_page_slotted_latch_free_impl());
 }
 
 void stasis_page_deinit() {
@@ -147,7 +149,7 @@ void stasis_record_write(int xid, Page * p, recordid rid, const byte *dat) {
   assert(rid.size <= BLOB_THRESHOLD_SIZE);
 
   byte * buf = stasis_record_write_begin(xid, p, rid);
-  memcpy(buf, dat, stasis_record_length_read(xid, p, rid));
+  memcpy(buf, dat, stasis_record_type_to_size(rid.size));
   stasis_record_write_done(xid,p,rid,buf);
   assert( (p->id == rid.page) && (p->memAddr != NULL) );
 }
@@ -157,6 +159,7 @@ int stasis_record_read(int xid, Page * p, recordid rid, byte *buf) {
 
   const byte * dat = stasis_record_read_begin(xid,p,rid);
   memcpy(buf, dat, stasis_record_length_read(xid,p,rid));
+  stasis_record_read_done(xid,p,rid,dat);
 
   return 0;
 
@@ -182,7 +185,9 @@ const byte * stasis_record_read_begin(int xid, Page * p, recordid rid) {
 byte * stasis_record_write_begin(int xid, Page * p, recordid rid) {
   int page_type = p->pageType;
   assert(page_type);
-  assert(stasis_record_length_read(xid, p, rid) ==  stasis_record_type_to_size(rid.size));
+  if(p->pageType != SLOTTED_LATCH_FREE_PAGE) {
+    assert(stasis_record_length_read(xid, p, rid) ==  stasis_record_type_to_size(rid.size));
+  }
   return page_impls[page_type].recordWrite(xid, p, rid);
 }
 void stasis_record_read_done(int xid, Page *p, recordid rid, const byte *b) {

