Linux多线程学习（十）pthread_atfork

pthread_atfork 注册fork的函数

实例

 #define _UNIX03_THREADS 1
      2 #include <pthread.h>
      3 #include <stdio.h>
      4 #include <unistd.h>
      5 #include <fcntl.h>
      6 #include <sys/types.h>
      7 #include <sys/stat.h>
      8 #include <sys/wait.h>
      9 #include <stdlib.h>
     10 #include <errno.h>
     11
     12 char fn_c[] = "childq.out";
     13 char fn_p[] = "parentside.out";
     14 int  fd_c;
     15 int  fd_p;
     16
     17 void prep1(void)  {
     18   char buff[80] = "prep1\n";
     19   write(4,buff,sizeof(buff));
     20 }
     21
     22 void prep2(void)  {
     23   char buff[80] = "prep2\n";
     24   write(4,buff,sizeof(buff));
     25 }
     26
     27 void prep3(void)  {
     28   char buff[80] = "prep3\n";
     29   write(4,buff,sizeof(buff));
     30 }
     31
     32
     33 void parent1(void)  {
     34   char buff[80] = "parent1\n";
     35   write(4,buff,sizeof(buff));
     36 }
     37
     38 void parent2(void)  {
     39   char buff[80] = "parent2\n";
     40   write(4,buff,sizeof(buff));
     41 }
     42
     43 void parent3(void)  {
     44   char buff[80] = "parent3\n";
     45   write(4,buff,sizeof(buff));
     46 }
     47
     48
     49 void child1(void)  {
     50   char buff[80] = "child1\n";
     51   write(3,buff,sizeof(buff));
     52 }
     53
     54 void child2(void)  {
     55   char buff[80] = "child2\n";
     56   write(3,buff,sizeof(buff));
     57 }
     58
     59 void child3(void)  {

60   char buff[80] = "child3\n";
     61   write(3,buff,sizeof(buff));
     62 }
     63
     64 void *thread1(void *arg) {
     65
     66   printf("Thread1: Hello from the thread.\n");
     67
     68 }
     69
     70
     71 int main(void)
     72 {
     73   pthread_t thid;
     74   int       rc, ret;
     75   pid_t     pid;
     76   int       status;
     77   char   header[30] = "Called Child Handlers\n";
     78
     79
     80   if (pthread_create(&thid, NULL, thread1, NULL) != 0) {
     81     perror("pthread_create() error");
     82     exit(3);
     83   }
     84
     85   if (pthread_join(thid, NULL) != 0) {
     86     perror("pthread_join() error");
     87     exit(5);
     88   } else {
     89     printf("IPT: pthread_join success!  Thread 1 should be finished now.\n");
     90     printf("IPT: Prepare to fork!!!\n");
     91   }
     92
     93
     94   /*-----------------------------------------*/
     95   /*|  Start atfork handler calls in parent  */
     96   /*-----------------------------------------*/
     97   /* Register call 1 */
     98   rc = pthread_atfork(&prep1, &parent2, &child3);
     99 /*  if (rc != 0) {
    100      perror("IPT: pthread_atfork() error [Call #1]");
    101      printf("  rc= %d, errno: %d, ejr: %08x\n", rc, errno, __errno2());
    102   }*/
    103
    104
    105   /* Register call 2 */
    106   rc = pthread_atfork(&prep2, &parent3, &child1);
    107   /*if (rc != 0) {
    108      perror("IPT: pthread_atfork() error [Call #2]");
    109      printf("  rc= %d, errno: %d, ejr: %08x\n", rc, errno, __errno2());

}*/
    111   /* Register call 3 */
    112   rc = pthread_atfork(&prep3, &parent1, NULL);
    113   /*if (rc != 0) {
    114      perror("IPT: pthread_atfork() error [Call #3]");
    115      printf("  rc= %d, errno: %d, ejr: %08x\n", rc, errno, __errno2());
    116   }*/
    117   /* Create output files to expose the execution of fork handlers. */
    118   if ((fd_c = creat(fn_c, S_IWUSR)) < 0)
    119     perror("creat() error");
    120   else
    121     printf("Created %s and assigned fd= %d\n", fn_c, fd_c);
    122   if ((ret = write(fd_c,header,30)) == -1)
    123     perror("write() error");
    124   else
    125     printf("Write() wrote %d bytes in %s\n", ret, fn_c);
    126   if ((fd_p = creat(fn_p, S_IWUSR)) < 0)
    127     perror("creat() error");
    128   else
    129     printf("Created %s and assigned fd= %d\n", fn_p, fd_p);
    130   if ((ret = write(fd_p,header,30)) == -1)
    131     perror("write() error");
    132   else
    133     printf("Write() wrote %d bytes in %s\n", ret, fn_p);
    134   pid = fork();
    135   if (pid < 0)
    136     perror("IPT: fork() error");
    137   else {
    138     if (pid == 0) {
    139       printf("Child: I am the child!\n");
    140       printf("Child: My PID= %d, parent= %d\n", (int)getpid(),
    141               (int)getppid());
    142       exit(0);
    143     } else {
    144       printf("Parent: I am the parent!\n");
    145       printf("Parent: My PID= %d, child PID= %d\n", (int)getpid(), (int)pid);
    146       if (wait(&status) == -1)
    147         perror("Parent: wait() error");
    148       else if (WIFEXITED(status))
    149              printf("Child exited with status: %d\n",WEXITSTATUS(status));
    150            else
    151              printf("Child did not exit successfully\n");
    152     close(fd_c);
    153     close(fd_p);
    154     }
    155   }
    156 }

编译  gcc -o pthread_atfork -pthread pthread_atfork.c

这里注意 -pthread 而不是-lpthread 若是后者则会报错 pthread_atfork函数找不到

运行结果

Thread1: Hello from the thread.
IPT: pthread_join success!  Thread 1 should be finished now.
IPT: Prepare to fork!!!
Created childq.out and assigned fd= 3
Write() wrote 30 bytes in childq.out
Created parentside.out and assigned fd= 4
Write() wrote 30 bytes in parentside.out
Child: I am the child!
Child: My PID= 2616, parent= 2614
Parent: I am the parent!
Parent: My PID= 2614, child PID= 2616
Child exited with status: 0