fork

问题 I have a while loop that reads data from a child process using blocking I/O by redirecting stdout of the child process to the parent process. Normally, as soon as the child process exits, a blocking read() in this case will return since the pipe that is read from is closed by the child process. Now I have a case where the read() call does not exit for a child process that finishes. The child process ends up in a zombie state, since the operating system is waiting for my code to reap it, but

问题 I'm trying to understand how memory allocation work on fork, even on static or dynamic allocation. I've some trouble to understand some leaks as shown below. With this program : #include <unistd.h> #include <sys/wait.h> int main(int argc, char **argv) { pid_t pid; int status; pid = fork(); if (pid == 0) return (0); else { waitpid(pid, &status, 0); return (0); } } I'm getting this log file with valgrind : ==81268== Memcheck, a memory error detector ==81268== Copyright (C) 2002-2017, and GNU

问题 My first project for my OS class is to create a process tree using fork() that has a depth that the user specifies at the command line. Each leaf level node needs to sort data and pass it back to its parent using named-pipes (FIFOs). I can create an N-depth tree with fork() , each process having 2 children. What I can’t figure out is how to pass a FIFO to each child all the way down the tree and then have this process perform a sort on certain data in the FIFO and then also pass it back up

问题 use Parallel::ForkManager; use LWP::Simple; my $pm=new Parallel::ForkManager(10); our $a =0; @LINK=( 10,203, 20, 20 ,20 ,10 ,101 ,01 ,10 ) ; for my $link (@LINK) { $pm->start and next; my $lo = ($link * 120.22 )*12121.2121212121212121*( 12121212.1212121+ $link); $a = $a+ $lo ; print $a."\n" ; $pm->finish; }; print $a ; I was trying to access the global variable on parallel process using parallel fork manager module . end of the program the global variable still remaining same .. how to

问题 I have tried implementing an os program. Here is the code: #include<sys/types.h> #include<stdio.h> #include<unistd.h> int main() { pid_t pid, pid1; pid = fork(); if(pid<0) { fprintf(stderr,"Fork Failed"); return 1; } else if(pid == 0) /* child process */ { pid1 = getpid(); printf("child: pid = %d\n",pid); printf("child: pid1 = %d\n",pid1); } else /* parent process */ { pid1 = getpid(); printf("parent: pid = %d\n",pid); printf("parent: pid1 = %d\n",pid1); } return 0; } and its o/p: parent: pid

问题 The only overhead incurred by fork() is the duplication of the parent’s page tables and the creation of a unique process descriptor for the child. In Linux, fork() is implemented through the use of copy-on-write pages. Copy-on-write (or COW) is a technique to delay or altogether prevent copying of the data. so why is there a need to copy page tables . as long as the processes share the pages in read only mode or until they write something there is no need that the page tables need to be

问题 I would like to start a server in background, go back and execute some other targets, and then stop the server when Ant finishes executing all targets. I have come up with the following two solutions but they both block Ant from executing the subsequent targets. Since I want the process to die in the end, I do not want to use spawn="true". Is there any other solution? <target name="Start_Selenium_Server"> <java dir="lib" jar="lib/selenium-server-standalone-2.28.0.jar" fork="true"> <arg line="

问题 I have a doubt in the following piece of code and its behaviour: #include <stdio.h> #include <unistd.h> #include <stdlib.h> #define N 5 #define nt 1 int pm[N][2],pid[N]; int i,j,size; char s[100]; int count=0; int main() { for(i=1;i<N;i++) { printf("\n i=%d",i); if(pid[i]=fork() == -1) { printf("\n fork not wrking"); exit(1); } else if(pid[i]>0) { printf(" \n pid:%3d\n",pid[i]); break; } } return 0; } I initially thought that the code will spawn a process and skip out of the loop. Thereby, 1

问题 I'm trying to write a python script that can ssh into remote server and can execute simple commands like ls,cd from the python client. However, I'm not able to read the output from the pseudo-terminal after successfully ssh'ing into the server. Could anyone please help me here so that I could execute some commands on the server. Here is the sample code: #!/usr/bin/python2.6 import os,sys,time,thread pid,fd = os.forkpty() if pid == 0: os.execv('/usr/bin/ssh',['/usr/bin/ssh','user@host',]) sys

问题 I read that the new process created using vfork() system call executes as a thread in the parent's address space and until the child thread doesnot calls exit() or exec() system call, the parent is blocked. So I wrote a program using vfork() system call #include <stdio.h> #include <unistd.h> int main() { pid_t pid; printf("Parent\n"); pid = vfork(); if(pid==0) { printf("Child\n"); } return 0; } I got the output as follows: Parent Child Parent Child Parent Child .... .... .... I was assuming