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<?php |
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namespace MatthiasMullie\Scrapbook\Buffered\Utils; |
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use MatthiasMullie\Scrapbook\Adapters\Collections\MemoryStore as BufferCollection; |
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use MatthiasMullie\Scrapbook\KeyValueStore; |
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/** |
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* This is a helper class for BufferedStore & TransactionalStore, which buffer |
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* real cache requests in memory. |
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* |
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* This class accepts 2 caches: a KeyValueStore object (the real cache) and a |
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* Buffer instance (to read data from as long as it hasn't been committed) |
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* |
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* Every write action will first store the data in the Buffer instance, and |
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* then pas update along to $defer. |
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* Once commit() is called, $defer will execute all these updates against the |
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* real cache. All deferred writes that fail to apply will cause that cache key |
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* to be deleted, to ensure cache consistency. |
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* Until commit() is called, all data is read from the temporary Buffer instance. |
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* |
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* @author Matthias Mullie <[email protected]> |
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* @copyright Copyright (c) 2014, Matthias Mullie. All rights reserved |
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* @license LICENSE MIT |
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*/ |
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class Transaction implements KeyValueStore |
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{ |
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/** |
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* @var KeyValueStore |
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*/ |
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protected $cache; |
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/** |
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* @var Buffer |
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*/ |
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protected $local; |
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/** |
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* We'll return stub CAS tokens in order to reliably replay the CAS actions |
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* to the real cache. This will hold a map of stub token => value, used to |
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* verify when we do the actual CAS. |
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* |
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* @see cas() |
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* |
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* @var mixed[] |
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*/ |
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protected $tokens = array(); |
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/** |
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* Deferred updates to be committed to real cache. |
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* |
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* @var Defer |
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*/ |
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protected $defer; |
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/** |
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* Suspend reads from real cache. This is used when a flush is issued but it |
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* has not yet been committed. In that case, we don't want to fall back to |
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* real cache values, because they're about to be flushed. |
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* |
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* @var bool |
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*/ |
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protected $suspend = false; |
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/** |
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* @var Transaction[] |
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*/ |
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protected $collections = array(); |
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/** |
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* @param Buffer|BufferCollection $local |
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*/ |
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public function __construct(/* Buffer|BufferCollection */ $local, KeyValueStore $cache) |
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{ |
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// can't do double typehint, so let's manually check the type |
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if (!$local instanceof Buffer && !$local instanceof BufferCollection) { |
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$error = 'Invalid class for $local: '.get_class($local); |
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if (class_exists('\TypeError')) { |
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throw new \TypeError($error); |
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} |
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trigger_error($error, E_USER_ERROR); |
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} |
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$this->cache = $cache; |
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// (uncommitted) writes must never be evicted (even if that means |
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// crashing because we run out of memory) |
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$this->local = $local; |
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$this->defer = new Defer($this->cache); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function get($key, &$token = null) |
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{ |
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$value = $this->local->get($key, $token); |
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// short-circuit reading from real cache if we have an uncommitted flush |
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if ($this->suspend && null === $token) { |
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// flush hasn't been committed yet, don't read from real cache! |
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return false; |
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} |
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if (false === $value) { |
