feature #27031 [Cache] Use sub-second accuracy for internal expiry ca…

…lculations (nicolas-grekas)

This PR was merged into the 4.2-dev branch.

Discussion
----------

[Cache] Use sub-second accuracy for internal expiry calculations

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | not really
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Embeds #26929, #27009 and #27028, let's focus on the 4th commit for now.

This is my last significant PR in the Cache series :)

By using integer expiries internally, our current implementations are sensitive to abrupt transitions when time() goes to next second: `$s = time(); sleep(1); echo time() - $s;` *can* display 2 from time to time.
This means that we do expire items earlier than required by the expiration settings on items.
This also means that there is no way to have a sub-second expiry. For remote backends, that's fine, but for ArrayAdapter, that's a limitation we can remove.

This PR replaces calls to `time()` by `microtime(true)`, providing more accurate timing measurements internally.

Commits
-------

08554ea [Cache] Use sub-second accuracy for internal expiry calculations

src/Symfony/Component/Cache/Adapter/AbstractAdapter.php

@@ -68,15 +68,13 @@ function ($key, $value, $isHit) use ($defaultLifetime) {
         $this->mergeByLifetime = \Closure::bind(
             function ($deferred, $namespace, &$expiredIds) use ($getId) {
                 $byLifetime = array();
-                $now = time();
+                $now = microtime(true);
                 $expiredIds = array();
 
                 foreach ($deferred as $key => $item) {
                     if (null === $item->expiry) {
                         $ttl = 0 < $item->defaultLifetime ? $item->defaultLifetime : 0;
-                    } elseif ($item->expiry > $now) {
-                        $ttl = $item->expiry - $now;
-                    } else {
+                    } elseif (0 >= $ttl = (int) ($item->expiry - $now)) {
                         $expiredIds[] = $getId($key);
                         continue;
                     }
@@ -107,7 +105,7 @@ function ($deferred, $namespace, &$expiredIds) use ($getId) {
      */
     public static function createSystemCache($namespace, $defaultLifetime, $version, $directory, LoggerInterface $logger = null)
     {
-        @trigger_error(sprintf('The "%s()" method is deprecated since Symfony 4.2.', __CLASS__), E_USER_DEPRECATED);
+        @trigger_error(sprintf('The "%s()" method is deprecated since Symfony 4.2.', __METHOD__), E_USER_DEPRECATED);
 
         if (null === self::$apcuSupported) {
             self::$apcuSupported = ApcuAdapter::isSupported();

src/Symfony/Component/Cache/Adapter/ArrayAdapter.php

@@ -87,7 +87,7 @@ public function getItems(array $keys = array())
             CacheItem::validateKey($key);
         }
 
-        return $this->generateItems($keys, time(), $this->createCacheItem);
+        return $this->generateItems($keys, microtime(true), $this->createCacheItem);
     }
 
     /**
@@ -115,7 +115,7 @@ public function save(CacheItemInterface $item)
         $value = $item["\0*\0value"];
         $expiry = $item["\0*\0expiry"];
 
-        if (null !== $expiry && $expiry <= time()) {
+        if (null !== $expiry && $expiry <= microtime(true)) {
             $this->deleteItem($key);
 
             return true;
@@ -131,7 +131,7 @@ public function save(CacheItemInterface $item)
             }
         }
         if (null === $expiry && 0 < $item["\0*\0defaultLifetime"]) {
-            $expiry = time() + $item["\0*\0defaultLifetime"];
+            $expiry = microtime(true) + $item["\0*\0defaultLifetime"];
         }
 
         $this->values[$key] = $value;

src/Symfony/Component/Cache/Adapter/ProxyAdapter.php

@@ -81,7 +81,7 @@ function (CacheItemInterface $innerItem, array $item) {
                     $item["\0*\0value"] = array("\x9D".pack('VN', (int) $metadata[CacheItem::METADATA_EXPIRY] - CacheItem::METADATA_EXPIRY_OFFSET, $metadata[CacheItem::METADATA_CTIME])."\x5F" => $item["\0*\0value"]);
                 }
                 $innerItem->set($item["\0*\0value"]);
-                $innerItem->expiresAt(null !== $item["\0*\0expiry"] ? \DateTime::createFromFormat('U', $item["\0*\0expiry"]) : null);
+                $innerItem->expiresAt(null !== $item["\0*\0expiry"] ? \DateTime::createFromFormat('U.u', sprintf('%.6f', $item["\0*\0expiry"])) : null);
             },
             null,
             CacheItem::class
@@ -200,7 +200,7 @@ private function doSave(CacheItemInterface $item, $method)
         }
         $item = (array) $item;
         if (null === $item["\0*\0expiry"] && 0 < $item["\0*\0defaultLifetime"]) {
-            $item["\0*\0expiry"] = time() + $item["\0*\0defaultLifetime"];
+            $item["\0*\0expiry"] = microtime(true) + $item["\0*\0defaultLifetime"];
         }
         $innerItem = $item["\0*\0poolHash"] === $this->poolHash ? $item["\0*\0innerItem"] : $this->pool->getItem($this->namespace.$item["\0*\0key"]);
         ($this->setInnerItem)($innerItem, $item);

