mutex/unique_lock/try_lock_for

[6thC]

Can someone please explain for me why this code @ try_lock_for throws "Resource deadlock avoided" or what I"ve done wrong?

    {
       std::mutex mutex;
       std::unique_lock<std::mutex> locker(mutex);
       qDebug()<<"work";
    }

    {
        std::timed_mutex tMutex;
        std::unique_lock<std::timed_mutex> lock(tMutex);
        lock.try_lock_for(std::chrono::milliseconds(100));
        qDebug()<<"explode before here";    
    }

[SGaist]

Hi,

Where is that code called from ?

[6thC]

windows

Ubuntu

[6thC]

With mutex's in a class instance as members also:

[hskoglund]

Hi, I think because you trying to lock tMutex twice, easiest is remove the first lock, for example:

{
    std::timed_mutex tMutex;
    std::unique_lock<std::timed_mutex> lock(tMutex,std::defer_lock);
    lock.try_lock_for(std::chrono::milliseconds(100));
    qDebug()<<"no longer explode before here";
}

[6thC]

Yes, thanks that's great. I just had another developer (family member) give me this exact code so thanks to you and him, this is working as expected.

Not sure I understand why it tries to lock tMutex twice. Maybe I'll understand fully another time. I'm happy I'm out of the woods though. Thanks all.

[6thC]

I think I understand the double lock now.

std::unique_lock<std::timed_mutex> lock(tMutex); //  RAII lock attempt
lock.try_lock_for(std::chrono::milliseconds(100));     // another lock request == resource deadlock

This defer lock commands the unique lock to not lock on construction, so then I can command locking behavior myself.