stream_select() not working on regular files?

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

--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php

Re: stream_select() not working on regular files?

--=-42Wk3PyIfgM65/VJmZof
Content-Type: text/plain
Content-Transfer-Encoding: 7bit

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?

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.

Thanks,
Ash
http://www.ashleysheridan.co.uk



--=-42Wk3PyIfgM65/VJmZof--

Re: stream_select() not working on regular files?

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.

Regards,
Dennis

--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php

Re: stream_select() not working on regular files?

--001636c924929026e6047ebf7846
Content-Type: text/plain; charset=UTF-8

On Thu, Feb 4, 2010 at 9:20 AM, Dennis J. 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 !


$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
>
> --
> PHP General Mailing List (http://www.php.net/)
> To unsubscribe, visit: http://www.php.net/unsub.php
>
>

--001636c924929026e6047ebf7846--

Re: 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. 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 !
>
> >
> $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

--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php

Re: stream_select() not working on regular files?

Dennis J. wrote:
> The issue is that once I've hit the EOF I need to continue the loop
> using the stream_select() waiting for new data.

AFAIK you can't; you see stream_select checks to see if something will
be blocked; if EOF is reached it considers this as not blocked; in other
words the second you hit a file EOF stream_select will continue to
instantly return a positive (without the wait of 1 second).

As far as I know every related function will always return the second
EOF is hit; meaning that the -f functionality you want can only be
gained by adding in the sleep (but i think every line reading function
will still instantly return with an empty line) - so maybe you just need
to proc_open to tail -f and read the stream with PHP - as it won't send
an EOF - example:

$stream = popen( 'tail -f access.log' , 'r' );
while( $line = fgets($stream) ) {
echo $line;
}
pclose( $stream ); // won't get here unless an error i guess..

good luck!

Nathan


--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php