Re: apr_global_mutex_create vs apr_proc_mutex_create

[Ali Shah]

Thanks Luca and William, Thats very informative!

Re: apr_global_mutex_create vs apr_proc_mutex_create

[William A Rowe Jr]

proc_mutex can only be used to block on a cross process event.  It can be
used in a threaded server, but cannot be held in multiple threads, you
might use it to block in a single thread queue per-process.

Thread_mutex will not block between processes, this is used for the
mutex-per-process logic such as a across accept wait queues.

Global_mutex will block, across threads and across processes, as
appropriate.
On Mar 24, 2016 04:08, "Luca Toscano"  wrote:

> +httpd-dev@
>
> Hello!
>
> 2016-03-23 21:49 GMT+01:00 Ali Shah :
>
>> Hi Module maintainers,
>>
>> I'm writing a simple apache module and I'd like to aggregate some
>> statistics.
>> I saw an example module that does this (
>> https://wiki.apache.org/httpd/ModuleLife) using shared memory.
>>
>> My question for those on this list following:
>>
>> What is the main difference between using mutexes created
>> via apr_global_mutex_create and apr_proc_mutex_create in terms of
>> performance and safety of the resource that being protected?
>>
>> The docs seem to discourage usage of apr_global_mutex_create:
>> "There is considerable overhead in using this API if only cross-process or
>> cross-thread mutual exclusion is required."
>>
>> Is the overhead purely in code setup (since global mutex should be
>> initialized in post_config), or is this describing some performance
>> penalties as well?
>>
>
> From what I can see in [1] a global lock uses both apr_proc_mutex_create
> and apr_thread_mutex_create, so this is why the documentation suggests the
> use of a more specialized one if only cross-process or cross-thread sync is
> needed.
>
> Not a great explanation I know, somebody else with more experience will
> give you a better answer on this list :)
>
> Luca
>
>
>
> [1]:
> https://github.com/apache/apr/blob/7951861fb029fd0fb60e5ec8da73015d03afa28d/locks/unix/global_mutex.c#L46
>
>
>

Re: apr_global_mutex_create vs apr_proc_mutex_create

[William A Rowe Jr]

proc_mutex can only be used to block on a cross process event.  It can be
used in a threaded server, but cannot be held in multiple threads, you
might use it to block in a single thread queue per-process.

Thread_mutex will not block between processes, this is used for the
mutex-per-process logic such as a across accept wait queues.

Global_mutex will block, across threads and across processes, as
appropriate.
On Mar 24, 2016 04:08, "Luca Toscano"  wrote:

> +httpd-dev@
>
> Hello!
>
> 2016-03-23 21:49 GMT+01:00 Ali Shah :
>
>> Hi Module maintainers,
>>
>> I'm writing a simple apache module and I'd like to aggregate some
>> statistics.
>> I saw an example module that does this (
>> https://wiki.apache.org/httpd/ModuleLife) using shared memory.
>>
>> My question for those on this list following:
>>
>> What is the main difference between using mutexes created
>> via apr_global_mutex_create and apr_proc_mutex_create in terms of
>> performance and safety of the resource that being protected?
>>
>> The docs seem to discourage usage of apr_global_mutex_create:
>> "There is considerable overhead in using this API if only cross-process or
>> cross-thread mutual exclusion is required."
>>
>> Is the overhead purely in code setup (since global mutex should be
>> initialized in post_config), or is this describing some performance
>> penalties as well?
>>
>
> From what I can see in [1] a global lock uses both apr_proc_mutex_create
> and apr_thread_mutex_create, so this is why the documentation suggests the
> use of a more specialized one if only cross-process or cross-thread sync is
> needed.
>
> Not a great explanation I know, somebody else with more experience will
> give you a better answer on this list :)
>
> Luca
>
>
>
> [1]:
> https://github.com/apache/apr/blob/7951861fb029fd0fb60e5ec8da73015d03afa28d/locks/unix/global_mutex.c#L46
>
>
>

Re: apr_global_mutex_create vs apr_proc_mutex_create

[Luca Toscano]

+httpd-dev@

Hello!

2016-03-23 21:49 GMT+01:00 Ali Shah :

> Hi Module maintainers,
>
> I'm writing a simple apache module and I'd like to aggregate some
> statistics.
> I saw an example module that does this (
> https://wiki.apache.org/httpd/ModuleLife) using shared memory.
>
> My question for those on this list following:
>
> What is the main difference between using mutexes created
> via apr_global_mutex_create and apr_proc_mutex_create in terms of
> performance and safety of the resource that being protected?
>
> The docs seem to discourage usage of apr_global_mutex_create:
> "There is considerable overhead in using this API if only cross-process or
> cross-thread mutual exclusion is required."
>
> Is the overhead purely in code setup (since global mutex should be
> initialized in post_config), or is this describing some performance
> penalties as well?
>

>From what I can see in [1] a global lock uses both apr_proc_mutex_create
and apr_thread_mutex_create, so this is why the documentation suggests the
use of a more specialized one if only cross-process or cross-thread sync is
needed.

Not a great explanation I know, somebody else with more experience will
give you a better answer on this list :)

Luca



[1]:
https://github.com/apache/apr/blob/7951861fb029fd0fb60e5ec8da73015d03afa28d/locks/unix/global_mutex.c#L46

apr_global_mutex_create vs apr_proc_mutex_create

[Ali Shah]

Hi Module maintainers,

I'm writing a simple apache module and I'd like to aggregate some
statistics.
I saw an example module that does this (
https://wiki.apache.org/httpd/ModuleLife) using shared memory.

My question for those on this list following:

What is the main difference between using mutexes created
via apr_global_mutex_create and apr_proc_mutex_create in terms of
performance and safety of the resource that being protected?

The docs seem to discourage usage of apr_global_mutex_create:
"There is considerable overhead in using this API if only cross-process or
cross-thread mutual exclusion is required."

Is the overhead purely in code setup (since global mutex should be
initialized in post_config), or is this describing some performance
penalties as well?

Thanks!
Ali