...

This may seem like a silly question, but is someone able to point me to where in the Boost docs it tells me which files I need to #include to use Boost Threads?

It doesn't. Oops. I'll raise a trac issue for it.

Ah, glad it's not me being dumb for once :-)

You can include to get everything.

Does this include shared_mutex? I was still getting errors about boost::shared_mutex when I included , which prompted my hunt through the docs in the first place! Cheers, Adam.

The way I use mutex is to protect one shared resource. Here is sample code that I cooked up. I am not sure why you want to use a single mutex to protect multiple resources. However, if your use case demands it than wrap those resources in a class and have a mutex as a member variable of that class. HTH. Call this file let say ThreadSafeQueue.hpp #include #include <iostream> #include <queue> #include <deque> namespace std { namespace threadsafe { template class tsqueue { private: std::queue m_queue; boost::mutex mutex; public: tsqueue() { } ~tsqueue() { } void push(const T& x) { boost::lock_guardboost::mutex lock(mutex); m_queue.push(x); std::cout << "Push element: " << x << std::endl; } const T& front() { boost::lock_guardboost::mutex lock(mutex); std::cout << "Pop element: " << m_queue.front() << std::endl; return m_queue.front(); } void pop() { boost::lock_guardboost::mutex lock(mutex); return m_queue.pop(); } int size() { boost::lock_guardboost::mutex lock(mutex); return m_queue.size(); } }; } // namespace threadsafe } // namespace std Here is how you can use it. #include "ThreadSafeQueue.hpp" int main() { std::threadsafe::tsqueue<int> tsf; tsf.push(1); tsf.front(); return 0; } g++ -Wall -DBOOST_HAS_THREADS <relevant includes> <relevant library path> test.cpp -lboost_thread-gcc32-mt -----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 6:34 AM To: boost-users@lists.boost.org Subject: Re: [Boost-users] [Thread] What do I #include? Adam Nielsen writes:

...

...

This may seem like a silly question, but is someone able to point me

...

...

to where in the Boost docs it tells me which files I need to #include to use Boost Threads?

It doesn't. Oops. I'll raise a trac issue for it.

Ah, glad it's not me being dumb for once :-)

...

You can include to get everything.

Does this include shared_mutex? I was still getting errors about boost::shared_mutex when I included , which prompted

my hunt through the docs in the first place!

It does in the trunk version, but not in 1.35.0 shared_mutex is in 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.

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 ? -----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 9:14 AM To: boost-users@lists.boost.org Subject: Re: [Boost-users] [Thread] What do I #include? "Khandelwal, Amit" writes:

The way I use mutex is to protect one shared resource. Here is sample code that I cooked up. I am not sure why you want to use a single mutex to protect multiple resources. However, if your use case demands

it than wrap those resources in a class and have a mutex as a member variable of that class.

template class tsqueue {

const T& front() { boost::lock_guardboost::mutex lock(mutex); std::cout << "Pop element: " << m_queue.front() << std::endl; return m_queue.front(); }

void pop() { boost::lock_guardboost::mutex lock(mutex); return m_queue.pop(); }

This code is not thread safe unless there is only one consumer. Though each operation is safe, the front()/pop() model gives you a race condition: some other thread may steal your element between the call to front() and pop(). See http://www.justsoftwaresolutions.co.uk/threading/implementing-a-thread-s afe-queue-using-condition-variables.html for a description of a thread-safe queue that uses a condition variable to provide waiting and allows multiple consumers. 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.

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" writes:

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.

Agreed. I didn't realize that I had typed return by reference. My bad. -----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Johan Nilsson Sent: Friday, July 11, 2008 9:42 AM To: boost-users@lists.boost.org Subject: Re: [Boost-users] [Thread] What do I #include? Khandelwal, Amit wrote:

The way I use mutex is to protect one shared resource. Here is sample code that I cooked up. I am not sure why you want to use a single mutex to protect multiple resources. However, if your use case demands

it than wrap those resources in a class and have a mutex as a member variable of that class.

HTH.

Call this file let say ThreadSafeQueue.hpp

#include #include <iostream> #include <queue> #include <deque>

namespace std { namespace threadsafe {

template class tsqueue {

private: std::queue m_queue; boost::mutex mutex;

public:

[snip]

const T& front() { boost::lock_guardboost::mutex lock(mutex); std::cout << "Pop element: " << m_queue.front() << std::endl; return m_queue.front(); }

Ouch. Returning an element by reference could easily lead to trouble when the container is accessed from multiple threads. / Johan _______________________________________________ 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.