declare (directive) statement
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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.
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 occurs on each tick is specified using the register_tick_function(). See the example below
for more details. Note that more than one event can occur for each tick.
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Example 11-1. Profile a section of PHP code
<pre>
<?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)), "∓lt;br∓gt;";
}
}
// Display the data stored in the profiler
print_r (profile (TRUE));
?>
</pre>
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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, backgrounded I/O
and many other tasks.
See also
register_tick_function() and
unregister_tick_function().
