Simplify thread-safety of mutex initialization.

FossilOrigin-Name: da0587c522163833e5e542f7722aeb69b3183ac1

diff --git a/manifest b/manifest
index 7c03eb7b19e5380a7f8ddbdd3cc07c04c821e011..44fb638a3a3365e09adb7f2c9c75d82ca68bdc19 100644 (file)
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Merge\supdates\sfrom\strunk.
-D 2015-09-23T15:54:36.389
+C Simplify\sthread-safety\sof\smutex\sinitialization.
+D 2015-09-23T16:24:19.976
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in e1afa6fb2de2bddd50e0ddae8166c2ee9d69b301
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -296,7 +296,7 @@ F src/expr.c 3a76afcdac925294c39903b7002ddb9e5fd29863
 F src/fault.c 160a0c015b6c2629d3899ed2daf63d75754a32bb
 F src/fkey.c 83e1baba999bed3144ea5a2143fc922edf51135f
 F src/func.c ecdd69ec6a1e406f04cc73324be2ebbf6354197f
-F src/global.c d824163680839be79b53204105a78e5be5d4ac4a
+F src/global.c 508e4087f7b41d688e4762dcf4d4fe28cfbc87f9
 F src/hash.c 4263fbc955f26c2e8cdc0cf214bc42435aa4e4f5
 F src/hash.h c8f3c31722cf3277d03713909761e152a5b81094
 F src/hwtime.h d32741c8f4df852c7d959236615444e2b1063b08
@@ -305,7 +305,7 @@ F src/journal.c b4124532212b6952f42eb2c12fa3c25701d8ba8d
 F src/legacy.c ba1863ea58c4c840335a84ec276fc2b25e22bc4e
 F src/lempar.c d344a95d60c24e2f490ee59db9784b1b17439012
 F src/loadext.c f0b66d28e377fd6c6d36cc9d92df1ff251ebee44
-F src/main.c 9f196a4364270af28ab97c1d62046e56e32dd11d
+F src/main.c cf4d6d94709fc2caf2f92066d24a0f9d125b9260
 F src/malloc.c 3a37ce6979a40f499d8cea9e9ab4e8517854d35d
 F src/mem0.c 6a55ebe57c46ca1a7d98da93aaa07f99f1059645
 F src/mem1.c abe6ee469b6c5a35c7f22bfeb9c9bac664a1c987
@@ -314,7 +314,7 @@ F src/mem3.c 61c9d47b792908c532ca3a62b999cf21795c6534
 F src/mem5.c 61eeb90134f9a5be6c2e68d8daae7628b25953fb
 F src/memjournal.c 3eb2c0b51adbd869cb6a44780323f05fa904dc85
 F src/msvc.h d9ba56c6851227ab44b3f228a35f3f5772296495
-F src/mutex.c b0fbea2cda9f8e81444f5f1b4b9f07c1a904269e
+F src/mutex.c 7eb31a23d213416e6e0edafec1b949f9f4be32e4
 F src/mutex.h 779d588e3b7756ec3ecf7d78cde1d84aba414f85
 F src/mutex_noop.c f03e26ba8258399da23b51234f6b6a97197c1900
 F src/mutex_unix.c a72043f2560147d8e85fe48a6aef682896deb3a0
@@ -345,7 +345,7 @@ F src/shell.c 6332ef06db1390ef812cfdff1fc97b4fd76cdd42
 F src/sqlite.h.in 4e06cb5fed36736242c66237991db6f3e2395eb9
 F src/sqlite3.rc 992c9f5fb8285ae285d6be28240a7e8d3a7f2bad
 F src/sqlite3ext.h 64350bf36833a56ad675e27392a913f417c5c308
-F src/sqliteInt.h ed65bcb0a6a7c11978c8f75d5476d6edaa024e8d
+F src/sqliteInt.h 2e5280bf7e66b68ebb8df46877dd745c3e8436af
 F src/sqliteLimit.h 216557999cb45f2e3578ed53ebefe228d779cb46
 F src/status.c f266ad8a2892d659b74f0f50cb6a88b6e7c12179
 F src/table.c 51b46b2a62d1b3a959633d593b89bab5e2c9155e
@@ -1388,7 +1388,10 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 48bd54594752d5be3337f12c72f28d2080cb630b
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P c9400ff167d9520119081c9b92436794dcd53d22 10a214fdb3c13b25e0bdd15c975c21c8890c47ee
-R b42897c3c8ae6a403b71a2f426cb59b5
+P 6b85f8cd4d87d616a3cb362647ae3869c45c2801
+R 6f093adcb01e89e126d8f89920b100ca
+T *branch * mutexInitSimpleCmpSwap
+T *sym-mutexInitSimpleCmpSwap *
+T -sym-mutexInitCmpSwap *
 U mistachkin
-Z 6c86ab7133863d50d8bbe949c96c8dea
+Z a42e1b6d07186b23163577b2bca4803f

