diff --git a/manifest b/manifest
index 7d2418f3e2..19d0d1e03d 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Updated\ssqlite3AtoF()\sthat\sperforms\sslightly\sbetter\swith\sGCC,\sand\ssignificantly\sbetter\swith\sMSVC.
-D 2009-08-21T02:13:14
+C Add\sassert()\sstatements\sto\sos_unix.c\sto\scheck\sthat\sthe\smutex\sis\sheld\swhen\sit\sshould\sbe.
+D 2009-08-21T08:29:10
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in 73ddeec9dd10b85876c5c2ce1fdce627e1dcc7f8
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -145,7 +145,7 @@ F src/os.c 9fea283e336ee31caa4654d6cb05a129a1c42d2f
 F src/os.h 00a1334a4eecee7f7bef79ac606b88d325119f21
 F src/os_common.h 8c61457df58f1a4bd5f5adc3e90e01b37bf7afbc
 F src/os_os2.c bed77dc26e3a95ce4a204936b9a1ca6fe612fcc5
-F src/os_unix.c 6895098a9e7bd5630fab59060da6397bebcf2ff9
+F src/os_unix.c 85f6ed28690a3c4546edaa25252d52761490aa33
 F src/os_win.c 58bb163f327e79726dd119344d908e4d98483c3f
 F src/pager.c a47be286477ed6c7b9a342dd53d4e4043f29d8c2
 F src/pager.h 11852d044c86cf5a9d6e34171fb0c4fcf1f6265f
@@ -747,7 +747,7 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl 672f81d693a03f80f5ae60bfefacd8a349e76746
-P 3ba316e9a32de406a4390fb3f52fccb48da4da30
-R bbc63800e202da4f72f0395afa840353
-U shane
-Z aada4480e610c2af2b7cf949ce420cab
+P f084f5a8ba850de627ca8e9de6c81ab1ad9b7a1b
+R 86b75a5cb6d64dfb1579ca1b08107e59
+U dan
+Z 23bb429f975133621e0fd91ccb484fc5
diff --git a/manifest.uuid b/manifest.uuid
index 5e57603799..2d0783b604 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-f084f5a8ba850de627ca8e9de6c81ab1ad9b7a1b
\ No newline at end of file
+11a669b6537d6bac67764fd91a319234345ac504
\ No newline at end of file
diff --git a/src/os_unix.c b/src/os_unix.c
index cfaf2a2bda..f972b591d8 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -260,7 +260,18 @@ struct unixFile {
 
 
 /*
-** Helper functions to obtain and relinquish the global mutex.
+** Helper functions to obtain and relinquish the global mutex. The
+** global mutex is used to protect the unixOpenCnt, unixLockInfo and
+** vxworksFileId objects used by this file, all of which may be 
+** shared by multiple threads.
+**
+** Function unixMutexHeld() is used to assert() that the global mutex 
+** is held when required. This function is only used as part of assert() 
+** statements. e.g.
+**
+**   unixEnterMutex()
+**     assert( unixMutexHeld() );
+**   unixEnterLeave()
 */
 static void unixEnterMutex(void){
   sqlite3_mutex_enter(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER));
@@ -268,6 +279,11 @@ static void unixEnterMutex(void){
 static void unixLeaveMutex(void){
   sqlite3_mutex_leave(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER));
 }
+#ifdef SQLITE_DEBUG
+static int unixMutexHeld(void) {
+  return sqlite3_mutex_held(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER));
+}
+#endif
 
 
 #ifdef SQLITE_DEBUG
@@ -278,11 +294,11 @@ static void unixLeaveMutex(void){
 */
 static const char *locktypeName(int locktype){
   switch( locktype ){
-  case NO_LOCK: return "NONE";
-  case SHARED_LOCK: return "SHARED";
-  case RESERVED_LOCK: return "RESERVED";
-  case PENDING_LOCK: return "PENDING";
-  case EXCLUSIVE_LOCK: return "EXCLUSIVE";
+    case NO_LOCK: return "NONE";
+    case SHARED_LOCK: return "SHARED";
+    case RESERVED_LOCK: return "RESERVED";
+    case PENDING_LOCK: return "PENDING";
+    case EXCLUSIVE_LOCK: return "EXCLUSIVE";
   }
   return "ERROR";
 }
@@ -737,7 +753,7 @@ struct unixOpenCnt {
   int nRef;                   /* Number of pointers to this structure */
   int nLock;                  /* Number of outstanding locks */
   int nPending;               /* Number of pending close() operations */
-  int *aPending;            /* Malloced space holding fd's awaiting a close() */
+  int *aPending;              /* Malloced space holding fds awaiting close() */
 #if OS_VXWORKS
   sem_t *pSem;                     /* Named POSIX semaphore */
   char aSemName[MAX_PATHNAME+1];   /* Name of that semaphore */
@@ -848,8 +864,12 @@ static void testThreadLockingBehavior(int fd_orig){
 
 /*
 ** Release a unixLockInfo structure previously allocated by findLockInfo().
+**
+** The mutex entered using the unixEnterMutex() function must be held
+** when this function is called.
 */
 static void releaseLockInfo(struct unixLockInfo *pLock){
+  assert( unixMutexHeld() );
   if( pLock ){
     pLock->nRef--;
     if( pLock->nRef==0 ){
@@ -871,8 +891,12 @@ static void releaseLockInfo(struct unixLockInfo *pLock){
 
 /*
 ** Release a unixOpenCnt structure previously allocated by findLockInfo().
+**
+** The mutex entered using the unixEnterMutex() function must be held
+** when this function is called.
 */
 static void releaseOpenCnt(struct unixOpenCnt *pOpen){
+  assert( unixMutexHeld() );
   if( pOpen ){
     pOpen->nRef--;
     if( pOpen->nRef==0 ){
@@ -898,6 +922,9 @@ static void releaseOpenCnt(struct unixOpenCnt *pOpen){
 ** describes that file descriptor.  Create new ones if necessary.  The
 ** return values might be uninitialized if an error occurs.
 **
+** The mutex entered using the unixEnterMutex() function must be held
+** when this function is called.
+**
 ** Return an appropriate error code.
 */
 static int findLockInfo(
@@ -913,6 +940,8 @@ static int findLockInfo(
   struct unixLockInfo *pLock = 0;/* Candidate unixLockInfo object */
   struct unixOpenCnt *pOpen;     /* Candidate unixOpenCnt object */
 
+  assert( unixMutexHeld() );
+
   /* Get low-level information about the file that we can used to
   ** create a unique name for the file.
   */