It occurred to me that it may be due to the fact that I am creating
bufferevents using the BEV_OPT_UNLOCK_CALLBACKS flag and not locking
the bufferevents when executing the tasks. Perhaps if the close task
does the following then the problem will disappear:
1. Lock the buffer event
(http://www.wangafu.net/~nickm/libevent-2.0/doxygen/html/bufferevent_8h.html#a56a61802037478591048b4967fa15599)
2. Disable all callbacks
3. Unlock the buffer event
4. Close the connection
5. Remove all pending tasks in the task queue for this connection
Nick.
Quoting [email protected]:
Situation:
----------
I am building a multithreaded socket server built with Libevent.
The event loop is run in its own thread and each callback creates a
task into a queue. A pool of worker threads then processes the
tasks, (of course ensuring that tasks for any given connection are
processed in the correct order).
When a close event arrives, a task is created to close the
connection and free all related structures. When this task is
processed by a worker thread, it does the following things:
1. Disable all callbacks
2. Close the connection
3. Remove all pending tasks in the task queue for this connection
Problem:
--------
The problem is that after the connection is closed, there could
still be events in the Libevent event loop either waiting to be
processed in a callback or actually being processed by the event
thread (i.e. callback running). This could lead to tasks being
created for the connection _after_ step 3 which would result in
tasks in the task queue for a closed connection - which I want to
avoid.
Solution?
---------
I could use a mutex to lock the connection in the event callbacks,
but I do not want to introduce blocking methods in the event loop
thread.
I could ensure that a connection is valid when I take a task.
But ideally I would like to the bufferevent close method, or the
callback disable methods to block until all curently running
callbacks for that bufferevent have finished. This way I could be
sure that no tasks can be created after the connection is closed.
Question:
---------
Do the methods work like this, or is there a way to achieve this?
Many thanks in advance.
Nick.
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