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Simplify thread-safety of mutex initialization.

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FossilOrigin-Name: da0587c522163833e5e542f7722aeb69b3183ac1
This commit is contained in:
mistachkin
2015-09-23 16:24:19 +00:00
parent 4221e628c1
commit ffce11ae54
6 changed files with 36 additions and 82 deletions
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manifest
+12 -9
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@@ -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
manifest.uuid
+1 -1
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@@ -1 +1 @@
6b85f8cd4d87d616a3cb362647ae3869c45c2801
da0587c522163833e5e542f7722aeb69b3183ac1
src/global.c
-1
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@@ -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 */
src/main.c
+8 -28
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@@ -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
src/mutex.c
+13 -42
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@@ -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;
src/sqliteInt.h
+2 -1
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@@ -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)