fork | 易学教程

communicating between two child processes with pipes

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问题 I'm trying to write code that spawns two child processes that send each other a message over a pipe then terminate. However, when I run the following code only child2 prints it's greeting but child 1 still prints the message it gets from child 2 where child 1 doesn't. Does anybody know what's wrong with my methodology? #include <string.h> #include <stdlib.h> #include <stdio.h> #include <sys/types.h> #include <unistd.h> int main(int argc, char** argv) { char chld_1_send[20] = "hello from child

ProcessBuilder - Start another process / JVM - HowTo?

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问题 I'm writing a network app, where each Client has a Singleton ClientManager. For testing , I would like to create several clients (each in their own VM / process) without starting the program by hand n-times. The following two questions on stackoverflow already describe how-to do that: Is this really the best way to start a second JVM from Java code? Java: Executing a Java application in a separate process My Code is based on these, but it's not working: The main program doesn't continue after

socket() returns 0 in C client server application

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I'm working on an application that contains several server sockets that each run in a unique thread. An external utility (script) is called by one of the threads. This script calls a utility (client) that sends a message to one of the server sockets. Initially, I was using system() to execute this external script, but we couldn't use that because we had to make sure the server sockets were closed in the child that was forked to execute the external script. I now call fork() and execvp() myself. I fork() and then in the child I close all the server sockets and then call execvp() to execute the

Fork and drop privileges with Java

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问题 I'm writing a server program in Java that will allow users to submit jobs using DRMAA. Although the main server process runs as root , all it does is authenticate the user, then start another Java program which runs as that user and actually does the work in order to comply with the principle of minimising privileges. Initially, I was doing this with Runtime.exec() and sudo (example below) which works fine until the process is dæmonised, at which point sudo gets upset because it doesn't have

Fork/Join框架

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Fork/Join是一个用户并行执行任务的框架,把一个大任务分割成若干个小人物,最终汇总每个小任务的结果后得到大任务的结果。讲到Fork/Join必须要讲工作窃取算法。下面讲下什么叫工作窃取算法：某个线程从其他队列里窃取任务来执行，听名字感觉很奇怪，不经想什么鬼？黑人问号脸。。。。我们来举个例子：假如我们需要做一个比较大的任务，可以把这个任务分割为若干互不相依的子任务，为了减少线程间的竞争，把这些子任务放到不同的队列里，并为每个队列创建一个单独的线程来执行队列里的任务，线程和队列对应。这时A线程负责的A队列里的任务都处理完了，而其他队列里还有任务等待处理，干完活的线程如果干等着就显得很傻，老板也不愿意是不（ps：老板就喜欢压榨我们搬砖的），于是A就去其他线程的队列里窃取一个任务来执行。这里A和B（被窃取的线程）同时访问一个队列会出现竞争问题，那么为了避免这个问题，A（窃取线程）会从双端队列的尾部拿任务，B从头部拿任务。上面讲了理论，那么在执行的时候其实会有几个问题，比如 1.双端队列只有一个任务时会出现竞争 2.该算法会消耗更多的系统资源，比如创建多个线程和多个双端队列好处也显而易见：充分利用线程并行计算，减少线程间的竞争我们来看代码如果实现 ForkJoinTask:ForkJoin任务类,它提供在任务中执行fork和join的操作机制

Debug fork() in eclipse cdt

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I'm trying to debug some fork() mechanism with eclipse cdt (Juno). I wrote the program in C. if( -1 == (pid = fork()) ) /* error */ goto cleanup; else if ( 0 == pid ) /* child */ { execlp("gcc", "gcc", cFilePath, "-o" , GCC_OUTPUT_FILE_NAME, NULL); goto cleanup; /* Arrives here only on error! */ } else if (pid > 0) /* parent - checks: correct pid returns, returns normally, with exit status = 0*/ { returnedpid = wait(exitStatus); if( pid != returnedpid || exitStatus == NULL || !WIFEXITED(*exitStatus) || !WEXITSTATUS(*exitStatus) ) goto cleanup; } I tried to add " set follow-fork-mode child " as

Go语言_flag_Go的命令行参数 /命令行处理

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原文来自： http://studygolang.com/articles/2878 1.命令行参数(命令行参数是指定程序运行参数的一个常见方式。例如，go run hello.go，程序 go 使用了 run 和 hello.go 两个参数。) package main import " os " import " fmt " func main() { // os.Args 提供原始命令行参数访问功能。注意，切片中的第一个参数是该程序的路径，并且 os.Args[1:]保存所有程序的的参数。 argsWithProg := os.Args argsWithoutProg : = os.Args[ 1 :] // 你可以使用标准的索引位置方式取得单个参数的值。 arg := os.Args[ 3 ] fmt.Println(argsWithProg) fmt.Println(argsWithoutProg) fmt.Println(arg) } /* 要实验命令行参数，最好先使用 go build 编译一个可执行二进制文件 $ go build command-line-arguments.go $ ./command-line-arguments a b c d [./command-line-arguments a b c d] [a b c d] c */ 2.命令行标志

Prevent fork() from copying sockets

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问题 I have the following situation (pseudocode): function f: pid = fork() if pid == 0: exec to another long-running executable (no communication needed to that process) else: return "something" f is exposed over a XmlRpc++ server. When the function is called over XML-RPC, the parent process prints "done closing socket" after the function returned "something". But the XML-RPC client hangs as long as the child process is still running. When I kill the child process, the XML-RPC client correctly

了解Github

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一、什么是Github Github是全球最大的社交编程及代码托管网站（ https://github.com/ ）。 Github可以托管各种git库，并提供一个web界面（用户名.github.io/仓库名） GitHub 平台于 2007 年 10 月 1 日开始开发。网站于 2008 年 2 月以 beta 版本开始上线，4 月份正式上线。 GitHub 里面的项目可以通过标准的 Git 命令进行访问和操作。同时，所有的 Git 命令都可以用到 GitHub 项目上面。GitHub 开发了针对 Windows 和 iOS X 操作系统的桌面客户端。此外，也可以使用第三方插件来实现 Git 功能。网站提供了一系列社交网络具有的功能，例如赞(star)、关注(follow)、评论。用户可以通过复刻(fork)他人项目的形式参与开发，并可通过协作示意图来查看有多少开发者参与了开发并追踪最新的复刻版本。此外网站还有 Wiki（通过一个名为 gollum 的软件实现）等功能。 GitHub 同时允许注册用户和非注册用户在网页中浏览项目，也可以以 ZIP 格式打包下载。但是用户必须注册一个账号然后才能进行讨论、创建并编辑项目、参与他人的项目和代码审查。二、Github的作用 1.共享代码（可以几个人共同完成一个项目） 2.项目托管

Errno::ENOMEM: Cannot allocate memory - cat

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I have a job running on production which process xml files. xml files counts around 4k and of size 8 to 9 GB all together. After processing we get CSV files as output. I've a cat command which will merge all CSV files to a single file I'm getting: Errno::ENOMEM: Cannot allocate memory on cat (Backtick) command. Below are few details: System Memory - 4 GB Swap - 2 GB Ruby : 1.9.3p286 Files are processed using nokogiri and saxbuilder-0.0.8 . Here, there is a block of code which will process 4,000 XML files and output is saved in CSV (1 per xml) (sorry, I'm not suppose to share it b'coz of

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