This patch contains an update of my mutex implementation that should apply
to current.
2002-09-23 Thomas Pfaff <[EMAIL PROTECTED]>
* include/pthread.h: Change default mutex type to errorcheck.
* thread.cc (pthread_cond::TimedWait): Fix mutex unlock call.
(pthread_mutex::pthread_mutex): Rewrite.
(pthread_mutex::~pthread_mutex): Ditto.
(pthread_mutex::Lock): Ditto.
(pthread_mutex::TryLock): Ditto.
(pthread_mutex::UnLock): Ditto.
(pthread_mutex::Destroy): New method.
(pthread_mutex::SetOwner): Ditto.
(pthread_mutex::LockRecursive): Ditto.
(pthread_mutex::fixup_after_fork): Restore mutex after fork.
(__pthread_mutex_destroy): Call pthread_mutex::Destroy to destroy
mutex.
(__pthread_mutexattr_settype): Allow errorchecking and recursive
types.
* thread.h (MUTEX_LOCK_COUNTER_INITIAL): New define.
(pthread_mutex::criticalsection): Remove.
(pthread_mutex::lock_counter): New member.
(pthread_mutex::recursion_counter): Ditto.
(pthread_mutex::owner): Ditto.
(pthread_mutex::type): Ditto.
(pthread_mutex::Destroy): New method.
(pthread_mutex::SetOwner): Ditto.
(pthread_mutex::LockRecursive): Ditto.
diff -urp src.old/winsup/cygwin/include/pthread.h src/winsup/cygwin/include/pthread.h
--- src.old/winsup/cygwin/include/pthread.h Sat Jul 6 22:41:08 2002
+++ src/winsup/cygwin/include/pthread.h Mon Sep 23 10:01:49 2002
@@ -50,12 +50,11 @@ extern "C"
#define PTHREAD_CREATE_JOINABLE 0
#define PTHREAD_EXPLICIT_SCHED 1
#define PTHREAD_INHERIT_SCHED 0
-#define PTHREAD_MUTEX_DEFAULT 0
-#define PTHREAD_MUTEX_ERRORCHECK 1
-#define PTHREAD_MUTEX_NORMAL 2
+#define PTHREAD_MUTEX_ERRORCHECK 0
+#define PTHREAD_MUTEX_RECURSIVE 1
+#define PTHREAD_MUTEX_DEFAULT PTHREAD_MUTEX_ERRORCHECK
/* this should be too low to ever be a valid address */
#define PTHREAD_MUTEX_INITIALIZER (void *)20
-#define PTHREAD_MUTEX_RECURSIVE 0
#define PTHREAD_ONCE_INIT { PTHREAD_MUTEX_INITIALIZER, 0 }
#define PTHREAD_PRIO_INHERIT
#define PTHREAD_PRIO_NONE
diff -urp src.old/winsup/cygwin/thread.cc src/winsup/cygwin/thread.cc
--- src.old/winsup/cygwin/thread.cc Sun Sep 22 21:11:38 2002
+++ src/winsup/cygwin/thread.cc Mon Sep 23 11:00:56 2002
@@ -878,27 +878,20 @@ int
pthread_cond::TimedWait (DWORD dwMilliseconds)
{
DWORD rv;
- if (!wincap.has_signal_object_and_wait ())
- {
- // FIXME: race condition (potentially drop events
- // Possible solution (single process only) - place this in a critical section.
- ReleaseMutex (mutex->win32_obj_id);
- rv = WaitForSingleObject (win32_obj_id, dwMilliseconds);
- }
- else
- {
- LeaveCriticalSection (&mutex->criticalsection);
- rv = WaitForSingleObject (win32_obj_id, dwMilliseconds);
+
+ // FIXME: race condition (potentially drop events
+ // Possible solution (single process only) - place this in a critical section.
