c++ - Win32 Read/Write Lock Using Only Critical Sections

Question

I have to implement a read/write lock in C++ using the Win32 api as part of a project at work. All of the existing solutions use kernel objects (semaphores and mutexes) that require a context switch during execution. This is far too slow for my application.

I would like implement one using only critical sections, if possible. The lock does not have to be process safe, only threadsafe. Any ideas on how to go about this?

Answer 1

If you can target Vista or greater, you should use the built-in SRWLock's. They are lightweight like critical sections, entirely user-mode when there is no contention.

Joe Duffy's blog has some recent entries on implementing different types of non-blocking reader/writer locks. These locks do spin, so they would not be appropriate if you intend to do a lot of work while holding the lock. The code is C#, but should be straightforward to port to native.

You can implement a reader/writer lock using critical sections and events - you just need to keep enough state to only signal the event when necessary to avoid an unnecessary kernel mode call.