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Subject: Re: [boost] [1.44] Beta progress?
From: Anthony Williams (anthony.ajw_at_[hidden])
Date: 2010-07-26 10:01:40

On 26/07/10 14:55, Gaetano Mendola wrote:
> On 07/26/2010 11:25 AM, Anthony Williams wrote:
>> I have thought about this problem lots, and decided that you cannot
>> safely interrupt a condition variable wait on POSIX unless you have a
>> mutex tied directly to each condition variable (as with
>> condition_variable_any). I'm therefore not sure how to approach this ---
>> either every boost::condition_variable has an extra pthread_mutex_t
>> inside it, or interruption is limited to waits on
>> boost::condition_variable_any.
> I have to look in detail the boost::thread implementation to help you
> here.

Of course.

> Is pthread_cancel() still a no go to be used in threads::interrupt
> implementation?

pthread_cancel is no-go because it has different semantics and cannot be
translated into an exception.

> Another source of hang with notify_all (and then with interrupt), is
> the following usage pattern:
> 1. Thread A: acquires a lock on mutex Ma
> 2. Thread A: does a wait on the condition C: C.wait(Ma)
> 3. Thread B: acquires a lock on mutex Mb
> 4. Thread B: does a wait on the condition C: C.wait(Mb)

Undefined behaviour --- all concurrent calls to condition_variable::wait
must use the same mutex. You can use different mutexes with
condition_variable_any, and you can use different mutexes for separate
waits, but not for concurrent ones.


Author of C++ Concurrency in Action
just::thread C++0x thread library   
Just Software Solutions Ltd
15 Carrallack Mews, St Just, Cornwall, TR19 7UL, UK. Company No. 5478976

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