time_sleep_until

    (PHP 5 >= 5.1.0, PHP 7, PHP 8)

    time_sleep_until — Make the script sleep until the specified time

    Description

    time_sleep_until(float $timestamp): bool

    Makes the script sleep until the specified timestamp.

    Parameters

    timestamp

    The timestamp when the script should wake.

    Return Values

    Returns true on success or false on failure.

    Errors/Exceptions

    If the specified timestamp is in the past, this function will generate a E_WARNING.

    Examples

    Example #1 A time_sleep_until() example

    <?php

    //returns false and generates a warning
    var_dump(time_sleep_until(time()-1));

    // may only work on faster computers, will sleep up to 0.2 seconds
    var_dump(time_sleep_until(microtime(true)+0.2));

    ?>

    Notes

    Note: All signals will be delivered after the script wakes up.

    See Also

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    User Contributed Notes 3 notes

    up
    2
    purdue at nc dot rr dot com
    13 years ago
    At least on my Windows machine, the time_sleep_until function appears to calculate the number of microseconds between now and the sleep-until timestamp, and it appears to use unsigned 32-bit math in this calculation. This roundoff leads to a maximum sleep time of just under 4295 seconds (1 hour, 11 minutes, 35 seconds). To get longer sleep times, while still using time_sleep_until to minimize processor overhead, the following loop may be some help to you:

    <?php

    $sleepuntil     = strtotime("tuesday 3pm");

    while (    time() < $sleepuntil)
    time_sleep_until($sleepuntil);

    // proceed with dated processing

    ?>

    Of course, one could use something like "cron" instead, to avoid the script doing the extended sleep. Also note that time_nanosleep appears to do similar math, but it is somewhat more intuitive that the seconds parameter has an upper limit on what it can be. Still, both functions might report a warning when waking up prematurely due to roundoff.
    up
    -2
    rowan dot collins at cwtdigital dot com
    12 years ago
    Not realising that this function existed, I wrote something similar, but it has the additional facility to specify a minimum pause even if the target time has already been reached, for instance in a processor-intensive loop.

    It's in seconds rather than microseconds (it's intended for heavy-duty CLI scripts), but that could easily be changed by using microtime(true) and usleep if greater granularity was required.

    <?php
    /**
    * Pause processing until the specified time, to avoid hammering a DB or service
    *
    * @param int $target_time Timestamp
    * @param int $min_sleep Always sleep for a minimum number of seconds,
    * even if the target timestamp has already passed.
    * Default 0, meaning only sleep until the target timestamp is reached.
    *
    * @example <code>
    while ( ! $finished )
    {
    $minimum_start_of_next_loop = time() + $min_secs_per_loop;

    # DO STUFF THAT MAY OR MAY NOT TAKE VERY LONG

    sleep_until( $minimum_start_of_next_loop, $min_pause_between_loops );
    }
    </code>
    */
    function sleep_until($target_time, $min_sleep = 0)
    {
    $time_now = time();

    $time_to_target = $target_time - $time_now;

    // If we've already reached the target time, that's fine
    if ( $time_to_target <= $min_sleep )
    {
    // If required, sleep for a bit anyway
    sleep( $min_sleep );
    }
    else
    {
    // Sleep for the number of seconds until the target time
    sleep( $time_to_target );
    }
    }
    ?>
    up
    -4
    divinity76 at gmail dot com
    5 years ago
    if you for some reason need a constant-time implementation of realpath(), try

    <?php

    function realpath_constant_time(string $path, float $target_seconds, bool &$constant_time_success = null){
    $start_time=microtime(true);
    $ret=realpath($path);
    $constant_time_success = @time_sleep_until($start_time+$target_seconds);
    return     $ret;
    }
    ?>

    for example, a realtime that always uses exactly 1 millisecond (should be more than enough for SSD-based servers, perhaps rotating harddrive based servers may need something closer to 10 milliseconds, i don't know):

    <?php
    realpath_constant_time    ("/path/to/../to/file.txt",0.001,$constant_time_success);
    ?>

    and you can use $constant_time_success to see if you needed more time (and thus failed to do realpath() in constant-time), or if you succeeded.
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