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libphutil/src/cache/PhutilKeyValueCacheStack.php
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PhutilKeyValueCacheStack.php
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<?php
/**
* Stacks multiple caches on top of each other, with readthrough semantics:
*
* - For reads, we try each cache in order until we find all the keys.
* - For writes, we set the keys in each cache.
*
* @task config Configuring the Stack
* @group cache
*/
final class PhutilKeyValueCacheStack extends PhutilKeyValueCache {
/**
* Forward list of caches in the stack (from the nearest cache to the farthest
* cache).
*/
private $cachesForward;
/**
* Backward list of caches in the stack (from the farthest cache to the
* nearest cache).
*/
private $cachesBackward;
/**
* TTL to use for any writes which are side effects of the next read
* operation.
*/
private $nextTTL;
/* -( Configuring the Stack )---------------------------------------------- */
/**
* Set the caches which comprise this stack.
*
* @param list<PhutilKeyValueCache> Ordered list of key-value caches.
* @return this
* @task config
*/
public function setCaches(array $caches) {
assert_instances_of($caches, 'PhutilKeyValueCache');
$this->cachesForward = $caches;
$this->cachesBackward = array_reverse($caches);
return $this;
}
/**
* Set the readthrough TTL for the next cache operation. The TTL applies to
* any keys set by the next call to @{method:getKey} or @{method:getKeys},
* and is reset after the call finishes.
*
* // If this causes any caches to fill, they'll fill with a 15-second TTL.
* $stack->setNextTTL(15)->getKey('porcupine');
*
* // TTL does not persist; this will use no TTL.
* $stack->getKey('hedgehog');
*
* @param int TTL in seconds.
* @return this
*
* @task config
*/
public function setNextTTL($ttl) {
$this->ttl = $ttl;
return $this;
}
/* -( Key-Value Cache Implementation )------------------------------------- */
public function getKeys(array $keys) {
$remaining = array_combine($keys, $keys);
$results = array();
$missed = array();
try {
foreach ($this->cachesForward as $cache) {
$result = $cache->getKeys($remaining);
$remaining = array_diff_key($remaining, $result);
$results += $result;
if (!$remaining) {
while ($cache = array_pop($missed)) {
// TODO: This sets too many results in the closer caches, although
// it probably isn't a big deal in most cases; normally we're just
// filling the request cache.
$cache->setKeys($result, $this->nextTTL);
}
break;
}
$missed[] = $cache;
}
$this->nextTTL = null;
} catch (Exception $ex) {
$this->nextTTL = null;
throw $ex;
}
return $results;
}
public function setKeys(array $keys, $ttl = null) {
foreach ($this->cachesBackward as $cache) {
$cache->setKeys($keys, $ttl);
}
}
public function deleteKeys(array $keys) {
foreach ($this->cachesBackward as $cache) {
$cache->deleteKeys($keys);
}
}
public function destroyCache() {
foreach ($this->cachesBackward as $cache) {
$cache->destroyCache();
}
}
}
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