* The rw_lock is now using a mutex to protect its reader/writer counts. This

makes the reader case a lot less expensive, and should relieve the thread
  spinlock contention a bit.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@33643 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/lock.h

@@ -42,6 +42,7 @@ struct rw_lock_waiter;
 
 typedef struct rw_lock {
 	const char*				name;
+	mutex					lock;
 	struct rw_lock_waiter*	waiters;
 	thread_id				holder;
 	int32					reader_count;
@@ -85,7 +86,8 @@ typedef struct rw_lock {
 #	define RECURSIVE_LOCK_INITIALIZER(name)	{ MUTEX_INITIALIZER(name), -1, 0 }
 #endif
 
-#define RW_LOCK_INITIALIZER(name)			{ name, NULL, -1, 0, 0, 0 }
+#define RW_LOCK_INITIALIZER(name)			{ name, MUTEX_INITIALIZER(name), \
+												NULL, -1, 0, 0, 0 }
 
 
 #if KDEBUG

src/system/kernel/lock.cpp

@@ -164,6 +164,10 @@ rw_lock_wait(rw_lock* lock, bool writer)
 
 	lock->waiters->last = &waiter;
 
+	InterruptsSpinLocker locker(gThreadSpinlock);
+
+	_mutex_unlock(&lock->lock, true);
+
 	// block
 	thread_prepare_to_block(waiter.thread, 0, THREAD_BLOCK_TYPE_RW_LOCK, lock);
 	return thread_block_locked(waiter.thread);
@@ -190,6 +194,7 @@ rw_lock_unblock(rw_lock* lock)
 			lock->holder = waiter->thread->id;
 
 			// unblock thread
+			InterruptsSpinLocker locker(gThreadSpinlock);
 			thread_unblock_locked(waiter->thread, B_OK);
 		}
 		return;
@@ -205,6 +210,7 @@ rw_lock_unblock(rw_lock* lock)
 		lock->reader_count++;
 
 		// unblock thread
+		InterruptsSpinLocker locker(gThreadSpinlock);
 		thread_unblock_locked(waiter->thread, B_OK);
 	}
 }
@@ -221,6 +227,8 @@ rw_lock_init(rw_lock* lock, const char* name)
 	lock->owner_count = 0;
 	lock->flags = 0;
 
+	mutex_init(&lock->lock, name);
+
 	T_SCHEDULING_ANALYSIS(InitRWLock(lock, name));
 	NotifyWaitObjectListeners(&WaitObjectListener::RWLockInitialized, lock);
 }
@@ -237,6 +245,8 @@ rw_lock_init_etc(rw_lock* lock, const char* name, uint32 flags)
 	lock->owner_count = 0;
 	lock->flags = flags & RW_LOCK_FLAG_CLONE_NAME;
 
+	mutex_init(&lock->lock, lock->name);
+
 	T_SCHEDULING_ANALYSIS(InitRWLock(lock, name));
 	NotifyWaitObjectListeners(&WaitObjectListener::RWLockInitialized, lock);
 }
@@ -252,8 +262,8 @@ rw_lock_destroy(rw_lock* lock)
 	InterruptsSpinLocker locker(gThreadSpinlock);
 
 #if KDEBUG
-	if (lock->waiters != NULL && thread_get_current_thread_id()
+	if (lock->waiters != NULL
-		!= lock->holder) {
+		&& thread_get_current_thread_id() != lock->holder) {
 		panic("rw_lock_destroy(): there are blocking threads, but the caller "
 			"doesn't hold the write lock (%p)", lock);
 
@@ -275,6 +285,7 @@ rw_lock_destroy(rw_lock* lock)
 	lock->name = NULL;
 
 	locker.Unlock();
+	mutex_destroy(&lock->lock);
 
 	free(name);
 }
@@ -286,7 +297,7 @@ rw_lock_read_lock(rw_lock* lock)
 #if KDEBUG_RW_LOCK_DEBUG
 	return rw_lock_write_lock(lock);
 #else
-	InterruptsSpinLocker locker(gThreadSpinlock);
+	MutexLocker locker(lock->lock);
 
 	if (lock->writer_count == 0) {
 		lock->reader_count++;
@@ -297,6 +308,8 @@ rw_lock_read_lock(rw_lock* lock)
 		return B_OK;
 	}
 
+	locker.Detach();
+
 	return rw_lock_wait(lock, false);
 #endif
 }
@@ -308,7 +321,7 @@ rw_lock_read_unlock(rw_lock* lock)
 #if KDEBUG_RW_LOCK_DEBUG
 	return rw_lock_write_unlock(lock);
 #else
-	InterruptsSpinLocker locker(gThreadSpinlock);
+	MutexLocker locker(lock->lock);
 
 	if (lock->holder == thread_get_current_thread_id()) {
 		if (--lock->owner_count > 0)
@@ -338,7 +351,7 @@ rw_lock_read_unlock(rw_lock* lock)
 status_t
 rw_lock_write_lock(rw_lock* lock)
 {
-	InterruptsSpinLocker locker(gThreadSpinlock);
+	MutexLocker locker(lock->lock);
 
 	if (lock->reader_count == 0 && lock->writer_count == 0) {
 		lock->writer_count++;
@@ -352,6 +365,7 @@ rw_lock_write_lock(rw_lock* lock)
 	}
 
 	lock->writer_count++;
+	locker.Detach();
 
 	status_t status = rw_lock_wait(lock, true);
 	if (status == B_OK) {
@@ -365,7 +379,7 @@ rw_lock_write_lock(rw_lock* lock)
 status_t
 rw_lock_write_unlock(rw_lock* lock)
 {
-	InterruptsSpinLocker locker(gThreadSpinlock);
+	MutexLocker locker(lock->lock);
 
 	if (thread_get_current_thread_id() != lock->holder) {
 		panic("rw_lock_write_unlock(): lock %p not write-locked by this thread",