1. /*
    2. * =====================================================================================
    3. *
    4. *    Filename:  atomic.c
    5. *
    6. *    Description:  gcc-4.1.1: Built-in functions for atomic memory access
    7. *                  http://gcc.gnu.org/onlinedocs/gcc-4.1.1/gcc/Atomic-Builtins.html
    8.     compile:
    9.          gcc atomic.c -lpthead
    10.     run:
    11.         time ./a.out 
    12.     modify Macro VER to choose the version
    13.             1. no lock
    14.             2. pthread_mutex
    15.             3. atomic
    16.     ref:
    17.         http://gcc.gnu.org/onlinedocs/gcc-4.1.1/gcc/Atomic-Builtins.html
    18.         http://www.alexonlinux.com/multithreaded-simple-data-type-access-and-atomic-variables
    19.         http://www.cnblogs.com/FrankTan/archive/2010/12/11/1903377.html
    20.     the demo, create 4 threads. the odd thread do --, the even threads do ++. 
    21.     so, the global_int should be zero. we can see:
    22.             1. the "no lock version", fastest but not thread safe
    23.             2. the "pthread mutex version" slowest, but thread safe
    24.             3. the "atomic version", fast and thread safe
    25. *        Version:  1.0
    26. *        Created:  09/11/2012 05:28:13 PM
    27. *       Revision:  none
    28. *       Compiler:  gcc
    29. *
    30. *         Author:  TED (cn), guolb57@163.com
    31. *       
    32. * ===================================================================================
    33. */
    35. #include <stdio.h>
    36. #include <pthread.h>
    37. #include <unistd.h>
    38. #include <stdlib.h>
    39. #include <errno.h>
    41. /************************** for test the time cost begin *********************/
    42. #include <sys/time.h>
    44. struct timeval tp1, tp2;
    46. static void start_timer()
    47. {
    48.     gettimeofday(&tp1, NULL);
    49. }
    51. /* return by seconds */
    52. static double end_timer()
    53. {
    54.     gettimeofday(&tp2, NULL);
    55.     return((tp2.tv_sec - tp1.tv_sec) + 
    56.             (tp2.tv_usec - tp1.tv_usec) * 1.0e-6);
    57. }
    59. /* for test the time cost end */
    61. #define LOOP_NUM 1000000
    63. int global_int = 0;
    65. #define VER              3  /* modify VER to choose the version here */
    67. #define NO_LOCK_VER      1  /* quickest & not thread safe */
    68. #define MUTEX_VER        2  /* slowest & thread safe */ 
    69. #define ATOMIC_VER       3  /* quick & thread safe */
    71. #if (VER == MUTEX_VER)
    72.     pthread_mutex_t lock;
    73. #endif
    75. void *thread_proc( void *arg )
    76. {
    77.     int i;
    78.     int flag = (int)arg;
    80.     for (i = 0; i < LOOP_NUM; i++)    {
    81.         if(flag % 2 == 0){
    82. #if (VER == NO_LOCK_VER)
    83.             global_int++;
    84. #elif (VER == ATOMIC_VER)
    85.             __sync_fetch_and_add( &global_int, 1 );
    86. #elif (VER == MUTEX_VER)
    87.             pthread_mutex_lock(&lock);
    88.             global_int++;
    89.             pthread_mutex_unlock(&lock);
    90. #endif
    91.         }
    92.         else{
    93. #if (VER == NO_LOCK_VER)
    94.             global_int--;
    95. #elif (VER == ATOMIC_VER)
    96.             __sync_fetch_and_sub(&global_int, 1);
    97. #elif (VER == MUTEX_VER)
    98.             pthread_mutex_lock(&lock);
    99.             global_int--;
    100.             pthread_mutex_unlock(&lock);
    101. #endif
    102.         }
    103.     }
    105.     return NULL;
    106. }
    108. int main(int argc, const char *argv[])
    109. {
    110.        int i;
    111.     int thread_num = 4;
    112.     pthread_t *pthread_id;
    114. #if (VER == MUTEX_VER)
    115.     pthread_mutex_init(&lock,NULL);
    116. #endif
    118.     int ntimes = 100;
    119.     start_timer();
    120.     while(ntimes--){
    121.         pthread_id = (pthread_t*)malloc( sizeof( pthread_t ) * thread_num);
    122.         if (NULL == pthread_id)    {
    123.             perror( "malloc" );
    124.             exit(1);
    125.         }
    127.         for (i = 0; i < thread_num; i++){
    128.             if (pthread_create( &pthread_id[i], NULL, thread_proc, (void*)i)){
    129.                 perror( "pthread_create" );
    130.                 exit(1);
    131.             }
    132.         }
    134.         for (i = 0; i < thread_num; i++){
    135.             pthread_join(pthread_id[i], NULL);
    136.         }
    138.         free(pthread_id);
    140.         printf( "global_int value is: %d\n", global_int );
    141.         printf( "The Value should be: 0\n");
    143.         global_int = 0;
    144.     }
    146.     printf("cost %g\n", (double)end_timer());
    148.     return 0;
    149. }

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