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if ($this->local->expired($key)) { |
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/* |
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* Item used to exist in local cache, but is now expired. This |
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* is used when values are to be deleted: we don't want to reach |
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* out to real storage because that would respond with the not- |
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* yet-deleted value. |
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*/ |
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return false; |
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} |
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// unknown in local cache = fetch from source cache |
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$value = $this->cache->get($key, $token); |
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} |
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// no value = quit early, don't generate a useless token |
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if (false === $value) { |
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return false; |
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} |
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/* |
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* $token will be unreliable to the deferred updates so generate |
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* a custom one and keep the associated value around. |
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* Read more details in PHPDoc for function cas(). |
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* uniqid is ok here. Doesn't really have to be unique across |
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* servers, just has to be unique every time it's called in this |
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* one particular request - which it is. |
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*/ |
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$token = uniqid(); |
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$this->tokens[$token] = serialize($value); |
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return $value; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function getMulti(array $keys, array &$tokens = null) |
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{ |
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// retrieve all that we can from local cache |
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$values = $this->local->getMulti($keys); |
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$tokens = array(); |
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// short-circuit reading from real cache if we have an uncommitted flush |
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if (!$this->suspend) { |
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// figure out which missing key we need to get from real cache |
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$keys = array_diff($keys, array_keys($values)); |
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foreach ($keys as $i => $key) { |
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// don't reach out to real cache for keys that are about to be gone |
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if ($this->local->expired($key)) { |
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unset($keys[$i]); |
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} |
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} |
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// fetch missing values from real cache |
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if ($keys) { |
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$missing = $this->cache->getMulti($keys); |
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$values += $missing; |
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} |
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} |
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// any tokens we get will be unreliable, so generate some replacements |
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// (more elaborate explanation in get()) |
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foreach ($values as $key => $value) { |
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$token = uniqid(); |
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$tokens[$key] = $token; |
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$this->tokens[$token] = serialize($value); |
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} |
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return $values; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function set($key, $value, $expire = 0) |
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{ |
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// store the value in memory, so that when we ask for it again later in |
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// this same request, we get the value we just set |
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$success = $this->local->set($key, $value, $expire); |
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if (false === $success) { |
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return false; |
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} |
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$this->defer->set($key, $value, $expire); |
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return true; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function setMulti(array $items, $expire = 0) |
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{ |
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// store the values in memory, so that when we ask for it again later in |
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// this same request, we get the value we just set |
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$success = $this->local->setMulti($items, $expire); |
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// only attempt to store those that we've set successfully to local |
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$successful = array_intersect_key($items, $success); |
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if (!empty($successful)) { |
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$this->defer->setMulti($successful, $expire); |
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} |
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return $success; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function delete($key) |
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{ |
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// check the current value to see if it currently exists, so we can |
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// properly return true/false as would be expected from KeyValueStore |
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$value = $this->get($key); |
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if (false === $value) { |
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return false; |
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} |
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/* |
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* To make sure that subsequent get() calls for this key don't return |
