switch
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
declare
Il costrutto declare si usa per definire direttive di esecuzione per blocchi di istruzioni. La sintassi è simile alla sintassi di altre strutture di controllo:
declare (direttiva)
istruzione
La sezione direttiva permette di impostare il comportamento del blocco declare . Attualmente è riconosciuta una sola direttiva: la direttiva ticks. (Fare riferimento più in basso per ulteriori informazioni relative alla direttiva ticks)
Verrà eseguita la parte istruzione del blocco declare -- come verrà eseguita e quali effetti collaterali emergeranno durante l'esecuzione potrà dipendere dalla direttiva impostata nel blocco direttiva.
L'istruzione declare può essere usata anche con visubilità globale, influenzando tutto il codice che la segue.
<?php
// queste righe hanno il medesimo effetto:
// si può utitlizzare in questo modo:
declare(ticks=1) {
// inserire tutto il codice
}
// o in questo modo
declare(ticks=1);
// inserire tutto il codice
?>
Ticks
Un tick è un evento che si verifica per ogni N istruzioni di basso livello eseguite dal parser all'interno del blocco declare. Il valore per N viene specificato usando ticks=N all'interno della sezione direttiva del blocco declare.
L'evento (o gli eventi) che si verifica su ogni tick è specificato usando register_tick_function(). Vedere l'esempio più in basso per ulteriori dettagli. Notare che può verificarsi più di un evento per ogni tick.
Example #1 Segue una sezione di codice PHP
<?php
// Una funzione che registra il tempo quando viene chiamata
function profile($dump = FALSE)
{
static $profile;
// Restituisce il tempo immagazinato in $profile, successivamente lo cancella
if ($dump) {
$temp = $profile;
unset($profile);
return $temp;
}
$profile[] = microtime();
}
// Imposta un tick handler
register_tick_function("profile");
// Inizializza la funzione prima del blocco declare
profile();
// Esegue un blocco di codice, attraverso un tick ogni seconda istruzione
declare(ticks = 2) {
for ($x = 1; $x < 50; ++$x) {
echo similar_text(md5($x), md5($x*$x)), "<br />;";
}
}
// Mostra i dati immagazionati nel profilo
print_r(profile(TRUE));
?>
I tick sono ben adeguati per il debugging, l'implementazione di semplici multitasking, backgrounded I/O e molti altri compiti.
Vedere anche register_tick_function() e unregister_tick_function().
add a note
User Contributed Notesdeclare
zabmilenko at charter dot net
08-Jan-2008 01:49
08-Jan-2008 01:49
rsemil at gmail dot com
06-Jan-2008 06:30
06-Jan-2008 06:30
rosen_ivanov's solution can be replaced by a simple call to memory_get_peak_usage() if you're running at least PHP 5.2.0
rosen_ivanov at abv dot bg
28-Aug-2006 06:06
28-Aug-2006 06:06
As Chris already noted, ticks doesn't make your script multi-threaded, but they are still great. I use them mainly for profiling - for example, placing the following at the very beginning of the script allows you to monitor its memory usage:
<?php
function profiler($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 12:06
30-May-2006 12:06
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 12:39
18-Dec-2005 12:39
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 12:16
28-Feb-2005 12:16
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
07-Jul-2003 06:45
07-Jul-2003 06:45
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 - $RX1 ] bytes/s"
#--= the end. =--
daniel@swn
01-Feb-2003 11:56
01-Feb-2003 11:56
<?php
ob_end_clean();
ob_implicit_flush(1);
function a() {
for($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 02:23
08-Jan-2003 02:23
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 02:45
19-Mar-2002 02:45
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 01:58
19-Mar-2002 01:58
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.