Linux多線程──3個子線程輪流運行

迅雷筆試題：

編寫一個程序，開啟3個線程，這3個線程的ID分別為A、B、C，每個線程將自己的ID在屏幕上打印10遍，要求輸出結果必須按ABC的順序顯示；如：ABCABC….依次遞推。

程序：

1. #include <pthread.h>
2. #include <cstdio>
4. const int THREAD_NUMBER = 3;
6. // 子線程的互斥量和條件變量
7. pthread_mutex_t thread_mutex[THREAD_NUMBER];
8. pthread_cond_t thread_cond[THREAD_NUMBER];
10. // 子線程是否正在等待
11. bool thread_wait_flag[THREAD_NUMBER];
13. // 標識輪到哪個子線程輸出其ID
14. pthread_mutex_t mutex;
15. int thread_turn;
17. void *thread_func(void *arg);
19. int main(int argc, char **argv)
20. {
21. pthread_t tids[THREAD_NUMBER];
23. for (int i = 0; i < THREAD_NUMBER; ++i)
24. {
25. pthread_mutex_init(&thread_mutex[i], NULL);
26. pthread_cond_init(&thread_cond[i], NULL);
27. }
29. pthread_mutex_init(&mutex, NULL);
30. thread_turn = 0;
32. for (int i = 0; i < THREAD_NUMBER; ++i)
33. thread_wait_flag[i] = false;
35. for (int i = 0; i < THREAD_NUMBER; ++i)
36. {
37. pthread_create(&tids[i], NULL, thread_func, (void *)i);
38. }
40. for (int i = 0; i < THREAD_NUMBER; ++i)
41. {
42. pthread_join(tids[i], NULL);
43. }
44. printf("\n");
45. return 0;
46. }
48. void *thread_func(void *arg)
49. {
50. int id = (int)arg;
51. char ch = 'A' + id;
52. int count = 0;
54. while (true)
55. {
56. if (id == thread_turn) // 若輪到當前子線程，輸出ID，發送信號
57. {
58. printf("%c", ch);
59. ++count;
60. if (id == THREAD_NUMBER-1 && count == 10) // 若是第3個子線程，輸出ID後，可直接退出。
61. break;
62. pthread_mutex_lock(&mutex);
63. ++thread_turn;
64. thread_turn %= THREAD_NUMBER;
65. pthread_mutex_unlock(&mutex);
67. while (true)
68. {
69. pthread_mutex_lock(&thread_mutex[thread_turn]);
70. if (true == thread_wait_flag[thread_turn])
71. {
72. pthread_cond_signal(&thread_cond[thread_turn]);
73. pthread_mutex_unlock(&thread_mutex[thread_turn]);
74. break;
75. }
76. pthread_mutex_unlock(&thread_mutex[thread_turn]);
77. }
78. if (count == 10) // 若是第1、2個子線程，發出信號後，退出
79. break;
80. }
81. else // 否則，等待
82. {
83. pthread_mutex_lock(&thread_mutex[id]);
84. thread_wait_flag[id] = true;
85. pthread_cond_wait(&thread_cond[id], &thread_mutex[id]);
86. thread_wait_flag[id] = false;
87. pthread_mutex_unlock(&thread_mutex[id]);
88. }
89. }
90. return (void *)0;
91. }