Added RWLockable and RWLockManager classes. The former is basically a

light-weight read-write lock, that doesn't use a semaphore itself. Locking
and unlocking has to be done via methods of RWLockManager. This combo allows
lots of locks without risking to hit the semaphore limit.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@29686 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/shared/RWLockManager.h

@@ -0,0 +1,131 @@
+/*
+ * Copyright 2009, Ingo Weinhold, [email protected].
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _RW_LOCK_MANAGER_H
+#define _RW_LOCK_MANAGER_H
+
+#include <Locker.h>
+
+#include <util/DoublyLinkedList.h>
+
+
+namespace BPrivate {
+
+
+class RWLockManager;
+
+
+class RWLockable {
+public:
+								RWLockable();
+
+private:
+	struct Waiter : DoublyLinkedListLinkImpl<Waiter> {
+		Waiter(bool writer)
+			:
+			thread(find_thread(NULL)),
+			writer(writer),
+			queued(false)
+		{
+		}
+
+		thread_id		thread;
+		status_t		status;
+		bool			writer;
+		bool			queued;
+	};
+
+	typedef DoublyLinkedList<Waiter> WaiterList;
+
+	friend class RWLockManager;
+
+private:
+				thread_id		fOwner;
+				int32			fOwnerCount;
+				int32			fReaderCount;
+				WaiterList		fWaiters;
+};
+
+
+class RWLockManager {
+public:
+								RWLockManager();
+								~RWLockManager();
+
+			status_t			Init()		{ return fLock.InitCheck(); }
+
+			bool				Lock()		{ return fLock.Lock(); }
+			void				Unlock()	{ return fLock.Unlock(); }
+
+			bool				ReadLock(RWLockable* lockable);
+			bool				TryReadLock(RWLockable* lockable);
+			status_t			ReadLockWithTimeout(RWLockable* lockable,
+									bigtime_t timeout);
+			void				ReadUnlock(RWLockable* lockable);
+
+			bool				WriteLock(RWLockable* lockable);
+			bool				TryWriteLock(RWLockable* lockable);
+			status_t			WriteLockWithTimeout(RWLockable* lockable,
+									bigtime_t timeout);
+			void				WriteUnlock(RWLockable* lockable);
+
+	inline	bool				GenericLock(bool write, RWLockable* lockable);
+	inline	bool				TryGenericLock(bool write,
+									RWLockable* lockable);
+	inline	status_t			GenericLockWithTimeout(bool write,
+									RWLockable* lockable, bigtime_t timeout);
+	inline	void				GenericUnlock(bool write, RWLockable* lockable);
+
+private:
+			status_t			_Wait(RWLockable* lockable, bool writer,
+									bigtime_t timeout);
+			void				_Unblock(RWLockable* lockable);
+
+private:
+			BLocker				fLock;
+};
+
+
+inline bool
+RWLockManager::GenericLock(bool write, RWLockable* lockable)
+{
+	return write ? WriteLock(lockable) : ReadLock(lockable);
+}
+
+
+inline bool
+RWLockManager::TryGenericLock(bool write, RWLockable* lockable)
+{
+	return write ? TryWriteLock(lockable) : TryReadLock(lockable);
+}
+
+
+inline status_t
+RWLockManager::GenericLockWithTimeout(bool write, RWLockable* lockable,
+	bigtime_t timeout)
+{
+	return write
+		? WriteLockWithTimeout(lockable, timeout)
+		: ReadLockWithTimeout(lockable, timeout);
+}
+
+
+inline void
+RWLockManager::GenericUnlock(bool write, RWLockable* lockable)
+{
+	if (write)
+		WriteUnlock(lockable);
+	else
+		ReadUnlock(lockable);
+}
+
+
+}	// namespace BPrivate
+
+
+using BPrivate::RWLockable;
+using BPrivate::RWLockManager;
+
+
+#endif	// _RW_LOCK_MANAGER_H

src/kits/shared/Jamfile

@@ -6,6 +6,10 @@ AddSubDirSupportedPlatforms libbe_test ;
 UseLibraryHeaders agg ;
 UsePrivateHeaders shared ;
 
