PHP: declare - Manual

Last updated: Fri, 01 Aug 2008

declare

The declare construct is used to set execution directives for a block of code. The syntax of declare is similar to the syntax of other flow control constructs:

declare (directive)
    statement

The directive section allows the behavior of the declare block to be set. Currently only one directive is recognized: the ticks directive. (See below for more information on the ticks directive)

The statement part of the declare block will be executed -- how it is executed and what side effects occur during execution may depend on the directive set in the directive block.

The declare construct can also be used in the global scope, affecting all code following it.


<?php
// these are the same:

// you can use this:
declare(ticks=1) {
    // entire script here
}

// or you can use this:
declare(ticks=1);
// entire script here
?>

Ticks

A tick is an event that occurs for every N low-level statements executed by the parser within the declare block. The value for N is specified using ticks=N within the declare blocks's directive section.

The event(s) that occur on each tick are specified using the register_tick_function(). See the example below for more details. Note that more than one event can occur for each tick.

Example #1 Profile a section of PHP code


<?php
// A function that records the time when it is called
function profile($dump = FALSE)
{
    static $profile;

    // Return the times stored in profile, then erase it
    if ($dump) {
        $temp = $profile;
        unset($profile);
        return $temp;
    }

    $profile[] = microtime();
}

// Set up a tick handler
register_tick_function("profile");

// Initialize the function before the declare block
profile();

// Run a block of code, throw a tick every 2nd statement
declare(ticks=2) {
    for ($x = 1; $x < 50; ++$x) {
        echo similar_text(md5($x), md5($x*$x)), "<br />;";
    }
}

// Display the data stored in the profiler
print_r(profile(TRUE));
?>

The example profiles the PHP code within the 'declare' block, recording the time at which every second low-level statement in the block was executed. This information can then be used to find the slow areas within particular segments of code. This process can be performed using other methods: using ticks is more convenient and easier to implement.

Ticks are well suited for debugging, implementing simple multitasking, background I/O and many other tasks.

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Last updated: Fri, 01 Aug 2008

add a note User Contributed Notes
declare

anotheruser at example dot com
24-Aug-2008 12:50


Code evaluation script which uses debug_backtrace() to get execution time in ns, relative current line number, function, file, and calling function info on each tick, and shove it all in $script_stats array.  See debug_backtrace manual to customize what info is collected.



Warning: this will exhaust allowed memory very easily, so adjust tick counter according to the size of your code.  Also, array_key_exists checking on debug_backtrace arrays is removed here only to keep this example simple, but should be added to avoid a large number of resulting PHP Notice errors.



<?php



$script_stats = array();

$time = microtime(true);



function track_stats(){

    global $script_stats,$time;

    $trace = debug_backtrace();

    $exe_time = (microtime(true) - $time) * 1000;

    $func_args = implode(", ",$trace[1]["args"]);

    $script_stats[] = array(

        "current_time" => microtime(true),

        "memory" => memory_get_usage(true),

        "file" => $trace[1]["file"].': '.$trace[1]["line"],

        "function" => $trace[1]["function"].'('.$func_args.')',

        "called_by" => $trace[2]["function"].' in '.$trace[2]["file"].': '.$trace[2]["line"],

        "ns" => $exe_time

        );

    $time = microtime(true);

    }



declare(ticks = 1);

register_tick_function("track_stats");



// the rest of your project code



// output $script_stats into a html table or something



?>

zabmilenko at charter dot net
08-Jan-2008 09:49


If you misspell the directive, you won't get any error or warning.  The declare block will simply act as a nest for statements:



<?php

declare(tocks="four hundred")

{

    // Has no affect on code and produces

    // no error or warning.

}

?>



Tested in php 5.2.5 on XPsp2

rsemil at gmail dot com
06-Jan-2008 02:30


rosen_ivanov's solution can be replaced by a simple call to memory_get_peak_usage() if you're running at least PHP 5.2.0

rosen_ivanov at abv dot bg
28-Aug-2006 02:06


As Chris already noted, ticks doesn't make your script multi-threaded, but they are still great. I use them mainly for profiling - for example, placing the following at the very beginning of the script allows you to monitor its memory usage:



<?php



function profiler($return=false) {

    static $m=0;

    if ($return) return "$m bytes";

    if (($mem=memory_get_usage())>$m) $m = $mem;

}



register_tick_function('profiler');

declare(ticks=1);



/*

Your code here

*/



echo profiler(true);



?>



This approach is more accurate than calling memory_get_usage only in the end of the script. It has some performance overhead though :)

aeolianmeson at NOSPAM dot blitzeclipse dot com
30-May-2006 08:06


The scope of the declare() call if used without a block is a little unpredictable, in my experience. It appears that if placed in a method or function, it may not apply to the calls that ensue, like the following:





<?php


function a()


{


   declare(ticks=2);


   b();


}





function b()


{


   // The declare may not apply here, sometimes.


