perl.h: Convert reentrant locks to allow many readers, avoid deadlock if hold write lock then request it as read-only #22282
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This is in preparation for future use of these. The only current mutex that is reentrant is the one for locales. This simply changes the reentrant locks from using the single reader locks to using the multiple reader locks.
In a reentrant mutex, the previous commit added the ability to have multiple readers. But if a thread already owns a mutex for writing, and requests a read lock as well, prior to this commit the thread will be deadlocked by itself. Avoid this by testing for the condition and handling separately. All reentrant mutexes currently have no read lock attempts. So this case is entirely theoretical for the moment.
tonycoz
approved these changes
Jun 24, 2024
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This is in preparation for future use of these.
The only current mutex that is reentrant is the one for locales.