Re: [PHP] 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reopen the file to check if it has been replaced by a new one.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