Tick Functions

Ticks provide simulated background processing within PHP.

OverviewTicks were added to PHP 4.0.3 as a way to simulate background processing for blocks of code. They allow one or more functions to be called as a side effect of having expressions evaluated. Simply put, developers can set up functions that are called automatically as the script runs - this is useful for running functions that perform status checking, cleanup, notification, and so on. Ticks can also be indispensable for quick and dirty debugging - see the simple example below.

How Ticks WorkTicks work via the conjunction of two different mechanisms - a special type of control block called a declare block and the register_tick_function() function. The declare block allows zero or more expressions to be grouped together, while register_tick_function() allows the developer to set a tick function. The tick function will be called once for every one or more expressions within the declare block.

Declare BlocksDeclare blocks use a structure similar to other control blocks (such as while or for). The block has an initialization block, followed by a body section.

The initialization block (enclosed in parentheses) can contain special declare directives. As of PHP 4.0.6, only one directive is valid: ticks. Syntax for the ticks directive is ticks= n, where n denotes an integer value. The integer value controls how many expressions are evaluated before the tick functions (if any) are called.

The body of the block is enclosed in braces and can contain zero or more expressions. For example:

declare (ticks=1 /* Initialization block */) {
   /* body block */
   "statement 1";
   "statement 2";
   "etc...";
}

Tick FunctionsA tick function is a normal function or method that has been registered with register_tick_function() . The function can either be a built-in function or a user-defined function. Methods should be registered using array ($object, 'method_name') syntax, as in the following examples:

// Register a built-in function
register_tick_function ('flush');

// Register a user-defined function
function say_hi () {
   echo 'Hi!<br />';
}
register_tick_function ('say_hi');

// Register a method
class foo {
   // Empty constructor to avoid trouble with older versions of PHP
   function foo (){}

   function test () {
      echo "test<br />";
   }
}
$f = new foo ();
register_tick_function (array ($f, 'test'));

At the time a function (or method) is registered, it can be passed one or more arguments. These arguments can be literal values (such as 'Apple' or 42), variables (such as $choices), or variables passed by reference (such as &$HTTP_POST_VARS). For example:

<pre>
<?php
// Print the value of $x every 10 statements
register_tick_function ('printf', "The value of \$x is %d\n", &$x);

declare (ticks=10) {
   for ($x = 1; $x <= 10; ++$x) {
      echo $x, "\n";
   }
}
?>
</pre>

The script will output:
1
2
3
4
5
The value of $x is 5
6
7
8
9
10
The value of $x is 10

Multiple functions may be registed and a function may be registered multiple times. The tick functions are called sequentially in the same order that they were registered.

Tick functions and methods can be unregistered by using unregister_tick_function() .

Configuring TicksNo configuration directives currently affect how ticks function.

Installing Tick SupportTick support is built into PHP by default and cannot be disabled.

Additional InformationFor more information on ticks, see: