switch
The tick handler is intended for code profiling. You can use it to determine the number of time units (ticks) that a chunk of code takes. And you can vary the tick frequency so profiling doesn't impact your specific code too much. A tick handler can gather other useful performance data, besides just counting ticks.
You can use the tick handler to poll that your connection is a alive, but this will block your entire script. Polling connection status is no substitute for checking return values, and using timeouts on any function that connects to an external system.
declare
declare 结构用来设定一段代码的执行指令。declare 的语法和其它流程控制结构相似：
declare (directive)
statement
directive 部分允许设定 declare 代码段的行为。目前只认识两个指令：ticks（更多信息见下面 ticks 指令）以及 encoding(更多信息见下面 encoding指令)。
Note: encoding 是 PHP 5.3.0 新增指令。
declare 代码段中的 statement 部分将被执行——怎样执行以及执行中有什么副作用出现取决于 directive 中设定的指令。
declare 结构也可用于全局范围，影响到其后的所有代码(但如果有 declare 结构的文件被其它文件包含，它对包含它的文件不起作用)。
<?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
Caution
ticks 指令在 PHP 5.3.0 中是过时指令，将会从 PHP 6.0.0 移除。
Tick 是一个在 declare 代码段中解释器每执行
N 条低级语句就会发生的事件。N
的值是在 declare 中的 directive 部分用
ticks=N 来指定的。
在每个 tick 中出现的事件是由 register_tick_function() 来指定的。更多细节见下面的例子。注意每个 tick 中可以出现多个事件。
Example #1 评估一段 PHP 代码的执行时间
<?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 很适合用来做调试，以及实现简单的多任务，后台 I/O 和很多其它任务。
Encoding
A script's encoding can be specified per-script using the encoding directive.
Example #2 Declaring an encoding for the script.
<?php
declare(encoding='ISO-8859-1');
// code here
?>
Caution
When combined with namespaces, the only legal syntax for declare is declare(encoding='...'); where ... is the encoding value. declare(encoding='...') {} will result in a parse error when combined with namespaces.
The encoding declare value is ignored in PHP 5.3 unless php is compiled with --enable-zend-multibyte. In PHP 6.0, the encoding directive will be used to inform the scanner what encoding the file is created in. Legal values are encoding names such as UTF-8.
add a note
User Contributed Notes
declare
Tom Samplonius
01-Apr-2011 03:02
ramamneh at gmail dot com
19-Dec-2010 11:15
check loaded server connection
<?php
$connection = false;
function checkConnection( $connectionWaitingTime = 3 )
{
// check connection & time
global $time,$connection;
if( ($t = (time() - $time)) >= $waitingTime && !$connection){
echo ("<p> Server not responding for <strong>$t</strong> seconds !! </p>");
die("Connection aborted");
}
}
register_tick_function("checkConnection");
$time = time();
declare (ticks=1)
{
while( true ){ // connecting to loaded server
}
$connection = true ;
}
?>
Anonymous
27-Sep-2010 02:10
It's amazing how many people didn't grasp the concept here. Note the wording in the documentation. It states that the tick handler is called every n native execution cycles. That means native instructions, not including system calls (i'm guessing). This can give you a very good idea if you need to optimize a particular part of your script, since you can measure quite effectively how many native instructions are in your actual code.
A good profiler would take that into account, and force you, the developer, to include calls to the profiler as you're entering and leaving every function. That way you'd be able to keep an eye on how many cycles it took each function to complete. Independent of time.
That is extremely powerful, and not to be underestimated. A good solution would allow aggregate stats, so the total time in a function would be counted, including inside called functions.
markandrewslade at dontspamemeat dot gmail
13-Feb-2009 09:06
Note that the two methods for calling declare are not identical.
Method 1:
<?php
// Print "tick" with a timestamp and optional suffix.
function do_tick($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.
anotheruser at example dot com
23-Aug-2008 04:50
Code evaluation script which uses debug_backtrace() to get execution time in ns, relative current line number, function, file, and calling function info on each tick, and shove it all in $script_stats array. See debug_backtrace manual to customize what info is collected.
Warning: this will exhaust allowed memory very easily, so adjust tick counter according to the size of your code. Also, array_key_exists checking on debug_backtrace arrays is removed here only to keep this example simple, but should be added to avoid a large number of resulting PHP Notice errors.
<?php
$script_stats = array();
$time = microtime(true);
function track_stats(){
global $script_stats,$time;
$trace = debug_backtrace();
$exe_time = (microtime(true) - $time) * 1000;
$func_args = implode(", ",$trace[1]["args"]);
$script_stats[] = array(
"current_time" => microtime(true),
"memory" => memory_get_usage(true),
"file" => $trace[1]["file"].': '.$trace[1]["line"],
"function" => $trace[1]["function"].'('.$func_args.')',
"called_by" => $trace[2]["function"].' in '.$trace[2]["file"].': '.$trace[2]["line"],
"ns" => $exe_time
);
$time = microtime(true);
}
declare(ticks = 1);
register_tick_function("track_stats");
// the rest of your project code
// output $script_stats into a html table or something
?>
zabmilenko at charter dot net
08-Jan-2008 01:49
If you misspell the directive, you won't get any error or warning. The declare block will simply act as a nest for statements:
<?php
declare(tocks="four hundred")
{
// Has no affect on code and produces
// no error or warning.
}
?>
Tested in php 5.2.5 on XPsp2
rsemil at gmail dot com
06-Jan-2008 06:30
rosen_ivanov's solution can be replaced by a simple call to memory_get_peak_usage() if you're running at least PHP 5.2.0
rosen_ivanov at abv dot bg
28-Aug-2006 06:06
As Chris already noted, ticks doesn't make your script multi-threaded, but they are still great. I use them mainly for profiling - for example, placing the following at the very beginning of the script allows you to monitor its memory usage:
<?php
function profiler($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
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
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
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
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 - $RX1 ] bytes/s"
#--= the end. =--
daniel@swn
01-Feb-2003 11:56
<?php
ob_end_clean();
ob_implicit_flush(1);
function a() {
for($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
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
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
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.