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From Saju Pillai <>
Subject Re: custom background thread and module sharing a data structure
Date Fri, 13 Mar 2009 16:14:50 GMT
Andrej van der Zee wrote:
> Hi,
> Thanks for your comments. See below...
> Worker mpm is a multithreaded, multiprocess mpm. Multiple child processes
>> host multiple worker threads that run your module code.
>> If your module services 2 concurrent requests in 2 different threads in the
>> same process and both the threads need to access critical code at the same
>> time, you will have to use thread locking to prevent race conditions.
> Yes, I understand the concept of mpm worker. My point was slightly
> different: When I start a background thread in the post_config()-hook, it is
> created in the address space of the server, and not of the processes that
> run worker threads for handling HTTP requests. Therefore, threads that
> handle HTTP requests always execute in a different process than the
> background thread, and thus thread-based locking is not necessary for
> sharing inter-process data.

My point is that within a single process, multiple threads can service 
requests that can end up firing your module code. If you only do process 
locking you can still have more than 1 thread executing your module code 
at the same time.

Just a process level lock will *not* guarantee that only a single thread 
is executing your code within the process holding the lock. A inter 
thread lock is needed to synchronize multiple threads within that 
processes from stomping on a shared resource.


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