/**
* Revert a set of keys to the empty state. Will loop on this several times just in case the
* memcache write fails - we don't want to leave the cache in a nasty state.
*/
public void empty(Iterable<Key> keys) {
Map<Key, Object> updates = new HashMap<>();
for (Key key : keys) if (cacheControl.getExpirySeconds(key) != null) updates.put(key, null);
this.memcacheWithRetry.putAll(updates);
}
/**
* Gets the Buckets for the specified keys. A bucket is built around an IdentifiableValue so you
* can putAll() them without the risk of overwriting other threads' changes. Buckets also hide the
* underlying details of storage for negative, empty, and uncacheable results.
*
* <p>Note that worst case (a cold cache), obtaining each bucket might require three memcache
* requests: a getIdentifiable() which returns null, a put(EMPTY), and another getIdentifiable().
* Since there is no batch getIdentifiable(), this is *per key*.
*
* <p>When keys are uncacheable (per CacheControl) or the memcache is down, you will still get an
* empty bucket back. The bucket will have null IdentifiableValue so we can identify it as
* uncacheable.
*
* @return the buckets requested. Buckets will never be null. You will always get a bucket for
* every key.
*/
public Map<Key, Bucket> getAll(Iterable<Key> keys) {
Map<Key, Bucket> result = new HashMap<>();
// Sort out the ones that are uncacheable
Set<Key> potentials = new HashSet<>();
for (Key key : keys) {
if (cacheControl.getExpirySeconds(key) == null) result.put(key, new Bucket(key));
else potentials.add(key);
}
Map<Key, IdentifiableValue> ivs;
try {
ivs = this.memcache.getIdentifiables(potentials);
} catch (Exception ex) {
// This should really only be a problem if the serialization format for an Entity changes,
// or someone put a badly-serializing object in the cache underneath us.
log.log(Level.WARNING, "Error obtaining cache for " + potentials, ex);
ivs = new HashMap<>();
}
// Figure out cold cache values
Map<Key, Object> cold = new HashMap<>();
for (Key key : potentials) if (ivs.get(key) == null) cold.put(key, null);
if (!cold.isEmpty()) {
// The cache is cold for those values, so start them out with nulls that we can make an IV for
this.memcache.putAll(cold);
try {
Map<Key, IdentifiableValue> ivs2 = this.memcache.getIdentifiables(cold.keySet());
ivs.putAll(ivs2);
} catch (Exception ex) {
// At this point we should just not worry about it, the ivs will be null and uncacheable
}
}
// Now create the remaining buckets
for (Key key : keys) {
// iv might still be null, which is ok - that means uncacheable
IdentifiableValue iv = ivs.get(key);
Bucket buck = (iv == null) ? new Bucket(key) : new Bucket(key, iv);
result.put(key, buck);
if (buck.isEmpty()) this.stats.recordMiss(buck.getKey());
else this.stats.recordHit(buck.getKey());
}
return result;
}
/**
* Put buckets in the cache, checking for cacheability and collisions.
*
* @return the set of keys that were *successfully* put without collision
*/
private Set<Key> cachePutIfUntouched(Iterable<Bucket> buckets) {
Map<Key, CasValues> payload = new HashMap<>();
for (Bucket buck : buckets) {
if (!buck.isCacheable()) continue;
Integer expirySeconds = cacheControl.getExpirySeconds(buck.getKey());
if (expirySeconds == null) continue;
Expiration expiration = expirySeconds == 0 ? null : Expiration.byDeltaSeconds(expirySeconds);
payload.put(buck.getKey(), new CasValues(buck.iv, buck.getNextToStore(), expiration));
}
return this.memcache.putIfUntouched(payload);
}
