c-带有FIFO的Posix信号量工作不正常

Question

我编写了一个小型客户端-服务器演示程序，该程序应该使用FIFO和两个信号量实现两个进程之间的简单通信。问题是，即使我在客户端读取fifo之前放入了sem_wait，他也不会等待服务器在fifo上写入，因此客户端读取旧值("2"而不是"pippo"(。我真的找不到错误在哪里。遵循服务器和客户端的代码。我希望有人能帮助我。

客户：

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
#include <sys/mman.h>
#include <sys/stat.h>   
#include <sys/types.h>
#include <signal.h>
#include <stdarg.h>
#include <fcntl.h>
#define FIFO_FILE "MIA_FIFO"
FILE * fiforw ; 
int fifo_write ( char * buf );  
int fifo_read ( char * buf );
sem_t *pizz;
sem_t *cli;
int main(void){
fiforw=fopen ( FIFO_FILE, "rw");
pizz=sem_open("pizz",  O_EXCL, S_IRUSR | S_IWUSR, 0);
cli=sem_open("cli",  O_EXCL, S_IRUSR | S_IWUSR, 0);
char buff[20];
int pieces=10;;
sprintf(buff,"%d",pieces);
fifo_write(buff);
sem_post(cli);
sem_wait(pizz);
fifo_read(buff);
printf("I've read %s n",buff);  //here he should read "pippo" instead of "2"

fclose ( fiforw );
}
int fifo_write ( char * buf ) {
fputs ( buf, fiforw );
return 1;
}
int fifo_read ( char * buf ) {
fgets( buf, sizeof(buf)+1, fiforw);
return 1;
}

服务器：

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
#include <sys/mman.h>
#include <sys/stat.h>   
#include <sys/types.h>
#include <signal.h>
#include <stdarg.h>
#include <fcntl.h>
#define FIFO_FILE "MIA_FIFO"
int fifo_write ( char * buf );  
int fifo_read ( char * buf );
sem_t *pizz;
sem_t *cli;
FILE * fiforw;
int main(void){
mkfifo(FIFO_FILE,0666);
fiforw = fopen ( FIFO_FILE, "rw");  
char buff[20];
char temp[]="pippo";
pizz = sem_open("pizz", O_CREAT, S_IRUSR | S_IWUSR, 0);
cli= sem_open("cli", O_CREAT, S_IRUSR | S_IWUSR, 0);
//while(1) {
sem_wait(cli);
fifo_read(buff);
printf("the value is %s n",buff);  
sprintf(buff,"%s",temp);    
printf("i will write pippo on the fifo n");
fifo_write(buff);
sem_post(pizz);
fclose ( fiforw );
//}
}

int fifo_write ( char * buf ) {
fputs ( buf, fiforw );
return 1;
}
int fifo_read ( char * buf ) {
fgets( buf, sizeof(buf)+1, fiforw);
return 1;
}

Answer 1

首先运行服务器，然后需要客户端。如果是这种情况，检查系统调用的返回代码会很有帮助。