Re: [boost] [singleton] call_once

From: Anthony Williams (anthony_w.geo_at_[hidden])
Date: 2005-09-13 11:37:25

Jason Hise <chaos_at_[hidden]> writes:

> Anthony Williams wrote:
>
>>Calls through call_once are only atomic with respect to other calls that
>>reference the same once_flag. If you want mutual exclusion, you need a shared
>>mutex --- why not just create a function-local static mutex, lock it before
>>your function call, and unlock it afterwards?
>>
>>Anthony
>>  
>>
> Because static variables are not initialized in a thread safe manner 
> (except on some versions of gcc which lock the operation).  Multiple 
> threads could end up calling the mutex's constructor simultaneously, 
> resulting in a corrupted mutex object.  If I have a global mutex, I need 
> to find a way to initialize it before the program starts spawning threads.

You can use call_once to initialize the mutex, or you can use a mutex type
that supports static initialization (unlike the current boost ones, but like a
pthread_mutex)

Anthony
-- 
Anthony Williams
Software Developer
Just Software Solutions Ltd
http://www.justsoftwaresolutions.co.uk