編程之道

?1 #include? < string .h >
?2 #include? < errno.h >
?3 #include? < pthread.h >
?4 #include? < stdlib.h >
?5
?6 extern ? char ? ** environ;
?7
?8 pthread_mutex_t?env_mutex;
?9 static ?pthread_once_t?init_donw? = ?PTHREAD_ONCE_INIT;
10
11 static ? void ?thread_init( void )
12 {
13 ????pthread_mutexattr_t?attr;
14 ????pthread_mutexattr_init( & attr);
15 ????pthread_mutexattr_settype( & attr,PTHREAD_MUTEX_RECURSIVE);? // ?設置可遞歸的互斥量
16 ????pthread_mutex_init( & env_mutex, & attr);
17 ????pthread_mutexattr_destroy( & attr);
18 }
19
20 int ?getevn_r( const ? char ? * name,? char ? * buf,? int ?buflen)
21 {
22 ???? int ?i,?len,?olen;
23 ????
24 ????pthread_once( & init_done,thread_init);? // ?確保每個進程只調用一次threaad_init()
25 ????len? = ?strlen(name);
26 ????pthread_mutex_lock( & env_mutex);
27 ???? for (i = 0 ;environ[i] != NULL;i ++ )
28 ???? {
29 ???????? if (?(strncmp(name,environ[i],len) == 0 ? && ?(environ[i][len]? == ? " = " )?)
30 ???????? {
31 ????????????olen? = ?strlen( & environ[i][len + 1 ]);
32 ???????????? if (?olen? > ?buflen?)? // ?檢查緩沖區長度是否足夠
33 ???????????? {
34 ????????????????pthread_mutex_unlock( & env_mutex);
35 ???????????????? return (ENOSPC);
36 ????????????}
37 ????????????strcpy(buf, & environ[i][len + 1 ]);
38 ????????????pthread_mutex_unlock( & env_mutex);
39 ???????????? return ( 0 );
40 ????????}
41 ????}
42 ????pthread_mutex_unlock( & env_mutex);
43 ???? return (ENOENT);
44 }
45