线程读取与写入锁定

Question

I'm writing a CPU intensive program in C++ that has several threads needing to access a shared data structure, so locking will be required. To maximize throughput, I want to keep the bottleneck to a minimum. It looks like maybe nine times out of ten it will only be necessary to read the data structure, and one time out of ten it will be necessary to modify it.

Is there a way to have threads take read or write locks, so that write locks block everything but read locks don't block each other?

A portable solution would be ideal, but if there is one solution for Windows and another for Linux that would be okay.

Answer 1

Yes, this is a common situation that can be solved with a reader-writer lock .

Note that depending on the dynamic properties of your program, you may need to be careful about writer starvation . If there are enough readers that their attempts to read always overlap (or overlap for a long time), then a simple implementation of a reader-writer lock will "starve" the writer by making the writer wait until there are no readers reading. In a more advanced implementation, a writer request will be conceptually inserted into the queue before subsequent readers, allowing the writer to have a chance to access after all the previously active readers finish.

Most implementations require you to know ahead of time whether you want a read lock or a write lock. Some implementations allow you to "upgrade" a read lock into a write lock without having to release the read lock first (which would give another writer an opportunity to enter the lock).