Preventing writers/readers from receiving further messages after a

failure.

Once a writer/reader Do* method has returned false, no further ones
will be executed anymore. This is primarily a safety mechanism to make
it easier for writer/reader authors as otherwise they would often need
to track the failure state themselves (because with the now delayed
termination from the earlier commit, furhter messages can now still
arrive for a little bit).

src/threading/MsgThread.h

@@ -201,6 +201,12 @@ protected:
 	 */
 	void HeartbeatInChild();
 
+	/** Returns true if a child command has reported a failure. In that case, we'll
+	  * be in the process of killing this thread and no further activity
+	  * should carried out. To be called only from this child thread.
+	  */
+	bool Failed() const { return failed; }
+
 	/**
 	 * Regulatly triggered for execution in the child thread.
 	 *
@@ -294,6 +300,7 @@ private:
 	uint64_t cnt_sent_out;	// Counts message sent by child.
 
 	bool finished;	// Set to true by Finished message.
+	bool failed;	// Set to true when a command failed.
 };
 
 /**