getenv3.c

来自「UNIX环境高级编程书的源代码」· C语言 代码 · 共 47 行

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

static pthread_key_t key;
static pthread_once_t init_done = PTHREAD_ONCE_INIT;
pthread_mutex_t env_mutex = PTHREAD_MUTEX_INITIALIZER;

extern char **environ;

static void
thread_init(void)
{
	pthread_key_create(&key, free);
}

char *
getenv(const char *name)
{
	int		i, len;
	char	*envbuf;

	pthread_once(&init_done, thread_init);
	pthread_mutex_lock(&env_mutex);
	envbuf = (char *)pthread_getspecific(key);
	if (envbuf == NULL) {
		envbuf = malloc(ARG_MAX);
		if (envbuf == NULL) {
			pthread_mutex_unlock(&env_mutex);
			return(NULL);
		}
		pthread_setspecific(key, envbuf);
	}
	len = strlen(name);
	for (i = 0; environ[i] != NULL; i++) {
		if ((strncmp(name, environ[i], len) == 0) &&
		  (environ[i][len] == '=')) {
			strcpy(envbuf, &environ[i][len+1]);
			pthread_mutex_unlock(&env_mutex);
			return(envbuf);
		}
	}
	pthread_mutex_unlock(&env_mutex);
	return(NULL);
}