管道使用注意事项

When using pipes, we must be careful to close unused descriptors in order to ensure that reading processes detect end-of-file and writing processes receive the SIGPIPE signal or the EPIPE error.

在使用管道时，父进程创建了管道，然后再创建子进程时，父进程和子进程都保留了管道的读文件描述符和写文件描述符，所以如果想让管道的读操作能够读到EOF，父进程要关闭自己保留的写文件描述符

如下的管道测试代码：

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

int pipe_default[2];

int main(int argc, char *argv[]) {

	pid_t pid;
	char buffer[32];

	memset(buffer, 0, 32);

	if (pipe(pipe_default) < 0) {
		printf("Failed to create pipe!\n");
		return 0;
	}


	pid = fork();

	printf("pid = %d\n", pid);

	if (pid == 0) {
		close(pipe_default[1]);
		//sleep(5);
		if (read(pipe_default[0], buffer, 32) > 0) {
			printf("Received data from server, %s!\n", buffer);

		}

		close(pipe_default[0]);
	}else {
		close(pipe_default[0]);

		char * contentToSend = "Hey, guy. Nice to meet you!!";

		if (-1 != write(pipe_default[1], contentToSend, strlen(contentToSend))) {
			printf("Send data to the other side\n");
		}

		close(pipe_default[1]);
		wait(pid, NULL, 0);
	}

	return 1;
}