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Matthew Lugg
4f16e80cea
On NetBSD and Illumos, we were using the `std.Thread.Futex`-based implementation of `std.Thread.Mutex`. But since futex is not a primitive on these targets, the implementation of `std.Thread.Futex` was based on pthread primitives, including `pthread_mutex_t`. This had the amusing consequence that locking a contended mutex on NetBSD would actually perform 2 mutex locks, 2 mutex unlocks, and 1 condition wait; likewise, unlocking a contended mutex would perform 2 mutex locks, 2 mutex unlocks, and 1 condition signal. Having read some cutting-edge studies, I have concluded that this is a slightly suboptimal approach. Instead, let's just use pthread mutexes directly in this case; that's an obviously better idea. In the future, I think we can probably entirely remove our usages of pthread sync primitives---no platform actually treats them as the base primitives. Of the platforms which std has any meaningful support for today, most support futexes, and the exceptions (NetBSD and Illumos) support a thread parking API. We can implement futex and/or mutex on top of thread parking and drop the pthread dependency entirely.