【发布时间】：2014-05-04 14:17:22
【问题描述】：
我有一个父进程和一个子进程。
我想将数据从我的父进程发送到我的子进程。
这就是我尝试的方式：
#include<stdio.h>
#include<string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <fcntl.h>
#include <unistd.h>
#include <signal.h>
//Handler - Exiting a process
void sigHandler(int signumber){
printf("SIGQUIT catched.\n");
exit(3);
}
void writeToPipe(int myData, int *pipe){
close(pipe[0]);
write(pipe[1], &myData,sizeof(myData));
close(pipe[1]);
}
int readFromPipe(int *pipe){
int myData;
close(pipe[1]);
read(pipe[0],&myData,sizeof(myData));
close(pipe[0]);
return myData;
}
int main(){
int *pipefd = (int *)malloc(sizeof(int)*2);
//Pipe Error handling
if (pipe(pipefd) == -1){
perror("Error on pipe init.");
exit(EXIT_FAILURE);
}
fflush(stdout);
char option=-1;
pid_t child_a;
pid_t child_b;
child_a = fork();
//A Child Proc which is not used atm, it will be
if (child_a == 0) {
signal(SIGQUIT ,sigHandler);
while(1) {
//idle
sleep(2);
printf("child_a iddle work\n");
}
}
//Child B Proc for reading form the PIPE
else {
child_b = fork();
if (child_b == 0) {
signal(SIGQUIT ,sigHandler);
while(1) {
//idle
sleep(2);
printf("child_b iddle work\n");
//So lets read from pipe
int ret = readFromPipe(pipefd);
printf("Read from pipe: %d\n", ret);
}
}
//Parent Proc for writing to a pipe
else {
//MENU WHILE
while(option!=0){
scanf("%d", &option);
printf("input was: %d\n", option);
writeToPipe(option, pipefd);
}
}//End of Menu while
//Exiting child prcoesses then exiting parent prcoess
if(option==0){
int status_a, status_b;
waitpid(child_b, &status_b, WNOHANG|WUNTRACED);
waitpid(child_a, &status_a, WNOHANG|WUNTRACED);
kill(child_b,SIGQUIT);
kill(child_a,SIGQUIT);
}
}
return 1;
}
在输出中看到错误：
child_a iddle work
child_b iddle work
child_a iddle work
4
input was: 4
Read from pipe: 4 ///Wow its cool i got read nicely from the pipe with my child proc
child_a iddle work
child_b iddle work
Read from pipe: -1438072844 ///Okay.. so why is it junk? but lets go ahead with an input again
child_a iddle work
child_b iddle work
Read from pipe: -1438072844
child_a iddle work
1
input was: 1 //Input again, it is 1
child_b iddle work
Read from pipe: -1438072844 //Read from pipe remains the same junk, and not 1, why?
child_a iddle work
child_b iddle work
Read from pipe: -1438072844
child_a iddle work
3
input was: 3 //Same here with 3
child_b iddle work
Read from pipe: -1438072844
child_a iddle work
0
input was: 0 //I exit with 0, that is okay.
SIGQUIT catched.
SIGQUIT catched.
我搜索了很多但找不到解决方案，我只找到了只有一个数据在管道中发送的示例，而且数量不多。
【问题讨论】：
-
你不能有两个进程从同一个管道读取。也许有人可以告诉你如何做相当于 main |三通 > (child_a) > (child_b)
-
我有一个从一个管道读取的进程。 child_a 不使用 atm。
-
@cup：您可以从单个管道中读取任意数量的进程（但最常见的情况是一个数量级）。当多个进程读取管道时发生的情况是，每个进程都获取一些数据，但写入管道的任何给定字节仅由一个进程读取，而不是由每个进程读取。
-
另见Reading from pipe on signal sending。查看代码很快就会意识到这些问题是相关的。 OTOH，这不仅仅是另一个的复制品。
-
@JonathanLeffler 这就是我的意思，但我没有正确表达它。