如何使用管道进行非阻塞 IPC（UART 仿真）

Question

问题：

我想编写一些模拟串行端口连接的测试/模拟代码。这 真实的代码如下所示：

DUT <- UART ->测试工具.exe

我的计划是在 Linux 上创建一个测试应用程序 (CodeUnderTest.out)，该应用程序分叉以两个（读和写）命名管道作为参数来启动 testtool.out。但我不知道如何使所有管道 IO 非阻塞！

设置看起来像这样：

CodeUnderTest.out <- 命名管道 -> testTool.out（从 CodeUnderTest.out 启动）

我尝试按如下方式打开管道：

open(wpipe,O_WRONLY|O_NONBLOCK);
open(rpipe,O_RDONLY|O_NONBLOCK);

但是写入会阻塞，直到读取器打开 wpipe。接下来我尝试了以下操作：

open(wpipe,O_RDWR|O_NONBLOCK);
open(rpipe,O_RDONLY|O_NONBLOCK);

但是第一条消息的阅读器永远不会获取任何数据（尽管不会阻塞）

我还尝试在每条消息周围添加打开和关闭调用，但这也不起作用...

测试代码：

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>

pid_t pid;
char* rpipe, *wpipe,*x;
FILE *rh,*wh;
int rfd,wfd;

void openrpipe( void )
   {
   rfd = open(rpipe,O_RDONLY|O_NONBLOCK);
   rh = fdopen(rfd,"rb");
   printf("%sopeningr %x\n",x,rh);
   }
void openwpipe( void )
   {
   //Fails when reader not already opened
   //wfd = open(wpipe,O_WRONLY|O_NONBLOCK);
   wfd = open(wpipe,O_RDWR|O_NONBLOCK);
   wh = fdopen(wfd,"wb");
   printf("%sopeningw %x\n",x,wh);
   }
void closerpipe( void )
   {
   int i;
   i = fclose(rh);
   printf("%sclosingr %d\n",x,i);
   }
void closewpipe( void )
   {
   int i;
   i = fclose(wh);
   printf("%sclosingw %d\n",x,i);
   }
void readpipe( char* expect, int len)
   {
   char buf[1024];
   int i=0;
   printf("%sreading\n",x);
   while(i==0)
      {
      //printf(".");
      i = fread(buf,1,len,rh);
      }
   printf("%sread (%d) %s\n",x,i,buf);
   }
void writepipe( char* data, int len)
   {
   int i,j;
   printf("%swriting\n",x);
   i = fwrite(data,1,len,rh);
   j = fflush(rh); //No help!
   printf("%sflush %d\n",x,j);
   printf("%swrite (%d) %s\n",x,i,data);
   }
int main(int argc, char **argv)
   {
   rpipe = "readfifo";
   wpipe = "writefifo";
   x = "";
   pid = fork();
   if( pid == 0)
      {
      wpipe = "readfifo";
      rpipe = "writefifo";
      x = "   ";
      openrpipe();
      openwpipe();
      writepipe("paul",4);
      readpipe("was",3);
      writepipe("here",4);
      closerpipe();
      closewpipe();
      exit(0);
      }
   openrpipe();
   openwpipe();
   readpipe("paul",4);
   writepipe("was",3);
   readpipe("here",4);
   closerpipe();
   closewpipe();
   return( -1 );
   }

顺便说一句：

要使用上面的测试代码，您需要在当前目录中创建 2 个管道：

mkfifo ./readfifo

mkfifo ./writefifo

更新：

好的，我想我现在有正确的设置。请告诉我是否可以做得更好

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>

pid_t pid;
char* rpipe, *wpipe,*x;
int rfd,wfd;

FILE* openpipe( char* str, char* access )
   {
   FILE* fh;
   rfd = open(str,O_RDWR|O_NONBLOCK);
   fh = fdopen(rfd,access);
   printf("%sopen(%s,%s)=%x\n",x,str,access,fh);
   return(fh);
   }
void closepipe( FILE* fh )
   {
   int i;
   i = fclose(fh);
   printf("%sclosing %d\n",x,i);
   }
void readpipe( char* expect, int len, FILE* fh)
   {
   char buf[1024];
   int i=0;
   printf("%sreading\n",x);
   while(i==0)
      {
      //printf("%c",strlen(x)?'.':'#');
      i = fread(buf,1,len,fh);
      }
   buf[i] = 0;
   printf("%sread (%d) %s\n",x,i,buf);
   }
void writepipe( char* data, int len, FILE* fh)
   {
   int i=0,j;
   printf("%swriting\n",x);
   //while(i==0)
   i = fwrite(data,1,len,fh);
   j=fflush(fh);
   printf("%sflush %d\n",x,j);
   printf("%swrite (%d) %s\n",x,i,data);
   }
int main(int argc, char **argv)
   {
   FILE *rh,*wh;
   rpipe = "readfifo";
   wpipe = "writefifo";
   x = "";
   pid = fork();
   if( pid == 0)
      {
      FILE *rh,*wh;
      wpipe = "readfifo";
      rpipe = "writefifo";
      x = "   ";
      rh=openpipe(rpipe,"rb");
      wh=openpipe(wpipe,"wb");
      writepipe("paul",4,wh);
      readpipe("was",3,rh);
      writepipe("here",4,wh);
      closepipe(rh);
      closepipe(wh);
      exit(0);
      }
   rh=openpipe(rpipe,"rb");
   wh=openpipe(wpipe,"wb");
   readpipe("paul",4,rh);
   writepipe("was",3,wh);
   readpipe("here",4,rh);
   closepipe(rh);
   closepipe(wh);
   return( -1 );
   }

Answer 1

一般来说，模拟串行端口进行此类测试的最佳方法是使用伪终端，因为串行端口是 tty，因此是 pty 。

posix_openpt()、grantpt()、unlockpt() 和 ptsname() 是您需要的调用。 Master端通过设备模拟器进行读写，Slave端作为串口打开给被测试的程序。

Answer 2

在有读取器之前不要写入管道。您应该能够使用 select 或 poll 来确定阅读器何时连接。