Josh Haberman » wanted http://blog.reverberate.org parsing, performance, minimalism with C99 Wed, 02 Dec 2009 20:45:36 +0000 http://wordpress.org/?v=2.8.6 en hourly 1 Wanted: a portable mutex and atomic refcount http://blog.reverberate.org/2009/08/14/wanted-a-portable-mutex-and-atomic-refcount/ http://blog.reverberate.org/2009/08/14/wanted-a-portable-mutex-and-atomic-refcount/#comments Sat, 15 Aug 2009 02:12:02 +0000 Josh http://blog.reverberate.org/?p=275 upb needs to have some lightweight thread-aware behavior. I’m leaving most synchronization up to users (individual messages will not be thread-safe), but there are a few central structures I need to make thread-safe and reference-counted.

I need only the tiniest bit of functionality:

  • a portable mutex.
  • a portable atomic_t that lets me atomic_inc() and atomic_dec().

We’re talking “lives in one single header” small. The mutex would just be wrappers around existing mutex implementations (pthreads, windows, etc), and since those routines typically take care of any memory barriers you need to safely read/mutate the shared state, I wouldn’t have to worry about that.

The atomic type would have to be hand-coded and architecture-specific, since most threading libraries don’t provide one. The reason for providing this would be reference-counting. If you are reference-counting an immutable structure, then you don’t need to worry about memory barriers to ensure the consistency of that structure; if you’re reference-counting a mutable structure, then you’ll need to protect the mutable state with mutexes and acquire the mutex before freeing anything.

The library (er, header file) should also support compiling everything to nothing if NO_THREAD_SAFETY is defined as a preprocessor symbol.

Yes, that all sounds good. Tiny yet functional. I’ll be writing this very soon unless something exactly like what I’ve described happens to already exist.

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