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.
Пример #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));
?>
Ticks are well suited for debugging, implementing simple multitasking, background I/O and many other tasks.
See also register_tick_function() and unregister_tick_function().
Коментарии
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 - $RX1 ] bytes/s"
#--= the end. =--
Note that the two methods for calling declare are not identical.
Method 1:
<?php
// Print "tick" with a timestamp and optional suffix.
function do_tick($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.
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.
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.
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
Note that in PHP 7 <?php declare(encoding='...'); ?> throws an E_WARNING if Zend Multibyte is turned off.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
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:
function.register-tick-function#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.
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.
It's possible to set directives at one time if every directive is supported.<?php
declare(strict_types=1, encoding='UTF-8');
?>