关于多线程fork()文件描述符复制问题

spiritX

最近遇到一个问题, 很郁闷.
----------------------------

一个程序有A, B两个线程.

A线程会执行fork()操作, B线程会打开比较多的文件(fopen).

请问:B线程打开的文件描述符会被A线程的fork复制吗 ?


我使用的操作系统是solaris5.8, 线程库是POSIX Threads.


我man了fork看到了这2段话, 好象不会复制的意思.请大虾解答, 谢谢!

  Solaris Threads
     In applications that use the Solaris threads API rather than
     the POSIX threads API (applications linked with -lthread but
     not -lpthread),fork() duplicates in the  child  process  all
     threads  (see  thr_create(3THR)) and LWPs in the parent pro-
     cess. The  fork1()  function  duplicates  only  the  calling
     thread (LWP) in the child process.

  POSIX Threads
     In applications that use the POSIX threads API  rather  than
     the   Solaris   threads   API  (  applications  linked  with
     -lpthread, whether or not linked with -lthread), a  call  to
     fork() is like a call to  fork1(), which replicates only the
     calling thread. There is no call that forks a child with all
     threads and LWPs duplicated in the child.

     Note that if a program is  linked  with  both  libraries  (-
     lthread  and  -lpthread),  the POSIX semantic of fork() pre-
     vails.

timespace

#include <stdio.h> #include <stdlib.h> #include <assert.h> #include <time.h> #include <errno.h> #include <unistd.h> #include <pthread.h> #include <sys/wait.h> pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; pthread_cond_t cond = PTHREAD_COND_INITIALIZER; int nowait = 0; void* thFork(void*); void pFiles(); /* gcc -g -O2 -Wall fork.c -o foo -lpthread -lrt */ int main() {     int ret = 0;     pthread_t tid;     struct timespec timeout;     FILE* fp;         pFiles("main");     fp = fopen("my.txt", "w");     assert(fp);         assert(pthread_create(&tid, NULL, thFork, NULL) == 0);         timeout.tv_sec = time(NULL) + 60;     timeout.tv_nsec = 0;     pthread_mutex_lock(&mutex);     while (!nowait && ret != ETIMEDOUT) {         ret = pthread_cond_timedwait(&cond, &mutex, &timeout);     }     pthread_mutex_unlock(&mutex);         fprintf(stdout, "Main is done\n");     fclose(fp);         return 0; } void pFiles(char* prefix) {     FILE* fp;     char cmd[64];     char buf[1024];         fprintf(stdout, "%s:\n", prefix);     sprintf(cmd, "pfiles %ld", getpid());     fp = popen(cmd, "r");     assert(fp);     while (fgets(buf, sizeof(buf), fp) != NULL) {         fputs(buf, stdout);     }     pclose(fp); } void* thFork(void* args) {     struct timespec rqtm;     int status;     pid_t pid;         rqtm.tv_sec = 3;     rqtm.tv_nsec = 0;     pthread_detach(pthread_self());         pFiles("thFork");     pid = fork();     if (pid == 0) {         nanosleep(&rqtm, NULL);         pFiles("child");         exit(0);     } else if (pid < 0) {         perror("fork");         assert(0);     }     wait(&status);         pthread_mutex_lock(&mutex);     nowait = 1;     pthread_cond_signal(&cond);     pthread_mutex_unlock(&mutex);     fprintf(stdout, "thFork is done\n");         return NULL; }

1. -bash-3.00$ uname -a
   
2. SunOS v440test-2 5.10 Generic_118833-36 sun4u sparc SUNW,Sun-Fire-V440
   
3. -bash-3.00$ gcc -g -O2 -Wall fork.c -o foo -lpthread -lrt
   
4. -bash-3.00$ ./foo
   
5. main1:
   
6. 1042:   ./foo
   
7.   Current rlimit: 256 file descriptors
   
8.    0: S_IFCHR mode:0620 dev:336,0 ino:12582946 uid:1010 gid:7 rdev:24,15
   
9.       O_RDWR|O_NOCTTY|O_LARGEFILE
   
10.       /devices/pseudo/pts@0:15
    
11.    1: S_IFCHR mode:0620 dev:336,0 ino:12582946 uid:1010 gid:7 rdev:24,15
    
12.       O_RDWR|O_NOCTTY|O_LARGEFILE
    
13.       /devices/pseudo/pts@0:15
    
14.    2: S_IFCHR mode:0620 dev:336,0 ino:12582946 uid:1010 gid:7 rdev:24,15
    
15.       O_RDWR|O_NOCTTY|O_LARGEFILE
    
16.       /devices/pseudo/pts@0:15
    
17.    3: S_IFIFO mode:0000 dev:344,0 ino:30884122 uid:1010 gid:101 size:0
    
18.       O_RDWR
    
19. main2:
    
