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D20087.id47992.diff
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diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -3552,6 +3552,8 @@
'PhabricatorMetaMTASchemaSpec' => 'applications/metamta/storage/PhabricatorMetaMTASchemaSpec.php',
'PhabricatorMetaMTASendGridReceiveController' => 'applications/metamta/controller/PhabricatorMetaMTASendGridReceiveController.php',
'PhabricatorMetaMTAWorker' => 'applications/metamta/PhabricatorMetaMTAWorker.php',
+ 'PhabricatorMetronome' => 'infrastructure/util/PhabricatorMetronome.php',
+ 'PhabricatorMetronomeTestCase' => 'infrastructure/util/__tests__/PhabricatorMetronomeTestCase.php',
'PhabricatorMetronomicTriggerClock' => 'infrastructure/daemon/workers/clock/PhabricatorMetronomicTriggerClock.php',
'PhabricatorModularTransaction' => 'applications/transactions/storage/PhabricatorModularTransaction.php',
'PhabricatorModularTransactionType' => 'applications/transactions/storage/PhabricatorModularTransactionType.php',
@@ -9477,6 +9479,8 @@
'PhabricatorMetaMTASchemaSpec' => 'PhabricatorConfigSchemaSpec',
'PhabricatorMetaMTASendGridReceiveController' => 'PhabricatorMetaMTAController',
'PhabricatorMetaMTAWorker' => 'PhabricatorWorker',
+ 'PhabricatorMetronome' => 'Phobject',
+ 'PhabricatorMetronomeTestCase' => 'PhabricatorTestCase',
'PhabricatorMetronomicTriggerClock' => 'PhabricatorTriggerClock',
'PhabricatorModularTransaction' => 'PhabricatorApplicationTransaction',
'PhabricatorModularTransactionType' => 'Phobject',
diff --git a/src/infrastructure/util/PhabricatorMetronome.php b/src/infrastructure/util/PhabricatorMetronome.php
new file mode 100644
--- /dev/null
+++ b/src/infrastructure/util/PhabricatorMetronome.php
@@ -0,0 +1,92 @@
+<?php
+
+/**
+ * Tick at a given frequency with a specifiable offset.
+ *
+ * One use case for this is to flatten out load spikes caused by periodic
+ * service calls. Give each host a metronome that ticks at the same frequency,
+ * but with different offsets. Then, have hosts make service calls only after
+ * their metronome ticks. This spreads service calls out evenly more quickly
+ * and more predictably than adding random jitter.
+ */
+final class PhabricatorMetronome
+ extends Phobject {
+
+ private $offset = 0;
+ private $frequency;
+
+ public function setOffset($offset) {
+ if (!is_int($offset)) {
+ throw new Exception(pht('Metronome offset must be an integer.'));
+ }
+
+ if ($offset < 0) {
+ throw new Exception(pht('Metronome offset must be 0 or more.'));
+ }
+
+ // We're not requiring that the offset be smaller than the frequency. If
+ // the offset is larger, we'll just clamp it to the frequency before we
+ // use it. This allows the offset to be configured before the frequency
+ // is configured, which is useful for using a hostname as an offset seed.
+
+ $this->offset = $offset;
+
+ return $this;
+ }
+
+ public function setFrequency($frequency) {
+ if (!is_int($frequency)) {
+ throw new Exception(pht('Metronome frequency must be an integer.'));
+ }
+
+ if ($frequency < 1) {
+ throw new Exception(pht('Metronome frequency must be 1 or more.'));
+ }
+
+ $this->frequency = $frequency;
+
+ return $this;
+ }
+
+ public function setOffsetFromSeed($seed) {
+ $offset = PhabricatorHash::digestToRange($seed, 0, PHP_INT_MAX);
+ return $this->setOffset($offset);
+ }
+
+ public function getFrequency() {
+ if ($this->frequency === null) {
+ throw new PhutilInvalidStateException('setFrequency');
+ }
+ return $this->frequency;
+ }
+
+ public function getOffset() {
+ $frequency = $this->getFrequency();
+ return ($this->offset % $frequency);
+ }
+
+ public function getNextTickAfter($epoch) {
+ $frequency = $this->getFrequency();
+ $offset = $this->getOffset();
+
+ $remainder = ($epoch % $frequency);
+
+ if ($remainder < $offset) {
+ return ($epoch - $remainder) + $offset;
+ } else {
+ return ($epoch - $remainder) + $frequency + $offset;
+ }
+ }
+
+ public function didTickBetween($min, $max) {
+ if ($max < $min) {
+ throw new Exception(
+ pht(
+ 'Maximum tick window must not be smaller than minimum tick window.'));
+ }
+
+ $next = $this->getNextTickAfter($min);
+ return ($next <= $max);
+ }
+
+}
diff --git a/src/infrastructure/util/__tests__/PhabricatorMetronomeTestCase.php b/src/infrastructure/util/__tests__/PhabricatorMetronomeTestCase.php
new file mode 100644
--- /dev/null
+++ b/src/infrastructure/util/__tests__/PhabricatorMetronomeTestCase.php
@@ -0,0 +1,61 @@
+<?php
+
+final class PhabricatorMetronomeTestCase
+ extends PhabricatorTestCase {
+
+ public function testMetronomeOffsets() {
+ $cases = array(
+ 'web001.example.net' => 44,
+ 'web002.example.net' => 36,
+ 'web003.example.net' => 25,
+ 'web004.example.net' => 25,
+ 'web005.example.net' => 16,
+ 'web006.example.net' => 26,
+ 'web007.example.net' => 35,
+ 'web008.example.net' => 14,
+ );
+
+ $metronome = id(new PhabricatorMetronome())
+ ->setFrequency(60);
+
+ foreach ($cases as $input => $expect) {
+ $metronome->setOffsetFromSeed($input);
+
+ $this->assertEqual(
+ $expect,
+ $metronome->getOffset(),
+ pht('Offset for: %s', $input));
+ }
+ }
+
+ public function testMetronomeTicks() {
+ $metronome = id(new PhabricatorMetronome())
+ ->setFrequency(60)
+ ->setOffset(13);
+
+ $tick_epoch = strtotime('2000-01-01 11:11:13 AM UTC');
+
+ // Since the epoch is at "0:13" on the clock, the metronome should tick
+ // then.
+ $this->assertEqual(
+ $tick_epoch,
+ $metronome->getNextTickAfter($tick_epoch - 1),
+ pht('Tick at 11:11:13 AM.'));
+
+ // The next tick should be a minute later.
+ $this->assertEqual(
+ $tick_epoch + 60,
+ $metronome->getNextTickAfter($tick_epoch),
+ pht('Tick at 11:12:13 AM.'));
+
+
+ // There's no tick in the next 59 seconds.
+ $this->assertFalse(
+ $metronome->didTickBetween($tick_epoch, $tick_epoch + 59));
+
+ $this->assertTrue(
+ $metronome->didTickBetween($tick_epoch, $tick_epoch + 60));
+ }
+
+
+}

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