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From Nick Kew <...@apache.org>
Subject Fwd: Process lifetime and hooks to use
Date Sat, 17 Apr 2010 09:10:46 GMT
My reply seems to be lost in the ether ... try again.

Begin forwarded message:

> On 16 Apr 2010, at 20:51, Some Guy wrote:
> 
>> Hi all,
>> 
>> I would like to develop a module that periodically needs to fetch a file
>> from a remote site and update some data used by the child processes.  Is it
>> safe to create this thread in the post config hook?  I would like to do
>> something like:
>> 
>> Global thread fetches a file, and loads content
>> Thread signals that it has new data
>> A separate thread in each of the child processes gets the signal and updates
>> the cache in the child process.  The cache is only updated by this thread
>> and owned by the child process, so I lock it with a rwlock.  The cache is
>> read by request handlers, so I don't want to use a global lock since the
>> documentation implied it could be a performance issue.
>> 
>> Is this doable and which hooks / threading issues will I run into with this
>> approach?  It would be nice for the threads in the child process to be able
>> to concurrently read the data from the global thread after the global thread
>> has signaled new data is ready.  I did not see any type of global rw lock.
> 
> It's doable, with some reservations (and re your last sentence,
> see apr_global_mutex).  The hardest part will be to avoid leaking
> memory in the fetch.
> 
> However, it might be over-complicated.  Instead of your own thread
> in the parent process, why not use ap_hook_monitor?  And the mtime
> of the fetched file should work nicely as the signal to the children.
> 
> -- 
> Nick Kew


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