Hi,
I have two instances of a apache, mod_wsgi and flask based http rest
service. The only difference between the two services are the files being
loaded (python pickle files on flask start) and AWS regions, one is in US
while the other is in EU. The flask service itself is a wrapper over scikit
learn predictions which are the reason for the python pickle files
mentioned earlier.
Confusingly the instance in US works fine. No issues. However the EU
instance keeps getting into a deadlock situation because of which mod_wsgi
restarts. Apache is still up. I have had no luck using the different
mod_wsgi debug mechanisms, apparently there is no deadlock in the flask,
scikit learn side of the equation.
Today, found that on deadlock mod_wsgi emitted:
21720 [Mon Aug 29 21:31:26.979825 2016] [wsgi:crit] [pid 4317:tid
140495687612160] (35)Resource deadlock avoided: │EOE
mod_wsgi (pid=4317): Couldn't acquire accept mutex
'/path-to-apache/var/state.14843.0.1.sock'.
Shutting down daemon process
Apache conf contains
Mutex file:/path-to-pache/var/state mpm-accept
My suspicion is that one of the instance is using fcntl while the other
uses flock, and probably the one using fcntl has deadlocks based on apache
documentation. But I have no way to verify it.
Is there a way to find which of fcntl or flock is being used by Apache?
httpd -V shows
-D APR_HAS_SENDFILE
-D APR_HAS_MMAP
-D APR_USE_SYSVSEM_SERIALIZE
-D APR_USE_PTHREAD_SERIALIZE
-D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
-D APR_HAS_OTHER_CHILD
-D AP_HAVE_RELIABLE_PIPED_LOGS
-D DYNAMIC_MODULE_LIMIT=256
Thanks
Santhosh
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