declare

(PHP 4, PHP5)

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 two directives are recognized: the ticks directive (See below for more information on the directive) and the encoding directive (See below for more information on the directive).

Nota: The encoding directive was added in PHP 5.3.0

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 (however if the file with declare was included then it does not affect the parent file).

<?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 tickable 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.

Not all statements are tickable. Typically, condition expressions and argument expressions are not tickable.

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

Exemplo #1 Tick usage example

<?php

declare(ticks=1);

// A function called on each tick event
function tick_handler()
{
    echo "tick_handler() called\n";
}

register_tick_function('tick_handler');

$a = 1;

if ($a > 0) {
    $a += 2;
    print($a);
}

?>

Exemplo #2 Ticks usage example

<?php

function tick_handler()
{
  echo "tick_handler() called\n";
}

$a = 1;
tick_handler();

if ($a > 0) {
    $a += 2;
    tick_handler();
    print($a);
    tick_handler();
}
tick_handler();

?>

See also and .

Encoding

A script's encoding can be specified per-script using the encoding directive.

Exemplo #3 Declaring an encoding for the script.

<?php
declare(encoding='ISO-8859-1');
// code here
?>
Cuidado

When combined with namespaces, the only legal syntax for declare is declare(encoding='...'); where ... is the encoding value. declare(encoding='...') {} will result in a parse error when combined with namespaces.

The encoding declare value is ignored in PHP 5.3 unless php is compiled with --enable-zend-multibyte.

Note that PHP does not expose whether --enable-zend-multibyte was used to compile PHP other than by .

User Contributed Notes

Tom Samplonius
The tick handler is intended for code profiling.  You can use it to determine the number of time units (ticks) that a chunk of code takes.  And you can vary the tick frequency so profiling doesn't impact your specific code too much.  A tick handler can gather other useful performance data, besides just counting ticks.

You can use the tick handler to poll that your connection is a alive, but this will block your entire script.  Polling connection status is no substitute for checking return values, and using timeouts on any function that connects to an external system.
ramamneh at gmail dot com
check loaded server connection

<?php
$connection  = false;
function checkConnection( $connectionWaitingTime = 3 )
{
    // check connection & time
    global $time,$connection;
    if( ($t = (time() - $time)) >= $waitingTime  && !$connection){ 
        echo ("<p> Server not responding  for <strong>$t</strong> seconds !! </p>");
        die("Connection aborted");
           
    }
   
}

register_tick_function("checkConnection");
$time = time();
declare (ticks=1)
{
    while( true ){ // connecting to loaded server
    }
    $connection = true ;
}
?>
Anonymous
It's amazing how many people didn't grasp the concept here. Note the wording in the documentation. It states that the tick handler is called every n native execution cycles. That means native instructions, not including system calls (i'm guessing). This can give you a very good idea if you need to optimize a particular part of your script, since you can measure quite effectively how many native instructions are in your actual code.

A good profiler would take that into account, and force you, the developer, to include calls to the profiler as you're entering and leaving every function. That way you'd be able to keep an eye on how many cycles it took each function to complete. Independent of time.

That is extremely powerful, and not to be underestimated. A good solution would allow aggregate stats, so the total time in a function would be counted, including inside called functions.
markandrewslade at dontspamemeat dot gmail
Note that the two methods for calling declare are not identical.

Method 1:

<?php
// Print "tick" with a timestamp and optional suffix.
function do_tick($str = '') {
    list($sec, $usec) = explode(' ', microtime());
    printf("[%.4f] Tick.%s\n", $sec + $usec, $str);
}
register_tick_function('do_tick');

// Tick once before declaring so we have a point of reference.
do_tick('--start--');

// Method 1
declare(ticks=1);
while(1) sleep(1);

/* Output:
[1234544435.7160] Tick.--start--
[1234544435.7161] Tick.
[1234544435.7162] Tick.
[1234544436.7163] Tick.
[1234544437.7166] Tick.
*/

?>

Method 2:
<?php
// Print "tick" with a timestamp and optional suffix.
function do_tick($str = '') {
    list($sec, $usec) = explode(' ', microtime());
    printf("[%.4f] Tick.%s\n", $sec + $usec, $str);
}
register_tick_function('do_tick');

// Tick once before declaring so we have a point of reference.
do_tick('--start--');

// Method 2
declare(ticks=1) {
    while(1) sleep(1);
}

/* Output:
[1234544471.6486] Tick.--start--
[1234544472.6489] Tick.
[1234544473.6490] Tick.
[1234544474.6492] Tick.
[1234544475.6493] Tick.
*/
?>

Notice that when using {} after declare, do_tick wasn't auto-called until about 1 second after we entered the declare {} block.  However when not using the {}, do_tick was auto-called not once but twice immediately after calling declare();.

I'm assuming this is due to how PHP handles ticking internally.  That is, declare() without the {} seems to trigger more low-level instructions which in turn fires tick a few times (if ticks=1) in the act of declaring.
anotheruser at example dot com
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
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
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
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
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
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
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
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
<?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
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
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
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.