fix(AsyncChannel): race condition in AsyncChannel close/log #1039

Foundation/include/Poco/AsyncChannel.h

@@ -25,6 +25,7 @@
 #include "Poco/Runnable.h"
 #include "Poco/AutoPtr.h"
 #include "Poco/NotificationQueue.h"
+#include <atomic>
 
 
 namespace Poco {
@@ -110,6 +111,7 @@ private:
 	NotificationQueue _queue;
 	std::size_t _queueSize = 0;
 	std::size_t _dropCount = 0;
+	std::atomic<bool> _closed;
 };
 
 

Foundation/src/AsyncChannel.cpp

@@ -51,7 +51,8 @@ private:
 
 AsyncChannel::AsyncChannel(Channel::Ptr pChannel, Thread::Priority prio):
 	_pChannel(pChannel),
-	_thread("AsyncChannel")
+	_thread("AsyncChannel"),
+	_closed(false)
 {
 	_thread.setPriority(prio);
 }
@@ -94,21 +95,25 @@ void AsyncChannel::open()
 
 void AsyncChannel::close()
 {
-	if (_thread.isRunning())
+	if (!_closed.exchange(true))
 	{
-		while (!_queue.empty()) Thread::sleep(100);
-
-		do
+		if (_thread.isRunning())
 		{
-			_queue.wakeUpAll();
+			while (!_queue.empty()) Thread::sleep(100);
+
+			do
+			{
+				_queue.wakeUpAll();
+			}
+			while (!_thread.tryJoin(100));
 		}
-		while (!_thread.tryJoin(100));
 	}
 }
 
 
 void AsyncChannel::log(const Message& msg)
 {
+	if (_closed) return;
 	if (_queueSize != 0 && _queue.size() >= _queueSize)
 	{
 		++_dropCount;

Foundation/testsuite/src/ChannelTest.cpp

@@ -31,6 +31,8 @@ using Poco::StreamChannel;
 using Poco::Formatter;
 using Poco::Message;
 using Poco::AutoPtr;
+using Poco::Thread;
+using Poco::Runnable;
 
 
 class SimpleFormatter: public Formatter
@@ -45,6 +47,32 @@ public:
 };
 
 
+class LogRunnable : public Runnable
+{
+public:
+	LogRunnable(AutoPtr<AsyncChannel> pAsync):
+		_pAsync(pAsync),
+		_stop(false)
+	{
+	}
+
+	void run()
+	{
+		Message msg;
+		while (!_stop) _pAsync->log(msg);
+	}
+
+	void stop()
+	{
+		_stop = true;
+	}
+
+private:
+	AutoPtr<AsyncChannel> _pAsync;
+	std::atomic<bool> _stop;
+};
+
+
 ChannelTest::ChannelTest(const std::string& name): CppUnit::TestCase(name)
 {
 }
@@ -71,12 +99,17 @@ void ChannelTest::testAsync()
 {
 	AutoPtr<TestChannel> pChannel = new TestChannel;
 	AutoPtr<AsyncChannel> pAsync = new AsyncChannel(pChannel);
+	LogRunnable lr(pAsync);
 	pAsync->open();
+	Thread t;
+	t.start(lr);
 	Message msg;
 	pAsync->log(msg);
 	pAsync->log(msg);
 	pAsync->close();
-	assertTrue (pChannel->list().size() == 2);
+	lr.stop();
+	t.join();
+	assertTrue (pChannel->list().size() >= 2);
 }