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* a value (it's supposed to be deleted), we'll make it expired in our |
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* temporary bag (as opposed to deleting it from out bag, in which case |
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* we'd fall back to fetching it from real store, where the transaction |
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* might not yet be committed) |
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*/ |
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$this->local->set($key, $value, -1); |
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$this->defer->delete($key); |
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return true; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function deleteMulti(array $keys) |
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{ |
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// check the current values to see if they currently exists, so we can |
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// properly return true/false as would be expected from KeyValueStore |
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$items = $this->getMulti($keys); |
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$success = array(); |
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foreach ($keys as $key) { |
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$success[$key] = array_key_exists($key, $items); |
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} |
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// only attempt to store those that we've deleted successfully to local |
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$values = array_intersect_key($success, array_flip($keys)); |
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if (empty($values)) { |
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return array(); |
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} |
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// mark all as expired in local cache (see comment in delete()) |
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$this->local->setMulti($values, -1); |
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$this->defer->deleteMulti(array_keys($values)); |
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return $success; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function add($key, $value, $expire = 0) |
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{ |
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// before adding, make sure the value doesn't yet exist (in real cache, |
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// nor in memory) |
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if (false !== $this->get($key)) { |
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return false; |
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} |
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// store the value in memory, so that when we ask for it again later |
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// in this same request, we get the value we just set |
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$success = $this->local->set($key, $value, $expire); |
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if (false === $success) { |
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return false; |
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} |
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$this->defer->add($key, $value, $expire); |
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return true; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function replace($key, $value, $expire = 0) |
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{ |
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// before replacing, make sure the value actually exists (in real cache, |
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// or already created in memory) |
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if (false === $this->get($key)) { |
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return false; |
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} |
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// store the value in memory, so that when we ask for it again later |
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// in this same request, we get the value we just set |
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$success = $this->local->set($key, $value, $expire); |
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if (false === $success) { |
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return false; |
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} |
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$this->defer->replace($key, $value, $expire); |
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return true; |
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} |
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/** |
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* Since our CAS is deferred, the CAS token we got from our original |
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* get() will likely not be valid by the time we want to store it to |
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* the real cache. Imagine this scenario: |
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* * a value is fetched from (real) cache |
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* * an new value key is CAS'ed (into temp cache - real CAS is deferred) |
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* * this key's value is fetched again (this time from temp cache) |
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* * and a new value is CAS'ed again (into temp cache...). |
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* |
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* In this scenario, when we finally want to replay the write actions |
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* onto the real cache, the first 3 actions would likely work fine. |
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* The last (second CAS) however would not, since it never got a real |
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* updated $token from the real cache. |
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* |
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* To work around this problem, all get() calls will return a unique |
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* CAS token and store the value-at-that-time associated with that |
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* token. All we have to do when we want to write the data to real cache |
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* is, right before was CAS for real, get the value & (real) cas token |
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* from storage & compare that value to the one we had stored. If that |
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* checks out, we can safely resume the CAS with the real token we just |
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* received. |
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* |
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* {@inheritdoc} |
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*/ |
