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Section: 33.6.4 [thread.mutex.requirements] Status: LEWG Submitter: INCITS Opened: 2010-08-25 Last modified: 2017-03-01
Priority: Not Prioritized
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Discussion:
Addresses US-189
mutex and recursive_mutex should have an is_locked() member function. is_locked allows a user to test a lock without acquiring it and can be used to implement a lightweight try_try_lock.
[ Resolution proposed by ballot comment: ]
Add a member function:
bool is_locked() const;to std::mutex and std::recursive_mutex. These functions return true if the current thread would not be able to obtain a mutex. These functions do not synchronize with anything (and, thus, can avoid a memory fence).
[ 2010 Batavia ]
The Concurrency subgroup reviewed this issue and deemed it to be an extension to be handled after publishing C++0x.
Rationale:
The LWG does not wish to make a change at this time.
[2017-03-01, Kona]
SG1 recommends: Close as NAD
Several participants voiced strong objections, based on either memory model issues or lock elision. No support. It is already possible to write a wrapper that explicitly tracks ownership for testing in the owning thread, which may have been part of the intent here.Proposed resolution: