From c83f8e243463554ecf3a91e45d3e0b3b9c11895c Mon Sep 17 00:00:00 2001
From: Guenter Obiltschnig <guenter.obiltschnig@appinf.com>
Date: Wed, 17 Sep 2008 19:13:50 +0000
Subject: [PATCH] fixed SF# 1896482: tryReadLock intermittent error

---
 Foundation/include/Poco/RWLock_WIN32.h  |  3 ++-
 Foundation/src/RWLock_WIN32.cpp         | 21 ++++++++++++++-------
 Foundation/testsuite/src/RWLockTest.cpp | 16 +++++++++++++++-
 3 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/Foundation/include/Poco/RWLock_WIN32.h b/Foundation/include/Poco/RWLock_WIN32.h
index 2572a3646..7345ec5a7 100644
--- a/Foundation/include/Poco/RWLock_WIN32.h
+++ b/Foundation/include/Poco/RWLock_WIN32.h
@@ -1,7 +1,7 @@
 //
 // RWLock_WIN32.h
 //
-// $Id: //poco/svn/Foundation/include/Poco/RWLock_WIN32.h#2 $
+// $Id: //poco/1.3/Foundation/include/Poco/RWLock_WIN32.h#3 $
 //
 // Library: Foundation
 // Package: Threading
@@ -67,6 +67,7 @@ private:
 	HANDLE   _readEvent;
 	HANDLE   _writeEvent;
 	unsigned _readers;
+	unsigned _writersWaiting;
 	unsigned _writers;
 };
 
diff --git a/Foundation/src/RWLock_WIN32.cpp b/Foundation/src/RWLock_WIN32.cpp
index f28a2411d..6a3296470 100644
--- a/Foundation/src/RWLock_WIN32.cpp
+++ b/Foundation/src/RWLock_WIN32.cpp
@@ -1,7 +1,7 @@
 //
 // RWLock_WIN32.cpp
 //
-// $Id: //poco/svn/Foundation/src/RWLock_WIN32.cpp#2 $
+// $Id: //poco/1.3/Foundation/src/RWLock_WIN32.cpp#3 $
 //
 // Library: Foundation
 // Package: Threading
@@ -40,7 +40,7 @@
 namespace Poco {
 
 
-RWLockImpl::RWLockImpl(): _readers(0), _writers(0)
+RWLockImpl::RWLockImpl(): _readers(0), _writersWaiting(0), _writers(0)
 {
 	_mutex = CreateMutexW(NULL, FALSE, NULL);
 	if (_mutex == NULL)
@@ -69,7 +69,7 @@ inline void RWLockImpl::addWriter()
 	switch (WaitForSingleObject(_mutex, INFINITE))
 	{
 	case WAIT_OBJECT_0:
-		if (++_writers == 1) ResetEvent(_readEvent);
+		if (++_writersWaiting == 1) ResetEvent(_readEvent);
 		ReleaseMutex(_mutex);
 		break;
 	default:
@@ -83,7 +83,7 @@ inline void RWLockImpl::removeWriter()
 	switch (WaitForSingleObject(_mutex, INFINITE))
 	{
 	case WAIT_OBJECT_0:
-		if (--_writers == 0) SetEvent(_readEvent);
+		if (--_writersWaiting == 0 && _writers == 0) SetEvent(_readEvent);
 		ReleaseMutex(_mutex);
 		break;
 	default:
@@ -104,6 +104,7 @@ void RWLockImpl::readLockImpl()
 		++_readers;
 		ResetEvent(_writeEvent);
 		ReleaseMutex(_mutex);
+		poco_assert_dbg(_writers == 0);
 		break;
 	default:
 		throw SystemException("cannot lock reader/writer lock");
@@ -123,6 +124,7 @@ bool RWLockImpl::tryReadLockImpl()
 		++_readers;
 		ResetEvent(_writeEvent);
 		ReleaseMutex(_mutex);
+		poco_assert_dbg(_writers == 0);
 		return true;
 	case WAIT_TIMEOUT:
 		return false;
@@ -142,11 +144,13 @@ void RWLockImpl::writeLockImpl()
 	{
 	case WAIT_OBJECT_0:
 	case WAIT_OBJECT_0 + 1:
-		--_writers;
+		--_writersWaiting;
 		++_readers;
+		++_writers;
 		ResetEvent(_readEvent);
 		ResetEvent(_writeEvent);
 		ReleaseMutex(_mutex);
+		poco_assert_dbg(_writers == 1);
 		break;
 	default:
 		removeWriter();
@@ -165,11 +169,13 @@ bool RWLockImpl::tryWriteLockImpl()
 	{
 	case WAIT_OBJECT_0:
 	case WAIT_OBJECT_0 + 1:
-		--_writers;
+		--_writersWaiting;
 		++_readers;
+		++_writers;
 		ResetEvent(_readEvent);
 		ResetEvent(_writeEvent);
 		ReleaseMutex(_mutex);
+		poco_assert_dbg(_writers == 1);
 		return true;
 	case WAIT_TIMEOUT:
 		removeWriter();
@@ -186,7 +192,8 @@ void RWLockImpl::unlockImpl()
 	switch (WaitForSingleObject(_mutex, INFINITE))
 	{
 	case WAIT_OBJECT_0:
-		if (_writers == 0) SetEvent(_readEvent);
+		_writers = 0;
+		if (_writersWaiting == 0) SetEvent(_readEvent);
 		if (--_readers == 0) SetEvent(_writeEvent);
 		ReleaseMutex(_mutex);
 		break;
diff --git a/Foundation/testsuite/src/RWLockTest.cpp b/Foundation/testsuite/src/RWLockTest.cpp
index 28873a2df..5c5e1d082 100644
--- a/Foundation/testsuite/src/RWLockTest.cpp
+++ b/Foundation/testsuite/src/RWLockTest.cpp
@@ -1,7 +1,7 @@
 //
 // RWLockTest.cpp
 //
-// $Id: //poco/svn/Foundation/testsuite/src/RWLockTest.cpp#2 $
+// $Id: //poco/1.3/Foundation/testsuite/src/RWLockTest.cpp#2 $
 //
 // Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
 // and Contributors.
@@ -60,13 +60,20 @@ public:
 			for (int k = 0; k < 100; ++k)
 			{
 				if (_counter != lastCount) _ok = false;
+				Thread::yield();
 			}
 			_lock.unlock();
 			_lock.writeLock();
 			for (int k = 0; k < 100; ++k)
+			{
 				--_counter;
+				Thread::yield();
+			}
 			for (int k = 0; k < 100; ++k)
+			{
 				++_counter;
+				Thread::yield();
+			}
 			++_counter;
 			if (_counter <= lastCount) _ok = false;
 			_lock.unlock();
@@ -102,13 +109,20 @@ public:
 			for (int k = 0; k < 100; ++k)
 			{
 				if (_counter != lastCount) _ok = false;
+				Thread::yield();
 			}
 			_lock.unlock();
 			while (!_lock.tryWriteLock()) Thread::yield();
 			for (int k = 0; k < 100; ++k)
+			{
 				--_counter;
+				Thread::yield();
+			}
 			for (int k = 0; k < 100; ++k)
+			{
 				++_counter;
+				Thread::yield();
+			}
 			++_counter;
 			if (_counter <= lastCount) _ok = false;
 			_lock.unlock();