CODEWITHSUNDEEP
c++multithreadingmutex
Alexey
Alexey

Reputation: 683

How to use std::mutex in different threads?

How to properly write multithreaded code with mutex:

std::mutex m, m2;    

... thread
m2.lock(); 
if ((++reference) == 1) m.lock(); 
m2.unlock();

... differenet thread
m2.lock();
if ((reference--) == 0) m.unlock(); // error here
m2.unlock ();

When I call m.unlock() visual studio 2012 raises error R6010. Mutex m2 works fine, because it locks and unlocks in one thread.

I tried to replace code with std::contidional_variable, but its not notified at start and first enter to cond_var.wait_one waits infinitely.

UPD: Replace with conditional_variable and all works fine now. Article: C++0x has no semaphores? How to synchronize threads?

Upvotes: 2

Views: 2417

Answers (1)

Marek Fekete
Marek Fekete

Reputation: 641

Mutex needs to be unlocked by the owning thread (the thread that locked it):

If the mutex is not currently locked by the calling thread, it causes undefined behavior. (http://www.cplusplus.com/reference/mutex/mutex/unlock/)

You'll need to use conditional variable - I think building a semaphore implementation around it will be nice in your case. See the accepted answer here: C++0x has no semaphores? How to synchronize threads?

Upvotes: 1

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