Submitter: Torvald Riegel [email protected], Martin Sebor [email protected]
Submission Date: 2015-09-25
Summary
The specification of mtx_trylock if applied to a non-recursive mutex is
not clear. Whereas it is spelled out for mtx_lock that a thread must
not attempt to lock a non-recursive mutex more than once, there is no
such requirement for mtx_trylock. The existing wording for mtx_trylock
could be understood as requiring mtx_trylock to fail; however, that
would defeat the purpose of separating recursive from non-recursive
mutexes because it would require implementations to track which thread
owns the mutex.
(It might also be good if the standard would define what recursive locking actually is, but this is outside of the focus of this paper.)
Suggested Technical Corrigendum
The standard should specify the requirement for mtx_lock explicitly for mtx_trylock
as well. Specifically, add the following sentence to 7.26.4.5p2:
If the mutex is non-recursive, it shall not be locked by the calling thread.