waitpid

How to make parent process wait for child processes to finish?

由 社会主义新天地 提交于 2021-02-10 18:20:37
问题 I have an assignment which gives me this code to transform into a code that makes the parent process wait for all children processes to finish. PS: the first code has 4 processes and needs to use waitpid to solve this. #include <stdio.h> #include <stdlib.h> #include <sys/types.h> #include <unistd.h> int main(){ pid_t p = fork(); pid_t k = fork(); if(p>0){ printf("p=%d: PID = %d\n", p, getpid()); sleep(45); exit(0); } else if(p==0){ printf("p=%d: PID = %d\n", p, getpid()); exit(0); } else if(p

How to make parent process wait for child processes to finish?

由 左心房为你撑大大i 提交于 2021-02-10 18:19:43
问题 I have an assignment which gives me this code to transform into a code that makes the parent process wait for all children processes to finish. PS: the first code has 4 processes and needs to use waitpid to solve this. #include <stdio.h> #include <stdlib.h> #include <sys/types.h> #include <unistd.h> int main(){ pid_t p = fork(); pid_t k = fork(); if(p>0){ printf("p=%d: PID = %d\n", p, getpid()); sleep(45); exit(0); } else if(p==0){ printf("p=%d: PID = %d\n", p, getpid()); exit(0); } else if(p

Get signal when tid status change

由 倾然丶 夕夏残阳落幕 提交于 2021-02-08 11:19:33
问题 There is a way to look when pid/tid status change with waitpid but this is blocking function. I want to monitor all threads in specific pid and get signal when one of them change and print the tid. For now I open threads as count of threads in that process and each 1 make waitpid on 1 tid and after that blocking function finish I print that tid that changed. How can I get a signal that tid change so I can monitor all tid's in 1 thread. I didn't want to monitor all pid in system only specific

Variable modification in a child process

由 我怕爱的太早我们不能终老 提交于 2021-01-27 16:46:37
问题 I am working on Bryant and O'Hallaron's Computer Systems, A Programmer's Perspective . Exercise 8.16 asks for the output of a program like (I changed it because they use a header file you can download on their website): #include <stdio.h> #include <stdlib.h> #include <sys/types.h> #include <sys/wait.h> #include <errno.h> #include <unistd.h> #include <string.h> int counter = 1; int main() { if (fork() == 0){ counter--; exit(0); } else{ Wait(NULL); printf("counter = %d\n", ++counter); } exit(0)

How to get the full returned value of a child process?

由 做~自己de王妃 提交于 2021-01-23 07:57:30
问题 I need to catch the returned value of a child process.. The problem is: with using the waitpid() function I can catch only 8 bits of the returned value WEXITSTATUS(wstatus) returns the exit status of the child. This consists of the least significant 8 bits of the status argument that the child specified in a call to exit(3) or _exit(2) or as the argument for a return statement in main(). This macro should be employed only if WIFEXITED returned true. How can I catch the full int value that is

How to get the full returned value of a child process?

由 瘦欲@ 提交于 2021-01-23 07:53:46
问题 I need to catch the returned value of a child process.. The problem is: with using the waitpid() function I can catch only 8 bits of the returned value WEXITSTATUS(wstatus) returns the exit status of the child. This consists of the least significant 8 bits of the status argument that the child specified in a call to exit(3) or _exit(2) or as the argument for a return statement in main(). This macro should be employed only if WIFEXITED returned true. How can I catch the full int value that is

How to get the full returned value of a child process?

由 为君一笑 提交于 2021-01-23 07:53:25
问题 I need to catch the returned value of a child process.. The problem is: with using the waitpid() function I can catch only 8 bits of the returned value WEXITSTATUS(wstatus) returns the exit status of the child. This consists of the least significant 8 bits of the status argument that the child specified in a call to exit(3) or _exit(2) or as the argument for a return statement in main(). This macro should be employed only if WIFEXITED returned true. How can I catch the full int value that is

为何要fork()两次来避免产生僵尸进程？

由 邮差的信 提交于 2020-04-08 06:12:58
为何要fork()两次来避免产生僵尸进程？ 当我们只fork()一次后，存在父进程和子进程。这时有两种方法来避免产生僵尸进程： 父进程调用waitpid()等函数来接收子进程退出状态。 父进程先结束，子进程则自动托管到Init进程（pid = 1）。 目前先考虑 子进程先于父进程结束 的情况： 若父进程未处理子进程退出状态，在父进程退出前，子进程一直处于僵尸进程状态。 若父进程调用waitpid()（这里使用阻塞调用确保子进程先于父进程结束）来等待子进程结束，将会使父进程在调用waitpid()后进入睡眠状态，只有子进程结束父进程的waitpid()才会返回。 如果存在子进程结束，但父进程还未执行到waitpid()的情况，那么这段时期子进程也将处于僵尸进程状态。 由此，可以看出父进程与子进程有父子关系，除非 保证父进程先于子进程结束 或者 保证父进程在子进程结束前执行waitpid() ，子进程均有机会成为僵尸进程。那么如何使父进程更方便地创建不会成为僵尸进程的子进程呢？这就要用两次fork()了。 父进程一次fork()后产生一个子进程随后立即执行waitpid(子进程pid, NULL, 0)来等待子进程结束，然后子进程fork()后产生孙子进程随后立即exit(0)。这样子进程顺利终止（父进程仅仅给子进程收尸，并不需要子进程的返回值），然后父进程继续执行

孤儿进程与僵尸进程[总结]

由 早过忘川 提交于 2020-02-27 17:12:09
今天遇到一个linux进程启动时指定Max open files不对的问题，导致程序建立socket异常，进而导致fullgc问题，影响正常服务。所以顺带又温习了下linux下的父子进程的特性。 孤儿进程与僵尸进程[总结] 1、前言 　　之前在看《unix环境高级编程》第八章进程时候，提到孤儿进程和僵尸进程，一直对这两个概念比较模糊。今天被人问到什么是孤儿进程和僵尸进程，会带来什么问题，怎么解决，我只停留在概念上面，没有深入，倍感惭愧。晚上回来google了一下，再次参考APUE，认真总结一下，加深理解。 2、基本概念 　　我们知道在unix/linux中，正常情况下，子进程是通过父进程创建的，子进程在创建新的进程。子进程的结束和父进程的运行是一个异步过程,即父进程永远无法预测子进程 到底什么时候结束。 当一个 进程完成它的工作终止之后，它的父进程需要调用wait()或者waitpid()系统调用取得子进程的终止状态。 　　孤儿进程：一个父进程退出，而它的一个或多个子进程还在运行，那么那些子进程将成为孤儿进程。孤儿进程将被init进程(进程号为1)所收养，并由init进程对它们完成状态收集工作。 　　僵尸进程：一个进程使用fork创建子进程，如果子进程退出，而父进程并没有调用wait或waitpid获取子进程的状态信息，那么子进程的进程描述符仍然保存在系统中。这种进程称之为僵死进程
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