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### 1224. condition_variable_any support for recursive mutexes?

Section: 33.7.5 [thread.condition.condvarany] Status: NAD Submitter: Jeffrey Yasskin Opened: 2009-09-30 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

For `condition_variable_any`, are recursive mutexes allowed? (I think "no")

[ 2009-11-17 Moved to Tentatively NAD after 5 positive votes on c++std-lib. Rationale added below. ]

Proposed resolution:

Rationale:

`condition_variable_any::wait` accepts any type of mutex. It calls `unlock` precisely once on entry and `lock` precisely once on exit. It is up to the user to ensure that this provides the required synchronization. Use of a recursive mutex is safe if either its lock count is 1, so after the single unlock it can be acquired by another thread, or another mechanism is used to synchronize the data.