+ mutex->UnLock ();
+ rv = WaitForSingleObject (win32_obj_id, dwMilliseconds);
#if 0
- /* we need to use native win32 mutex's here, because the cygwin ones now use
- * critical sections, which are faster, but introduce a race _here_. Until then
- * The NT variant of the code is redundant.
- */
+ /* we need to use native win32 mutex's here, because the cygwin ones now use
+ * critical sections, which are faster, but introduce a race _here_. Until then
+ * The NT variant of the code is redundant.
+ */
- rv = SignalObjectAndWait (mutex->win32_obj_id, win32_obj_id, dwMilliseconds,
- false);
+ rv = SignalObjectAndWait (mutex->win32_obj_id, win32_obj_id, dwMilliseconds,
+ false);
#endif
- }
switch (rv)
{
case WAIT_FAILED:
@@ -1090,39 +1083,40 @@ pthread_mutex::isGoodInitializerOrObject
return true;
}
-pthread_mutex::pthread_mutex (pthread_mutexattr *attr):verifyable_object
(PTHREAD_MUTEX_MAGIC)
+pthread_mutex::pthread_mutex (pthread_mutexattr *attr) :
+ verifyable_object (PTHREAD_MUTEX_MAGIC),
+ lock_counter (MUTEX_LOCK_COUNTER_INITIAL),
+ win32_obj_id (NULL), recursion_counter (0),
+ condwaits (0), owner (NULL), type (PTHREAD_MUTEX_DEFAULT),
+ pshared(PTHREAD_PROCESS_PRIVATE)
{
- /*attr checked in the C call */
- if (attr && attr->pshared == PTHREAD_PROCESS_SHARED)
+ win32_obj_id = ::CreateSemaphore (&sec_none_nih, 0, LONG_MAX, NULL);
+ if (!win32_obj_id)
{
- // fail
magic = 0;
return;
}
- if (wincap.has_try_enter_critical_section ())
- InitializeCriticalSection (&criticalsection);
- else
+ /*attr checked in the C call */
+ if (attr)
{
- this->win32_obj_id = ::CreateMutex (&sec_none_nih, false, NULL);
- if (!win32_obj_id)
- magic = 0;
+ if (attr->pshared == PTHREAD_PROCESS_SHARED)
+ {
+ // fail
+ magic = 0;
+ return;
+ }
+
+ type = attr->mutextype;
}
- condwaits = 0;
- pshared = PTHREAD_PROCESS_PRIVATE;
+
/* threadsafe addition is easy */
next = (pthread_mutex *) InterlockedExchangePointer (&MT_INTERFACE->mutexs, this);
}
pthread_mutex::~pthread_mutex ()
{
- if (wincap.has_try_enter_critical_section ())
- DeleteCriticalSection (&criticalsection);
- else
- {
- if (win32_obj_id)
- CloseHandle (win32_obj_id);
- win32_obj_id = NULL;
- }
+ if (win32_obj_id)
+ CloseHandle (win32_obj_id);
/* I'm not 100% sure the next bit is threadsafe. I think it is... */
if (MT_INTERFACE->mutexs == this)
/* TODO: printf an error if the return value != this */
@@ -1131,7 +1125,7 @@ pthread_mutex::~pthread_mutex ()
{
pthread_mutex *tempmutex = MT_INTERFACE->mutexs;
while (tempmutex->next && tempmutex->next != this)
- tempmutex = tempmutex->next;
+ tempmutex = tempmutex->next;
/* but there may be a race between the loop above and this statement */
/* TODO: printf an error if the return value != this */
InterlockedExchangePointer (&tempmutex->next, this->next);
@@ -1141,33 +1135,96 @@ pthread_mutex::~pthread_mutex ()
int
pthread_mutex::Lock ()
{
- if (wincap.has_try_enter_critical_section ())
+ int result = 0;
