fork | 易学教程

what else '\n' do except printing newline?

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问题 After commenting Line 2 "Hello" is printed nine times but commenting Line 1 outputs "Hello" more than nine times. My question is what's the role of '\n' in this? #include<stdio.h> #include<stdlib.h> int main() { int tmp[10], i, n=0; for(i=0;i<9;i++) { tmp[i]=fork(); if(tmp[i]>0) break; else { printf("Hello\n"); // ---- Line 1 printf("Hello "); // ---- Line 2 } } } 回答1: \n also flushes the standard output buffer. If it is not present, it is possible that you have previously entered data in it.

Calculations in childs using pipes

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问题 My task is a. A parent and two childs b. Parent take data from the user c. Send to a child for addition and subtraction. d. Again take input from user and send to another child for multiplication and division. e. First child process creates another child C3. f. Both the childs send result to the child process C3 to show output. g. Parent process after completion of each child process task kill the process. I've write the following code but i don't know where I'm doing wrong, I tried to debug

Calculations in childs using pipes

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Does multiprocess in python re-initialize globals?

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问题 I have a multiprocessing program where I'm unable to work with global variables. I have a program which starts like this:- from multiprocessing import Process ,Pool print ("Initializing") someList = [] ... ... ... Which means I have someList variables which get initialized before my main is called. Later on in the code someList is set to some value and then I create 4 processes to process it pool = Pool(4) combinedResult = pool.map(processFn, someList) pool.close() pool.join() Before spawning

NodeJS — Fork Child Process with function string instead of file

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问题 I've looked at the documentation for the fork method, and it only describes providing a file path to the child module file. Does anyone know if it is possible (and undocumented) to pass in the child module directly instead of via a file? Point being, I would like to dynamically generate the module, then create a child process with it. 回答1: This would not be possible -- fork() creates a completely different process that do not share context or variables with its parent process. One option you

Functionality of fork()

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问题 System information: I am running 64bit Ubuntu 10.10 on a 2 month old laptop. Hi everyone, I've got a question about the fork() function in C. From the resources I'm using (Stevens/Rago, YoLinux, and Opengroup) it is my understanding that when you fork a process, both the parent and child continue execution from the next command. Since fork() returns 0 to the child, and the process id of the child to the parent, you can diverge their behavior with two if statements, one if(pid == 0) for the

Difference between multi-process programming with fork and MPI

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问题 Is there a difference in performance or other between creating a multi-process program using the linux "fork" and the functions available in the MPI library? Or is it just easier to do it in MPI because of the ready to use functions? 回答1: They don't solve the same problem. Note the difference between parallel programming and distributed-memory parallel programming. Using the fork/join model you mentioned usually is for parallel programming on the same physical machine. You generally don't

五种主要多核并行编程方法分析与比较

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随着多核时代的到来与流行，传统的单线程串行程序的编程模式必将改变，取而代之的将是并行编程。目前已经有五种主要并行编程模型，下面将对此五种模型进行概括性的分析与比较： 1. MPI 　　MPI(Message Passing Interface)消息传递接口是MPI论坛发布的一个库，而不是一门实现语言，支持C/C++/Fortran。是一种消息传递编程模型，为进程间通信服务。MPI提供了一种与平台无关，可以被广泛使用的编写消息传递程序的标准。用它来编写消息传递程序，不仅实用、可移植、高效和灵活，而且和当前已有的实现没有太大的变化。目前MPI的主要实现有以下三种：　　优点：可以在集群上使用，也可以在单核/多核CPU上使用，它能协调多台主机间的并行计算，因此并行规模上的可伸缩性很强，能在从个人电脑到世界TOP10的超级计算机上使用。　　缺点：第一，基于消息传递，需要显示划分和分布计算任务，显示进行消息传递与同步，且不易增量开发串行程序的并行性；第二，使用进程间通信的方式协调并行计算，这导致并行效率较低、内存开销大、不直观、编程麻烦。　　参考资料： MPI论坛 2. OpenMP 　　OpenMP(Open Multi Processing)是由Open ARB发布的一种用于并行编程的规范，是建立在串行语言上的扩展，目前可以在C/C++/Fortran中使用。　

Redirect stdout of one process to two processes

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问题 Im having big troubles in doing what i said in title. Basically, i want a program, say broadcast.c, that accepts input from the user and then sends that input to the input of two processes. So if would run this command: ./broadcast prog1 prog2 It would block awaiting the input from the user and then sending that input to prog1 and prog2. Now, i want to use pipes, thing is, i dont know if i have to use 1 pipe or 2 pipes. broadcast.c #include <stdio.h> #include <stdlib.h> #include <unistd.h>

How to fork process without inheriting handles?

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问题 In my C/C++ server application which runs on Mac (Darwin Kernel Version 10.4.0) I'm forking child processes and want theses childes to not inherit file handles (files, sockets, pipes, ...) of the server. Seems that by default all handles are being inherited, even more, netstat shows that child processes are listening to the server's port. How can I do such kind of fork? 回答1: Normally, after fork() but before exec() one does getrlimit(RLIMIT_NOFILE, fds); and then closes all file descriptors