【发布时间】：2017-11-09 19:05:09
【问题描述】：
所以我试图从第一个子进程中创建 2 个子进程和一个孙子进程。我试图运行第一个子进程，然后是孙子进程，然后是第二个子进程，当进程完成时，父进程调用 pid。我完全陷入困境 - 我有许多代码版本，但无法让它们以正确的顺序触发。任何帮助、建议或链接将不胜感激。
期望的输出是
-我是第一个孩子
----我是孙子
我是家长，第一个孩子的 pid 为 21505
-我是第一个孩子，孙子的pid是21506
-再试一次
--我是老二
-- -->第二个孩子：传输了 1317 个字节。
我又是家长了，第二个孩子的 pid 为 21507
父 - 子 21507 已完成
-再试一次
**** 应该在这里看到 lab4.c 文件的前 20 行
父母 - 其他孩子 21505 已完成
int main(int* argc, char* args[])
{
pid_t child1, child2, gchild; //process ids
child1 = fork(); //Create the two child processes
if (child1 == 0)
{ // parent
child2 = fork();
if (child2 == 0)
{ //parent
printf("P: first child has pid %d\n", child1);
printf("P: second child has pid %d\n", child2);
pid_t wpid; // process id that is finished
int status; //status code returned by process
//Wait for all child processes to complete
while ((wpid = wait(&status)) > 0)
{
if (wpid > 0)
{
printf("P: Child %d is done \n", wpid);
}
};
exit(0); //exit main parent process
}
else
{
//Second process's code
printf("SC: I am the second child.\n");
int totalBytes = 0; //total number of bytes in the file we are going to read in
char buffer[2056]; //file contents size 2056 bytes
ssize_t read_bytes = 0; //Bytes from each chunk get placed here temporarily
///Read in file contents: home/common/lab_sourcefile
int fd_in = open("/home/COIS/3380/lab4_sourcefile", O_RDONLY);//open the file
do
{
//read the file chunk by chunk to the buffer
read_bytes = read(fd_in, buffer, (size_t)2056);
// End of file or error.
if (read_bytes <= 0)
{
break; //done reading file
}
//Save the total number of bytes
totalBytes = totalBytes + read_bytes;
} while (1); //infinite loop until we are done reading the file
//Write out contents to: lab4_file_copy
char filepath[1024]; //temp path
getcwd(filepath, sizeof(filepath)); //Get the current working directory
strcat(filepath, "/lab4_file_copy"); //Tack on the filename
int fd = open(filepath, O_RDWR | O_CREAT, S_IRUSR | S_IRGRP | S_IROTH); //open the file. O_RDWR = read and write flag, O_CREAT = create if doesnt exist, S_* flags are permission flags from fstat
write(fd, buffer, strlen(buffer)); //write to the file
close(fd_in);//close file we were reading
close(fd); //close copy file
// print out the number of bytes the file
printf("SC: --> Second child: %d bytes transferred.\n", totalBytes);
exit(0); //done kill second child process
}
}
else
{
//First child process
printf("FC: I'm the first child.\n");
//Create the granchild process
gchild = fork();
if (gchild == 0)
{
printf("GC: I am the grandchild.\n");
sleep(3); //sleep for 3 seconds
printf("GC: #### Output start ####\n");
execlp("head", "head", "-n", "20", "l.c", NULL); //this should exit automatically
printf("ERROR: execlp command failed\n");//This will only run if the execlp process fails
exit(1); //FAILED!
}
else
{
//Output the granchild pid
printf("FC: I am the first child, grandchild has pid %d\n", gchild);
int grandchildStatus;
//Wait for grandchild process to be done. Polling...
while ((waitpid(gchild, &grandchildStatus, WNOHANG)) != gchild)
{
printf("FC: Try again\n");
sleep(1);
};
printf("GC: #### Output end ####\n");
//End of first child. Grandchild must have completed.
exit(0); //Done. kill first child process
}
}
}
【问题讨论】：
-
如果您交换了第 3 行和第 4 行，您可以简单地在每次分叉后与
wait调用同步。如果您希望它们保持原样，您将需要一个额外的同步机制。有很多可供选择：管道、信号、共享内存信号量等。随便挑吧。 -
学习信号量。