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Subject: Re: [Boost-users] Some trouble using mutexes
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2010-08-20 13:10:22


Ernest Galbrun wrote:
> I would be really grateful if someone could give me a hint about what I am
> doing wrong with the mutex and thread class (I am using boost 1.43, on
> windows XP running visual c++ 2010, the library has been built using the
> bjam utility).
> I have a main thread that creates an object of class robot :
> class Robot
> {
> private:
> boost::mutex tcpLock;
> boost::thread continuousThread;
> ...
> }
> Robot k3;
> this thread launches a thread that makes continuous calls to a member
> function of the robot. Since this function uses network ressources, I want
> it to be safe so i use a lock The function called is the only function in my
> program that uses this lock :
> int Robot::sendMsg(string msg, int n, vector<string>* answer)
> {
> tcpLock.lock();
> (do stuff with the tcp io service)
> tcpLock.unlock();
> return 0;
> }
> Of course, I also call this function from the main thread.
> And I have disruptive behavior, which I don't understand.

Do you have multiple Robots? Is the io_service shared between them?

> When debugging, I
> see that the 'active_count' of the tcpLock object stays negative or ==0,
> which seem absolutely wrong to me, but I don't understand how it could ever
> be anything other than 0 or 1.

The implementation indicates that the mutex is locked with the
high-order bit, which means that a locked mutex will have
a negative active count.

In Christ,
Steven Watanabe

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