Fixing threads' DoFinish() method.

It wasn't called reliably. Now, it's always called before the thread
is destroyed (assuming processing has went normally so far).

src/threading/MsgThread.cc

@@ -10,13 +10,21 @@ namespace threading  {
 
 ////// Messages.
 
-// Signals child thread to terminate. This is actually a no-op; its only
+// Signals child thread to shutdown operation.
-// purpose is unblock the current read operation so that the child's Run()
+class FinishMessage : public InputMessage<MsgThread>
-// methods can check the termination status.
-class TerminateMessage : public InputMessage<MsgThread>
 {
 public:
-	TerminateMessage(MsgThread* thread) : InputMessage<MsgThread>("Terminate", thread)	{ }
+	FinishMessage(MsgThread* thread) : InputMessage<MsgThread>("Finish", thread)	{ }
+
+	virtual bool Process()	{ return Object()->DoFinish(); }
+};
+
+// A dummy message that's only purpose is unblock the current read operation
+// so that the child's Run() methods can check the termination status.
+class UnblockMessage : public InputMessage<MsgThread>
+{
+public:
+	UnblockMessage(MsgThread* thread) : InputMessage<MsgThread>("Unblock", thread)	{ }
 
 	virtual bool Process()	{ return true; }
 };
@@ -130,13 +138,30 @@ bool ReporterMessage::Process()
 MsgThread::MsgThread() : BasicThread()
 	{
 	cnt_sent_in = cnt_sent_out = 0;
+	finished = false;
 	thread_mgr->AddMsgThread(this);
 	}
 
 void MsgThread::OnStop()
 	{
-	// This is to unblock the current queue read operation.
+	// Signal thread to terminate and wait until it has acknowledged.
-	SendIn(new TerminateMessage(this), true);
+	SendIn(new FinishMessage(this), true);
+
+	int cnt = 0;
+	while ( ! finished )
+		{
+		if ( ++cnt > 1000 ) // Insurance against broken threads ...
+			{
+			abort();
+			reporter->Warning("thread %s didn't finish in time", Name().c_str());
+			break;
+			}
+
+		usleep(1000);
+		}
+
+	// One more message to make sure the current queue read operation unblocks.
+	SendIn(new UnblockMessage(this), true);
 	}
 
 void MsgThread::Heartbeat()
@@ -157,6 +182,14 @@ bool MsgThread::DoHeartbeat(double network_time, double current_time)
 	return true;
 	}
 
+bool MsgThread::DoFinish()
+	{
+	// This is thread-safe "enough", we're the only one ever writing
+	// there.
+	finished = true;
+	return true;
+	}
+
 void MsgThread::Info(const char* msg)
 	{
 	SendOut(new ReporterMessage(ReporterMessage::INFO, this, msg));

src/threading/MsgThread.h

@@ -171,6 +171,8 @@ public:
 protected:
 	friend class Manager;
 	friend class HeartbeatMessage;
+	friend class FinishMessage;
+	friend class FinishedMessage;
 
 	/**
 	 * Pops a message sent by the child from the child-to-main queue.
@@ -215,6 +217,12 @@ protected:
 	 */
 	virtual bool DoHeartbeat(double network_time, double current_time);
 
+	/** Triggered for execution in the child thread just before shutting threads down.
+	 *  The child thread shoudl finish its operations and then *must*
+	 *  call this class' implementation.
+	 */
+	virtual bool DoFinish();
+
 private:
 	/**
 	 * Pops a message sent by the main thread from the main-to-chold
@@ -270,6 +278,8 @@ private:
 
 	uint64_t cnt_sent_in;	// Counts message sent to child.
 	uint64_t cnt_sent_out;	// Counts message sent by child.
+
+	bool finished;	// Set to true by Finished message.
 };
 
 /**