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From Martin Sebor <se...@roguewave.com>
Subject Re: [PATCH] std::messages thread safety
Date Sat, 15 Sep 2007 19:08:41 GMT
Travis Vitek wrote:
> 
> Martin Sebor wrote:
>> Farid Zaripov wrote:
>>>   The 22.locale.messages.cpp test fails due to using incorrect
>>> guard type in functions from messages.cpp file. There used
>>> _RWSTD_MT_STATIC_GUARD(), so that the functions are protected
>>> from working simultaneously with itself only. But from every that
>>> functions invoked __rw_manage_cat_data() which working with
>>> shared global repository of open catalogs.
>> _RWSTD_MT_STATIC_GUARD() lock a static local mutex, which guards
>> the rest of the block from being entered by more than 1 thread
>> across the whole process.
> 
> Yes, that is the problem. The current static guard prevents multiple
> threads from entering the same function simultaneously [i.e. two threads
> cannot call __rw_cat_open simultaneously], but it does nothing to
> prevent one thread from calling __rw_cat_open() and another thread from
> calling __rw_cat_close() at the same time. 

How come? Aren't all the calls guarded using the same mutex?

     _RWSTD_MT_STATIC_GUARD (__rw_open_cat_data);

This provides mutual exclusion across all othe such guards
(i.e, those with the same type as an argument).

>Since __rw_manage_cat_data
> has shared data, access to it must be synchronized using one common
> lock.
> 
>> AFAIK, catopen() and catgets() are not required to be thread
>> safe so we need to guard calls to them across all instances of
>> the facet.
>>
> 
> Yes, but the affected functions are doing more than just calling
> catgets() and catopen(). Since they are using shared data, they need to
> lock that shared data with a shared mutex.

And unless I'm missing something, they are.

Martin

> 
>>   * messages.cpp (__rw_cat_open): Use _RWSTD_MT_CLASS_GUARD instead of
>>   _RWSTD_MT_STATIC_GUARD to synchronize acces to global repository of
>> open
>>   catalogs.
>>   (__rw_get_message): Ditto.
>>   (__rw_get_locale): Ditto.
>>   (__rw_cat_close): Ditto.
>> Martin
> 


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