UNIX环境高级编程学习之第十二章线程控制-可重入（线程安全）的getenv方法

UNIX环境高级编程学习之第十二章线程控制-可重入（线程安全）的getenv方法

/* FileName: getenv_r.c Date: 20100625 Desc: gcc getenv_r.c -lpthread -o demo 可重入（线程安全）的getenv方法 */ #include #include #include #include #include #include #include extern char **environ; pthread_mutex_t g_env_mutex; // 互斥锁定义 环境变量互斥锁 static pthread_once_t g_init_done = PTHREAD_ONCE_INIT; // 每个进程里只调用一次 static void thread_init(void) // 线程里初始化互斥锁 { pthread_mutexattr_t attr; // 定义互斥锁属性 pthread_mutexattr_init(&attr); pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE_NP); // 设置互斥锁为多次加锁 pthread_mutex_init(&g_env_mutex, &attr); // 互斥锁定义并初始化 pthread_mutexattr_destroy(&attr); } int getenv_r(const char *name, char *buf, const int buflen) { int i, len, olen; pthread_once(&g_init_done, thread_init); // 本进程只调用一次thread_init方法 len = strlen(name); pthread_mutex_lock(&g_env_mutex); for (i=0; environ[i] != NULL; i++) { if (strncmp(name, environ[i], len) == 0 && environ[i][len] == '=') { olen = strlen(&environ[i][len+1]); if (olen >= buflen) { pthread_mutex_unlock(&g_env_mutex); return ENOSPC; } strcpy(buf, &environ[i][len+1]); pthread_mutex_unlock(&g_env_mutex); return 0; } } pthread_mutex_unlock(&g_env_mutex); return ENOENT; } void* thread_fun(void * arg) { while (1) { char buf[256] = { 0x00 }; getenv_r("PWD", buf, sizeof(buf)); printf("PID=%ul getenv_r(/"PWD/")=%s /n", pthread_self(), buf); usleep(1); } return (void*)1; } int main(int argc, char* argv[]) { int ret; pthread_t t1, t2; ret = pthread_create(&t1, NULL, thread_fun, NULL); if (ret != 0) { printf("pthread_create() is Error t1 /n"); exit(-1); } ret = pthread_create(&t2, NULL, thread_fun, NULL); if (ret != 0) { printf("pthread_create() is Error t2 /n"); exit(-1); } while (1) { if (getchar() == 'q') { break; } } pthread_mutex_destroy(&g_env_mutex); // 销毁互斥锁 环境变量互斥锁 return 0; }