On Linux and OpenBSD you can use futex(FUTEX_WAKE, 1) to wake precisely any one of the threads or processes waiting on futex(FUTEX_WAIT). Are you telling me th

On Linux and OpenBSD you can use futex(FUTEX_WAKE, 1) to wake precisely any one of the threads or processes waiting on futex(FUTEX_WAIT). Are you telling me that's broken? I understand that sophisticated synchronization primitives usually maintain a list of waiters, but I wasn't under the impression they do that because kernels are broken, but rather because userspace libraries want to be in control of which waiter gets selected. The reason why things are racey as you describe probably has more to do with userspace libraries wanting to avoid issuing a system call, than it does with the kernel's design. Things would probably be easier if you always used a system call, such as the case with most WIN32 locks, but it's slow so people try not to do it and sometimes fail. Also yes, I understand it's hard. That's why Google tasked the guy who built their fiercest rival (Altavista) with building their locking primitives (Chubby and *NSYNC).