Re: [PHP] stream_select() not working on regular files?

On Thu, Feb 4, 2010 at 9:20 AM, Dennis J. <[email protected]> wrote:

> On 02/04/2010 02:03 AM, Ashley Sheridan wrote:
>
>> On Thu, 2010-02-04 at 01:41 +0100, Dennis J. wrote:
>>
>>> Hi,
>>> I'm trying to implement something similar to"tail -f"  in php but I'm
>>> running into a problem.
>>> The issue occurs when I've reached the end of the file. From here I
>>> basically have to loop until new lines get appended to the file but I
>>> would
>>> like to respond immediately when then happens. There are three options
>>> that
>>> I can see:
>>>
>>> 1. Busy-loop
>>> pro: I can process new lines immediately
>>> contra: Excessivley CPU intensive =>  not a real option
>>>
>>> 2. add a sleep(1) to the loop
>>> pro: No longer kills the CPU
>>> contra: I might get a 1 second delay until I can process new lines
>>>
>>> 3. stream_select(array($fh),null,null,1)
>>> pro: sleeps for one second but returns earlier if new data arrives
>>> contra: doesn't seem to work in files?
>>>
>>> Method 3 is the preferable one but doesn't seem to work:
>>>
>>> $fh = fopen("testfile","r");
>>> $r = array($fh);
>>> while( ($n = stream_select($r,$w=null,$e=null,1)) == 1 ) {
>>>      echo fgets($fh);
>>> }
>>>
>>> This program will loop forever because stream_select() will always return
>>> 1
>>> even at the end of the file.
>>>
>>> Is there any other way to accomplish this?
>>>
>>> Regards,
>>>    Dennis
>>>
>>>
>> I thought that once it reached the end of the file, it will return a 0
>> indicating no new activity?
>>
>
> That's what I thought too but apparently that is not the case.
>
>
>  Although, surely you want the loop to continue forever, so that new
>> entries added to the end of the file are shown as soon as they appear.
>>
>
> Yes the loop is supposed to continue forever in the final version. In fact
> I what I'm trying to get at is a "tail -F" which means I will repeatedly
> reopen the file to check if it has been replaced by a new one. I just
> simplified the problem above to get rid of all the additional complexity and
> concentrate on the specific problem I have.
>
> My expectation was that once the end of the file is reached (i.e. fgets()
> has consumed all lines) stream_select() should wait for 1 second (in the
> above example) and if nothing happens with the file in that second it should
> return 0. But that doesn't happen.
>
>
>
Dennis

I have just been bulit a simple test script.
It works for me with a feof call if the stream was at end of file.
But I'am not sure that is that what you want !

<?php

$fp = fopen('test.xml', 'r');
$arr = array($fp);

$w = $e = null;
while (($result = stream_select($arr, $w, $e, 1)) !== false)
{
    $line = fgets($fp);
    if (!empty($line))
    {
        echo $line;
    }
    else
    {
        if (feof($fp))
            echo 'eof',"\n";
        fclose($fp);
        $fp = null;
        break;
    }
}




Regards,
Eric,




> Regards,
>  Dennis
>
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