+ pthread_t self = pthread::self ();
+
+ if (0 == InterlockedIncrement (&lock_counter))
+ SetOwner ();
+ else if (__pthread_equal (&owner, &self))
+ {
+ InterlockedDecrement (&lock_counter);
+ if (PTHREAD_MUTEX_RECURSIVE == type)
+ result = LockRecursive ();
+ else
+ result = EDEADLK;
+ }
+ else
{
- EnterCriticalSection (&criticalsection);
- return 0;
+ WaitForSingleObject (win32_obj_id, INFINITE);
+ SetOwner ();
}
- /* FIXME: Return 0 on success */
- return WaitForSingleObject (win32_obj_id, INFINITE);
+
+ return result;
}
/* returns non-zero on failure */
int
pthread_mutex::TryLock ()
{
- if (wincap.has_try_enter_critical_section ())
- return (!TryEnterCriticalSection (&criticalsection));
- return (WaitForSingleObject (win32_obj_id, 0) == WAIT_TIMEOUT);
+ int result = 0;
+ pthread_t self = pthread::self ();
+
+ if (MUTEX_LOCK_COUNTER_INITIAL ==
+ InterlockedCompareExchange (&lock_counter, 0, MUTEX_LOCK_COUNTER_INITIAL ))
+ SetOwner ();
+ else if (__pthread_equal (&owner, &self) && PTHREAD_MUTEX_RECURSIVE == type)
+ result = LockRecursive ();
+ else
+ result = EBUSY;
+
+ return result;
}
int
pthread_mutex::UnLock ()
{
- if (wincap.has_try_enter_critical_section ())
+ pthread_t self = pthread::self ();
+
+ if (!__pthread_equal (&owner, &self))
+ return EPERM;
+
+ if (0 == --recursion_counter)
{
- LeaveCriticalSection (&criticalsection);
- return 0;
+ owner = NULL;
+ if (MUTEX_LOCK_COUNTER_INITIAL != InterlockedDecrement (&lock_counter))
+ // Another thread is waiting
+ ::ReleaseSemaphore (win32_obj_id, 1, NULL);
}
- return (!ReleaseMutex (win32_obj_id));
+
+ return 0;
+}
+
+int
+pthread_mutex::Destroy ()
+{
+ if (condwaits || TryLock ())
+ // Do not destroy a condwaited or locked mutex
+ return EBUSY;
+ else if (recursion_counter != 1)
+ {
+ // Do not destroy a recursive locked mutex
+ --recursion_counter;
+ return EBUSY;
+ }
+
+ delete this;
+ return 0;
+}
+
+void
+pthread_mutex::SetOwner ()
+{
+ recursion_counter = 1;
+ owner = pthread::self ();
+}
+
+int
+pthread_mutex::LockRecursive ()
+{
+ if (UINT_MAX == recursion_counter)
+ return EAGAIN;
+ ++recursion_counter;
+ return 0;
}
void
@@ -1176,15 +1233,18 @@ pthread_mutex::fixup_after_fork ()
debug_printf ("mutex %x in fixup_after_fork", this);
if (pshared != PTHREAD_PROCESS_PRIVATE)
api_fatal ("pthread_mutex::fixup_after_fork () doesn'tunderstand PROCESS_SHARED
mutex's");
- /* FIXME: duplicate code here and in the constructor. */
- if (wincap.has_try_enter_critical_section ())
- InitializeCriticalSection (&criticalsection);
- else
- {
- win32_obj_id = ::CreateMutex (&sec_none_nih, false, NULL);
- if (!win32_obj_id)
- api_fatal ("pthread_mutex::fixup_after_fork () failed to create new win32
mutex");
- }
+
+ if (NULL == owner)
+ /* mutex has no owner, reset to initial */
+ lock_counter = MUTEX_LOCK_COUNTER_INITIAL;
+ else if (lock_counter != MUTEX_LOCK_COUNTER_INITIAL)
+ /* All waiting threads are gone after a fork */
