Linux 線程私有數據 測試用例

 線程私有數據可以用來存儲線程本地的信息，tcmalloc就是用了該機制來減少鎖的開銷，加快內存分配。

下面給出了一個測試用例

通過pthread_key_create創建一個線程私有數據的key,並設置這個key對應私有數據的釋放函數；調用pthread_setspecific將key和私有數據進行關聯；可以調用pthread_getspecific進行獲取私有數據。

#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <stdlib.h>

static pthread_once_t once = PTHREAD_ONCE_INIT;
static pthread_key_t str_test_key;

#define MAX_STR_TEST_LEN 256	

static void destructor(void * buf) {
    free(buf);
}

static void create_key(void) {
    int s;
    s = pthread_key_create(&str_test_key, destructor);
    if (s != 0) {
        printf("pthread_key_create failed");
        exit(-1);
    }
}

char * str_test(char * arg) {
    int s;
    char *buf;
    s = pthread_once(&once, create_key);
    if (s != 0) {
        printf("pthread_once failed");
        exit(-1);
    }

    buf = pthread_getspecific(str_test_key);
    if (buf == NULL) {
        buf = malloc(MAX_STR_TEST_LEN);
        if (buf == NULL) {
            printf("pthread_once failed");
            exit(-1);
        }
       
        s = pthread_setspecific(str_test_key, buf);
        if (s != 0) {
            printf("pthread_setspecific failed");
            exit(-1);
        }
    }

    strncpy(buf, arg, MAX_STR_TEST_LEN - 1);
}


static void * thread_func(void * arg) {
    char *str;
    printf("Other thread about to call str_test()\n");
    str = str_test((char *) arg);
    printf("Other thread: str (%p) = %s\n", str, str);

    str = pthread_getspecific(str_test_key);
    printf("Other thread: tsd (%p) = %s\n", str, str);

    return NULL;

}

int main(int argc, char *argv[])
{
    pthread_t t;
    int s;
    char *str;

    str = str_test("hello world");
    printf("Main thread has called str_test()\n");

    s = pthread_create(&t, NULL, thread_func, "this is a test");
    if (s != 0) {
        printf("pthread_create failed");
        return -1;
    }
    
    s = pthread_join(t, NULL);
    if (s != 0) {
        printf("pthread_join failed");
        return -1;
    }

    printf("Main thread: str (%p) = %s\n", str, str);
    return 0;
}

結果：