src/Symfony/Component/Cache/CHANGELOG.md

@@ -5,6 +5,7 @@ CHANGELOG
 -----
 
  * added `CacheInterface`, which provides stampede protection via probabilistic early expiration and should become the preferred way to use a cache
+ * added sub-second expiry accuracy for backends that support it
  * throw `LogicException` when `CacheItem::tag()` is called on an item coming from a non tag-aware pool
  * deprecated `CacheItem::getPreviousTags()`, use `CacheItem::getMetadata()` instead
  * deprecated the `AbstractAdapter::createSystemCache()` method

src/Symfony/Component/Cache/CacheItem.php

@@ -89,9 +89,9 @@ public function set($value)
     public function expiresAt($expiration)
     {
         if (null === $expiration) {
-            $this->expiry = $this->defaultLifetime > 0 ? time() + $this->defaultLifetime : null;
+            $this->expiry = $this->defaultLifetime > 0 ? microtime(true) + $this->defaultLifetime : null;
         } elseif ($expiration instanceof \DateTimeInterface) {
-            $this->expiry = (int) $expiration->format('U');
+            $this->expiry = (float) $expiration->format('U.u');
         } else {
             throw new InvalidArgumentException(sprintf('Expiration date must implement DateTimeInterface or be null, "%s" given', is_object($expiration) ? get_class($expiration) : gettype($expiration)));
         }
@@ -105,11 +105,11 @@ public function expiresAt($expiration)
     public function expiresAfter($time)
     {
         if (null === $time) {
-            $this->expiry = $this->defaultLifetime > 0 ? time() + $this->defaultLifetime : null;
+            $this->expiry = $this->defaultLifetime > 0 ? microtime(true) + $this->defaultLifetime : null;
         } elseif ($time instanceof \DateInterval) {
-            $this->expiry = (int) \DateTime::createFromFormat('U', time())->add($time)->format('U');
+            $this->expiry = microtime(true) + \DateTime::createFromFormat('U', 0)->add($time)->format('U.u');
         } elseif (\is_int($time)) {
-            $this->expiry = $time + time();
+            $this->expiry = $time + microtime(true);
         } else {
             throw new InvalidArgumentException(sprintf('Expiration date must be an integer, a DateInterval or null, "%s" given', is_object($time) ? get_class($time) : gettype($time)));
         }

src/Symfony/Component/Cache/Simple/ArrayCache.php

@@ -64,7 +64,7 @@ public function getMultiple($keys, $default = null)
             CacheItem::validateKey($key);
         }
 
-        return $this->generateItems($keys, time(), function ($k, $v, $hit) use ($default) { return $hit ? $v : $default; });
+        return $this->generateItems($keys, microtime(true), function ($k, $v, $hit) use ($default) { return $hit ? $v : $default; });
     }
 
     /**
@@ -121,7 +121,7 @@ public function setMultiple($values, $ttl = null)
                 }
             }
         }
-        $expiry = 0 < $ttl ? time() + $ttl : PHP_INT_MAX;
+        $expiry = 0 < $ttl ? microtime(true) + $ttl : PHP_INT_MAX;
 
         foreach ($valuesArray as $key => $value) {
             $this->values[$key] = $value;

src/Symfony/Component/Cache/Tests/Adapter/AdapterTestCase.php

@@ -77,10 +77,10 @@ public function testGetMetadata()
         $item = $cache->getItem('foo');
 
         $expected = array(
-            CacheItem::METADATA_EXPIRY => 9 + time(),
+            CacheItem::METADATA_EXPIRY => 9.5 + time(),
             CacheItem::METADATA_CTIME => 1000,
         );
-        $this->assertSame($expected, $item->getMetadata());
+        $this->assertEquals($expected, $item->getMetadata(), 'Item metadata should embed expiry and ctime.', .6);
     }
 
     public function testDefaultLifeTime()

src/Symfony/Component/Cache/Tests/Fixtures/ArrayCache.php

@@ -21,12 +21,12 @@ protected function doContains($id)
 
         $expiry = $this->data[$id][1];
 
-        return !$expiry || time() <= $expiry || !$this->doDelete($id);
+        return !$expiry || microtime(true) < $expiry || !$this->doDelete($id);
     }
 
     protected function doSave($id, $data, $lifeTime = 0)
     {
-        $this->data[$id] = array($data, $lifeTime ? time() + $lifeTime : false);
+        $this->data[$id] = array($data, $lifeTime ? microtime(true) + $lifeTime : false);
 
         return true;
     }

src/Symfony/Component/Cache/Traits/ArrayTrait.php

@@ -44,7 +44,7 @@ public function hasItem($key)
     {
         CacheItem::validateKey($key);
 
-        return isset($this->expiries[$key]) && ($this->expiries[$key] >= time() || !$this->deleteItem($key));
+        return isset($this->expiries[$key]) && ($this->expiries[$key] > microtime(true) || !$this->deleteItem($key));
     }
 
     /**
@@ -81,7 +81,7 @@ private function generateItems(array $keys, $now, $f)
     {
         foreach ($keys as $i => $key) {
             try {
-                if (!$isHit = isset($this->expiries[$key]) && ($this->expiries[$key] >= $now || !$this->deleteItem($key))) {
+                if (!$isHit = isset($this->expiries[$key]) && ($this->expiries[$key] > $now || !$this->deleteItem($key))) {
                     $this->values[$key] = $value = null;
                 } elseif (!$this->storeSerialized) {
                     $value = $this->values[$key];