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More comments on the unix locking code. Ticket #1672. (CVS 3075)

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FossilOrigin-Name: 4b6f5688843ebe39f6bd3e863666a44d486fbe0f
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drh
2006-02-10 13:11:32 +00:00
parent ff293cad83
commit 6a3d670205
3 changed files with 23 additions and 11 deletions
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18
src/os_unix.c
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@@ -1675,22 +1675,34 @@ int sqlite3UnixSleep(int ms){
** inMutex the nesting depth of the recursive mutex. The thread
** holding mutexMain can read this variable at any time.
** But is must hold mutexAux to change this variable. Other
** threads must hold mutexAux to read the variable.
** threads must hold mutexAux to read the variable and can
** never write.
**
** mutexOwner The thread id of the thread holding mutexMain. Same
** access rules as for inMutex.
**
** mutexOwnerValid True if the value in mutexOwner is valid.
** mutexOwnerValid True if the value in mutexOwner is valid. The same
** access rules apply as for inMutex.
**
** mutexMain The main mutex. Hold this mutex in order to get exclusive
** access to SQLite data structures.
**
** mutexAux An auxiliary mutex needed to access variables defined above.
**
** Mutexes are always acquired in this order: mutexMain mutexAux. It
** is not necessary to acquire mutexMain in order to get mutexAux - just
** do not attempt to acquire them in the reverse order: mutexAux mutexMain.
** Either get the mutexes with mutexMain first or get mutexAux only.
**
** When running on a platform where the three variables inMutex, mutexOwner,
** and mutexOwnerValid can be set atomically, the mutexAux is not required.
** On many systems, all three are 32-bit integers and writing to a 32-bit
** integer is atomic. I think. But there are no guarantees. So it seems
** safer to protect them using mutexAux.
*/
static int inMutex = 0;
#ifdef SQLITE_UNIX_THREADS
static pthread_t mutexOwner; /* Thread holding the mutex */
static pthread_t mutexOwner; /* Thread holding mutexMain */
static int mutexOwnerValid = 0; /* True if mutexOwner is valid */
static pthread_mutex_t mutexMain = PTHREAD_MUTEX_INITIALIZER; /* The mutex */
static pthread_mutex_t mutexAux = PTHREAD_MUTEX_INITIALIZER; /* Aux mutex */