How to set a delay in php?

(PHP 4, PHP 5, PHP 7, PHP 8)

sleepDelay execution

Description

sleep(int $seconds): int

Delays the program execution for the given number of seconds.

Note:

In order to delay program execution for a fraction of a second, use usleep() as the sleep() function expects an int. For example, sleep(0.25) will pause program execution for 0 seconds.

Parameters

seconds

Halt time in seconds (must be greater than or equal to 0).

Return Values

Returns zero on success.

If the call was interrupted by a signal, sleep() returns a non-zero value. On Windows, this value will always be 192 (the value of the WAIT_IO_COMPLETION constant within the Windows API). On other platforms, the return value will be the number of seconds left to sleep.

Errors/Exceptions

If the specified number of seconds is negative, this function will throw a ValueError.

Changelog

VersionDescription
8.0.0 The function throws a ValueError on negative seconds; previously, an E_WARNING was raised instead, and the function returned false.

Examples

Example #1 sleep() example

// current time
echo date('h:i:s') . "\n";// sleep for 10 seconds
sleep(10);// wake up !
echo date('h:i:s') . "\n";?>

This example will output (after 10 seconds)

See Also

  • usleep() - Delay execution in microseconds
  • time_nanosleep() - Delay for a number of seconds and nanoseconds
  • time_sleep_until() - Make the script sleep until the specified time
  • set_time_limit() - Limits the maximum execution time

ash b

8 years ago

re: "mitigating the chances of a full bruit force attack by a limit of 30 lookups a minute."

Not really - the attacker could do 100 requests. Each request might take 2 seconds but it doesn't stop the number of requests done. You need to stop processing more than one request every 2 seconds rather than delay it by 2 seconds on each execution.

Anonymous

4 years ago

Diego Andrade's msleep function is not compatible with php7's `strict_types`, cast the usleep parameter to int, and it will be,
usleep((int)($time * 1000000));

barlow at fhtsolutions dot com

11 years ago

You should put sleep into both the pass and fail branches, since an attacker can check whether the response is slow and use that as an indicator - cutting down the delay time. But a delay in both branches eliminates this possibility.

MPHH

19 years ago

Note: The set_time_limit() function and the configuration directive max_execution_time only affect the execution time of the script itself. Any time spent on activity that happens outside the execution of the script such as system calls using system(), the sleep() function, database queries, etc. is not included when determining the maximum time that the script has been running.

Diego Andrade

6 years ago

Maybe obvious, but this my function to delay script execution using decimals for seconds (to mimic sleep(1.5) for example):

/**
* Delays execution of the script by the given time.
* @param mixed $time Time to pause script execution. Can be expressed
* as an integer or a decimal.
* @example msleep(1.5); // delay for 1.5 seconds
* @example msleep(.1); // delay for 100 milliseconds
*/
function msleep($time)
{
   
usleep($time * 1000000);
}
?>

hartmut at six dot de

22 years ago

it is a bad idea to use sleep() for delayed output effects as

1) you have to flush() output before you sleep

2) depending on your setup flush() will not work all the way to the browser as the web server might apply buffering of its own or the browser might not render output it thinks not to be complete

netscape for example will only display complete lines and will not show table parts until the

tag arrived

so use sleep if you have to wait  for events and don't want to burn  to much cycles, but don't use it for silly delayed output effects!

Anonymous

8 years ago

If you are having issues with sleep() and usleep() not responding as you feel they should, take a look at session_write_close()

as noted by anonymous on comments;
"If the ajax function doesn't do session_write_close(), then your outer page will appear to hang, and opening other pages in new tabs will also stall."

ealexs at gmail dot com

11 days ago

From my testing calling sleep(0); will do a `thread spin`.
It would be nice if this was to be put explicitly in the documentation as it is useful. You can do the minimum wait without overloading the CPU thread.

Anonymous

1 year ago

I wrote a simple method for sleeping with a float, which also allows you to do milliseconds (via fractional seconds).

  function sleepFloatSecs($secs) {
   
$intSecs = intval($secs);
   
$microSecs = ($secs - $intSecs) * 1000000;

    if(

$intSecs > 0) {
     
sleep($intSecs);
    }
    if(
$microSecs > 0) {
     
usleep($microSecs);
    }
  }
?>

And testing on my machine it works perfectly:

  $x = [0.100,0.250,0.5,1.0,1.5,2.0,2.5];

  foreach(

$x as $secs) {
   
$t = microtime(true);
   
sleepFloatSecs($secs);
   
