Programming with POSIX® Threads

11 PTHREAD_MUTEX_INITIALIZER,

12 PTHREAD_MUTEX_INITIALIZER

13 }; 14

15 int backoff = 1; /* Whether to backoff or deadlock */

16 int yield_flag = 0; /* 0: no yield, >0: yield, <0: sleep */ 17

18 /*

19 * This is a thread start routine that locks all mutexes in

20 * order, to ensure a conflict with lock reverse, which does the

21 * opposite.

22 */

23 void *lock_forward (void *arg)

24 {

25 int i, iterate, backoffs;

26 int status;

27

28 for (iterate = 0; iterate < ITERATIONS; iterate++) {

29 backoffs = 0;

30 for (i = 0; i < 3; i++) {

31 if (i == 0) {

32 status = pthread_mutex_lock (&mutex[i]);

33 if (status != 0)

34 err_abort (status, "First lock");

35 } else {

36 if (backoff)

37 status = pthread_mutex_trylock (&mutex[i]);

38 else

39 status = pthread_mutex_lock (&mutex[i]);

40 if (status == EBUSY) {

41 backoffs++;

42 DPRINTF ((

43 " [forward locker backing off at %d]\n",

44 i));

45 for (; i >= 0; i--) {

46 status = pthread_mutex_unlock (&mutex[i]);

47 if (status != 0)

48 err_abort (status, "Backoff");

49 }

50 } else {

51 if (status != 0)

52 err_abort (status, "Lock mutex");

53 DPRINTF ((" forward locker got %d\n", i));

54 }

55 }

56 /*

57 * Yield processor, if needed to be sure locks get

58 * interleaved on a uniprocessor.

59 */

60 if (yield_flag) {

61 if (yield_flag > 0)

62 sched_yield ();

63 else

64 sleep (1);

65 }

66 }

67 /*

68 * Report that we got 'em, and unlock to try again.

69 */

70 printf (

71 "lock forward got all locks, %d backoffs\n", backoffs);

72 pthread_mutex_unlock (&mutex[2]);

73 pthread_mutex_unlock (&mutex[1]);

74 pthread_mutex_unlock (&mutex[0]);

75 sched_yield ();

76 }

77 return NULL;

78 }

79

80 /*

81 * This is a thread start routine that locks all mutexes in

82 * reverse order, to ensure a conflict with lock_forward, which

83 * does the opposite.

84 */

85 void *lock_backward (void *arg)

86 {

87 int i, iterate, backoffs;

88 int status;

89

90 for (iterate = 0; iterate < ITERATIONS; iterate++) {

91 backoffs = 0;

92 for (i = 2; i >= 0; i--) {

93 if (i == 2) {

94 status = pthread_mutex_lock (&mutex[i]);

95 if (status != 0)

96 err_abort (status, "First lock");

97 } else {

98 if (backoff)

99 status = pthread_mutex_trylock (&mutex[i]);

100 else

101 status = pthread_mutex_lock (&mutex[i]);

102 if (status == EBUSY) {

103 backoffs++;

104 DPRINTF ((

105 " [backward locker backing off at %d]\n",

106 i));

107 for (; i < 3; i++) {

108 status = pthread_mutex_unlock (&mutex[i]);

109 if (status != 0)

110 err_abort (status, "Backoff");

111 }

112 } else {

113 if (status != 0)

114 err_abort (status, "Lock mutex");

115 DPRINTF ((" backward locker got %d\n", i));