I see what you mean to say. I overlooked the fact that the user will
call front and pop one after another. Thanks.
-----Original Message-----
From: boost-users-bounces@lists.boost.org
[mailto:boost-users-bounces@lists.boost.org] On Behalf Of Anthony
Williams
Sent: Friday, July 11, 2008 10:56 AM
To: boost-users@lists.boost.org
Subject: Re: [Boost-users] [Thread] What do I #include?
"Khandelwal, Amit"
Hmm...I don't know why you say that there will be a race condition. Let say 2 threads are calling pop on the queue and another thread is calling front(). Let us call these 3 thread p1, p2 (for pop) and f1 for front.
As per my understanding - this could be one possible scenario.
P1 -- acquire the lock P2 -- blocked on the lock F1 -- blocked on the lock
P1 -- done and waiting on the lock P2 -- still blocking F1 -- acquired the lock
So where is the race condition ?
Two threads retrieving a value: each does some_var=queue.front(); queue.pop(); Though each operation is thread-safe, the combination isn't, because they can interleave badly: T1: some_var=queue.front(); T2: some_var=queue.front(); // oops we just got the same value T1: queue.pop(); T2: queue.pop(); // Oops the second value in the queue just got //discarded without being read This is a race condition: the outcome depends on the ordering of operations in separate threads. There's a similar problem with empty(). Suppose each thread does if(!queue.empty()) { some_var=queue.front(); queue.pop(); } Two threads can interleave again to give a race condition: T1: if(!queue.empty()) // queue is not empty T2: if(!queue.empty()) // queue is not empty T1: some_var=queue.front(); T1: queue.pop(); T2: some_var=queue.front(); // oops reading non-existent element T2: queue.pop(); // oops no element to pop. Designing interfaces for multi-threaded use is not as simple as just slapping a mutex on the data and locking it in every member function. Anthony -- Anthony Williams | Just Software Solutions Ltd Custom Software Development | http://www.justsoftwaresolutions.co.uk Registered in England, Company Number 5478976. Registered Office: 15 Carrallack Mews, St Just, Cornwall, TR19 7UL _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - This message is intended only for the personal and confidential use of the designated recipient(s) named above. If you are not the intended recipient of this message you are hereby notified that any review, dissemination, distribution or copying of this message is strictly prohibited. This communication is for information purposes only and should not be regarded as an offer to sell or as a solicitation of an offer to buy any financial product, an official confirmation of any transaction, or as an official statement of Lehman Brothers. Email transmission cannot be guaranteed to be secure or error-free. Therefore, we do not represent that this information is complete or accurate and it should not be relied upon as such. All information is subject to change without notice. -------- IRS Circular 230 Disclosure: Please be advised that any discussion of U.S. tax matters contained within this communication (including any attachments) is not intended or written to be used and cannot be used for the purpose of (i) avoiding U.S. tax related penalties or (ii) promoting, marketing or recommending to another party any transaction or matter addressed herein.