Syscall API: sleep/wakeup: cancellation

• if the cancellation signal is delivered after thrsleep is called then the spinlock is no longer locked; if it's delivered before that then we need to keep thrsleep from blocking, but still release the spinlock

• int thrsleep(void *ident, clockid_t clock_id, const struct timespec *abstime, void *lock, const int *abort);

  • if *abort is non-zero after unlocking the spinlock, thrsleep() will return EINTR as-if the cancellation signal had occurred after the entry into the kernel

  • The signal handler for cancellation, when this can occur, just set that flag and returns instead of trying to call pthread_exit(PTHREAD_CANCELED)