diff --git a/manifest.uuid b/manifest.uuid
index f5defe22b2b877a8474d0113e87d3b47b78b612a..ffbd5aabf4b33d7518ffa4b8d2f263a652078a5e 100644 (file)
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-6b85f8cd4d87d616a3cb362647ae3869c45c2801
\ No newline at end of file
+da0587c522163833e5e542f7722aeb69b3183ac1
\ No newline at end of file

diff --git a/src/global.c b/src/global.c
index f995e9d7086b7b6b2603a9d559b37e5b37493c39..ef4fe56ae189a4b45f0c17c6d36f78003ec9b4f3 100644 (file)
--- a/src/global.c
+++ b/src/global.c
@@ -174,7 +174,6 @@ SQLITE_WSD struct Sqlite3Config sqlite3Config = {
    128,                       /* szLookaside */
    500,                       /* nLookaside */
    {0,0,0,0,0,0,0,0},         /* m */
-   (void*)0,                  /* pMutex */
    {0,0,0,0,0,0,0,0,0},       /* mutex */
    {0,0,0,0,0,0,0,0,0,0,0,0,0},/* pcache2 */
    (void*)0,                  /* pHeap */

diff --git a/src/main.c b/src/main.c
index 33e06678e2ed8faeaa5712297106d25a5807b297..5cc6f39e5e15e53c7f4ffbce4ba61a48d764170c 100644 (file)
--- a/src/main.c
+++ b/src/main.c
@@ -171,13 +171,7 @@ int sqlite3_initialize(void){
   */
   MUTEX_LOGIC( pMaster = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER); )
   sqlite3_mutex_enter(pMaster);
-  if( sqlite3GlobalConfig.isInit ){
-    assert( sqlite3GlobalConfig.isMutexInit );
-    assert( sqlite3GlobalConfig.isMallocInit );
-    sqlite3_mutex_leave(pMaster);
-    return SQLITE_OK;
-  }
-  sqlite3GlobalConfig.isMutexInit = 1; /* possibly redundant */
+  sqlite3GlobalConfig.isMutexInit = 1;
   if( !sqlite3GlobalConfig.isMallocInit ){
     rc = sqlite3MallocInit();
   }
@@ -335,17 +329,6 @@ int sqlite3_shutdown(void){
     sqlite3GlobalConfig.isMutexInit = 0;
   }
 
-  /*
-  ** Force the state of the mutex subsystem to be completely reset now, even
-  ** if the configured xMutexEnd(), if any, failed.  This is not thread-safe.
-  ** This is necessary even if the xMutexInit() was never called, due to the
-  ** possiblity of this state being changed via SQLITE_CONFIG_MUTEX.  After
-  ** this point, the application must enable any custom mutex implementation
-  ** again via SQLITE_CONFIG_MUTEX, if necessary.
-  */
-  sqlite3GlobalConfig.pMutex = 0;
-  memset(&sqlite3GlobalConfig.mutex, 0, sizeof(sqlite3_mutex_methods));
-
   return SQLITE_OK;
 }
 
@@ -401,22 +384,19 @@ int sqlite3_config(int op, ...){
 #endif
 #if defined(SQLITE_THREADSAFE) && SQLITE_THREADSAFE>0 /* IMP: R-63666-48755 */
     case SQLITE_CONFIG_MUTEX: {
-      /* Atomically compare-and-swap the mutex implementation pointer to
-       * help prevent a race condition with sqlite3MutexInit(). */
-      if( sqlite3CompareAndSwap((void * volatile *)&sqlite3GlobalConfig.pMutex,
-                                0, &sqlite3GlobalConfig.mutex)==0 ){
-        /* Specify an alternative mutex implementation */
-        sqlite3GlobalConfig.mutex = *va_arg(ap, sqlite3_mutex_methods*);
-      }else{
-        rc = SQLITE_ERROR;
-      }
+      /* Specify an alternative mutex implementation */
+      sqlite3MutexCopy(&sqlite3GlobalConfig.mutex,
+                       va_arg(ap, sqlite3_mutex_methods*));
+      sqlite3MemoryBarrier();
       break;
     }
 #endif
 #if defined(SQLITE_THREADSAFE) && SQLITE_THREADSAFE>0 /* IMP: R-14450-37597 */
     case SQLITE_CONFIG_GETMUTEX: {
       /* Retrieve the current mutex implementation */
-      *va_arg(ap, sqlite3_mutex_methods*) = sqlite3GlobalConfig.mutex;
+      sqlite3MemoryBarrier();
+      sqlite3MutexCopy(va_arg(ap, sqlite3_mutex_methods*),
+                       &sqlite3GlobalConfig.mutex);
       break;
     }
 #endif

diff --git a/src/mutex.c b/src/mutex.c
index 1d789ed17c77251ccd0bafd6b01e7b428c7a41c2..7c8505c8ec8f212db49bd16305f1b686761f0e25 100644 (file)
--- a/src/mutex.c
+++ b/src/mutex.c
@@ -26,37 +26,11 @@ static SQLITE_WSD int mutexIsInit = 0;
 
