cosmopolitan/third_party/nsync

DESCRIPTION

  *NSYNC is a synchronization primitives library.

LICENSE

  Apache 2.0

ORIGIN

  git@github.com:google/nsync
  commit ac5489682760393fe21bd2a8e038b528442412a7
  Author: Mike Burrows <m3b@google.com>
  Date:   Wed Jun 1 16:47:52 2022 -0700

LOCAL CHANGES

  - Fix nsync_mu_unlock() on Apple Silicon

  - Time APIs were so good that they're now in libc

  - Double linked list API was so good that it's now in libc

  - Support Apple's ulock futexes which are internal but nicer than GCD

  - Ensure resources such as POSIX semaphores are are released on fork.

  - Modified *NSYNC to allocate waiter objects on the stack. We need it
    because we use *NSYNC mutexes to implement POSIX mutexes, which are
    too low-level to safely depend on malloc, or even mmap in our case.

  - Rewrote most of the semaphore and futex system call support code so
    it works well with Cosmopolitan's fat runtime portability. *NSYNC's
    unit test suite passes on all supported platforms. However the BSDs
    currently appear to be overutilizing CPU time compared with others.
    This appears to be the fault of the OSes rather than *NSYNC / Cosmo

  - Support POSIX thread cancellation. APIs that wait on condition vars
    are now cancellation points. In PTHREAD_CANCEL_MASKED mode they may
    return ECANCELED. In PTHREAD_CANCEL_DEFERRED mode the POSIX threads
    library will unwind the stack to re-acquire locks and free waiters.
    On the other hand the *NSYNC APIs for mutexes will now safely block
    thread cancellation, but you can still use *NSYNC notes to do that.