CODEWITHSUNDEEP
c++multithreadingc++11openmp
Walter
Walter

Reputation: 45424

Does `std::mutex` and `std::lock` guarantee memory synchronisation in inter-processor code?

I'm currently using openMP to write code running on multi-core nodes. openMP has a specific memory model which guarantees that memory is synchronised between threads running on different cores when a lock is acquired.

I consider using C++11 constructs (std::thread with std::mutex and std::lock) instead of openMP (because of their larger flexibility) and wonder if/how memory synchronisation between processors is guaranteed here? And if not, how can I enforce it?

Upvotes: 6

Views: 1867

Answers (1)

Cubbi
Cubbi

Reputation: 47418

The standard makes the following guarantees about synchronization of std::mutex, in §30.4.1.2[thread.mutex.requirements.mutex]/6-25

The expression m.lock() shall be well-formed and have the following semantics

Synchronization: Prior unlock() operations on the same object shall synchronize with this operation.

And, likewise,

The expression m.unlock() shall be well-formed and have the following semantics

Synchronization: This operation synchronizes with subsequent lock operations that obtain ownership on the same object.

(Where "synchronizes with" is a specific term explained in $1.10, although it's much easier to understand by reading C++ Concurrency In Action)

Upvotes: 10

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