+# for RWLockManager only
+UsePrivateSystemHeaders ;
+UsePrivateHeaders kernel libroot ;
+
 StaticLibrary libshared.a :
 	AboutWindow.cpp
 	AffineTransform.cpp
@@ -14,4 +18,5 @@ StaticLibrary libshared.a :
 	CommandPipe.cpp
 	DateTime.cpp
 	HashString.cpp
+	RWLockManager.cpp
 ;

src/kits/shared/RWLockManager.cpp

@@ -0,0 +1,259 @@
+/*
+ * Copyright 2009, Ingo Weinhold, [email protected].
+ * Distributed under the terms of the MIT License.
+ */
+
+#include <RWLockManager.h>
+
+#include <AutoLocker.h>
+
+#include <syscalls.h>
+#include <user_thread.h>
+
+
+RWLockable::RWLockable()
+	:
+	fOwner(-1),
+	fOwnerCount(0),
+	fReaderCount(0)
+{
+}
+
+
+RWLockManager::RWLockManager()
+	:
+	fLock("r/w lock manager")
+{
+}
+
+
+RWLockManager::~RWLockManager()
+{
+}
+
+
+bool
+RWLockManager::ReadLock(RWLockable* lockable)
+{
+	AutoLocker<RWLockManager> locker(this);
+
+	if (lockable->fWaiters.IsEmpty()) {
+		lockable->fReaderCount++;
+		return true;
+	}
+
+	return _Wait(lockable, false, B_INFINITE_TIMEOUT) == B_OK;
+}
+
+
+bool
+RWLockManager::TryReadLock(RWLockable* lockable)
+{
+	AutoLocker<RWLockManager> locker(this);
+
+	if (lockable->fWaiters.IsEmpty()) {
+		lockable->fReaderCount++;
+		return true;
+	}
+
+	return false;
+}
+
+
+status_t
+RWLockManager::ReadLockWithTimeout(RWLockable* lockable, bigtime_t timeout)
+{
+	AutoLocker<RWLockManager> locker(this);
+
+	if (lockable->fWaiters.IsEmpty()) {
+		lockable->fReaderCount++;
+		return B_OK;
+	}
+
+	return _Wait(lockable, false, timeout);
+}
+
+
+void
+RWLockManager::ReadUnlock(RWLockable* lockable)
+{
+	AutoLocker<RWLockManager> locker(this);
+
+	if (lockable->fReaderCount <= 0) {
+		debugger("RWLockManager::ReadUnlock(): Not read-locked!");
+		return;
+	}
+
+	if (--lockable->fReaderCount == 0)
+		_Unblock(lockable);
+}
+
+
+bool
+RWLockManager::WriteLock(RWLockable* lockable)
+{
+	AutoLocker<RWLockManager> locker(this);
+
+	thread_id thread = find_thread(NULL);
+
+	if (lockable->fOwner == thread) {
+		lockable->fOwnerCount++;
+		return true;
+	}
+
+	if (lockable->fReaderCount == 0 && lockable->fWaiters.IsEmpty()) {
+		lockable->fOwnerCount = 1;
+		lockable->fOwner = find_thread(NULL);
+		return true;
+	}
+
+	return _Wait(lockable, true, B_INFINITE_TIMEOUT) == B_OK;
+}
+
+
+bool
+RWLockManager::TryWriteLock(RWLockable* lockable)
+{
+	AutoLocker<RWLockManager> locker(this);
+
+	thread_id thread = find_thread(NULL);
+
+	if (lockable->fOwner == thread) {
+		lockable->fOwnerCount++;
+		return true;
+	}
+
+	if (lockable->fReaderCount == 0 && lockable->fWaiters.IsEmpty()) {
+		lockable->fOwnerCount++;
+		lockable->fOwner = thread;
+		return true;
+	}
+
+	return false;
+}
+
+
+status_t
+RWLockManager::WriteLockWithTimeout(RWLockable* lockable, bigtime_t timeout)
+{
+	AutoLocker<RWLockManager> locker(this);
+
