On Wed, Dec 9, 2020 at 12:02 PM Dan Cropp <d...@amtelco.com> wrote: > We are working on a patch for the REFER support and have a question on > whether a lock is needed or not. > > > > In chan_pjsip.c function xfer_client_on_evsub_state, code is processing > the REFER-NOTIFY subscription. > > > > It gets an ast_sip_session reference, then it acquires a ast_channel > reference. > > Should we make the code bump the lock count for the session’s channel > while we use it? Unlocking when done using it? > > > > Is it safe to assume the channel will not be deleted while this routine is > running? > > Obviously, the safest approach is to increment/decrement the reference > count while using, but is that the necessary/preferred approach? >
The PJSIP implementation in Asterisk doesn't heavily use locks. Instead it approaches things from a serializer perspective - that is ensuring that things related to a dialog/session can't be done in multiple threads at the same time. To that end the xfer_client_on_evsub_state function should allocate a structure with the appropriate information and queue it up using ast_sip_push_task. You can find this being done in the chan_pjsip_transfer function. This will give you a guarantee that session won't go away, the channel pointer won't go away, and that other threads aren't doing things at the same time. -- Joshua C. Colp Asterisk Technical Lead Sangoma Technologies Check us out at www.sangoma.com and www.asterisk.org
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