+ lock_counter = 0;
+
+ win32_obj_id = ::CreateSemaphore (&sec_none_nih, 0, LONG_MAX, NULL);
+ if (!win32_obj_id)
+ api_fatal ("pthread_mutex::fixup_after_fork () failed to recreate win32 semaphore
+for mutex");
+
#if DETECT_BAD_APPS
if (condwaits)
api_fatal ("Forked () while a mutex has condition variables waiting on
it.\nReport to [EMAIL PROTECTED]");
@@ -2298,16 +2358,17 @@ __pthread_mutex_unlock (pthread_mutex_t
int
__pthread_mutex_destroy (pthread_mutex_t *mutex)
{
+ int rv;
+
if (pthread_mutex::isGoodInitializer (mutex))
return 0;
if (!pthread_mutex::isGoodObject (mutex))
return EINVAL;
- /*reading a word is atomic */
- if ((*mutex)->condwaits)
- return EBUSY;
+ rv = (*mutex)->Destroy ();
+ if (rv)
+ return rv;
- delete (*mutex);
*mutex = NULL;
return 0;
}
@@ -2345,10 +2406,6 @@ __pthread_mutexattr_getpshared (const pt
return 0;
}
-/*Win32 mutex's are equivalent to posix RECURSIVE mutexs.
- *We need to put glue in place to support other types of mutex's. We map
- *PTHREAD_MUTEX_DEFAULT to PTHREAD_MUTEX_RECURSIVE and return EINVAL for other types.
- */
int
__pthread_mutexattr_gettype (const pthread_mutexattr_t *attr, int *type)
{
@@ -2358,10 +2415,7 @@ __pthread_mutexattr_gettype (const pthre
return 0;
}
-/*Currently pthread_mutex_init ignores the attr variable, this is because
- *none of the variables have any impact on it's behaviour.
- *
- *FIXME: write and test process shared mutex's.
+/*FIXME: write and test process shared mutex's.
*/
int
__pthread_mutexattr_init (pthread_mutexattr_t *attr)
@@ -2438,9 +2492,17 @@ __pthread_mutexattr_settype (pthread_mut
{
if (!pthread_mutexattr::isGoodObject (attr))
return EINVAL;
- if (type != PTHREAD_MUTEX_RECURSIVE)
- return EINVAL;
- (*attr)->mutextype = type;
+
+ switch (type)
+ {
+ case PTHREAD_MUTEX_ERRORCHECK:
+ case PTHREAD_MUTEX_RECURSIVE:
+ (*attr)->mutextype = type;
+ break;
+ default:
+ return EINVAL;
+ }
+
return 0;
}
diff -urp src.old/winsup/cygwin/thread.h src/winsup/cygwin/thread.h
--- src.old/winsup/cygwin/thread.h Sat Sep 21 16:13:42 2002
+++ src/winsup/cygwin/thread.h Mon Sep 23 10:30:01 2002
@@ -152,6 +152,8 @@ private:
#define SEM_MAGIC PTHREAD_MAGIC+7
#define PTHREAD_ONCE_MAGIC PTHREAD_MAGIC+8;
+#define MUTEX_LOCK_COUNTER_INITIAL (-1)
+
/* verifyable_object should not be defined here - it's a general purpose class */
class verifyable_object
@@ -291,15 +293,21 @@ public:
static bool isGoodObject(pthread_mutex_t const *);
static bool isGoodInitializer(pthread_mutex_t const *);
static bool isGoodInitializerOrObject(pthread_mutex_t const *);
- CRITICAL_SECTION criticalsection;
+ LONG lock_counter;
HANDLE win32_obj_id;
+ unsigned int recursion_counter;
LONG condwaits;
+ pthread_t owner;
+ int type;
int pshared;
class pthread_mutex * next;
int Lock ();
int TryLock ();
int UnLock ();
+ int Destroy ();
+ void SetOwner ();
+ int LockRecursive ();
void fixup_after_fork ();
pthread_mutex (pthread_mutexattr * = NULL);