src/stasis/page/latchFree/lfSlotted.c

@@ -0,0 +1,113 @@
+/*
+ * lfSlotted.c
+ *
+ *  Created on: Aug 19, 2010
+ *      Author: sears
+ */
+
+#include <stasis/common.h>
+#include <stasis/page.h>
+#include <stasis/page/latchFree/lfSlotted.h>
+
+#define CAS(_a,_o,_n) __sync_bool_compare_and_swap(_a,_o,_n)
+#define BARRIER() __sync_synchronize()
+#define ATOMIC_ADD(_a, _i) __sync_add_and_fetch(_a, _i)
+
+static int notSupported(int xid, Page * p) { return 0; }
+
+static const byte* lfSlottedRead (int xid, Page *p, recordid rid) {
+  return stasis_page_slotted_record_cptr(p, rid.slot);
+}
+
+static byte* lfSlottedWrite(int xid, Page *p, recordid rid) {
+  assert(*stasis_page_slotted_numslots_cptr(p) == rid.slot);
+  return stasis_page_slotted_record_ptr(p, rid.slot);
+}
+static void lfSlottedWriteDone(int xid, Page *p, recordid rid, byte *buf) {
+  BARRIER();
+  int succ = CAS(stasis_page_slotted_numslots_ptr(p), rid.slot, rid.slot+1);
+  DEBUG("write done %d\n", rid.slot+1);
+  assert(succ);
+}
+static int lfSlottedRecordGetType(int xid, Page *p, recordid rid) {
+  if(*stasis_page_slotted_numslots_cptr(p) <= rid.slot) { return INVALID_SLOT; }
+  int ret = *stasis_page_slotted_slot_length_cptr(p, rid.slot);
+  return ret >= 0 ? NORMAL_SLOT : ret;
+}
+static int lfSlottedRecordGetLength(int xid, Page *p, recordid rid) {
+  if(*stasis_page_slotted_numslots_cptr(p) <= rid.slot) { return INVALID_SLOT; }
+  int ret = *stasis_page_slotted_slot_length_cptr(p, rid.slot);
+  return stasis_record_type_to_size(ret);
+}
+static recordid lfSlottedRecordFirst(int xid, Page *p) {
+  recordid ret;
+  ret.page = p->id;
+  ret.slot = 0;
+  ret.size = lfSlottedRecordGetType(xid, p, ret);
+  return ret.size == INVALID_SLOT ? NULLRID : ret;
+
+}
+static recordid lfSlottedRecordNext(int xid, Page *p, recordid ret) {
+  ret.slot++;
+  ret.size = lfSlottedRecordGetType(xid, p, ret);
+  DEBUG("next %d %d %d\n", ret.slot, (int)ret.size, *stasis_page_slotted_numslots_ptr(p));
+  return ret.size == INVALID_SLOT ? NULLRID : ret;
+}
+static recordid lfSlottedRecordLast(int xid, Page *p) {
+  recordid ret;
+  ret.page = p->id;
+  ret.slot = (*stasis_page_slotted_numslots_cptr(p))-1;
+  ret.size = lfSlottedRecordGetType(xid, p, ret);
+  return ret.size == INVALID_SLOT ? NULLRID : ret;
+}
+
+static void lfSlottedPostAlloc(int xid, Page * page, recordid rid) {
+  int16_t off = __sync_fetch_and_add(stasis_page_slotted_freespace_ptr(page), stasis_record_type_to_size(rid.size));
+  *stasis_page_slotted_slot_ptr(page, rid.slot) = off;
+  *stasis_page_slotted_slot_length_ptr(page, rid.slot) = rid.size;
+  // don't update numslots_ptr yet.  Note that we can only have one append at a time with this update protocol...
+}
+void lfSlottedRecordFree(int xid, Page *p, recordid rid) {
+  *stasis_page_slotted_slot_length_ptr(p, rid.slot) = INVALID_SLOT;
+  BARRIER();
+}
+
+void stasis_page_slotted_latch_free_initialize_page(Page * page) {
+  stasis_page_slotted_initialize_page(page);
+  page->pageType = SLOTTED_LATCH_FREE_PAGE;
+
+}
+
+page_impl stasis_page_slotted_latch_free_impl(void) {
+  page_impl slotted = stasis_page_slotted_impl();
+  page_impl pi =  {
+    SLOTTED_LATCH_FREE_PAGE,
+    1,
+    lfSlottedRead,
+    lfSlottedWrite,
+    0,// readDone (no-op)
+    lfSlottedWriteDone,
+    lfSlottedRecordGetType,
+    0, // not supported
+    lfSlottedRecordGetLength,
+    lfSlottedRecordFirst,
+    lfSlottedRecordNext,
+    lfSlottedRecordLast,
+    notSupported, // is block supported
+    stasis_block_first_default_impl,
+    stasis_block_next_default_impl,
+    stasis_block_done_default_impl,
+    slotted.pageFreespace, // this should work as is.
+    NULL, // slotted.pageCompact, // there is no chance of supporting this
+    NULL, //slotted.pageCompactSlotIDs, // ditto
+    slotted.recordPreAlloc, // this is fine; it's read only...
+    lfSlottedPostAlloc,
+    0, // can't splice lots of records atomically with the current scheme.
+    lfSlottedRecordFree,
+    0, // page_impl_dereference_identity,
+    slotted.pageLoaded,
+    slotted.pageFlushed,
+    slotted.pageCleanup
+  };
+  return pi;
+}

src/stasis/page/slotted.c

@@ -50,7 +50,8 @@ static inline void slottedFsck(const Page const * page) {
   assert(slotListStart < PAGE_SIZE && slotListStart >= 0);
   assert(page_type == SLOTTED_PAGE ||
          page_type == BOUNDARY_TAG_PAGE ||
-         page_type == SLOTTED_LSN_FREE_PAGE);
+         page_type == SLOTTED_LSN_FREE_PAGE ||
+         page_type == SLOTTED_LATCH_FREE_PAGE);
   assert(numslots >= 0);
   assert(numslots * SLOTTED_PAGE_OVERHEAD_PER_RECORD < PAGE_SIZE);
   assert(freespace >= 0);

stasis/constants.h

@@ -235,6 +235,7 @@ static const short SLOT_TYPE_LENGTHS[] = { -1, -1, sizeof(blob_record_t), -1};
 #define SLOTTED_LSN_FREE_PAGE 10
 #define SEGMENT_PAGE 11
 #define MULTI_PAGE 12 // Not really a page type, but used to denote operations that touch many pages.
+#define SLOTTED_LATCH_FREE_PAGE 13
 #define USER_DEFINED_PAGE(n) (100+n)  // 0 <= n < 155
 #define MAX_PAGE_TYPE       255
 

