I found this problem conceptually interesting and worth of
generalization in many contexts. I'd like to know if Neil got around the
problem with something that could be a satisfying solution.
thanks
-- Massimo
On 06/28/2011 04:57 AM, Neil McKee wrote:
Hi,
Here's an easy question for someone who knows their way around...
I want to maintain a new global counter, but for performance reasons I am
reluctant to use a mutex or atomic_increment to update it. I would rather
maintain a separate counter for every worker-thread, and only accumulate the
global counter when required. (If the per-worker-thread counter is 32-bit then
I shouldn't even need a mutex when accumulating the total across all the
current threads).
Obviously I shouldn't just declare something as "__thread apr_int32_t
mycounter;" and mince it together as a linux-only hack. I'd like to find the
portable apr-library way to do it. So I think I need to find the following:
* - a hook that is called whenever a worker thread is started
* - a hook that is called whenever a worker thread is about to die
* - a hook to find_or_create a 32-bit integer that is private to the current
worker-thread
* - a fn to iterate (safely) over all the current worker threads
It's the last one that seems particularly elusive. I could't find an ap_ or
apr_ library call that seemed to do anything like that.
If this has all been done before, please can you point me to the relevant
module sources? I think it would save me a lot of time. Alternatively, if
you think I should just relax and use an atomic increment instead, then let me
know.
Thanks!
Neil
