我分叉了多个流程,我想衡量完成整个任务需要多长时间,即所有分叉的流程都完成了。请告知如何使父进程等待所有子进程终止?我想确保在正确的时间停止计时器。
这是我使用的代码:
#include <iostream> #include <string> #include <fstream> #include <sys/time.h> #include <sys/wait.h> using namespace std; struct timeval first, second, lapsed; struct timezone tzp; int main(int argc, char* argv[])// query, file, num. of processes. { int pCount = 5; // process count gettimeofday (&first, &tzp); //start time pid_t* pID = new pid_t[pCount]; for(int indexOfProcess=0; indexOfProcess<pCount; indexOfProcess++) { pID[indexOfProcess]= fork(); if (pID[indexOfProcess] == 0) // child { // code only executed by child process // magic here // The End exit(0); } else if (pID[indexOfProcess] < 0) // failed to fork { cerr << "Failed to fork" << endl; exit(1); } else // parent { // if(indexOfProcess==pCount-1) and a loop with waitpid?? gettimeofday (&second, &tzp); //stop time if (first.tv_usec > second.tv_usec) { second.tv_usec += 1000000; second.tv_sec--; } lapsed.tv_usec = second.tv_usec - first.tv_usec; lapsed.tv_sec = second.tv_sec - first.tv_sec; cout << "Job performed in " <<lapsed.tv_sec << " sec and " << lapsed.tv_usec << " usec"<< endl << endl; } }//for }//main
我将在“ else // parent”行之后的所有内容都移到for循环之外。在分叉循环之后,使用waitpid进行另一个for循环,然后停止计时并执行其余操作:
for (int i = 0; i < pidCount; ++i) { int status; while (-1 == waitpid(pids[i], &status, 0)); if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) { cerr << "Process " << i << " (pid " << pids[i] << ") failed" << endl; exit(1); } } gettimeofday (&second, &tzp); //stop time
我假设如果子进程无法正常退出且状态为0,则它没有完成其工作,因此测试未能生成有效的计时数据。显然,如果子进程 应该 被信号杀死,或者退出非零返回状态,则必须相应地更改错误检查。
使用等待的替代方法:
while (true) { int status; pid_t done = wait(&status); if (done == -1) { if (errno == ECHILD) break; // no more child processes } else { if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) { cerr << "pid " << done << " failed" << endl; exit(1); } } }
这个不会告诉您顺序中哪个进程失败,但是如果您愿意,可以添加代码以在pids数组中查找并获取索引。