stasis/page.h

@@ -917,6 +917,7 @@ page_impl* stasis_page_impl_get(int id);
 	     returned by loadPage()
  */
 void stasis_page_slotted_initialize_page(Page * p);
+void stasis_page_slotted_latch_free_initialize_page(Page * page);
 void stasis_slotted_lsn_free_initialize_page(Page * p);
 void stasis_fixed_initialize_page(Page * page, size_t size, int count);
 void stasis_indirect_initialize_page(Page * p, int height);

stasis/page/latchFree/lfSlotted.h

@@ -0,0 +1,34 @@
+/**
+ * @file A special-purpose slotted page implementation for latch-free data structures
+ *
+ * This page format is similar to that provided by slotted.h (and
+ * uses an identical layout).  The difference is that this format
+ * allows readers and writers to access the same page concurrently.
+ *
+ * It does so by making use of GCC atomic operations, and by providing
+ * a restricted API.
+ *
+ * Only one thread may write to a given page at a time (this restriction
+ * may be limited in the future), records may only be written once, and
+ * the space taken up by freed records is not reused.  Instead, the writer
+ * thread must (somhehow) ensure that no readers are accessing the page,
+ * and then must either reinitialize the page (losing its contents), or
+ * simply free the page, allowing Stasis' page allocation routines to
+ * reuse the underlying storage.
+ *
+ * Readers are latch-free; they do not perform any explicit synchronization
+ * with the writer, except when they synchronize so that space can be reused.
+ *
+ *  Created on: Aug 19, 2010
+ *      Author: sears
+ */
+#ifndef LFSLOTTED_H_
+#define LFSLOTTED_H_
+
+#include <stasis/page/slotted.h>
+
+void stasis_page_slotted_latch_free_init();
+void stasis_page_slotted_latch_free_deinit();
+page_impl stasis_page_slotted_latch_free_impl();
+
+#endif /* LFSLOTTED_H_ */

stasis/page/slotted.h

@@ -59,7 +59,8 @@ Slotted page layout:
 		has been handled, except in slottedPostRalloc...
 
 ************************************************************************/
-
+#ifndef STASIS_PAGE_SLOTTED_H
+#define STASIS_PAGE_SLOTTED_H
 static inline int16_t* stasis_page_slotted_freespace_ptr(Page * p) { return stasis_page_int16_ptr_from_end((p), 1); }
 static inline int16_t* stasis_page_slotted_numslots_ptr(Page * p) { return stasis_page_int16_ptr_from_end(p, 2); }
 static inline int16_t* stasis_page_slotted_freelist_ptr(Page * p) { return stasis_page_int16_ptr_from_end(p, 3); }
@@ -78,3 +79,4 @@ void stasis_page_slotted_init();
 void stasis_page_slotted_deinit();
 page_impl stasis_page_slotted_impl();
 page_impl stasis_page_boundary_tag_impl();
+#endif //STASIS_PAGE_SLOTTED_H

test/stasis/check_page.c

@@ -48,6 +48,7 @@ terms specified in this license.
 
 #include <stasis/page.h>
 #include <stasis/page/slotted.h>
+#include <stasis/page/latchFree/lfSlotted.h>
 #include <stasis/blobManager.h>
 #include <stasis/bufferManager.h>
 #include <stasis/transactional.h>
@@ -152,6 +153,78 @@ static void* fixed_worker_thread(void * arg_ptr) {
   return NULL;
 }
 
