作为一项练习,我需要使用信号处理程序和管道在两个进程之间发送一些消息。下面是我的源代码。当我运行它时,只要在它们的主方法(在这种情况下是process1()和process2())中调用pipe,我就可以让管道工作,两个进程都可以通信。但我想在信号处理程序中使用管道。但现在管道不起作用了。这是我得到的一些输出:
3 - 4 and 5 - 6
Segv at 8825
USR1 at 8824
898 sent to 4
130 received on 3
130
“898”和“130”应该相等,但实际上并不相等。 我知道管道(pipes)正在正确工作,所以我认为这与信号(signal)有关。但是,具体是什么原因呢?
源代码:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>
int fd1[2], fd2[2], status;
int cpid, cpoid;
void process1() {
cpid = getpid(); /*What's my process ID?*/
cpoid = cpid + 1; /*And what's the other process ID?*/
close(fd1[0]);
close(fd2[1]);
while (1) {}
}
void process2() {
cpid = getpid();
cpoid = cpid - 1;
close(fd1[1]);
close(fd2[0]);
raise(SIGSEGV); /*Start with a SegV signal*/
while (1) {}
}
/*Method to send a message to the other process, by pipe*/
void send (int msg) {
if (cpid < cpoid) {
write(fd1[1], &msg, 1);
printf("%d sent to %d\n", msg, fd1[1]);
} else {
write(fd2[1], &msg, 1);
printf("%d sent to %d\n", msg, fd2[1]);
}
}
/*Method to receive a message from the other process*/
int receive () {
int msg = 0;
if (cpid < cpoid) {
read(fd2[0], &msg, 1);
printf("%d received on %d\n", msg, fd2[0]);
} else {
read(fd1[0], &msg, 1);
printf("%d received on %d\n", msg, fd1[0]);
}
return msg;
}
/*The SegV Signal handler*/
void segvHandler() {
int y = -1;
printf("Segv at %d\n", cpid);
kill(cpoid, SIGUSR1); /*Send an USR1 Signal to the other proces*/
while (y != 898) {
y = receive();
printf("%d\n", y);
}
}
/*The Usr1 Signal handler*/
void usr1Handler() {
int x = 898;
printf("USR1 at %d\n", cpid);
send(x);
}
int main (int argc, char *argv[]) {
if (pipe(fd1) < 0) {
fprintf (stderr, "Could not make pipe\n");
return (EXIT_FAILURE);
}
if (pipe(fd2) < 0) {
fprintf (stderr, "Could not make pipe\n");
return (EXIT_FAILURE);
}
printf("%d - %d and %d - %d\n", fd1[0], fd1[1], fd2[0], fd2[1]); /*Pipe numbers*/
signal(SIGUSR1, usr1Handler); /*Signal handlers*/
signal(SIGSEGV, segvHandler);
if (fork() != 0) {
process1();
} else {
process2();
}
waitpid(-1, &status, 0);
return EXIT_SUCCESS;
}
printf()
不是异步安全的,在信号处理函数中不要使用它。 - Šimon Tóth