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我编写了一段相对简单的代码来轮询在子进程中被重定向为标准输出的管道。但是当 poll 函数返回并说数据准备好时， read 函数总是返回零。

有什么原因可以说明为什么这不起作用？当我直接写入从子进程到父进程的管道时，它工作正常。我想我只是错误地重定向了io。

这是父进程代码：

注意：所有宏都说明错误并将它们打印到错误日志中。

pollData.fd = out.fd[ READ_INDEX ];
pollData.events = POLL_IN;
pollData.revents = 0;

printf( "Polling pipe for data...\n" );

if( poll( &pollData, 1, 5000 ) > 0 )
{
        int bytesRead = 0, trys = TRYS;
        printf( "Data has been received: " );

        Read:

        bytesRead = read( out.fd[ READ_INDEX ] , out.buf, BUF_SIZE );

             if( bytesRead > 0 ) printf( "%s" , out.buf );
        else if( bytesRead < 0 ) printf( "Error receiving data.\n" );
        else
        {
                trys--;
                printf( "No data was read.\n" );
                sleep( SLEEP );
                if( trys > 0 ) goto Read;
        }
}
else LOG( ERR_POLLING, 0 );

这是子进程代码： 注意：FD_REPLACE 使用 dup2 并关闭旧句柄。

FD_CLOSE_PACK(  out.fd[  READ_INDEX ],
                err.fd[  READ_INDEX ],
                 in.fd[ WRITE_INDEX ] );

FD_REPLACE( fileno( stdout ) , out.fd[ WRITE_INDEX ] , Child_Fail );
FD_REPLACE( fileno( stderr ) , err.fd[ WRITE_INDEX ] , Child_Fail );
FD_REPLACE( fileno( stdin  ) ,  in.fd[  READ_INDEX ] , Child_Fail );

printf( "This is a message from the test program!\n Hope it works!\n" );

sleep( 10 );

Child_Fail:

FD_CLOSE_PACK(  out.fd[ WRITE_INDEX  ],
                err.fd[ WRITE_INDEX  ],
                 in.fd[  READ_INDEX  ] );
return -1;

这是其中一个宏：

#define FD_REPLACE( old_fd, fd , addr )        
if( dup2( old_fd, fd ) < 0 )                                          
{ 
        LOG( ERR_DUP2, #old_fd " with " #fd );                 
        goto addr;           
}

这是终端的输出：

Polling pipe for data...
Data has been received: No data was read.
No data was read.
No data was read.
No data was read.
No data was read.

Now closing...
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1 回答 1

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我让它工作了。我错误地替换了文件描述符。我替换了错误的描述符，并且在关闭旧描述符之前就这样做了。我上面发布的代码显示了旧的宏。新宏是（没有错误检查）：

#define FD_REPLACE( old_fd, fd, addr )
close( old_fd );
dup2( fd, old_fd );
于 2013-03-21T06:26:08.807 回答