A condition variable allows a thread to be signaled when something of interest to that thread occurs. By itself, a mutex doesn’t do this. If you just need mutual exclusion, then condition variables don’t do anything for you. However, if you need to know when something happens, then condition variables can help. For example, if … Read more
Rock solid for 4 days straight. I’m declaring victory on this one. The answer is “stupid user error” (see comments above). A mutex should only be unlocked by the thread that locked it. Thanks for bearing with me.
It is more usual and convenient to use Windows events for this purpose. E.g. static EventWaitHandle s_event ; bool created ; s_event = new EventWaitHandle (false, EventResetMode.ManualReset, “my program#startup”, out created) ; if (created) Launch () ; else Exit () ; When your process exits or terminates, Windows will close the event for you, and … Read more
Yes, the std::unique_lock calls unlock on the mutex in its destructor. The benefit of this is that in case some exception is thrown, you are sure that the mutex will unlock when leaving the scope where the std::unique_lock is defined.
This is because there is only a single loop variable chart, and in each iteration just a new value is assigned to it. So if you attempt to take the address of the loop variable, it will be the same in each iteration, so you will store the same pointer, and the pointed object (the … Read more
Please see my updates at the end of the answer, the situation has dramatically changed since Visual Studio 2015. The original answer is below. I made a very simple test and according to my measurements the std::mutex is around 50-70x slower than CRITICAL_SECTION. std::mutex: 18140574us CRITICAL_SECTION: 296874us Edit: After some more tests it turned out … Read more
There are many text on the subject of condition variables and their usage, so I’ll not bore you with a ton of ugly details. The reason they exist at all is to allow you to notify change in a predicate state. The following are critical in understanding proper use of condition variables and their mutex … Read more
There are Several choices, Mutex Process manager Named Semaphore Use a listener socket Mutex Mutex myMutex ; private void Application_Startup(object sender, StartupEventArgs e) { bool aIsNewInstance = false; myMutex = new Mutex(true, “MyWPFApplication”, out aIsNewInstance); if (!aIsNewInstance) { MessageBox.Show(“Already an instance is running…”); App.Current.Shutdown(); } } Process manager private void Application_Startup(object sender, StartupEventArgs e) { … Read more
Simplest answer is volatile is not needed for multi-threading at all. The long answer is that sequence points like critical sections are platform dependent as is whatever threading solution you’re using so most of your thread safety is also platform dependent. C++0x has a concept of threads and thread safety but the current standard does … Read more
It is both complicated and differs from Unix to Unix variant. In Linux, for example, a system called Futex (Short for Fast Userspace Mutex) is used. In this system an atomic increment and test operation is performed on the mutex variable in user space. If the result of the operation indicates that there was no … Read more