fork | 易学教程

Visually what happens to fork() in a For Loop

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问题 I have been trying to understand fork() behavior. This time in a for-loop . Observe the following code: #include <stdio.h> void main() { int i; for (i=0;i<3;i++) { fork(); // This printf statement is for debugging purposes // getppid(): gets the parent process-id // getpid(): get child process-id printf("[%d] [%d] i=%d\n", getppid(), getpid(), i); } printf("[%d] [%d] hi\n", getppid(), getpid()); } Here is the output: [6909][6936] i=0 [6909][6936] i=1 [6936][6938] i=1 [6909][6936] i=2 [6909]

Forking a gem for a Rails project

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问题 I've found myself twice in this situation: I install a gem on my system and start using it from my Rails project. Eventually I need to make some changes to that gem. How should I proceed? Ideally I'd like to check out the source code of that gem somewhere, like ~/third_party/gems, work on it and have my Rails project use that instead. Is that possible? In all the cases the gems were at github so I would probably for it at github, clone it, make my chances and maintain my own branch. I suppose

Why does this program print “forked!” 4 times?

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问题 Why does this program print “forked!” 4 times? #include <stdio.h> #include <unistd.h> int main(void) { fork() && (fork() || fork()); printf("forked!\n"); return 0; } 回答1: The first fork() returns a non-zero value in the calling process (call it p0) and 0 in the child (call it p1). In p1 the shortcircuit for && is taken and the process calls printf and terminates. In p0 the process must evaluate the remainder of the expression. Then it calls fork() again, thus creating a new child process (p2)

How to spawn a new independent process in Python

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问题 I have a some Python code that occasionally needs to span a new process to run a shell script in a "fire and forget" manner, i.e. without blocking. The shell script will not communicate with the original Python code and will in fact probably terminate the calling Python process, so the launched shell script cannot be a child process of the calling Python process. I need it to be launched as an independent process. In other words, let's say I have mycode.py and that launches script.sh. Then

How is it possible for fork() to return two values?

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问题 Since a function in C returns only one value, all the time, how can fork() , which is also a function, return two values? 回答1: If you read, build, and run the following program you should get a better idea of what is going on. #include <stdio.h> #include <unistd.h> int main(void) { pid_t fk; printf("\tbefore fork my pid = %lu\n", (unsigned long)getpid() ); fflush(stdout); /* This may keep the above print statement from outputing twice. */ fk = fork(); /* The OS kernel makes a copy of the

Multiple child process

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问题 can someone help me about how to create multiple child processes which have the same parent in order to do "some" part of particular job? for example, an external sorting algorithm which is applied with child processes; each child process sorts a part of data and finally the parent merges them.. EDIT: Maybe I should mention the forking multiple child processes with loop.. 回答1: Here is how to fork 10 children and wait for them to finish: pid_t pids[10]; int i; int n = 10; /* Start children. */

fork并发进程处理

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 线程并发处理僵尸线程很多时候我们fork创建的子进程终止时，需要服务器进程进行清理，倘若未进行处理将会处理大量的僵尸线程，那么我们可以选择将进忽略，并交给init进程进行处理。 signal(SIGCHLD, SIG_IGN); //在fork创建的处理模块当中添加下列的代码，当子线程处理结束后将其退出，并由Init来释放资源。 exit(EXIT_SUCCESS); fork 创建进程 fork是创建一个当前运行进程的副本，只能通过返回值去区分当前是父线程还是子线程。fork是一次调用两次返回，通常返回下面两类. 当fork()返回的是>0的时候表示当前的是父进程当fork()返回的为0表示当前是子进程. 返回<0表示当前创建的进程出现错误 ###示例一 #include <stdio.h> #include <string.h> #include <unistd.h> int main( void ) { int pid = fork(); if ( pid == 0 ) { printf( "当前处于子线程运行" ); } else { printf("当处于父进程运行，当前所创建的子线程的ID: %d\n",pid); } return 0; } 运行的结果 gcc ForkTest.c .

Is it possible to 'fork a fork' in Github?

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问题 I am currently working on a project that is a spinoff (fork) from a framework I have been working on. This project is intended to be pretty generic, but now I need to fork the codebase again for a client of mine. At this moment, I have created a custom branch for my client, but I'd rather have a standalone repository for this. Is is possible to 'fork a fork'? If not, what alternatives do I have? Outline of the situation: Framework repository (original) Generic application repository (fork)

Having a private branch of a public repo on GitHub?

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问题 I have a public PHP project in a GitHub repo, which contains just one branch (master). I want to have a separate branch/fork that is private for me (I have paid for private GitHub repos). I would like to be able to merge changes from the private branch/fork to the public repo, and vice versa. With that in mind, here are my questions: Can I have a private branch on a public repo? Can I fork my own public repo into my own private branch/fork? If both of the above are possible, which is the best

Prevent file descriptors inheritance during Linux fork

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问题 How do you prevent a file descriptor from being copy-inherited across fork() syscalls (without closing it, of course) ? I am looking for a way to mark a single file descriptor as NOT to be (copy-)inherited by children at fork(), something like a FD_CLOEXEC-like hack but for forks (so a FD_DONTINHERIT feature if you like). Anybody did this? Or looked into this and has a hint for me to start with? Thank you UPDATE: I could use libc's __register_atfork __register_atfork(NULL, NULL, fdcleaner,