$t = microtime(true) - $t;
    echo
"$secs \t => \t $t\n";
  }
?>

Output:

  0.1     =>    0.10017800331116
  0.25   
=>    0.25016593933105
  0.5    
=>    0.50015211105347
  1      
=>    1.0001430511475
  1.5    
=>    1.5003218650818
  2      
=>    2.000167131424
  2.5    
=>    2.5002470016479
?>

LVT

9 years ago

Always close your SQL connection and free the memory before using sleep( ) or you will be needlessly holding a SQL connection for [xx] seconds, remember that a shared hosting environment only allows max 30 SQL connections at the same time.

joshmeister at gmail dot com

9 years ago

Here is a simplified way to flush output to browser before completing sleep cycle.  Note the buffer must be "filled" with 4096 characters (bytes?) for ob_flush() to work before sleep() occurs.
ob_implicit_flush(true);
$buffer = str_repeat(" ", 4096);
echo
"see this immediately.
"
;
echo
$buffer;
ob_flush();
sleep(5);
echo
"some time has passed";
?>

jimmy at powerzone dot dk

12 years ago

Notice that sleep() delays execution for the current session, not just the script. Consider the following sample, where two computers invoke the same script from a browser, which doesn't do anything but sleep.

PC 1 [started 14:00:00]: script.php?sleep=10 // Will stop after 10 secs
PC 1 [started 14:00:03]: script.php?sleep=0 // Will stop after 7 secs

PC 2 [started 14:00:05]: script.php?sleep=0 // Will stop immediately

http://php.net/session_write_close may be used to address this problem.

Anonymous

13 years ago

This will allow you to use negative values or valuer below 1 second.

(0.5); ?>

function slaap($seconds)
{
   
$seconds = abs($seconds);
    if (
$seconds < 1):
      
usleep($seconds*1000000);
    else:
      
sleep($seconds);
    endif;   
}
?>

manu7772 at gmail dot com

1 year ago

Sleep method with parameter in milliseconds :

public static function ms_sleep($milliseconds = 0) {
    if($milliseconds > 0) {
        $test = $milliseconds / 1000;
        $seconds = floor($test);
        $micro = round(($test - $seconds) * 1000000);
        if($seconds > 0) sleep($seconds);
        if($micro > 0) usleep($micro);
    }
}

f dot schima at ccgmbh dot de

12 years ago

Remember that sleep() means "Let PHP time to do some other stuff".
That means that sleep() can be interrupted by signals. That is important if you work with pcntl_signal() and friends.

toddjt78 at msn dot com

12 years ago

Simple function to report the microtime since last called or the microtime since first called.

function stopWatch($total = false,$reset = true){
    global
$first_called;
    global
$last_called;
   
$now_time = microtime(true);
    if (
$last_called === null) {
       
$last_called = $now_time;
       
$first_called = $now_time;
    }
    if (
$total) {
       
$time_diff = $now_time - $first_called;
    } else {
       
$time_diff = $now_time - $last_called;
    }
    if (
$reset)
       
$last_called = $now_time;
    return
$time_diff;
}
?>

$reset  - if true, resets the last_called value to now
$total - if true, returns the time since first called otherwise returns the time since last called

code {@} ashleyhunt [dot] co [dot] uk

11 years ago

A really simple, but effective way of majorly slowing down bruit force attacks on wrong password attempts.

In my example below, if the end-user gets the password correct, they get to log in at full speed, as expected. For every incorrect password attempt, the users response is delayed by 2 seconds each time; mitigating the chances of a full bruit force attack by a limit of 30 lookups a minute.

I hope this very simple approach will help make your web applications that little bit more secure.

Ashley

public function handle_login() {
    if(
$uid = user::check_password($_REQUEST['email'], $_REQUEST['password'])) {
        return
self::authenticate_user($uid);
    }
    else {
       
// delay failed output by 2 seconds
        // to prevent bruit force attacks
       
sleep(2);
        return
self::login_failed();
    }
}
?>

LVT

9 years ago

Another reason for not to abuse sleep( ) is that along with the maximum of 30 sql connections, a shared hosting environment usually limits the number of processes to 20, if your website has many users online and you put sleep( ) everywhere in the code, your server will throw a 508 error (resource limit reached) and will stop serving your website.

soulhunter1987 at post dot ru

12 years ago

Since sleep() can be interrupted by signals i've made a function which can also be interrupted, but will continue sleeping after the signal arrived (and possibly was handled by callback). It's very useful when you write daemons and need sleep() function to work as long as you 'ordered', but have an ability to accept signals during sleeping.

function my_sleep($seconds)
{
   
$start = microtime(true);
    for (
$i = 1; $i <= $seconds; $i ++) {
        @
time_sleep_until($start + $i);
    }
}
?>

smcbride at msn dot com

1 year ago

An example of using sleep to run a set of functions at different intervals.  This is not a replacement for multi-threading, but it could help someone that wants to do something cheap.  You don't have to use eval().  It is just used as an example.  This is different than running a standard 1 second sleep loop, due to sleeping longer does not consume as much CPU.

