Sergey Bugaev 690141ff8b LibPthread: Reimplement semaphores ...

This implementation does not use locking or condition variables
internally; it's purely based on atomics and futexes.

Notably, concurrent sem_wait() and sem_post() calls can run *completely
in parallel* without slowing each other down, as long as there are empty
slots for them all to succeed without blocking.

Additionally, sem_wait() never executes an atomic operation with release
ordering, and sem_post() never executes an atomic operation with acquire
ordering (unless you count the syscall). This means the compiler and the
hardware are free to reorder code *into* the critical section.

2021-07-05 20:26:01 +02:00

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