SIGSEGV waking up non-existant threads

[Ian Dall <ian@…>]

Version: v0.25pre-2556-gc12e7d7-dirty

I am seeing SIGSEGV almost immediately on starting mythbackend. This happens often but not always. I haven't been able to figure out the circumstances in which this happens. It might be related to the order in which threads are run.

There is no log file, but the console output is:

2011-07-02 15:43:33.136749 C mythbackend version: master [v0.25pre-2556-gc12e7d7-dirty] www.mythtv.org 2011-07-02 15:43:33.136925 C Enabled verbose msgs: important general 2011-07-02 15:43:33.136988 C Setting Log Level to LOG_INFO 2011-07-02 15:43:33.137259 I Added logging to the console 2011-07-02 15:43:33.137284 I Added database logging to table logging 2011-07-02 15:43:33.162102 C Setting up SIGHUP handler

A full backtrace is attached. The SIGSEGV is in thread #4.

The issue seems to be that MythSystemIOHandler::BuildFDs calls readThread->wake with NULL readThread.

Changing to:

if (readThread) readThread-wake

(and likewise for writeThread) seems to work, but maybe only solve the symptoms. Perhaps there is a race in thread startup

[Ian Dall <ian@…>]

Possible patch.

[beirdo]

Please do the following:

• revert all custom changes (store them somewhere of course)
• do a make distclean
• clear out ccache's cache
• remove the installed MythTV headers, libraries and binaries
• rebuild and try again

The only time I've seen funky behavior is when things are partially linked incorrectly to old versions of the code. Once you are on a known version (i.e. not -dirty from custom patches) and with a clean build, if this continues, then I'll look into it.

[beirdo]

Actually, gave it a quick look-see anyways, and I found what is likely the true issue. In the backend's main.cpp, we are calling setHttpProxy() before initializing gCoreContext (and gContext). setHttpProxy(), if configured to use a proxy, will attempt to ping the proxy, via myth_system, which is only usable with gCoreContext initialized.

I'll be committing a fix for this shortly. I don't think that the patches you have provided are bad, necessarily, but they are also not really fixing the problem.

[Github]

Setup http proxy after the gCoreContext is initialized

Fixes #9893. Fixes #9894.

The setHttpProxy() uses myth_system to ping the proxy. However, myth_system requires that gCoreContext be valid for proper use. Therefore, move the proxy setup to after where we setup the context.

Branch: master Changeset: df8b987413106d47701a6c8ff04185b411d1a5b5

[Github]

Check for thread existance before waking them

Refs #9893

This should never really happen if all else is correct, but no harm in being careful.

Signed-off-by: Gavin Hurlbut <ghurlbut@…>

Branch: master Changeset: 4c7e1b792595204c41ee8b2def84abc4b97130b8