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public function cas($token, $key, $value, $expire = 0) |
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{ |
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$originalValue = isset($this->tokens[$token]) ? $this->tokens[$token] : null; |
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// value is no longer the same as what we used for token |
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if (serialize($this->get($key)) !== $originalValue) { |
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return false; |
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} |
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// "CAS" value to local cache/memory |
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$success = $this->local->set($key, $value, $expire); |
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if (false === $success) { |
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return false; |
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} |
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// only schedule the CAS to be performed on real cache if it was OK on |
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// local cache |
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$this->defer->cas($originalValue, $key, $value, $expire); |
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return true; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function increment($key, $offset = 1, $initial = 0, $expire = 0) |
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{ |
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if ($offset <= 0 || $initial < 0) { |
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return false; |
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} |
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// get existing value (from real cache or memory) so we know what to |
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// increment in memory (where we may not have anything yet, so we should |
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// adjust our initial value to what's already in real cache) |
371
|
|
|
$value = $this->get($key); |
372
|
|
|
if (false === $value) { |
373
|
|
|
$value = $initial - $offset; |
374
|
|
|
} |
375
|
|
|
|
376
|
|
|
if (!is_numeric($value) || !is_numeric($offset)) { |
377
|
|
|
return false; |
378
|
|
|
} |
379
|
|
|
|
380
|
|
|
// store the value in memory, so that when we ask for it again later |
381
|
|
|
// in this same request, we get the value we just set |
382
|
|
|
$value = max(0, $value + $offset); |
383
|
|
|
$success = $this->local->set($key, $value, $expire); |
384
|
|
|
if (false === $success) { |
|
|
|
|
385
|
|
|
return false; |
386
|
|
|
} |
387
|
|
|
|
388
|
|
|
$this->defer->increment($key, $offset, $initial, $expire); |
389
|
|
|
|
390
|
|
|
return $value; |
391
|
|
|
} |
392
|
|
|
|
393
|
|
|
/** |
394
|
|
|
* {@inheritdoc} |
395
|
|
|
*/ |
396
|
|
|
public function decrement($key, $offset = 1, $initial = 0, $expire = 0) |
397
|
|
|
{ |
398
|
|
|
if ($offset <= 0 || $initial < 0) { |
399
|
|
|
return false; |
400
|
|
|
} |
401
|
|
|
|
402
|
|
|
// get existing value (from real cache or memory) so we know what to |
403
|
|
|
// increment in memory (where we may not have anything yet, so we should |
404
|
|
|
// adjust our initial value to what's already in real cache) |
405
|
|
|
$value = $this->get($key); |
406
|
|
|
if (false === $value) { |
407
|
|
|
$value = $initial + $offset; |
408
|
|
|
} |
409
|
|
|
|
410
|
|
|
if (!is_numeric($value) || !is_numeric($offset)) { |
411
|
|
|
return false; |
412
|
|
|
} |
413
|
|
|
|
414
|
|
|
// store the value in memory, so that when we ask for it again later |
415
|
|
|
// in this same request, we get the value we just set |
416
|
|
|
$value = max(0, $value - $offset); |
417
|
|
|
$success = $this->local->set($key, $value, $expire); |
418
|
|
|
if (false === $success) { |
|
|
|
|
419
|
|
|
return false; |
420
|
|
|
} |
421
|
|
|
|
422
|
|
|
$this->defer->decrement($key, $offset, $initial, $expire); |
423
|
|
|
|
424
|
|
|
return $value; |
425
|
|
|
} |
426
|
|
|
|
427
|
|
|
/** |
428
|
|
|
* {@inheritdoc} |
429
|
|
|
*/ |
430
|
|
|
public function touch($key, $expire) |
431
|
|
|
{ |
432
|
|
|
// grab existing value (from real cache or memory) and re-save (to |
433
|
|
|
// memory) with updated expiration time |
434
|
|
|
$value = $this->get($key); |
435
|
|
|
if (false === $value) { |
436
|
|
|
return false; |
437
|
|
|
} |
438
|
|
|
|
439
|
|
|
$success = $this->local->set($key, $value, $expire); |
440
|
|
|
if (false === $success) { |
|
|
|
|
441
|
|
|
return false; |
442
|
|
|
} |
443
|
|
|
|
444
|
|
|
$this->defer->touch($key, $expire); |
445
|
|
|
|
446
|
|
|
return true; |
447
|
|
|
} |
448
|
|
|
|
449
|
|
|
/** |
450
|
|
|
* {@inheritdoc} |
451
|
|
|
*/ |
452
|
|
|
public function flush() |
453
|
|
|
{ |
454
|
|
|
foreach ($this->collections as $collection) { |
455
|
|
|
$collection->flush(); |
456
|
|
|
} |
457
|
|
|
|
458
|
|
|
$success = $this->local->flush(); |
459
|
|
|
if (false === $success) { |
|
|
|
|
460
|
|
|
return false; |
461
|
|
|
} |
462
|
|
|
|
463
|
|
|
// clear all buffered writes, flush wipes them out anyway |
464
|
|
|
$this->clear(); |
465
|
|
|
|
466
|
|
|
// make sure that reads, from now on until commit, don't read from cache |
467
|
|
|
$this->suspend = true; |
468
|
|
|
|
469
|
|
|
$this->defer->flush(); |
470
|
|
|
|
471
|
|
|
return true; |
472
|
|
|
} |
473
|
|
|
|
474
|
|
|
/** |
475
|
|
|
* {@inheritdoc} |
476
|
|
|
*/ |
477
|
|
|
public function getCollection($name) |
478
|
|
|
{ |
479
|
|
|
if (!isset($this->collections[$name])) { |
480
|
|
|
$this->collections[$name] = new static( |
481
|
|
|
$this->local->getCollection($name), |
482
|
|
|
$this->cache->getCollection($name) |
483
|
|
|
); |
484
|
|
|
} |
485
|
|
|
|
486
|
|
|
return $this->collections[$name]; |
487
|
|
|
} |
488
|
|
|
|
489
|
|
|
/** |
490
|
|
|
* Commits all deferred updates to real cache. |
491
|
|
|
* that had already been written to will be deleted. |
492
|
|
|
* |
493
|
|
|
* @return bool |
494
|
|
|
*/ |
495
|
|
|
public function commit() |
496
|
|
|
{ |
497
|
|
|
$this->clear(); |
498
|
|
|
|
499
|
|
|
return $this->defer->commit(); |
500
|
|
|
} |
501
|
|
|
|
502
|
|
|
/** |
503
|
|
|
* Roll back all scheduled changes. |
504
|
|
|
* |
505
|
|
|
* @return bool |
506
|
|
|
*/ |
507
|
|
|
public function rollback() |
508
|
|
|
{ |
509
|
|
|
$this->clear(); |
510
|
|
|
$this->defer->clear(); |
511
|
|
|
|
512
|
|
|
return true; |
513
|
|
|
} |
514
|
|
|
|
515
|
|
|
/** |
516
|
|
|
* Clears all transaction-related data stored in memory. |
517
|
|
|
*/ |
518
|
|
|
protected function clear() |
519
|
|
|
{ |
520
|
|
|
$this->tokens = array(); |
521
|
|
|
$this->suspend = false; |
522
|
|
|
} |
523
|
|
|
} |
524
|
|
|
|
Let?s assume that you have a directory layout like this:
and let?s assume the following content of
Bar.php
:If both files
OtherDir/Foo.php
andSomeDir/Foo.php
are loaded in the same runtime, you will see a PHP error such as the following:PHP Fatal error: Cannot use SomeDir\Foo as Foo because the name is already in use in OtherDir/Foo.php
However, as
OtherDir/Foo.php
does not necessarily have to be loaded and the error is only triggered if it is loaded beforeOtherDir/Bar.php
, this problem might go unnoticed for a while. In order to prevent this error from surfacing, you must import the namespace with a different alias: