GCC原子操作(Atomic Builtins)

/** =====================================================================================**       Filename:  atomic.c**    Description:  gcc-4.1.1: Built-in functions for atomic memory access*                  http://gcc.gnu.org/onlinedocs/gcc-4.1.1/gcc/Atomic-Builtins.html    compile:         gcc atomic.c -lpthead    run:        time ./a.out     modify Macro VER to choose the version            1. no lock            2. pthread_mutex            3. atomic    ref:        http://gcc.gnu.org/onlinedocs/gcc-4.1.1/gcc/Atomic-Builtins.html        http://www.alexonlinux.com/multithreaded-simple-data-type-access-and-atomic-variableshttp://www.cnblogs.com/FrankTan/archive/2010/12/11/1903377.html    the demo, create 4 threads. the odd thread do --, the even threads do ++.     so, the global_int should be zero. we can see:            1. the "no lock version", fastest but not thread safe            2. the "pthread mutex version" slowest, but thread safe            3. the "atomic version", fast and thread safe*        Version:  1.0*        Created:  09/11/2012 05:28:13 PM*       Revision:  none*       Compiler:  gcc**         Author:  TED (cn), [e-mail]*       * ===================================================================================*/#include <stdio.h>#include <pthread.h>#include <unistd.h>#include <stdlib.h>#include <errno.h>/************************** for test the time cost begin *********************/#include <sys/time.h>struct timeval tp1, tp2;static void start_timer(){    gettimeofday(&tp1, NULL);}/* return by seconds */static double end_timer(){    gettimeofday(&tp2, NULL);    return((tp2.tv_sec - tp1.tv_sec) +             (tp2.tv_usec - tp1.tv_usec) * 1.0e-6);}/* for test the time cost end */#define LOOP_NUM 1000000int global_int = 0;#define VER              3  /* modify VER to choose the version here */#define NO_LOCK_VER      1  /* quickest & not thread safe */#define MUTEX_VER        2  /* slowest & thread safe */ #define ATOMIC_VER       3  /* quick & thread safe */#if (VER == MUTEX_VER)    pthread_mutex_t lock;#endifvoid *thread_proc( void *arg ){    int i;    int flag = (int)arg;    for (i = 0; i < LOOP_NUM; i++){        if(flag % 2 == 0){#if (VER == NO_LOCK_VER)            global_int++;#elif (VER == ATOMIC_VER)            __sync_fetch_and_add( &global_int, 1 );#elif (VER == MUTEX_VER)            pthread_mutex_lock(&lock);            global_int++;            pthread_mutex_unlock(&lock);#endif        }        else{#if (VER == NO_LOCK_VER)            global_int--;#elif (VER == ATOMIC_VER)            __sync_fetch_and_sub(&global_int, 1);#elif (VER == MUTEX_VER)            pthread_mutex_lock(&lock);            global_int--;            pthread_mutex_unlock(&lock);#endif        }}return NULL;}int main(int argc, const char *argv[]){   int i;int thread_num = 4;pthread_t *pthread_id;#if (VER == MUTEX_VER)    pthread_mutex_init(&lock,NULL);#endif    int ntimes = 100;    start_timer();    while(ntimes--){        pthread_id = (pthread_t*)malloc( sizeof( pthread_t ) * thread_num);        if (NULL == pthread_id){            perror( "malloc" );            exit(1);        }        for (i = 0; i < thread_num; i++){            if (pthread_create( &pthread_id[i], NULL, thread_proc, (void*)i)){                perror( "pthread_create" );                exit(1);            }        }        for (i = 0; i < thread_num; i++){            pthread_join(pthread_id[i], NULL);        }        free(pthread_id);        printf( "global_int value is: %d\n", global_int );        printf( "The Value should be: 0\n");        global_int = 0;    }    printf("cost %g\n", (double)end_timer());return 0;}