locks.c

   1 #include <signal.h>
   2 #include <unistd.h>
   3 #include "locks.h"
   4 #include "log.h"
   5 #include "pids.h"
   6
   7 #define STEAL_THRESHOLD 100000
   8
   9 void lock(lock_t *_lock)
  10 {
  11         while (_lock->lock == LOCKED) {
  12                 _lock->contention++;
  13                 usleep(1);
  14                 if (_lock->contention > STEAL_THRESHOLD) {
  15                         pid_t pid = _lock->owner;
  16
  17                         if (pid_alive(pid) == FALSE) {
  18                                 output(0, "[%d] more than %d attempts to get lock. pid %d looks dead, stealing.\n",
  19                                         getpid(), STEAL_THRESHOLD, pid);
  20                                 goto steal;
  21                         }
  22                 }
  23         }
  24
  25 steal:
  26         _lock->contention = 0;
  27         _lock->lock = LOCKED;
  28         _lock->owner = getpid();
  29 }
  30
  31 void unlock(lock_t *_lock)
  32 {
  33         asm volatile("" ::: "memory");
  34         _lock->contention = 0;
  35         _lock->lock = UNLOCKED;
  36         _lock->owner = 0;
  37 }