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Limit max. sleep duration per loop iteration #42

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mvorisek wants to merge 2 commits into from
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Limit max. sleep duration per loop iteration #42

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d678f4f
Limit max. sleep duration per loop iteration
mvorisek Nov 29, 2020
b3d64bc
prevent looping with 0 us on systems with unprecise microtime
mvorisek Nov 29, 2020
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47 changes: 18 additions & 29 deletions classes/util/Loop.php
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Original file line number Diff line number Diff line change
Expand Up @@ -17,20 +17,6 @@
*/
class Loop
{
/**
* Minimum time that we want to wait, between lock checks. In micro seconds.
*
* @var double
*/
private const MINIMUM_WAIT_US = 1e4; // 0.01 seconds

/**
* Maximum time that we want to wait, between lock checks. In micro seconds.
*
* @var double
*/
private const MAXIMUM_WAIT_US = 5e5; // 0.50 seconds

/**
* @var int The timeout in seconds.
*/
Expand Down Expand Up @@ -92,35 +78,38 @@ public function execute(callable $code)
$this->looping = true;

// At this time, the lock will time out.
$deadline = microtime(true) + $this->timeout;
$deadlineTs = microtime(true) + $this->timeout;

$minWaitSecs = 0.1e-3; // 0.1 ms
$maxWaitSecs = max(0.05, min(25, $this->timeout / 120)); // 50 ms to 25 s, based on timeout

$result = null;
for ($i = 0; $this->looping && microtime(true) < $deadline; ++$i) {
for ($i = 0; ; ++$i) {
$result = $code();
if (!$this->looping) {
break;
}

// Calculate max time remaining, don't sleep any longer than that.
$usecRemaining = intval(($deadline - microtime(true)) * 1e6);

// We've ran out of time.
if ($usecRemaining <= 0) {
throw TimeoutException::create($this->timeout);
$remainingSecs = $deadlineTs - microtime(true);
if ($remainingSecs <= 0) {
break;
}

$min = min(
(int) self::MINIMUM_WAIT_US * 1.25 ** $i,
self::MAXIMUM_WAIT_US
$minSecs = min(
$minWaitSecs * 1.5 ** $i,
max($minWaitSecs, $maxWaitSecs / 2)
);
$maxSecs = min($minSecs * 2, $maxWaitSecs);
$sleepMicros = min(
max(10, (int)($remainingSecs * 1e6)),
random_int((int)($minSecs * 1e6), (int)($maxSecs * 1e6))
);
$max = min($min * 2, self::MAXIMUM_WAIT_US);

$usecToSleep = min($usecRemaining, random_int((int)$min, (int)$max));

usleep($usecToSleep);
usleep($sleepMicros);
}

if (microtime(true) >= $deadline) {
if (microtime(true) >= $deadlineTs) {
throw TimeoutException::create($this->timeout);
}

Expand Down