signal related race conditions and deadlock

[Martin Pala]

Hi,

there are SIGTERM and SIGINT related problems:

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FIRST:
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1.) monit receives one of above mentioned signals and calls do_destroy()
2.) do_destroy() sets http engine stopped flag and returns - monit httpd 
then will stop in next cycle on 'while' condition
3.) monit will close all files and logs (asynchronously of monit httpd task)

Problem, is that monit httpd thread is able to log messages, while it is 
possible that the socket will be closed earlier.

The solution could probably be to wait for http thread termination (by 
joining the thread?)

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SECOND:
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During my tests it was possible to deadlock monit while running in the 
loop by:

while true; do monit -c /etc/monitrc validate; done

and sending it SIGTERM. It hung - gdb showed that it did validate() 
function as expected, entered do_destroy(), runned garbage collector and 
closed files but before it reached exit it received SIGTERM. It involved 
do_destroy() again and it blocked on log() function. Each next SIGTERM 
involved do_destroy() again, but blocked in the same place. I don't know 
what was bigger problem - whether closed files or freed memory (i 
suppose that it should fail on SIGSEGV because of memory, but it did not 
happened).

Maybe it could be solved by blocking signals in do_destroy() itself - it 
is called from main() if we are finalizing gracefully as well as signal 
handler (i don't know wheter it is possible to block signals in signal 
handler).


Martin