先进先出:一个进程永远不会从管道读取

我正在遵循 Linux Piping 的 THIS TutorialsPoint 指南，我特别需要使用 FIFO。

但是，该代码根本不适用于服务器端。

服务器文件要么无限期挂起，要么什么都不读取，而客户端则写入 FIFO 并立即读取它刚刚写入的内容。

以下是这两个文件的完整代码，以防您不想通过TutorialsPoint：

fifoserver_twoway.cpp

#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#define FIFO_FILE "/tmp/fifo_twoway"
void reverse_string(char *);
int main() {
int fd;
char readbuf[80];
char end[10];
int to_end;
int read_bytes;
/* Create the FIFO if it does not exist */
mkfifo(FIFO_FILE, S_IFIFO|0640);
strcpy(end, "end");
fd = open(FIFO_FILE, O_RDWR);
while(1) {
read_bytes = read(fd, readbuf, sizeof(readbuf));
readbuf[read_bytes] = '';
printf("FIFOSERVER: Received string: "%s" and length is %dn", readbuf, (int)strlen(readbuf));
to_end = strcmp(readbuf, end);
if (to_end == 0) {
close(fd);
break;
}
reverse_string(readbuf);
printf("FIFOSERVER: Sending Reversed String: "%s" and length is %dn", readbuf, (int) strlen(readbuf));
write(fd, readbuf, strlen(readbuf));
/*
sleep - This is to make sure other process reads this, otherwise this
process would retrieve the message
*/
sleep(2);
}
return 0;
}
void reverse_string(char *str) {
int last, limit, first;
char temp;
last = strlen(str) - 1;
limit = last/2;
first = 0;
while (first < last) {
temp = str[first];
str[first] = str[last];
str[last] = temp;
first++;
last--;
}
return;
}

fifoclient_twoway.cpp

#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#define FIFO_FILE "/tmp/fifo_twoway"
int main() {
int fd;
int end_process;
int stringlen;
int read_bytes;
char readbuf[80];
char end_str[5];
printf("FIFO_CLIENT: Send messages, infinitely, to end enter "end"n");
fd = open(FIFO_FILE, O_CREAT|O_RDWR);
strcpy(end_str, "end");
while (1) {
printf("Enter string: ");
fgets(readbuf, sizeof(readbuf), stdin);
stringlen = strlen(readbuf);
readbuf[stringlen - 1] = '';
end_process = strcmp(readbuf, end_str);
//printf("end_process is %dn", end_process);
if (end_process != 0) {
write(fd, readbuf, strlen(readbuf));
printf("FIFOCLIENT: Sent string: "%s" and string length is %dn", readbuf, (int)strlen(readbuf));
read_bytes = read(fd, readbuf, sizeof(readbuf));
readbuf[read_bytes] = '';
printf("FIFOCLIENT: Received string: "%s" and length is %dn", readbuf, (int)strlen(readbuf));
} else {
write(fd, readbuf, strlen(readbuf));
printf("FIFOCLIENT: Sent string: "%s" and string length is %dn", readbuf, (int)strlen(readbuf));
close(fd);
break;
}
}
return 0;
}

当我运行这两个进程时，这就是我得到的：

./fifoserver_twoway

FIFOSERVER: Received string: "" and length is 0
FIFOSERVER: Sending Reversed String: "" and length is 0
FIFOSERVER: Received string: "" and length is 0
FIFOSERVER: Sending Reversed String: "" and length is 0

./fifoclient_twoway

FIFOCLIENT: Sent string: "ciao" and string length is 4
FIFOCLIENT: Received string: "ciao" and length is 4
Enter string: why won't you reverse?
FIFOCLIENT: Sent string: "why won't you reverse?" and string length is 29
FIFOCLIENT: Received string: "why won't you reverse?" and length is 29

还值得注意的是，在开始编写这个问题之前，服务器的行为完全不同：它不会像您在这里看到的那样接收任何内容并打印，而是在"读取"后无限期挂起(除了更改FIFO_FILE路径外，我没有更改代码一点(