为什么打开FIFO时进程被阻塞？

我写了一个FIFO的testing。 服务器通过FIFO向客户端写入string“hello”。 但似乎这两个进程都被阻塞了。我认为FIFO是打开的，可供服务器和客户端读写。 但是这两个进程什么都不输出。

/* FIFO test */ #include <stdio.h> #include <sys/types.h> #include <sys.stat.h> #include <stdlib.h> #include <fcntl.h> #include <unistd.h> #include <string.h> #include <errno.h> #define FIFOPATH "/home/hel/fifo" // define file path int client(void); int server(void); int main(void) { pid_t pid; /* create FIFO */ if (mkfifo(FIFOPATH, S_IRUSR | S_IWUSR) < 0) { if (errno == EEXIST) { // already exists, ok } /* error */ else { exit(-1); } } /* create process */ pid = fork(); if (pid < 0) { // error, process exits. exit(-1); } else if (pid == 0) { // child, server server(); return 0; // exit } /* parent, client */ client(); return 0; } /* server */ int server(void) { int ret; int fd; /* open fifo for writing */ if ((fd = open(FIFOPATH, 0200)) < 0) { printf("%s\n", strerror(errno)); return -1; // error } ret = write(fd, "hello", 5); close(fd); return 0; } /* client */ int client(void) { char recvBuf[100]; int fd; int ret; /* open fifo for reading */ if ((fd = open(FIFOPATH, 0400)) < 0) { printf("%s\n", strerror(errno)); return -1; // error } ret = read(fd, recvBuf, 5); printf("ret: %d %d\n", ret, fd); printf("client receive %s\n", recvBuf); close(fd); return 0; } 

  O_RDONLY open for reading only O_WRONLY open for writing only O_RDWR open for reading and writing O_NONBLOCK do not block on open or for data to become available O_APPEND append on each write O_CREAT create file if it does not exist O_TRUNC truncate size to 0 O_EXCL error if O_CREAT and the file exists O_SHLOCK atomically obtain a shared lock O_EXLOCK atomically obtain an exclusive lock O_NOFOLLOW do not follow symlinks O_SYMLINK allow open of symlinks O_EVTONLY descriptor requested for event notifications only O_CLOEXEC mark as close-on-exec