Changed scheme used to lock the socket multiplexer's job list.

I think the new scheme is easier to understand.  It should have
exactly the same behavior.

lib/net/CSocketMultiplexer.cpp

@@ -32,10 +32,13 @@ CSocketMultiplexer*		CSocketMultiplexer::s_instance = NULL;
 
 CSocketMultiplexer::CSocketMultiplexer() :
 	m_mutex(new CMutex),
-	m_pollable(new CCondVar<bool>(m_mutex, false)),
-	m_polling(new CCondVar<bool>(m_mutex, false)),
 	m_thread(NULL),
-	m_update(false)
+	m_update(false),
+	m_jobsReady(new CCondVar<bool>(m_mutex, false)),
+	m_jobListLock(new CCondVar<bool>(m_mutex, false)),
+	m_jobListLockLocked(new CCondVar<bool>(m_mutex, false)),
+	m_jobListLocker(NULL),
+	m_jobListLockLocker(NULL)
 {
 	assert(s_instance == NULL);
 
@@ -57,8 +60,11 @@ CSocketMultiplexer::~CSocketMultiplexer()
 	m_thread->unblockPollSocket();
 	m_thread->wait();
 	delete m_thread;
-	delete m_polling;
-	delete m_pollable;
+	delete m_jobsReady;
+	delete m_jobListLock;
+	delete m_jobListLockLocked;
+	delete m_jobListLocker;
+	delete m_jobListLockLocker;
 	delete m_mutex;
 
 	// clean up jobs
@@ -82,18 +88,14 @@ CSocketMultiplexer::addSocket(ISocket* socket, ISocketMultiplexerJob* job)
 	assert(socket != NULL);
 	assert(job    != NULL);
 
-	CLock lock(m_mutex);
-
-	// prevent service thread from restarting poll
-	*m_pollable = false;
+	// prevent other threads from locking the job list
+	lockJobListLock();
 
 	// break thread out of poll
 	m_thread->unblockPollSocket();
 
-	// wait for poll to finish
-	while (*m_polling) {
-		m_polling->wait();
-	}
+	// lock the job list
+	lockJobList();
 
 	// insert/replace job
 	CSocketJobMap::iterator i = m_socketJobMap.find(socket);
@@ -114,9 +116,8 @@ CSocketMultiplexer::addSocket(ISocket* socket, ISocketMultiplexerJob* job)
 		m_update = true;
 	}
 
-	// there must be at least one socket so we can poll now
-	*m_pollable = true;
-	m_pollable->broadcast();
+	// unlock the job list
+	unlockJobList();
 }
 
 void
@@ -124,18 +125,14 @@ CSocketMultiplexer::removeSocket(ISocket* socket)
 {
 	assert(socket != NULL);
 
-	CLock lock(m_mutex);
-
-	// prevent service thread from restarting poll
-	*m_pollable = false;
+	// prevent other threads from locking the job list
+	lockJobListLock();
 
 	// break thread out of poll
 	m_thread->unblockPollSocket();
 
-	// wait until thread finishes poll
-	while (*m_polling) {
-		m_polling->wait();
-	}
+	// lock the job list
+	lockJobList();
 
 	// remove job.  rather than removing it from the map we put NULL
 	// in the list instead so the order of jobs in the list continues
@@ -149,8 +146,8 @@ CSocketMultiplexer::removeSocket(ISocket* socket)
 		}
 	}
 
-	*m_pollable = true;
-	m_pollable->broadcast();
+	// unlock the job list
+	unlockJobList();
 }
 
 void
@@ -162,22 +159,18 @@ CSocketMultiplexer::serviceThread(void*)
 	// service the connections
 	for (;;) {
 		CThread::testCancel();
+
+		// wait until there are jobs to handle
 		{
 			CLock lock(m_mutex);
-
-			// wait until pollable
-			while (!(bool)*m_pollable) {
-				m_pollable->wait();
+			while (!(bool)*m_jobsReady) {
+				m_jobsReady->wait();
+			}
 		}
 
