fork | 易学教程

Learning pipes, exec, fork, and trying to chain three processes together

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问题 I'm learning to use pipes and following along with this code on pipes. The program makes two child processes using fork. The first child runs 'ls' command and outputs to pipe1. The second reads from pipe1 runs 'wc' and outputs to stdout. I'm just trying to add a third process in the middle that reads from pipe1 and outputs to pipe2. Basically what I'm trying to do ls | cat | wc -l What I'm trying to do: (ls)stdout -> pipe1 -> stdin(cat)stdout-> stdin(wc -l) -> stdout Nothing ever prints to

How exactly does copy on write work

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问题 Say we have a certain parent process with some arbitrary amount of data stored in memory and we use fork to spawn a child process. I understand that in order for the OS to perform copy on write, the certain page in memory that contains the data that we are modifying will have its Read-only bit set, and the OS will use the exception that will result when the child tries to modify the data to copy the entire page into another area in memory so that the child gets it's own copy. What I don't

centos7下部署nginx与php

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背景介绍相信读者在看这篇文章之前已经fastcgi,php-fpm有所了解。大概来讲php语言需要fastcgi程序，即php解释器解释，而php解释器需要php-fpm管理器进行调度。以下对CGI、FastCGI、php-fpm之间关系进行通俗解释（来源于知乎用户Journey Lin）：讲Fastcgi之前需要先讲CGI，CGI是为了保证web server传递过来的数据是标准格式的，它是一个协议，方便CGI程序的编写者。Fastcgi是CGI的更高级的一种方式，是用来提高CGI程序性能的。web server（如nginx）只是内容的分发者。比如，如果请求/index.html，那么web server会去文件系统中找到这个文件，发送给浏览器，这里分发的是静态资源。如果现在请求的是/index.php，根据配置文件，nginx知道这个不是静态文件，需要去找PHP解析器来处理，那么他会把这个请求简单处理后交给PHP解析器。此时CGI便是规定了要传什么数据／以什么格式传输给php解析器的协议。当web server收到/index.php这个请求后，会启动对应的CGI程序，这个程序就是PHP的解析器。接下来PHP解析器会解析php.ini文件，初始化执行环境，然后处理请求，再以CGI规定的格式返回处理后的结果，退出进程。web server再把结果返回给浏览器

How the memory is mapped when fork is used?

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问题 i am new to "fork()",I read everywhere that when a fork() is called an exact copy of current (calling) process is started.Now when I run following code ,there should be two different processes, having two different memory locations assigned to their vars and functions. #include<stdio.h> int i=10; int pid; int main(){ if((pid=fork())==0){ i++;//somewhere I read that separate memory space for child is created when write is needed printf("parent address= %p\n",&i);// this should return the

Fork Concept in C#

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问题 Since C# supports threading, is there any way to implement fork concept in C#? Thanks in advance.... 回答1: This is more a matter of .NET / CLR than of C#. Generally, it's a matter of the underlying operating system. Windows do not support fork() -like semantics of spawning new processes. Also, fork() has nothing to do with multithreading support. The semantics of fork() involves duplicating the contents of the original process's address space. My opinion is this is an obsolete approach to

Redis持久化——rdb

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rdb是在指定的时间间隔内内存中的数据集快照写入磁盘，也就是常说的Snapshot快照，它恢复时是将快照文件直接读到内存里. Redis会单独创建（fork）一个子进程来进行持久化，会先将数据写入到一个临时文件中，待持久化过程都结束了，再将这个临时文件替换上次持久化好的文件，整个过程中，主进程是不进行任何IO操作的，这就确保了极高的性能，如果需要进行大规模的数据恢复，且对于数据恢复的完整性不是非常敏感，那RDB方式要比AOF方式更加高效，RDB的缺点是最后一次持久化后的数据可能会丢失。 Fork:作用是复制一个与当前进程一样的进程。新进程的所有数据（变量，环境变量，程序计数器等等），数值都会和当前进程一样，但是是一个全新的进程，并作为原进程的子进程。隐患就是如果当前进程特别大，本来程序就慢，又fork了一份，又会降低速度优势：适合大规模的数据恢复，对数据完整性和一致性要求不高劣势：在一定时间间隔做一次备份，所以如果redis意外down掉的话，就会丢失最后一次快照所有修改。Fork的时候内存中的数据被克隆了一份，大约2倍的膨胀性需要考虑 RDB保存的是dump.rdb文件满足3个条件之一就会触发RDB，生成dump.rdb文件，一般情况下生产上的dump文件都会有备份，如果生产机器上的rdb文件损坏，从备份文件中恢复。也就是冷拷贝，从主机拷贝到备机上，可以cp dump

fork(), pipe() and exec() process creation and communication

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问题 I have to write program that create process using pipe() . My first task is to write a parent process that generates four child processes using the fork() function. Once the fork() is successful, replace the child process with another process rover1, rover2, rover3, and rover4 , though all of them have the same code. The function of the processes is as follows. Each child process is initially given its own number. It receives a new number from the parent. Using the following formula it

Will ctrl+c send SIGINT signals to both parent and child processes in Linux?

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问题 In the terminal, I executed a main parent process which will fork a child process. In both the parent and child processes I implemented a SIGINT signal handler. So when I press "ctrl+c", will both the handlers be called at the same time? Or do I need to call the child process's signal handler explicitly in the parent process's handler? I looked up this post: How does Ctrl-C terminate a child process? which says that " The SIGINT signal is generated by the terminal line discipline, and

Ruby daemons and JRuby - alternative options

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问题 I have an app that I am migrating from Ruby to JRuby (due to need for better Web Service Security support via Java). One of the gems I use is daemons to create a background job. The issue is that it use fork+exec to create the background process, but thats a no-no with JRuby. So - is there an alternative gem/wrapper for creating background jobs? My current thoughts are to just call rake from a shell script and let the rake task run forever... Thanks in advance, Chris. UPDATE We are currently

J.U.C并发工具类

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目录目标 CountDownLatch Semaphore CyclicBarrier Runnable和Callable fork/join并发处理框架目标并发工具类：CountDownLatch Fork/Join的使用 Futrue的使用 CountDownLatch 倒计数器。共享锁。由AQS共享锁实现。 countDown();-》倒计数器减一，并阻塞。 await()；当countDown();为0时唤醒所有线程。使用场景：希望n个线程同时执行某一操作。基本使用 /* 没隔1s开启一个线程，共开启6个线程若希望6个线程同时执行某一操作可以用CountDownLatch实现 */ public static void test01 ( ) throws InterruptedException { CountDownLatch ctl = new CountDownLatch ( 6 ) ; for ( int i = 0 ; i < 6 ; i ++ ) { new Thread ( ) { @Override public void run ( ) { ctl . countDown ( ) ; try { ctl . await ( ) ; System . out . println ( "here I am..." ) ; } catch (

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