 
 #ifndef SQLITE_MUTEX_OMIT
-/*
-** This structure is for use by mutexIsInvalid() only.  It represents an
-** invalid mutex implementation (i.e. one where all the function pointers
-** are null).
-*/
-static const sqlite3_mutex_methods mutexNullMethods = {
-  0, /* xMutexInit */
-  0, /* xMutexEnd */
-  0, /* xMutexAlloc */
-  0, /* xMutexFree */
-  0, /* xMutexEnter */
-  0, /* xMutexTry */
-  0, /* xMutexLeave */
-  0, /* xMutexHeld */
-  0  /* xMutexNotheld */
-};
-
-/*
-** Returns non-zero if the currently configured mutex implemention is
-** invalid (i.e. all of its function pointers are null).
-*/
-static int mutexIsInvalid(void){
-  return memcmp(&sqlite3GlobalConfig.mutex, &mutexNullMethods,
-                sizeof(sqlite3_mutex_methods))==0;
-}
-
 /*
 ** Copies a mutex implementation.  Both arguments must point to valid
 ** memory.
 */
-static void mutexCopy(
+void sqlite3MutexCopy(
   sqlite3_mutex_methods *pTo,
   sqlite3_mutex_methods const *pFrom
 ){
@@ -75,31 +49,28 @@ static void mutexCopy(
 ** Initialize the mutex system.
 */
 int sqlite3MutexInit(void){ 
-  static int initPending = 0;
   int rc;
-  if( sqlite3CompareAndSwap((void * volatile *)&sqlite3GlobalConfig.pMutex,
-                   0, &sqlite3GlobalConfig.mutex)==0 || mutexIsInvalid() ){
-    /* If the mutex implementation pointer has not been set, then the user
-    ** did not install a mutex implementation via sqlite3_config() prior to
-    ** sqlite3_initialize() being called.  This block copies the pointers
-    ** for the default implementation into the sqlite3GlobalConfig structure.
+
+  sqlite3MemoryBarrier();
+  if( sqlite3CompareAndSwap(
+                   (void * volatile *)&sqlite3GlobalConfig.mutex.xMutexAlloc,
+                   0, sqlite3GlobalConfig.mutex.xMutexAlloc)==0 ){
+    /* If the xMutexAlloc method has not been set, then the user did not
+    ** install a mutex implementation via sqlite3_config() prior to 
+    ** sqlite3_initialize() being called. This block copies pointers to
+    ** the default implementation into the sqlite3GlobalConfig structure.
     */
     sqlite3_mutex_methods const *pFrom;
-
     if( sqlite3GlobalConfig.bCoreMutex ){
       pFrom = sqlite3DefaultMutex();
     }else{
       pFrom = sqlite3NoopMutex();
     }
-    mutexCopy(&sqlite3GlobalConfig.mutex, pFrom);
+    sqlite3MutexCopy(&sqlite3GlobalConfig.mutex, pFrom);
     sqlite3MemoryBarrier();
   }
-  if( !initPending ){
-    assert( sqlite3GlobalConfig.mutex.xMutexInit );
-    initPending = 1;
-    rc = sqlite3GlobalConfig.mutex.xMutexInit();
-    initPending = 0;
-  }
+  assert( sqlite3GlobalConfig.mutex.xMutexInit );
+  rc = sqlite3GlobalConfig.mutex.xMutexInit();
 
 #ifdef SQLITE_DEBUG
   GLOBAL(int, mutexIsInit) = 1;

diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 241294ae62a12ae0a75baf4757f3559c94a331a9..393f331ee3bfba6284506e67d0e593bc20a32e12 100644 (file)
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -2938,7 +2938,6 @@ struct Sqlite3Config {
   int szLookaside;                  /* Default lookaside buffer size */
   int nLookaside;                   /* Default lookaside buffer count */
   sqlite3_mem_methods m;            /* Low-level memory allocation interface */
-  sqlite3_mutex_methods *pMutex;    /* Address of mutex member or zero. */
   sqlite3_mutex_methods mutex;      /* Low-level mutex interface */
   sqlite3_pcache_methods2 pcache2;  /* Low-level page-cache interface */
   void *pHeap;                      /* Heap storage space */
@@ -3196,8 +3195,10 @@ const sqlite3_mem_methods *sqlite3MemGetMemsys5(void);
   int sqlite3MutexEnd(void);
 #endif
 #if !defined(SQLITE_MUTEX_OMIT) && !defined(SQLITE_MUTEX_NOOP)
+  void sqlite3MutexCopy(sqlite3_mutex_methods *, sqlite3_mutex_methods const *);
   void sqlite3MemoryBarrier(void);
 #else
+# define sqlite3MutexCopy(x,y)
 # define sqlite3MemoryBarrier()
 #endif
 #if !defined(SQLITE_MUTEX_OMIT)