Added new mutex_switch_from_read_lock() for unlocking a read lock and

starting to lock a mutex in an atomic operation.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@34935 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/lock.h

@@ -124,7 +124,6 @@ extern void rw_lock_init(rw_lock* lock, const char* name);
 extern void rw_lock_init_etc(rw_lock* lock, const char* name, uint32 flags);
 extern void rw_lock_destroy(rw_lock* lock);
 extern status_t rw_lock_write_lock(rw_lock* lock);
-extern void rw_lock_write_unlock(rw_lock* lock);
 
 extern void mutex_init(mutex* lock, const char* name);
 	// name is *not* cloned nor freed in mutex_destroy()
@@ -135,12 +134,16 @@ extern status_t mutex_switch_lock(mutex* from, mutex* to);
 	// for the lock is atomically. I.e. if "from" guards the object "to" belongs
 	// to, the operation is safe as long as "from" is held while destroying
 	// "to".
+extern status_t mutex_switch_from_read_lock(rw_lock* from, mutex* to);
+	// Like mutex_switch_lock(), just for a switching from a read-locked
+	// rw_lock.
 
 
 // implementation private:
 
 extern status_t _rw_lock_read_lock(rw_lock* lock);
-extern void _rw_lock_read_unlock(rw_lock* lock);
+extern void _rw_lock_read_unlock(rw_lock* lock, bool threadsLocked);
+extern void _rw_lock_write_unlock(rw_lock* lock, bool threadsLocked);
 
 extern status_t _mutex_lock(mutex* lock, bool threadsLocked);
 extern void _mutex_unlock(mutex* lock, bool threadsLocked);
@@ -171,11 +174,18 @@ rw_lock_read_unlock(rw_lock* lock)
 #else
 	int32 oldCount = atomic_add(&lock->count, -1);
 	if (oldCount >= RW_LOCK_WRITER_COUNT_BASE)
-		_rw_lock_read_unlock(lock);
+		_rw_lock_read_unlock(lock, false);
 #endif
 }
 
 
+static inline void
+rw_lock_write_unlock(rw_lock* lock)
+{
+	_rw_lock_write_unlock(lock, false);
+}
+
+
 static inline status_t
 mutex_lock(mutex* lock)
 {

src/system/kernel/lock.cpp

@@ -323,9 +323,9 @@ _rw_lock_read_lock(rw_lock* lock)
 
 
 void
-_rw_lock_read_unlock(rw_lock* lock)
+_rw_lock_read_unlock(rw_lock* lock, bool threadsLocked)
 {
-	InterruptsSpinLocker locker(gThreadSpinlock);
+	InterruptsSpinLocker locker(gThreadSpinlock, false, !threadsLocked);
 
 	// If we're still holding the write lock or if there are other readers,
 	// no-one can be woken up.
@@ -389,9 +389,9 @@ rw_lock_write_lock(rw_lock* lock)
 
 
 void
-rw_lock_write_unlock(rw_lock* lock)
+_rw_lock_write_unlock(rw_lock* lock, bool threadsLocked)
 {
-	InterruptsSpinLocker locker(gThreadSpinlock);
+	InterruptsSpinLocker locker(gThreadSpinlock, false, !threadsLocked);
 
 	if (thread_get_current_thread_id() != lock->holder) {
 		panic("rw_lock_write_unlock(): lock %p not write-locked by this thread",
@@ -558,6 +558,23 @@ mutex_switch_lock(mutex* from, mutex* to)
 }
 
 
+status_t
+mutex_switch_from_read_lock(rw_lock* from, mutex* to)
+{
+	InterruptsSpinLocker locker(gThreadSpinlock);
+
+#if KDEBUG_RW_LOCK_DEBUG
+	_rw_lock_write_unlock(from, true);
+#else
+	int32 oldCount = atomic_add(&from->count, -1);
+	if (oldCount >= RW_LOCK_WRITER_COUNT_BASE)
+		_rw_lock_read_unlock(from, true);
+#endif
+
+	return mutex_lock_threads_locked(to);
+}
+
+
 status_t
 _mutex_lock(mutex* lock, bool threadsLocked)
 {

src/tests/add-ons/kernel/kernelland_emu/lock.cpp

@@ -360,9 +360,9 @@ _rw_lock_read_lock(rw_lock* lock)
 
 
 void
-_rw_lock_read_unlock(rw_lock* lock)
+_rw_lock_read_unlock(rw_lock* lock, bool threadsLocked)
 {
-	AutoLocker<ThreadSpinlock> locker(sThreadSpinlock);
+	AutoLocker<ThreadSpinlock> locker(sThreadSpinlock, false, !threadsLocked);
 
 	// If we're still holding the write lock or if there are other readers,
 	// no-one can be woken up.
@@ -425,9 +425,9 @@ rw_lock_write_lock(rw_lock* lock)
 
 
 void
-rw_lock_write_unlock(rw_lock* lock)
+_rw_lock_write_unlock(rw_lock* lock, bool threadsLocked)
 {
-	AutoLocker<ThreadSpinlock> locker(sThreadSpinlock);
+	AutoLocker<ThreadSpinlock> locker(sThreadSpinlock, false, !threadsLocked);
 
 	if (find_thread(NULL) != lock->holder) {
 		panic("rw_lock_write_unlock(): lock %p not write-locked by this thread",
@@ -548,6 +548,23 @@ mutex_switch_lock(mutex* from, mutex* to)
 }
 
 
+status_t
+mutex_switch_from_read_lock(rw_lock* from, mutex* to)
+{
+	AutoLocker<ThreadSpinlock> locker(sThreadSpinlock);
+
+#if KDEBUG_RW_LOCK_DEBUG
+	_rw_lock_write_unlock(from, true);
+#else
+	int32 oldCount = atomic_add(&from->count, -1);
+	if (oldCount >= RW_LOCK_WRITER_COUNT_BASE)
+		_rw_lock_read_unlock(from, true);
+#endif
+
+	return mutex_lock_threads_locked(to);
+}
+
+
 status_t
 _mutex_lock(mutex* lock, bool threadsLocked)
 {