[Asterisk-Dev] Signal timing can bring down Asterisk

[Kristian Nielsen]

Hans Petter Selasky <hselasky at c2i.net> writes:

> Can the example above be done in some other way, so that I avoid these 
> problems?

I don't follow your arguments, so let's clarify the issue, and maybe you
can explain how your thoughts fit in. This is how I understand a channel
driver should be used:

1. Call tech->requester() to get struct ast_channel *chan.

2. Now call tech-call() to start an outgoing call on the channel.

3. Now loop, sleeping in ast_wait*(), processing events (including
   ANSWER, HANGUP) with tech->read() and tech->write().

4. Terminate the call using ast_softhangup() (which queues a HANGUP
   event).

5. Finally, when the channel is completely done with, call
   tech->hangup(). After this, the channel can no longer be used.

I don't think there is any problems like the races you mention. It is
the responsibility of the channel driver to make sure that it will not
reference the struct ast_channel * any more after tech->hangup()
returns.

Note that while tech->requestor() allocates the struct ast_channel *, it
is not freed by tech->hangup(). This is kind of asymetric, perhaps that
is what is causing your confusion?

 - Kristian.

-- 
Kristian Nielsen   kn at sifira.dk
Development Manager, Sifira A/S