Mutex in getter setter

Question

I was wondering about how to use mutex for multithreaded application. Do my getters need to lock too? I found this post. The answer is yes, I need to guard getters functions but that means I'll be able to perform one read at a time, and I wonder if it could be improved.

T.E.D's answer suggests that you can implement locks in a way that many threads can read the data at the same time if setters' functions didnt lock the mutex to perform a write. I tried to find some examples - reading Qt's documentation - tought, QMutex doesn't have a isLocked() function or something like this. So how can you praticly implements this kind of "intelligent's locks'.

Thanks

Miguel Grinberg · Accepted Answer · 2011-09-16T05:17:46.697

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You need a special kind of locking mechanism called readers-writer lock. With this lock any number of readers can access the resource simultaneously, but for a writer to have access all reader threads must block.

Looks like Qt has a QReadWriteLock class that implements this mechanism.

edited Sep 16 '11 at 05:17

answered Sep 16 '11 at 00:46

Miguel Grinberg

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Well it seems I didn't search well enough. Thank you ! – Xaqq Sep 16 '11 at 00:52
please read this [thread](http://stackoverflow.com/questions/4659295/why-c0x-standard-committee-rejected-boostshared-mutex) about reader-writer mutex – Andriy Tylychko Sep 16 '11 at 09:09

score 3 · Answer 2 · edited May 23 '17 at 11:51

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Yes, you need to synchronize access to your getters, not to lock them in common sence since they don't modify anything, but to put a memory barrier implicitly. So multithreaded operations will be put in right order and your getters will won't read partially modified data.

You don't need any intelligent locks, because reader-writer mutex won't provide you any benefit.

edited May 23 '17 at 11:51

Community

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answered Sep 16 '11 at 09:21

Andriy Tylychko

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Mutex in getter setter

2 Answers2