// current time
echo date('h:i:s') . "\n";// Some example functions
function function_a() { echo 'function_a called @ ' . date('h:i:s') . PHP_EOL; }
function
function_b() { echo 'function_b called @ ' . date('h:i:s') . PHP_EOL; }
function
function_c() { echo 'function_c called @ ' . date('h:i:s') . PHP_EOL; }// Add some timers (in seconds) with function calls
$sleeptimers = array();
$sleeptimers['5'][0]['func'] = 'function_a();';
$sleeptimers['10'][0]['func'] = 'function_b();';
$sleeptimers['15'][0]['func'] = 'function_c();';// Process the timers
while(true) {
   
$currenttime = time();
   
reset($sleeptimers);
   
$mintime = key($sleeptimers);
    foreach(
$sleeptimers as $SleepTime => $Jobs) {
        foreach(
$Jobs as $JobIndex => $JobDetail) {
            if(!isset(
$JobDetail['lastrun'])) {
               
$sleeptimers[$SleepTime][$JobIndex]['lastrun'] = time();
                if(
$SleepTime < $mintime) $mintime = $SleepTime;
            } elseif((
$currenttime - $JobDetail['lastrun']) >= $SleepTime) {
                eval(
$JobDetail['func']);
               
$lastrun = time();
               
$sleeptimers[$SleepTime][$JobIndex]['lastrun'] = $lastrun;
               
$mysleeptime = $SleepTime - ($currenttime - $lastrun);
                if(
$mysleeptime < 0) $mysleeptime = 0;
                if((
$currenttime - $JobDetail['lastrun']) < $mintime) $mintime = $mysleeptime// account for length of time function runs
               
echo 'Sleep time for function ' . $JobDetail['func'] . ' = ' . $mysleeptime . PHP_EOL;
            }
        }
    }
    echo
'Sleeping for ' . $mintime . ' seconds' . PHP_EOL;
   
sleep($mintime);
}
?>

webseos at gmail dot com

14 years ago

This is a critical thing to use time delay function as sleep() Because a beginner can find that this is not working and he/she will see that all output appearing at a time.

A good way to implement this is by using the function -  ob_implicit_flush() then you don't need to use flush() function explicitly.

A sample code :
ob_implicit_flush(true);
for(
$i=0;$i<5;$i++)
{
$dis=<<


$i

DIS;
echo
$dis;sleep(5);
//flush();
}

mohd at Bahrain dot Bz

12 years ago

I hope this code will help somebody to solve the problem of not being able to flush or output the buffer to the browser (I use IE7).
It may work for you with just [ echo str_repeat(".", 4096); ] and without even using ob_... and flush.

ob_start();ob_implicit_flush(true);
//[ OR ] echo "..."; ob_flush(); flush();set_time_limit(0);

function

sleep_echo($secs) {
   
$secs = (int) $secs;
   
$buffer = str_repeat(".", 4096);
   
//echo $buffer."\r\n
\r\n";
   
for ($i=0; $i<$secs; $i++) {
        echo
date("H:i:s", time())." (".($i+1).")"."\r\n
\r\n"
.$buffer."\r\n
\r\n"
;
       
ob_flush();
       
flush();
       
sleep(1);
       
//usleep(1000000);
   
}
}
sleep_echo(30);ob_end_flush();
?>

How do you delay a function in PHP?

The sleep() function delays execution of the current script for a specified number of seconds. Note: This function throws an error if the specified number of seconds is negative.

Is there a wait function in PHP?

The wait function suspends execution of the current process until a child has exited, or until a signal is delivered whose action is to terminate the current process or to call a signal handling function.

How do I make JavaScript sleep?

How to make your JavaScript functions sleep.
const sleep = (milliseconds) => { return new Promise(resolve => setTimeout(resolve, milliseconds)) } ... .
const { promisify } = require('util') const sleep = promisify(setTimeout) ... .
sleep(500). ... .
const doSomething = async () => { await sleep(2000) //do stuff } doSomething().

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