[Libevent-users] "Triggering" writes in an event loop from separate threads

[Jan Danielsson <jan.m.danielsson@xxxxxxxxx>]

Hello,

   I have an eventloop with a bufferevent set up in an application. When
handling read events everything is done on the event loop thread, and
some writes are done as a direct result of data being read there, but
writes are typically placed on a queue by a separate threads. But I want
the writes to be handled on the eventloop thread as well.

   i.e. I have a readcb() function which reads incoming frames from the
remote system. Each frame typically leads to some kind of response.
These I can send directly using bufferevent_write() as soon as the
complete frames have been received and parsed. However, the bufferevent
also has a context associated with it which contains a mutex and a
linked list which is shared with the rest of the application. Other
parts of the application can place frames on the outqueue at any time.

   Could one set up both a read and write callback, but not enable
EV_WRITE. Then, on the separate threads, lock the outqueue, add frames
to the queue, unlock the queue and finally call bufferevent_enable(bev,
EV_WRITE)? I.e. would enabling EV_WRITE cause the write callback to be
called? ..and once all the frames have been written, the write callback
would call bufferevent_disable(bev, EV_WRITE) again?

   .. essentially using the EV_WRITE flag as a condvar, in some
perverted sense. Does switching on EV_WRITE trigger a call to the write
callback? Is it safe to do it from another thread? (Yes, I have enabled
thread support in the library, and am initializing the thread support
properly).

   Is there some other way to do it? (For various reasons I don't want
to call bufferevent_write() directly from the threads which generate
output frames).

   /Jan
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