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Reputation: 4386

Mutex in getter setter

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

Upvotes: 1

Views: 2636

Answers (2)

Andriy Tylychko
Andriy Tylychko

Reputation: 16266

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.

Upvotes: 3

Miguel Grinberg
Miguel Grinberg

Reputation: 67509

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.

Upvotes: 5

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