如何不使用waitpid阻止父母
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【中文标题】如何不使用waitpid阻止父母【英文标题】:how to not block parent with waitpid 【发布时间】:2014-04-08 14:03:11 【问题描述】:我需要创建一个程序来创建 n 个进程并显示信息。当每个进程结束时,我要打印它的 PID 和退出状态。我这样做的方式是,父程序等待创建下一个进程,直到当前进程结束。我需要它,以便它继续创建子进程,并在一个进程结束时仅显示退出信息,而不会阻止父进程继续。我不知道在哪里等待以确保这一点。以下是我的代码:
int main (int argc, char *argv[])
if (argc < 2)
printf("\n\nUsage: %s <enter a number (12 or less)>\n\n", argv[0]);
exit (-1);
else
int *processNum = (int *)malloc(sizeof(12));
int processNumTemp;
processNumTemp = atoi(argv[1]);
processNum = &processNumTemp;
if(*processNum > 12 || *processNum < 1)
printf("\n\nUsage: %s <enter a number (12 or lrss)>\n\n", argv[0]);
else
parentInfo(processNum);
createChildProcess(processNum);
return 0;
//Name: parentInfo
//Description: Displays information about the parent process
//Parameters: processNum - stores the number of child processes to create
// (entered at the command line).
//Return: none
void parentInfo(int *processNum)
printf("Parent process ID: %d\n", getppid());
printf("Number of processes to create: %d\n", *processNum);
//Name: createChildProcess
//Description: Creates n number of child processes.
// For each child process, it says its a child process and it
// displays its PID.
// After each child process closes, the parent displays info.
//Parameters: processNum - stores the number of child processes to create
// (entered at the command line).
//Return: none
void createChildProcess(int *processNum)
int i;
int childStatus;
pid_t childpid;
/*The for loop will create n number of processes based on the value of processNum.*/
for(i = 1; i <= *processNum; i++)
childpid = fork();
//Executes if fork didn't work
if(childpid < 0)
perror("fork");
exit(1);
//Executes if the fork worked
else if( childpid == 0)
int pid = getpid();
//Prints a message and the child processe's PID
printf("\nHello I am a child process.\n");
printf("My PID is %d. \n", getpid());
for(int x = 1; x <= pid; x ++);
exit(15);
//Executes after the child process has ended
//Checks the child process's exit status
waitpid(childpid, &childStatus, WUNTRACED);
printf("\nPID of the child process that was just created: %d.\n", childpid);
if(WIFEXITED(childStatus))
printf("PID %d exited normally. Exit number: %d\n", childpid, WEXITSTATUS(childStatus));
else if(WIFSTOPPED(childStatus))
printf("PID %d was stopped by %d\n", childpid, WSTOPSIG(childStatus));
else if(WIFSIGNALED(childStatus))
printf("PID %d exited due to signal %d\n.", childpid, WTERMSIG(childStatus));
else
perror("waitpid");
【问题讨论】:
为 SIGCHLD 设置信号处理程序。在处理程序中调用wait
。
【参考方案1】:
fork
之前的代码
signal(SIGCHLD, childHandler);
在 childHandler 中输入您的 waitpid
代码。
void childHandler(int signum)
pid_t childpid;
int childstatus;
while ((childpid = waitpid( -1, &childstatus, WNOHANG)) > 0)
if (WIFEXITED(childStatus))
printf("PID %d exited normally. Exit number: %d\n", childpid, WEXITSTATUS(childStatus));
else
if (WIFSTOPPED(childStatus))
printf("PID %d was stopped by %d\n", childpid, WSTOPSIG(childStatus));
else
if (WIFSIGNALED(childStatus))
printf("PID %d exited due to signal %d\n.", childpid, WTERMSIG(childStatus));
else
perror("waitpid");
您不应该在信号处理程序中使用像 printf
这样的异步不安全调用,因此请更改您的代码以将状态保存在全局或堆分配数组中 - 您知道要从 processNum 创建的大小 - 并在外部打印状态信息处理程序。
此外,按照目前的结构,您的父母可能会在收割所有孩子之前结束。为孩子添加一个计数器,以便您在父母退出之前等待所有孩子。
【讨论】:
【参考方案2】:查看信号SIGCHLD
。如果您已阻止它,则必须取消阻止它,或者可能会明确检查它。
【讨论】:
什么是孤僻的孩子? 查看 *** 帖子 Detached vs. Joinable POSIX threads。在这种情况下,唯一重要的是它们没有分离。 OP 正在创建进程而不是线程。这是无关紧要的。苹果和橙子。【参考方案3】:wait
的目的是,嗯,等待,所以解决问题的方法是首先创建所有孩子,然后开始等待它们终止。
这是一个执行此操作的程序:
// fork
#include <unistd.h>
// wait
#include <sys/types.h>
#include <sys/wait.h>
// exit
#include <stdlib.h>
//printf
#include <stdio.h>
void child( int id)
int seed= id;
int x= rand_r( &seed) % 10;
sleep( x);
exit( x);
int main( int argc, char *argv[])
const int n= 5;
int i;
printf( "creating %d children.\n", n);
for ( i= 0; i < n; ++i)
pid_t pid= fork();
if ( !pid)
child( i); // does not return
else
printf( "child [0x%x] created.\n", pid);
// all the children are created now
// now we wait for them to terminate
printf( "waiting for children to terminate.\n", n);
for ( i= 0; i < n; ++i)
int result;
pid_t pid= wait( &result);
printf( "child [0x%x] terminated with result [%u].\n", pid, WEXITSTATUS( result));
puts( "all children terminated.");
【讨论】:
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