+	thread_id thread = find_thread(NULL);
+
+	if (lockable->fOwner == thread) {
+		lockable->fOwnerCount++;
+		return B_OK;
+	}
+
+	if (lockable->fReaderCount == 0 && lockable->fWaiters.IsEmpty()) {
+		lockable->fOwnerCount++;
+		lockable->fOwner = thread;
+		return B_OK;
+	}
+
+	return _Wait(lockable, true, timeout);
+}
+
+
+void
+RWLockManager::WriteUnlock(RWLockable* lockable)
+{
+	AutoLocker<RWLockManager> locker(this);
+
+	if (find_thread(NULL) != lockable->fOwner) {
+		debugger("RWLockManager::WriteUnlock(): Not write-locked by calling "
+			"thread!");
+		return;
+	}
+
+	if (--lockable->fOwnerCount == 0) {
+		lockable->fOwner = -1;
+		_Unblock(lockable);
+	}
+}
+
+
+status_t
+RWLockManager::_Wait(RWLockable* lockable, bool writer, bigtime_t timeout)
+{
+	if (timeout == 0)
+		return B_TIMED_OUT;
+
+	// enqueue a waiter
+	RWLockable::Waiter waiter(writer);
+	lockable->fWaiters.Add(&waiter);
+	waiter.queued = true;
+	get_user_thread()->wait_status = 1;
+
+	// wait
+	Unlock();
+
+	status_t error;
+	do {
+		error = _kern_block_thread(
+			timeout >= 0 ? B_RELATIVE_TIMEOUT : 0, timeout);
+			// TODO: When interrupted we should adjust the timeout, respectively
+			// convert to an absolute timeout in the first place!
+	} while (error == B_INTERRUPTED);
+
+	Lock();
+
+	if (!waiter.queued)
+		return waiter.status;
+
+	// we're still queued, which means an error (timeout, interrupt)
+	// occurred
+	lockable->fWaiters.Remove(&waiter);
+
+	_Unblock(lockable);
+
+	return error;
+}
+
+
+void
+RWLockManager::_Unblock(RWLockable* lockable)
+{
+	// Check whether there any waiting threads at all and whether anyone
+	// has the write lock
+	RWLockable::Waiter* waiter = lockable->fWaiters.Head();
+	if (waiter == NULL || lockable->fOwner >= 0)
+		return;
+
+	// writer at head of queue?
+	if (waiter->writer) {
+		if (lockable->fReaderCount == 0) {
+			waiter->status = B_OK;
+			waiter->queued = false;
+			lockable->fWaiters.Remove(waiter);
+			lockable->fOwner = waiter->thread;
+			lockable->fOwnerCount = 1;
+
+			_kern_unblock_thread(waiter->thread, B_OK);
+		}
+		return;
+	}
+
+	// wake up one or more readers -- we unblock more than one reader at
+	// a time to save trips to the kernel
+	while (!lockable->fWaiters.IsEmpty()
+			&& !lockable->fWaiters.Head()->writer) {
+		static const int kMaxReaderUnblockCount = 128;
+		thread_id readers[kMaxReaderUnblockCount];
+		int readerCount = 0;
+
+		while (readerCount < kMaxReaderUnblockCount
+				&& (waiter = lockable->fWaiters.Head()) != NULL
+				&& !waiter->writer) {
+			waiter->status = B_OK;
+			waiter->queued = false;
+			lockable->fWaiters.Remove(waiter);
+
+			readers[readerCount++] = waiter->thread;
+			lockable->fReaderCount++;
+		}
+
+		if (readerCount > 0)
+			_kern_unblock_threads(readers, readerCount, B_OK);
+	}
+}