-			// now we're polling
-			*m_polling = true;
-			m_polling->broadcast();
-		}
-
-		// we're now the only thread that can access m_sockets and
-		// m_update because m_polling and m_pollable are both true.
-		// therefore, we don't need to hold the mutex.
+		// lock the job list
+		lockJobListLock();
+		lockJobList();
 
 		// collect poll entries
 		if (m_update) {
@@ -251,7 +244,6 @@ CSocketMultiplexer::serviceThread(void*)
 		}
 
 		// delete any removed socket jobs
-		CLock lock(m_mutex);
 		for (CSocketJobMap::iterator i = m_socketJobMap.begin();
 							i != m_socketJobMap.end();) {
 			if (*(i->second) == NULL) {
@@ -262,13 +254,9 @@ CSocketMultiplexer::serviceThread(void*)
 				++i;
 			}
 		}
-		if (m_socketJobMap.empty()) {
-			*m_pollable = false;
-		}
 
-		// done polling
-		*m_polling = false;
-		m_polling->broadcast();
+		// unlock the job list
+		unlockJobList();
 	}
 }
 
@@ -304,3 +292,63 @@ CSocketMultiplexer::deleteCursor(CJobCursor cursor)
 	CLock lock(m_mutex);
 	m_socketJobs.erase(cursor);
 }
+
+void
+CSocketMultiplexer::lockJobListLock()
+{
+	CLock lock(m_mutex);
+
+	// wait for the lock on the lock
+	while (*m_jobListLockLocked) {
+		m_jobListLockLocked->wait();
+	}
+
+	// take ownership of the lock on the lock
+	*m_jobListLockLocked = true;
+	m_jobListLockLocker  = new CThread(CThread::getCurrentThread());
+}
+
+void
+CSocketMultiplexer::lockJobList()
+{
+	CLock lock(m_mutex);
+
+	// make sure we're the one that called lockJobListLock()
+	assert(*m_jobListLockLocker == CThread::getCurrentThread());
+
+	// wait for the job list lock
+	while (*m_jobListLock) {
+		m_jobListLock->wait();
+	}
+
+	// take ownership of the lock
+	*m_jobListLock      = true;
+	m_jobListLocker     = m_jobListLockLocker;
+	m_jobListLockLocker = NULL;
+
+	// release the lock on the lock
+	*m_jobListLockLocked = false;
+	m_jobListLockLocked->broadcast();
+}
+
+void
+CSocketMultiplexer::unlockJobList()
+{
+	CLock lock(m_mutex);
+
+	// make sure we're the one that called lockJobList()
+	assert(*m_jobListLocker == CThread::getCurrentThread());
+
+	// release the lock
+	delete m_jobListLocker;
+	m_jobListLocker = NULL;
+	*m_jobListLock  = false;
+	m_jobListLock->signal();
+
+	// set new jobs ready state
+	bool isReady = !m_socketJobMap.empty();
+	if (*m_jobsReady != isReady) {
+		*m_jobsReady = isReady;
+		m_jobsReady->signal();
+	}
+}

lib/net/CSocketMultiplexer.h

@@ -78,12 +78,28 @@ private:
 	CJobCursor			nextCursor(CJobCursor);
 	void				deleteCursor(CJobCursor);
 
+	// lock out locking the job list.  this blocks if another thread
+	// has already locked out locking.  once it returns, only the
+	// calling thread will be able to lock the job list after any
+	// current lock is released.
+	void				lockJobListLock();
+
+	// lock the job list.  this blocks if the job list is already
+	// locked.  the calling thread must have called requestJobLock.
+	void				lockJobList();
+
+	// unlock the job list and the lock out on locking.
+	void				unlockJobList();
+
 private:
 	CMutex*				m_mutex;
-	CCondVar<bool>*		m_pollable;
-	CCondVar<bool>*		m_polling;
 	CThread*			m_thread;
 	bool				m_update;
+	CCondVar<bool>*		m_jobsReady;
+	CCondVar<bool>*		m_jobListLock;
+	CCondVar<bool>*		m_jobListLockLocked;
+	CThread*			m_jobListLocker;
+	CThread*			m_jobListLockLocker;
 
 	CSocketJobs			m_socketJobs;
 	CSocketJobMap		m_socketJobMap;