我需要用管道创建父代和分叉子代之间的通信。父进程发送0,子进程回传1,父进程回复2,以此类推,直到计数器达到5。然后两个进程都会终止。
我尝试使用两个管道来实现这个功能。
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
int main(int argc, char *argv[])
{
int fd[2];
int fd2[2];
int val = 0;
// create pipe descriptors
pipe(fd);
pipe(fd2);
// fork() returns 0 for child process, child-pid for parent process.
if (fork() != 0) {
///0. Send: 0
// parent: writing only, so close read-descriptor.
close(fd[0]);
// send the value on the write-descriptor.
val = 0;
resend:
write(fd[1], &val, sizeof(val));
printf("0.Parent(%d) send value: %d\n", getpid(), val);
// close the write descriptor
close(fd[1]);
///3. Receive 1;
close(fd2[1]);
// now read the data
read(fd2[0], &val, sizeof(val));
printf("3.Parent(%d) received value: %d\n", getpid(), val);
// close the read-descriptor
close(fd2[0]);
wait(NULL);
val++;
if (val < 6)
goto resend;
else
return 0;
} else { // child: reading only, so close the write-descriptor
childStart:
wait(NULL);
///1. receive: 0
close(fd[1]);
// now read the data (will block)
read(fd[0], &val, sizeof(val));
printf("1.Child(%d) received value: %d\n", getpid(), val);
// close the read-descriptor
//close(fd[0]);
///2. Send: 1
// parent: writing only, so close read-descriptor.
close(fd2[0]);
// send the value on the write-descriptor.
val = val + 1;
write(fd2[1], &val, sizeof(val));
printf("2.Child(%d) send value: %d\n", getpid(), val);
// close the write descriptor
close(fd2[1]);
if(val <5) {
wait(NULL);
goto childStart;
}
else
return 0;
}
///////////////////////////////////////////////////////////////////////////////////
return 0 ;
}
得到的结果如下
0.Parent(120978) send value: 0
1.Child(120979) received value: 0
2.Child(120979) send value: 1
1.Child(120979) received value: 1
2.Child(120979) send value: 2
1.Child(120979) received value: 2
2.Child(120979) send value: 3
1.Child(120979) received value: 3
2.Child(120979) send value: 4
1.Child(120979) received value: 4
2.Child(120979) send value: 5
3.Parent(120978) received value: 1
0.Parent(120978) send value: 2
3.Parent(120978) received value: 2
0.Parent(120978) send value: 3
3.Parent(120978) received value: 3
0.Parent(120978) send value: 4
3.Parent(120978) received value: 4
0.Parent(120978) send value: 5
3.Parent(120978) received value: 5
我怎样才能让两个进程互相等待对方的消息?
你的代码有很多问题,我改了很多东西,结果是这样的。
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <signal.h>
int main(int argc, char *argv[])
{
int signo;
pid_t child_pid,parent_pid;
sigset_t newmask;
int fd[2];
int fd2[2];
int val = 0;
// create pipe descriptors
pipe(fd);
pipe(fd2);
// create mask for SIGUSR1
sigemptyset(&newmask);
sigaddset(&newmask,SIGUSR1);
sigaddset(&newmask,SIGUSR2);
sigprocmask(SIG_BLOCK,&newmask,NULL);
parent_pid = getpid();
// fork() returns 0 for child process, child-pid for parent process.
if ((child_pid = fork()) != 0) {
// Close unused file descriptors
close(fd[0]);
close(fd2[1]);
// send the value on the write-descriptor.
for(val = 0; val < 6; val++){
write(fd[1], &val, sizeof(val));
printf("0.Parent(%d) send value: %d\n", getpid(), val);
sigwait(&newmask,&signo);
kill(parent_pid,SIGUSR2);
// now read the data
read(fd2[0], &val, sizeof(val));
printf("3.Parent(%d) received value: %d\n", getpid(), val);
sigwait(&newmask,&signo);
kill(parent_pid,SIGUSR2);
}
return 0;
} else { // child: reading only, so close the write-descriptor
// Closing unused file descriptors
close(fd[1]);
close(fd2[0]);
for(; val <= 5; val++){
// now read the data (will block)
read(fd[0], &val, sizeof(val));
printf("1.Child(%d) received value: %d\n", getpid(), val);
kill(child_pid,SIGUSR1);
sigwait(&newmask,&signo);
// send the value on the write-descriptor.
write(fd2[1], &val, sizeof(val));
printf("2.Child(%d) send value: %d\n", getpid(), val);
kill(child_pid,SIGUSR1);
sigwait(&newmask,&signo);
}
wait(NULL);
return 0;
}
}
你的错误。
sigwait()
(https:/www.man7.orglinuxman-pagesman3sigwait.3.html)和 kill
(https:/www.man7.orglinuxman-pagesman2kill.2.html),wait(NULL)
在孩子和其他地方,它是没用的。输出。
0.Parent(14956) send value: 0
1.Child(14957) received value: 0
2.Child(14957) send value: 0
3.Parent(14956) received value: 0
0.Parent(14956) send value: 1
1.Child(14957) received value: 1
2.Child(14957) send value: 1
3.Parent(14956) received value: 1
0.Parent(14956) send value: 2
1.Child(14957) received value: 2
2.Child(14957) send value: 2
3.Parent(14956) received value: 2
0.Parent(14956) send value: 3
1.Child(14957) received value: 3
2.Child(14957) send value: 3
3.Parent(14956) received value: 3
0.Parent(14956) send value: 4
1.Child(14957) received value: 4
2.Child(14957) send value: 4
3.Parent(14956) received value: 4
0.Parent(14956) send value: 5
1.Child(14957) received value: 5
2.Child(14957) send value: 5
3.Parent(14956) received value: 5