为什么stream_set_blocking（）和stream_select（）给出错误？

Question

我是php的新手，我正在尝试编写一个PHP脚本来编译和执行C源代码。这是我的源代码：

      <?php
        $cmd = "gcc -g test.c -o test";

        $descriptors = array(
            2 => array("pipe","w+")
        );

        $process = proc_open($cmd,$descriptors,$pipes);

        stream_set_blocking($pipes[2],0);

        if($error = stream_get_contents($pipes[2]))
        {
            die($error);
        }

        fclose($pipes[2]);
        proc_close($process);

        $cmd = "./test";

        $descriptors = array(
            0 => array("file","input.txt","r"),
            1 => array("file","output.txt","w"),
            2 => array("pipe","w+")
        );

        $process = proc_open($cmd,$descriptors,$pipes);

        stream_set_blocking($pipes[2],0);

        if($error = stream_get_contents($pipes[2]))
        {
            die($error);
        }
        else
        {
        /*line -> 38 */ stream_set_blocking($pipes[1],1);

        /*line -> 40 */ $read = array($pipes[1],$pipes[2]);
            $write = NULL;
            $except = NULL;
            $tv_sec = 0;
            $tv_usec = 1000;

   /*line -> 46*/       if(false === ($rs = stream_select($read,$write,$except,$tv_sec,$tv_usec)) )
            {
                die("Error in stream_reader");
            }

   /*line -> 51*/       fclose($pipes[0]);
   /*line -> 52*/       fclose($pipes[1]);
            fclose($pipes[2]);

            proc_close($process);
        }

        $out = @fopen("output.txt","r");
        $test = @fopen("test.txt","r");

        while((($out_buffer = fgets($out)) !== false) && (($test_buffer = fgets($test)) !== false))
        {
            if($out_buffer !== $test_buffer)
            {
                die("Error in output.");
            }
        }

        if(!feof($out) || !feof($test))
        {
            die("Error in output.");
        }


    ?>

这是我的错误：

Undefined offset: 1 in file.php on line 38  
stream_set_blocking() expects parameter 1 to be resource, null given  in file.php on line 38  
Undefined offset: 1 in file.php on line 40  
stream_select(): supplied argument is not a valid stream resource in file.php on line 46  
stream_select(): supplied argument is not a valid stream resource in file.php on line 46  
stream_select(): supplied argument is not a valid stream resource in file.php on line 46  
Undefined offset: 0 in file.php on line 51  
fclose() expects parameter 1 to be resource, null given in file.php on line 51  
Undefined offset: 1 in file.php on line 52  
fclose() expects parameter 1 to be resource, null given in file.php on line 52 

请有人告诉我我错在哪里，当流是文件时，我们不能不使用stream_set_blocking（）吗？ 谢谢！