}


?>





So, if all of a sudden the signals are getting ignored, check this. At the risk of losing the ability to make a mathematical science out of placing a number of activities at varying durations of ticks like many people have chosen to do, I've found it simple to just put this at the top of the code, and just make it global.

warhog at warhog dot net
18-Dec-2005 08:39


as i read about ticks the first time i thought "wtf, useless crap" - but then i discovered some usefull application...



you can declare a tick-function which checks each n executions of your script whether the connection is still alive or not, very usefull for some kind of scripts to decrease serverload



<?php



function check_connection()

{ if (connection_aborted())

   { // do something here, e.g. close database connections

      // (or  use a shutdown function for this

      exit; }

}



register_tick_function("connection");



declare (ticks=20)

{

  // put your PHP-Script here

  // you may increase/decrease the number of ticks

}



?>

chris-at-free-source.com
28-Feb-2005 08:16


Also note that PHP is run in a single thread and so everything it does will be one line of code at a time.  I'm not aware of any true threading support in PHP, the closest you can get is to fork.



so, declare tick doens't "multi-thread" at all, it is simply is a way to automaticaly call a function every n-lines of code.

fok at nho dot com dot br
08-Jul-2003 02:45


This is a very simple example using ticks to execute a external script to show rx/tx data from the server



<?php



function traf(){

  passthru( './traf.sh' );

  echo "<br />\n";

  flush(); // keeps it flowing to the browser...

  sleep( 1 );

}



register_tick_function( "traf" );



declare( ticks=1 ){

  while( true ){}   // to keep it running...

}



?>



contents of traf.sh:

# Shows TX/RX for eth0 over 1sec

#!/bin/bash



TX1=`cat /proc/net/dev | grep "eth0" | cut -d: -f2 | awk '{print $9}'`

RX1=`cat /proc/net/dev | grep "eth0" | cut -d: -f2 | awk '{print $1}'`

sleep 1

TX2=`cat /proc/net/dev | grep "eth0" | cut -d: -f2 | awk '{print $9}'`

RX2=`cat /proc/net/dev | grep "eth0" | cut -d: -f2 | awk '{print $1}'`



echo -e "TX: $[ $TX2 - $TX1 ] bytes/s \t RX: $[ $RX2 - $RX1 ] bytes/s"

#--= the end. =--

daniel@swn
01-Feb-2003 07:56


<?php

ob_end_clean();

ob_implicit_flush(1);



function a() {

 for($i=0;$i<=100000;$i++) { }

 echo "function a() ";

}

function b() {

 for($i=0;$i<=100000;$i++) { }

 echo "function b() ";

}



register_tick_function ("a");

register_tick_function ("b");



declare (ticks=4)

{

    while(true)

    {

        sleep(1);

        echo "\n<br><b>".time()."</b><br>\n";;

    }

}

?>

You will see that a() and b() are slowing down this process. They are in fact not executed every second as expected. So this function is not a real alternative for multithreading using some slow functions..there is no difference to this way: while (true) { a(); b(); sleep(1); }

xxoes
08-Jan-2003 10:23


If i use ticks i must declare all functions before i call the function.



example:



Dosn't work

<?php

function ticks() {

   echo "tick";

}

register_tick_function("ticks");



declare (ticks=1) 1;



echo "";

echo "";



foo(); // Call to undefined function.



function foo() {

   echo "foo";

}

?>



Work

<?php

function ticks() {

   echo "tick";

}

register_tick_function("ticks");



//declare (ticks=1) 1;



echo "";

echo "";



foo();



function foo() {

   echo "foo";

}

?>



win2k : PHP 4.3.0 (cgi-fcgi)

rob_spamsux at rauchmedien dot ihatespam dot com
19-Mar-2002 10:45


Correction to above note:





Apparently, the end brace '}' at the end of the statement causes a tick.





So using





------------


declare (ticks=1) echo "1 tick after this prints";


------------





gives the expected behavior of causing 1 tick.





Note: the tick is issued after the statement executes.





Also, after playing around with this, I found that it is not really the multi-tasking I had expected. It behaves the same as simply calling the functions. I.e. each function must finish before passing the baton to the next function. They do not run in parallel.





It also seems that they always run in the order in which they were registered.





So,





<?php


------------


# register tick functions


register_tick_function ("a");


register_tick_function ("b");





# make the tick functions run


declare (ticks=1);


?>


------------





is equivalent to





------------


a();


b();


------------





It is simply a convenient way to have functions called periodically while some other code is being executed. I.e. you could use it to periodically check the status of something and then exit the script or do something else based on the status.

rob_spamsux at rauchmedien dot ihatespam dot com
19-Mar-2002 09:58


Here is an example of multi-tasking / multi-threading:





<?php


# declare functions


function a() {


  echo "a";


}


function b() {


  echo "b";


}





# register tick functions


register_tick_function ("a");


register_tick_function ("b");





# make the tick functions run


declare (ticks=1);





# that's all there is to it.


?>





Notes:


This will make functions a and b run once each at the same time.





If you try:





declare (ticks=1) {


  1;


}





They will run twice each. That is because it seems to be an undocumented fact that there is always an extra tick.





Therefore:





declare (ticks=2) {


  1;


}





Will cause them to run once.

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Last updated: Fri, 01 Aug 2008