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

On 02/04/2010 06:18 AM, Eric Lee wrote:
> 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 reopen the file to check if it has been replaced by a new one.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;
>      }
> }

This script terminates before it hits the actual problem.
The issue is that once I've hit the EOF I need to continue the loop using 
the stream_select() waiting for new data.

Regards,
   Dennis