20. 1042:   ./foo
    
21.   Current rlimit: 256 file descriptors
    
22.    0: S_IFCHR mode:0620 dev:336,0 ino:12582946 uid:1010 gid:7 rdev:24,15
    
23.       O_RDWR|O_NOCTTY|O_LARGEFILE
    
24.       /devices/pseudo/pts@0:15
    
25.    1: S_IFCHR mode:0620 dev:336,0 ino:12582946 uid:1010 gid:7 rdev:24,15
    
26.       O_RDWR|O_NOCTTY|O_LARGEFILE
    
27.       /devices/pseudo/pts@0:15
    
28.    2: S_IFCHR mode:0620 dev:336,0 ino:12582946 uid:1010 gid:7 rdev:24,15
    
29.       O_RDWR|O_NOCTTY|O_LARGEFILE
    
30.       /devices/pseudo/pts@0:15
    
31.    3: S_IFREG mode:0644 dev:32,39 ino:72743 uid:1010 gid:101 size:0
    
32.       O_WRONLY|O_CREAT|O_TRUNC
    
33.       /export/home1/lbs/my.txt
    
34.    4: S_IFIFO mode:0000 dev:344,0 ino:30884123 uid:1010 gid:101 size:0
    
35.       O_RDWR
    
36. thFork:
    
37. 1042:   ./foo
    
38.   Current rlimit: 256 file descriptors
    
39.    0: S_IFCHR mode:0620 dev:336,0 ino:12582946 uid:1010 gid:7 rdev:24,15
    
40.       O_RDWR|O_NOCTTY|O_LARGEFILE
    
41.       /devices/pseudo/pts@0:15
    
42.    1: S_IFCHR mode:0620 dev:336,0 ino:12582946 uid:1010 gid:7 rdev:24,15
    
43.       O_RDWR|O_NOCTTY|O_LARGEFILE
    
44.       /devices/pseudo/pts@0:15
    
45.    2: S_IFCHR mode:0620 dev:336,0 ino:12582946 uid:1010 gid:7 rdev:24,15
    
46.       O_RDWR|O_NOCTTY|O_LARGEFILE
    
47.       /devices/pseudo/pts@0:15
    
48.    3: S_IFREG mode:0644 dev:32,39 ino:72743 uid:1010 gid:101 size:0
    
49.       O_WRONLY|O_CREAT|O_TRUNC
    
50.       /export/home1/lbs/my.txt
    
51.    4: S_IFIFO mode:0000 dev:344,0 ino:30884124 uid:1010 gid:101 size:0
    
52.       O_RDWR
    
53. child:
    
54. 1049:   ./foo
    
55.   Current rlimit: 256 file descriptors
    
56.    0: S_IFCHR mode:0620 dev:336,0 ino:12582946 uid:1010 gid:7 rdev:24,15
    
57.       O_RDWR|O_NOCTTY|O_LARGEFILE
    
58.       /devices/pseudo/pts@0:15
    
59.    1: S_IFCHR mode:0620 dev:336,0 ino:12582946 uid:1010 gid:7 rdev:24,15
    
60.       O_RDWR|O_NOCTTY|O_LARGEFILE
    
61.       /devices/pseudo/pts@0:15
    
62.    2: S_IFCHR mode:0620 dev:336,0 ino:12582946 uid:1010 gid:7 rdev:24,15
    
63.       O_RDWR|O_NOCTTY|O_LARGEFILE
    
64.       /devices/pseudo/pts@0:15
    
65.    3: S_IFREG mode:0644 dev:32,39 ino:72743 uid:1010 gid:101 size:0
    
66.       O_WRONLY|O_CREAT|O_TRUNC
    
67.       /export/home1/lbs/my.txt
    
68.    4: S_IFIFO mode:0000 dev:344,0 ino:30884132 uid:1010 gid:101 size:0
    
69.       O_RDWR
    
70. thFork is done
    
71. Main is done
    

复制代码

[ 本帖最后由 timespace 于 2009-4-16 22:51 编辑 ]

xinglp

高级货 solaris 没玩过

timespace

亲自写个代码就一目了然了。POSIX thread虽然要求fork仅复制calling thread，但是已经存在的多个线程共享的进程资源依然会到child process,比如信号量，互斥锁，文件描述符等等，所以清理工作变得很重要。看看下面这个函数的manual：
#include <pthread.h>
int pthread_atfork(void (*prepare)(void), void (*parent)(void),
       void (*child)(void));

spiritX

原帖由 timespace 于 2009-4-16 20:59 发表
亲自写个代码就一目了然了。POSIX thread虽然要求fork仅复制calling thread，但是已经存在的多个线程共享的进程资源依然会到child process,比如信号量，互斥锁，文件描述符等等，所以清理工作变得很重要。看看下 ...

那就是会被复制了 ?
你写的代码我没怎么细看,谢谢!

JohnBull

man atfork