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

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

src/interfaces/ecpg/ecpglib/misc.c

@@ -453,17 +453,38 @@ ECPGis_noind_null(enum ECPGttype type, const void *ptr)
 #ifdef WIN32
 #ifdef ENABLE_THREAD_SAFETY
 
-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;

src/interfaces/ecpg/include/ecpg-pthread-win32.h

@@ -14,29 +14,23 @@
 
 typedef struct pthread_mutex_t
 {
-	HANDLE		handle;
-	LONG		initlock;
+	/* initstate = 0: not initialized; 1: init done; 2: init in progress */
+	LONG		initstate;
+	CRITICAL_SECTION csection;
 } pthread_mutex_t;
 
 typedef DWORD pthread_key_t;
 typedef bool pthread_once_t;
 
-#define PTHREAD_MUTEX_INITIALIZER	{ NULL, 0 }
+#define PTHREAD_MUTEX_INITIALIZER	{ 0 }
 #define PTHREAD_ONCE_INIT			false
 
-void		win32_pthread_mutex(volatile pthread_mutex_t *mutex);
+int			pthread_mutex_init(pthread_mutex_t *, void *attr);
+int			pthread_mutex_lock(pthread_mutex_t *);
+int			pthread_mutex_unlock(pthread_mutex_t *);
+
 void		win32_pthread_once(volatile pthread_once_t *once, void (*fn) (void));
 
-#define pthread_mutex_lock(mutex) \
-	do { \
-		if ((mutex)->handle == NULL) \
-			win32_pthread_mutex((mutex)); \
-		WaitForSingleObject((mutex)->handle, INFINITE); \
-	} while(0)
-
-#define pthread_mutex_unlock(mutex) \
-	ReleaseMutex((mutex)->handle)
-
 #define pthread_getspecific(key) \
 	TlsGetValue((key))
 

src/interfaces/libpq/fe-connect.c

@@ -7443,24 +7443,8 @@ static void
 default_threadlock(int acquire)
 {
 #ifdef ENABLE_THREAD_SAFETY
-#ifndef WIN32
 	static pthread_mutex_t singlethread_lock = PTHREAD_MUTEX_INITIALIZER;
-#else
-	static pthread_mutex_t singlethread_lock = NULL;
-	static long mutex_initlock = 0;
 
-	if (singlethread_lock == NULL)
-	{
-		while (InterlockedExchange(&mutex_initlock, 1) == 1)
-			 /* loop, another thread own the lock */ ;
-		if (singlethread_lock == NULL)
-		{
-			if (pthread_mutex_init(&singlethread_lock, NULL))
-				Assert(false);
-		}
-		InterlockedExchange(&mutex_initlock, 0);
-	}
-#endif
 	if (acquire)
 	{
 		if (pthread_mutex_lock(&singlethread_lock))

src/interfaces/libpq/fe-secure-openssl.c

@@ -96,12 +96,7 @@ static bool ssl_lib_initialized = false;
 #ifdef ENABLE_THREAD_SAFETY
 static long crypto_open_connections = 0;
 
-#ifndef WIN32
 static pthread_mutex_t ssl_config_mutex = PTHREAD_MUTEX_INITIALIZER;
-#else
-static pthread_mutex_t ssl_config_mutex = NULL;
-static long win32_ssl_create_mutex = 0;
-#endif
 #endif							/* ENABLE_THREAD_SAFETY */
 
 static PQsslKeyPassHook_OpenSSL_type PQsslKeyPassHook = NULL;
@@ -777,20 +772,6 @@ int
 pgtls_init(PGconn *conn, bool do_ssl, bool do_crypto)
 {
 #ifdef ENABLE_THREAD_SAFETY
-#ifdef WIN32
-	/* Also see similar code in fe-connect.c, default_threadlock() */
-	if (ssl_config_mutex == NULL)
-	{
-		while (InterlockedExchange(&win32_ssl_create_mutex, 1) == 1)
-			 /* loop, another thread own the lock */ ;
-		if (ssl_config_mutex == NULL)
-		{
-			if (pthread_mutex_init(&ssl_config_mutex, NULL))
-				return -1;
-		}
-		InterlockedExchange(&win32_ssl_create_mutex, 0);
-	}
-#endif
 	if (pthread_mutex_lock(&ssl_config_mutex))
 		return -1;
 
@@ -881,7 +862,6 @@ static void
 destroy_ssl_system(void)
 {
 #if defined(ENABLE_THREAD_SAFETY) && defined(HAVE_CRYPTO_LOCK)
-	/* Mutex is created in pgtls_init() */
 	if (pthread_mutex_lock(&ssl_config_mutex))
 		return;
 

src/interfaces/libpq/pthread-win32.c

@@ -34,27 +34,33 @@ pthread_getspecific(pthread_key_t key)
 int
 pthread_mutex_init(pthread_mutex_t *mp, void *attr)
 {
-	*mp = (CRITICAL_SECTION *) malloc(sizeof(CRITICAL_SECTION));
-	if (!*mp)
-		return 1;
-	InitializeCriticalSection(*mp);
+	mp->initstate = 0;
 	return 0;
 }
 
 int
 pthread_mutex_lock(pthread_mutex_t *mp)
 {
-	if (!*mp)
-		return 1;
-	EnterCriticalSection(*mp);
+	/* Initialize the csection if not already done */
+	if (mp->initstate != 1)
+	{
+		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)
-		return 1;
-	LeaveCriticalSection(*mp);
+	if (mp->initstate != 1)
+		return EINVAL;
+	LeaveCriticalSection(&mp->csection);
 	return 0;
 }

src/port/pthread-win32.h

@@ -5,7 +5,16 @@
 #define __PTHREAD_H
 
 typedef ULONG pthread_key_t;
-typedef CRITICAL_SECTION *pthread_mutex_t;
+
+typedef struct pthread_mutex_t
+{
+	/* initstate = 0: not initialized; 1: init done; 2: init in progress */
+	LONG		initstate;
+	CRITICAL_SECTION csection;
+} pthread_mutex_t;
+
+#define PTHREAD_MUTEX_INITIALIZER	{ 0 }
+
 typedef int pthread_once_t;
 
 DWORD		pthread_self(void);