Added AsyncExponentialBackoffExceptionHandler and accompanying test.

Author: Bilge

src/AsyncExponentialBackoffExceptionHandler.php

@@ -0,0 +1,30 @@
+<?php
+declare(strict_types=1);
+
+namespace ScriptFUSION\Retry\ExceptionHandler;
+
+use ScriptFUSION\Retry\ExceptionHandler\Sequence\PowersOfTwoSequence;
+
+/**
+ * Delays the current asynchronous execution context for an exponentially increasing series of delays.
+ *
+ * e.g. 102ms, 204ms, 408ms, 816ms, 1.632s...
+ */
+class AsyncExponentialBackoffExceptionHandler extends AsyncMilliSleepExceptionHandler
+{
+    const DEFAULT_COEFFICIENT = 102;
+
+    private $millisecondCoefficient;
+
+    public function __construct(int $millisecondCoefficient = self::DEFAULT_COEFFICIENT)
+    {
+        parent::__construct($this->generateSequence($this->millisecondCoefficient = $millisecondCoefficient));
+    }
+
+    private function generateSequence($coefficient): \Generator
+    {
+        foreach (new PowersOfTwoSequence as $base) {
+            yield $base * $coefficient;
+        }
+    }
+}

src/AsyncMilliSleepExceptionHandler.php

@@ -6,7 +6,7 @@
 use Amp\Delayed;
 
 /**
- * Delays for a series of millisecond delays on each invocation.
+ * Delays the current asynchronous execution context for a series of millisecond delays on each invocation.
  */
 class AsyncMilliSleepExceptionHandler
 {
@@ -19,6 +19,7 @@ public function __construct(\Iterator $delays)
 
     public function __invoke()
     {
+        // TODO: Iterator validation. i.e. What happens when the iterator is no longer valid?
         $delay = $this->delays->current();
 
         $this->delays->next();

src/ExponentialBackoffExceptionHandler.php

@@ -1,11 +1,14 @@
-<?php declare(strict_types=1);
+<?php
+declare(strict_types=1);
 
 namespace ScriptFUSION\Retry\ExceptionHandler;
 
 use ScriptFUSION\Retry\ExceptionHandler\Sequence\PowersOfTwoSequence;
 
 /**
  * Sleeps for an exponentially increasing series of delays.
+ *
+ * e.g. 102ms, 204ms, 408ms, 816ms, 1.632s...
  */
 class ExponentialBackoffExceptionHandler extends MicroSleepExceptionHandler
 {

src/MicroSleepExceptionHandler.php

@@ -1,4 +1,5 @@
-<?php declare(strict_types=1);
+<?php
+declare(strict_types=1);
 
 namespace ScriptFUSION\Retry\ExceptionHandler;
 

src/Sequence/PowersOfTwoSequence.php

@@ -1,7 +1,13 @@
-<?php declare(strict_types=1);
+<?php
+declare(strict_types=1);
 
 namespace ScriptFUSION\Retry\ExceptionHandler\Sequence;
 
+/**
+ * Represents a sequence of values of the power two.
+ *
+ * e.g. 1, 2, 4, 8, 16...
+ */
 final class PowersOfTwoSequence implements \IteratorAggregate
 {
     private $power = 0;

test/Unit/AsyncExponentialBackoffExceptionHandlerTest.php

@@ -0,0 +1,28 @@
+<?php
+declare(strict_types=1);
+
+namespace ScriptFUSIONTest\Retry\ExceptionHandler\Unit;
+
+use PHPUnit\Framework\TestCase;
+use ScriptFUSION\Retry\ExceptionHandler\AsyncExponentialBackoffExceptionHandler;
+
+/**
+ * @see AsyncExponentialBackoffExceptionHandler
+ */
+final class AsyncExponentialBackoffExceptionHandlerTest extends TestCase
+{
+    public function test()
+    {
+        $handler = new AsyncExponentialBackoffExceptionHandler;
+
+        \Amp\Loop::run(static function () use ($handler): \Generator {
+            $start = microtime(true);
+
+            for ($counter = 0; $counter < 4; ++$counter) {
+                yield $handler();
+            }
+
+            self::assertGreaterThan($start + 1.5, microtime(true));
+        });
+    }
+}

test/Unit/AsyncMilliSleepExceptionHandlerTest.php

@@ -27,14 +27,14 @@ public function testSeries()
             new \ArrayIterator($delays = array_fill(0, $limit = 10, 100))
         );
 
-        $start = microtime(true);
-
         \Amp\Loop::run(static function () use ($handler, $limit): \Generator {
+            $start = microtime(true);
+
             for ($counter = 0; $counter < $limit; ++$counter) {
                 yield $handler();
             }
-        });
 
-        self::assertGreaterThan($start + 1, microtime(true));
+            self::assertGreaterThan($start + 1, microtime(true));
+        });
     }
 }

test/Unit/ExponentialBackoffExceptionHandlerTest.php

@@ -1,10 +1,14 @@
-<?php declare(strict_types=1);
+<?php
+declare(strict_types=1);
 
 namespace ScriptFUSIONTest\Retry\Unit\ExceptionHandler;
 
 use PHPUnit\Framework\TestCase;
 use ScriptFUSION\Retry\ExceptionHandler\ExponentialBackoffExceptionHandler;
 
+/**
+ * @see ExponentialBackoffExceptionHandler
+ */
 final class ExponentialBackoffExceptionHandlerTest extends TestCase
 {
     public function test()

test/Unit/MicroSleepExceptionHandlerTest.php

@@ -1,4 +1,5 @@
-<?php declare(strict_types=1);
+<?php
+declare(strict_types=1);
 
 namespace ScriptFUSIONTest\Retry\Unit\ExceptionHandler;
 

test/Unit/Sequence/PowersOfTwoSequenceTest.php

@@ -1,19 +1,29 @@
-<?php declare(strict_types=1);
+<?php
+declare(strict_types=1);
 
 namespace ScriptFUSIONTest\Retry\Unit\ExceptionHandler\Sequence;
 
 use PHPUnit\Framework\TestCase;
 use ScriptFUSION\Retry\ExceptionHandler\Sequence\PowersOfTwoSequence;
 
+/**
+ * @see PowersOfTwoSequence
+ */
 final class PowersOfTwoSequenceTest extends TestCase
 {
+    /**
+     * Tests that the iterator yields the expected sequence values.
+     */
     public function testSequence()
     {
         $powers = new \LimitIterator((new PowersOfTwoSequence)->getIterator(), 0, 6);
 
         self::assertSame([1, 2, 4, 8, 16, 32], iterator_to_array($powers));
     }
 
+    /**
+     * Tests that the iterator will not yield values forever.
+     */
     public function testIsFiniteSequence()
     {
         $counter = 0;