fork | 易学教程

17、fork函数

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1、定义 #include <unistd.h> #include<sys/types.h> pid_t fork( void ); pid_t 是一个宏定义，其实质是 int ，被定义在 #include<sys/types.h> 中返回值：若成功调用一次则返回两个值，子进程返回 0 ，父进程返回子进程 ID ；否则，出错返回 -1 2、函数说明：一个现有进程可以调用 fork 函数创建一个新进程。由 fork 创建的新进程被称为子进程（ child process ）。 fork 函数被调用一次但返回两次。两次返回的唯一区别是子进程中返回 0 值而父进程中返回子进程 ID 。子进程是父进程的副本，它将获得父进程数据空间、堆、栈等资源的副本。注意，子进程持有的是上述存储空间的“副本”，这意味着父子进程间不共享这些存储空间。 File locks and pending signals are not inherited. 【 3 】 If the call to fork() is executed successfully, Unix will ① make two identical copies of address spaces, one for the parent and the other for the child. ② Both processes

How to use fork() in Perl?

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问题 I have hundreds of file names in an array. I want to create a child process for every 4 files in the array, and have that child do some stuff to each of those 4 files. (So with 100 files, I'll create 25 processes.) I'm having some trouble understanding the order in which lines are processed when there's a fork. I was thinking I could do something like this, but I'm getting stuck: foreach $file (@files) { if ($f++ % 4 == 0) { my $pid = fork(); if ($pid) { push(@childs, $pid); } elsif ($pid ==

How to choose the right branch/fork to use by looking on the github's network graph?

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问题 I need to use 3rd-party code that's available publicly on github. I'm looking at the github's network graph of that code and I can see that other forks have some commits that aren't merged into the original repository. How should decide which of the branches/forks is right for me? Please enlist your considerations while facing a problem like this. As suggested by John Feminella, one should always use the (usually stable) 'released versions of a project'. I agree with that of course, but this

What is pycryptodomex and how does it differ from pycryptodome?

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问题 Today I saw PySNMP installing pycryptodomex. The x in that name looked suspicious and surprising. I tried to track it down, but it looks like both pycryptodome and pycryptodomex are owned by the same account and point back to the same Github repository. Especially because a cryptography library is a core security feature, I'm suspicious of the duplication. What's the purpose of this duplication? Could I have discovered this information from open sources? 回答1: It's the same code, just

Fork/Join 框架框架使用

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1、介绍 Fork/Join 框架是 Java7 提供了的一个用于并行执行任务的框架，是一个把大任务分割成若干个小任务，最终汇总每个小任务结果后得到大任务结果的框架。在多核计算机中正确使用可以很好的发挥cpu的作用，提高程序的执行效率。框架采用工作窃取算法，当有子任务线程处理完当前任务时，它会从其他线程执行的任务队列里窃取任务来执行，从而提高整体的执行效率。为了减少线程间的任务资源竞争，队列通常使用双端队列，别窃取任务线程永远从啥UN广大UN队列的呕吐不获取任务执行，而窃取任务的线程永远从双端队列的尾部获取任务执行。 2、使用根据业务场景来考虑是否需要使用Fork/Join框架来进行任务的拆分和汇总操作。当需要时，比如说需要执行一个很大的业务计算之类的，此时使用Fork/Join框架分以下两步：对任务进行分割把大任务分割成子任务，有可能子任务还是很大，所以还需要不停的分割，直到分割出的子任务足够小执行分割的子任务并汇总结果分割的子任务分别放在双端队列里，然后几个启动线程分别从双端队列里获取任务执行。子任务执行完的结果都统一放在一个队列里，启动一个线程从队列里拿数据，然后合并这些数据具体实现以上两步：创建ForkJoinTask 它提供在任务中执行 fork() 和 join() 操作的机制，通常情况下我们不需要直接继承 ForkJoinTask 类

fork() and wait() calls

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问题 I have a question about the following code. This is an example found on this page, not my code. The parent process forks 2 child processes, each of them counting to 200 then exiting. What I don't understand is why aren't the children printing their messages immediately after they are forked and they allow their father to enter waiting status? Also, how is the wait system call returning the pid of the child that finishes first? pid = wait(&status); #include <stdio.h> #include <string.h>

Difference in behavior between os.fork and multiprocessing.Process

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问题 I have this code : import os pid = os.fork() if pid == 0: os.environ['HOME'] = "rep1" external_function() else: os.environ['HOME'] = "rep2" external_function() and this code : from multiprocessing import Process, Pipe def f(conn): os.environ['HOME'] = "rep1" external_function() conn.send(some_data) conn.close() if __name__ == '__main__': os.environ['HOME'] = "rep2" external_function() parent_conn, child_conn = Pipe() p = Process(target=f, args=(child_conn,)) p.start() print parent_conn.recv()

Waiting for Ruby child pid to exit

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问题 I'm trying to fork a sub-process, wait for it to finish, if it doesn't finish within a certain amount of time, kill it. This is what I have so far: servers.each do |server| pid = fork do puts "Forking #{server}." output = "doing stuff here" puts output end Process.wait puts "#{server} child exited, pid = #{pid}" end Somewhere after/around Process.wait, I would like some sort of utility to wait 20 seconds, and if the process is still out there, I'd like to kill it and mark output as "ERROR." I

Waiting for Ruby child pid to exit

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Redux05 Redux-Saga

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简介 redux-saga 是用来管理应用程序副作用的库，可以认为，一个saga就像是应用程序中一个单独的线程，独自负责处理副作用。 redux-saga 是一个Redux中间件，也就意味着这个线程可以通过正常的Redux的Action从主应用启动暂停和取消，它能够访问完整的Redux的State，也可以进行 dispatch redux-saga 使用了 Generator ，让异步流程看起来像是同步代码，有更强大的异步流程控制能力。 Hello Saga 安装： npm install --save redux-saga # 或者 yarn add redux-saga 创建 sagas.js 文件，我们的异步逻辑都会包含在这个文件中： // sagas/index.js export default function* helloSaga() { console.log('Hello Sagas!'); } Redux-Saga是一个中间件，我们需要建立它与Redux Store的联系，在 store/configureStore.js 中对 store 进行配置，注入中间件： // store/configureStore.js import { createStore, applyMiddleware } from 'redux'; import rootReducer