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Clean up Windows-specific mutex code in libpq and ecpglib.

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Fix pthread-win32.h and pthread-win32.c to provide a more complete
emulation of POSIX pthread mutexes: define PTHREAD_MUTEX_INITIALIZER
and make sure that pthread_mutex_lock() can operate on a mutex
object that's been initialized that way.  Then we don't need the
duplicative platform-specific logic in default_threadlock() and
pgtls_init(), which we'd otherwise need yet a third copy of for
an upcoming bug fix.

Also, since default_threadlock() supposes that pthread_mutex_lock()
cannot fail, try to ensure that that's actually true, by getting
rid of the malloc call that was formerly involved in initializing
an emulated mutex.  We can define an extra state for the spinlock
field instead.

Also, replace the similar code in ecpglib/misc.c with this version.
While ecpglib's version at least had a POSIX-compliant API, it
also had the potential of failing during mutex init (but here,
because of CreateMutex failure rather than malloc failure).  Since
all of misc.c's callers ignore failures, it seems like a wise idea
to avoid failures here too.

A further improvement in this area could be to unify libpq's and
ecpglib's implementations into a src/port/pthread-win32.c file.
But that doesn't seem like a bug fix, so I'll desist for now.

In preparation for the aforementioned bug fix, back-patch to all
supported branches.

Discussion: https://postgr.es/m/264860.1707163416@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2024-02-09 11:11:39 -05:00
parent 5c7038d70b
commit 0028b55bc8
6 changed files with 63 additions and 69 deletions
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37
src/interfaces/ecpg/ecpglib/misc.c
View File

@ -407,17 +407,38 @@ ECPGis_noind_null(enum ECPGttype type, const void *ptr)
#ifdef WIN32
void
win32_pthread_mutex(volatile pthread_mutex_t *mutex)
int
pthread_mutex_init(pthread_mutex_t *mp, void *attr)
{
if (mutex->handle == NULL)
mp->initstate = 0;
return 0;
}
int
pthread_mutex_lock(pthread_mutex_t *mp)
{
/* Initialize the csection if not already done */
if (mp->initstate != 1)
{
while (InterlockedExchange((LONG *) &mutex->initlock, 1) == 1)
Sleep(0);
if (mutex->handle == NULL)
mutex->handle = CreateMutex(NULL, FALSE, NULL);
InterlockedExchange((LONG *) &mutex->initlock, 0);
LONG istate;
while ((istate = InterlockedExchange(&mp->initstate, 2)) == 2)
Sleep(0); /* wait, another thread is doing this */
if (istate != 1)
InitializeCriticalSection(&mp->csection);
InterlockedExchange(&mp->initstate, 1);
}
EnterCriticalSection(&mp->csection);
return 0;
}
int
pthread_mutex_unlock(pthread_mutex_t *mp)
{
if (mp->initstate != 1)
return EINVAL;
LeaveCriticalSection(&mp->csection);
return 0;
}
static pthread_mutex_t win32_pthread_once_lock = PTHREAD_MUTEX_INITIALIZER;