PHP: Hypertext Preprocessor

declare

(PHP 4, PHP 5, PHP 7, PHP 8)

A instrução declare é usada para definir diretivas de execução para um bloco de código. A sintaxe do declare é similar à sintaxe de outros construtos de controle de fluxo:

declare (directive)
    statement

A seção directive permite que o comportamento do bloco do declare seja definido. Atualmente somente três diretivas são reconhecidas:

As diretivas são manipuladas na compilação do arquivo, somente literais podem ser usadas como valores da diretiva. Variáveis e constantes não podem ser usadas. Para ilustrar:

<?php
// Isto é válido:
declare(ticks=1);

// isto é inválido:
const TICK_VALUE = 1;
declare(ticks=TICK_VALUE);
?>

A parte statement do bloco do declare será executada - como é executada e quais os efeitos colaterais que ocorrem durante a execução depende da diretiva definida no bloco directive.

O construtor do declare também pode ser usado no escopo global, afetando todo o código que o segue (entretanto se o arquivo com o declare for incluído, não afetará o arquivo principal).

<?php
// Os exemplos abaixo tem o mesmo efeito

// Pode ser usado assim:
declare(ticks=1) {
    // script aqui
}

// ou assim:
declare(ticks=1);
// script inteiro aqui
?>

Ticks

Um 'tick' é um evento que ocorre a cada N declarações de baixo nível executadas pelo interpretador dentro do bloco declare. O valor de N é especificado usando ticks=N dentro do bloco declare da seção directive.

Nem todas declarações são passíveis de executar um 'tick'. Normalmente, expressões de condições e argumentos de expressões não são.

Os eventos que serão executados a cada tick são especificados usando a função register_tick_function(). Veja o exemplo abaixo para mais detalhes. Note que mais de um evento pode ser executado para cada tick.

Exemplo #1 Exemplo de uso do Tick

<?php

declare(ticks=1);

// A função a ser chamada em cada evento tick
function tick_handler()
{
    echo "tick_handler() chamada.\n";
}

register_tick_function('tick_handler'); // Causa um evento tick

$a = 1; // Causa um evento tick

if ($a > 0) {
    $a += 2; // Causa um evento tick
    print $a; // Causa um evento tick
}

?>

Consulte também register_tick_function() e unregister_tick_function().

Codificação

A codificação de um script pode ser especificada em cada arquivo com uma diretiva encoding.

Exemplo #2 Declarando a codificação do script

<?php
declare(encoding='ISO-8859-1');
// código aqui
?>

Cuidado

Quando usada com namespaces, a única sintaxe válida para declarar é declare(encoding='...'); onde ... é o valor da codificação. declare(encoding='...') {} irá resultar em um erro de sintaxe quando usada com namespaces.

Veja mais zend.script_encoding.

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Notas Enviadas por Usuários (em inglês) 10 notes

down

Anonymous ¶

14 years ago

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.

down

Kubo2 ¶

9 years ago

Note that in PHP 7 <?php declare(encoding='...'); ?> throws an E_WARNING if Zend Multibyte is turned off.

down

sawyerrken at gmail dot com ¶

11 years ago

In the following example:

<?php
function handler(){
    print "hello <br />";
}

register_tick_function("handler");

declare(ticks = 1){
    $b = 2;
} //closing curly bracket tickable
?>

"Hello" will be displayed twice because the closing curly bracket is also tickable. 

One may wonder why the opening curly bracket is not tickable if the closing is tickable. This is because the instruction for PHP to start ticking is given by the opening curly bracket so the ticking starts immediately after it.

down

digitalaudiorock at gmail dot com ¶

5 years ago

Regarding my previous comment as to the change in scope of declare(ticks=1) between 5.6 and 7.x, I intended to mention another example of the affect this can have on signal handlers:

If your script uses declare(ticks=1) and assigns handlers, in 5.6 signals will get caught and call the handler even when the code that is running is in an included file (where the included file doesn't have the declaration). However in 7.x the signal wouldn't get caught until the code returns to the main script.

The best solution to that is to use pcntl_async_signals(true) when it's available, which will allow the signals to get caught regardless of what file the code happens to be in.

down

digitalaudiorock at gmail dot com ¶

5 years ago

A few important things to note for anyone using this in conjunction with signal handlers:

If anyone is trying to optionally use either pcntl_async_signals() when available (PHP >= 7.1) or ticks for older versions, this is not possible...at least not in a way that does NOT enable ticks for newer PHP versions. This is because there is simply no way to conditionally declare ticks. For example, the following will "work" but not in the way you might expect:

<?php
if (function_exists('pcntl_async_signals')) {
    pcntl_async_signals(true);
} else {
    declare(ticks=1);
}
?>

While signal handlers will work with this for old and new version, ticks WILL be enabled even in the case where pcntl_async_signals exists, simply because the declare statement exists. So the above is functionally equivalent to:

<?php
if (function_exists('pcntl_async_signals')) pcntl_async_signals(true);
declare(ticks=1);
?>

Another thing to be aware of is that the scoping of this declaration changed a bit from PHP 5.6 to 7.x...actually it was corrected apparently as noted here:

http://php.net/manual/en/function.register-tick-function.php#121204

This can cause some very confusing behavior. One example is with the pear/System_Daemon module. With PHP 5.6 that will work with a SIGTERM handler even if the script using it doesn't itself use declare(ticks=1), but does not work in PHP 7 unless the script itself has the declaration. Not only does the handler not get called, but the signal does nothing at all, and the script doesn't exit.

A side note regarding ticks that's annoyed me for some time: As if there wasn't enough confusion around all this, the Internet is full of false rumors that ticks were deprecated and are being removed, and I believe they all started here:

http://www.hackingwithphp.com/4/21/0/the-declare-function-and-ticks

Despite a very obscure author's note at the very end of the page saying he got that wrong (that even I just noticed), the first very prominent sentence of the article still says this, and that page is near the top of any Google search.

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php dot net at e-z dot name ¶

11 years ago

you can register multiple tick functions:

<?PHP
function a() { echo "a\n"; }
function b() { echo "b\n"; }

register_tick_function('a');
register_tick_function('b');
register_tick_function('b');
register_tick_function('b');

?>

will output on every tick:
a
b
b
b

down

ja2016 at wir dot pl ¶

7 years ago

Don't use uft-8 encoding with BOM. Then fatal error occurs ALWAYS. Substitute it with utf-8 without BOM.

---

*BOM*
<?php 
declare(strict_types=1);
//Fatal error: strict_types declaration must be the very first statement in the script

down

fok at nho dot com dot br ¶

21 years ago

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. =--

down

markandrewslade at dontspamemeat dot gmail ¶

15 years ago

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.

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ohcc at 163 dot com ¶

4 years ago

It's possible to set directives at one time if every directive is supported.
<?php
    declare(strict_types=1, encoding='UTF-8');
?>

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