+typedef struct {
+  Page ** pages;
+  int num_pages;
+  int my_page;
+} latchFree_worker_thread_args;
+
+static void* latchFree_worker_thread(void * arg_ptr) {
+  latchFree_worker_thread_args * arg = arg_ptr;
+
+  int alloced_count = 0;
+  while(1) {
+    int off = myrandom(arg->num_pages);
+    Page * p = arg->pages[off];
+    if(off == arg->my_page) {
+      recordid rid = stasis_record_alloc_begin(-1, p, sizeof(char));
+      if(rid.size == INVALID_SLOT) {
+        assert(alloced_count > 200);
+        return 0;
+      } else {
+        stasis_record_alloc_done(-1, p, rid);
+        alloced_count++;
+        assert(alloced_count < PAGE_SIZE/2);
+        unsigned char c = (unsigned char)rid.slot;
+        stasis_record_write(-1, p, rid, &c);
+      }
+    } else if(*stasis_page_slotted_numslots_cptr(p)) { // if the page is empty, try another.
+      // read a random record
+      int slot = myrandom(stasis_record_last(-1, p).slot+1);
+      recordid rid;
+      rid.page = p->id;
+      rid.slot = slot;
+      rid.size = sizeof(char);
+      assert(stasis_record_type_read(-1, p, rid) == NORMAL_SLOT);
+      assert(stasis_record_length_read(-1, p, rid) == sizeof(char));
+      unsigned char c = 0;
+      stasis_record_read(-1, p, rid, &c);
+      assert(c == (unsigned char) rid.slot);
+    }
+  }
+}
+START_TEST(latchFreeThreadTest) {
+  Tinit();
+  int NUM_THREADS = 200;
+  Page ** pages = malloc(sizeof(Page*)*NUM_THREADS);
+  int xid = Tbegin();
+
+  pageid_t region = TregionAlloc(xid, NUM_THREADS, -1);
+
+  for(int i = 0; i < NUM_THREADS; i++) {
+    pages[i] = loadPage(xid, i+region);
+    stasis_page_slotted_latch_free_initialize_page(pages[i]);
+  }
+
+  pthread_t * threads = malloc(sizeof(pthread_t) * NUM_THREADS);
+
+  for(int i = 0; i < NUM_THREADS; i++) {
+    latchFree_worker_thread_args * arg = malloc(sizeof(*arg));
+    arg->pages = pages;
+    arg->my_page = i;
+    arg->num_pages = NUM_THREADS;
+    pthread_create(&threads[i], 0, &latchFree_worker_thread, arg);
+  }
+  for(int i = 0; i < NUM_THREADS; i++) {
+    pthread_join(threads[i],0);
+  }
+  for(int i = 0; i < NUM_THREADS; i++) {
+    releasePage(pages[i]);
+  }
+  Tcommit(xid);
+  Tdeinit();
+
+} END_TEST
 static void* worker_thread(void * arg_ptr) {
   Page * p = (Page*)arg_ptr;
   int i;
@@ -313,9 +386,12 @@ static void assertRecordCountSizeType(int xid, Page *p, int count, int size, int
 static void checkPageIterators(int xid, Page *p,int record_count) {
   recordid first = stasis_record_alloc_begin(xid, p, sizeof(int64_t));
   stasis_record_alloc_done(xid,p,first);
-
+  int64_t i = 0;
-  for(int i = 1; i < record_count; i++) {
+  stasis_record_write(xid,p,first,(byte*)&i);
-    stasis_record_alloc_done(xid,p,stasis_record_alloc_begin(xid,p,sizeof(int64_t)));
+  for(i = 1; i < record_count; i++) {
+    recordid rid = stasis_record_alloc_begin(xid,p,sizeof(int64_t));
+    stasis_record_alloc_done(xid,p,rid);
+    stasis_record_write(xid,p,rid,(byte*)&i);
   }
 
   assertRecordCountSizeType(xid, p, record_count, sizeof(int64_t), NORMAL_SLOT);
@@ -356,6 +432,11 @@ START_TEST(pageRecordSizeTypeIteratorTest) {
 
   checkPageIterators(xid,p,10);
 
+  memset(p->memAddr, 0, PAGE_SIZE);
+  stasis_page_slotted_latch_free_initialize_page(p);
+
+  checkPageIterators(xid,p,10);
+
   releasePage(p);
 
   Tcommit(xid);
@@ -647,6 +728,7 @@ Suite * check_suite(void) {
   tcase_add_test(tc, pageNoThreadTest);
   tcase_add_test(tc, pageThreadTest);
   tcase_add_test(tc, fixedPageThreadTest);
+  tcase_add_test(tc, latchFreeThreadTest);
 
   /* --------------------------------------------- */