C++ named requirements: Mutex (since C++11)

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The Mutex requirements extends the Lockable requirements to include inter-thread synchronization.


[edit] Requirements

For an object m of Mutex type:

  • The expression m.lock() has the following properties
  • Behaves as an atomic operation.
  • Blocks the calling thread until exclusive ownership of the mutex can be obtained.
  • Prior m.unlock() operations on the same mutex synchronize-with this lock operation (equivalent to release-acquire std::memory_order).
  • The behavior is undefined if the calling thread already owns the mutex (except if m is std::recursive_mutex or std::recursive_timed_mutex).
  • Exception of type std::system_error may be thrown on errors, with the following error codes:
  • The expression m.try_lock() has the following properties
  • Behaves as an atomic operation.
  • Attempts to obtain exclusive ownership of the mutex for the calling thread without blocking. If ownership is not obtained, returns immediately. The function is allowed to spuriously fail and return even if the mutex is not currently owned by another thread.
  • If try_lock() succeeds, prior unlock() operations on the same object synchronize-with this operation (equivalent to release-acquire std::memory_order). lock() does not synchronize with a failed try_lock().
  • Does not throw exceptions.
  • The expression m.unlock() has the following properties
  • Behaves as an atomic operation.
  • Releases the calling thread's ownership of the mutex and synchronizes-with the subsequent successful lock operations on the same object.
  • The behavior is undefined if the calling thread does not own the mutex.
  • Does not throw exceptions.
  • All lock and unlock operations on a single mutex occur in a single total order that can be viewed as modification order of an atomic variable: the order is specific to this individual mutex.

[edit] Library types

The following standard library types satisfy Mutex:

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2309 C++11 lock might throw std::system_error
with error code std::errc::device_or_resource_busy
not allowed

[edit] See also