/**
* Retrieves an array of values for an array of keys.
*
* Using this function comes with potential performance implications.
* Not all cache stores will support get_many/set_many operations and in order to replicate this functionality will call
* the equivalent singular method for each item provided.
* This should not deter you from using this function as there is a performance benefit in situations where the cache store
* does support it, but you should be aware of this fact.
*
* @param array $keys The keys of the data being requested.
* Each key can be any structure although using a scalar string or int is recommended in the interests of performance.
* In advanced cases an array may be useful such as in situations requiring the multi-key functionality.
* @param int $strictness One of IGNORE_MISSING or MUST_EXIST.
* @return array An array of key value pairs for the items that could be retrieved from the cache.
* If MUST_EXIST was used and not all keys existed within the cache then an exception will be thrown.
* Otherwise any key that did not exist will have a data value of false within the results.
* @throws coding_exception
*/
public function get_many(array $keys, $strictness = IGNORE_MISSING)
{
$keysparsed = array();
$parsedkeys = array();
$resultpersist = array();
$resultstore = array();
$keystofind = array();
// First up check the persist cache for each key.
$isusingpersist = $this->is_using_persist_cache();
foreach ($keys as $key) {
$pkey = $this->parse_key($key);
$keysparsed[$key] = $pkey;
$parsedkeys[$pkey] = $key;
$keystofind[$pkey] = $key;
if ($isusingpersist) {
$value = $this->get_from_persist_cache($pkey);
if ($value !== false) {
$resultpersist[$pkey] = $value;
unset($keystofind[$pkey]);
}
}
}
// Next assuming we didn't find all of the keys in the persist cache try loading them from the store.
if (count($keystofind)) {
$resultstore = $this->store->get_many(array_keys($keystofind));
// Process each item in the result to "unwrap" it.
foreach ($resultstore as $key => $value) {
if ($value instanceof cache_ttl_wrapper) {
if ($value->has_expired()) {
$value = false;
} else {
$value = $value->data;
}
}
if ($value instanceof cache_cached_object) {
$value = $value->restore_object();
}
if ($value !== false && $this->is_using_persist_cache()) {
$this->set_in_persist_cache($key, $value);
}
$resultstore[$key] = $value;
}
}
// Merge the result from the persis cache with the results from the store load.
$result = $resultpersist + $resultstore;
unset($resultpersist);
unset($resultstore);
// Next we need to find any missing values and load them from the loader/datasource next in the chain.
$usingloader = $this->loader !== false;
$usingsource = !$usingloader && $this->datasource !== false;
if ($usingloader || $usingsource) {
$missingkeys = array();
foreach ($result as $key => $value) {
if ($value === false) {
$missingkeys[] = $parsedkeys[$key];
}
}
if (!empty($missingkeys)) {
if ($usingloader) {
$resultmissing = $this->loader->get_many($missingkeys);
} else {
$resultmissing = $this->datasource->load_many_for_cache($missingkeys);
}
foreach ($resultmissing as $key => $value) {
$result[$keysparsed[$key]] = $value;
if ($value !== false) {
$this->set($key, $value);
}
}
unset($resultmissing);
}
unset($missingkeys);
}
// Create an array with the original keys and the found values. This will be what we return.
$fullresult = array();
foreach ($result as $key => $value) {
$fullresult[$parsedkeys[$key]] = $value;
}
unset($result);
// Final step is to check strictness.
if ($strictness === MUST_EXIST) {
foreach ($keys as $key) {
if (!array_key_exists($key, $fullresult)) {
throw new coding_exception('Not all the requested keys existed within the cache stores.');
}
}
}
if ($this->perfdebug) {
$hits = 0;
$misses = 0;
foreach ($fullresult as $value) {
if ($value === false) {
$misses++;
} else {
$hits++;
}
}
cache_helper::record_cache_hit($this->storetype, $this->definition->get_id(), $hits);
cache_helper::record_cache_miss($this->storetype, $this->definition->get_id(), $misses);
}
// Return the result. Phew!
return $fullresult;
}
