import com.google.appengine.api.memcache.MemcacheService.SetPolicy; //导入依赖的package包/类
/**
 * Retrieve the value of this sharded counter.
 *
 * @return Summed total of all shards' counts
 */
public long getCount() {
  Long value = (Long) mc.get(kind);
  if (value != null) {
    return value;
  }

  long sum = 0;
  Query query = new Query(kind);
  for (Entity shard : ds.prepare(query).asIterable()) {
    sum += (Long) shard.getProperty(CounterShard.COUNT);
  }
  mc.put(kind, sum, Expiration.byDeltaSeconds(60),
      SetPolicy.ADD_ONLY_IF_NOT_PRESENT);

  return sum;
}
 

import com.google.appengine.api.memcache.MemcacheService.SetPolicy; //导入依赖的package包/类
/**
 * Retrieve the value of this sharded counter.
 *
 * @return Summed total of all shards' counts
 */
public final long getCount() {
    Long value = (Long) mc.get(kind);
    if (value != null) {
        return value;
    }

    long sum = 0;
    Query query = new Query(kind);
    for (Entity shard : DS.prepare(query).asIterable()) {
        sum += (Long) shard.getProperty(CounterShard.COUNT);
    }
    mc.put(kind, sum, Expiration.byDeltaSeconds(CACHE_PERIOD),
            SetPolicy.ADD_ONLY_IF_NOT_PRESENT);

    return sum;
}
 

import com.google.appengine.api.memcache.MemcacheService.SetPolicy; //导入依赖的package包/类
/**
 * @return true if a new entry was created, false if not because of the
 *         policy.
 */
public boolean put(@Nullable K key, @Nullable V value, @Nullable Expiration expires,
    SetPolicy policy) {
  TaggedKey<K> taggedKey = tagKey(key);
  String expiresString = expires == null ? null : "" + expires.getMillisecondsValue();
  log.info("cache put " + taggedKey + " = " + value + ", " + expiresString + ", " + policy);
  return service.put(taggedKey, value, expires, policy);
}
 

import com.google.appengine.api.memcache.MemcacheService.SetPolicy; //导入依赖的package包/类
/**
 * @return the set of keys for which new entries were created (some may not
 *         have been created because of the policy).
 */
public Set<K> putAll(Map<K, V> mappings, @Nullable Expiration expires, SetPolicy policy) {
  Map<TaggedKey<K>, V> rawMappings = Maps.newHashMapWithExpectedSize(mappings.size());
  for (Map.Entry<K, V> entry : mappings.entrySet()) {
    rawMappings.put(tagKey(entry.getKey()), entry.getValue());
  }
  Set<TaggedKey<K>> rawResult = service.putAll(rawMappings, expires, policy);
  Set<K> result = Sets.newHashSetWithExpectedSize(rawResult.size());
  for (TaggedKey<K> key : rawResult) {
    result.add(key.getKey());
  }
  return result;
}
 

import com.google.appengine.api.memcache.MemcacheService.SetPolicy; //导入依赖的package包/类
/**
 * @return true if a new entry was created, false if not because of the policy.
 */
public boolean put(@Nullable K key, @Nullable V value, @Nullable Expiration expires,
    SetPolicy policy) {
  TaggedKey<K> taggedKey = tagKey(key);
  String expiresString = expires == null ? null : "" + expires.getMillisecondsValue();
  log.info("cache put " + taggedKey + " = " + value + ", " + expiresString + ", " + policy);
  return service.put(taggedKey, value, expires, policy);
}
 

import com.google.appengine.api.memcache.MemcacheService.SetPolicy; //导入依赖的package包/类
/**
 * @return the set of keys for which new entries were created (some may not have been created
 *         because of the policy).
 */
public Set<K> putAll(Map<K, V> mappings, @Nullable Expiration expires, SetPolicy policy) {
  Map<TaggedKey<K>, V> rawMappings = Maps.newHashMapWithExpectedSize(mappings.size());
  for (Map.Entry<K, V> entry : mappings.entrySet()) {
    rawMappings.put(tagKey(entry.getKey()), entry.getValue());
  }
  Set<TaggedKey<K>> rawResult = service.putAll(rawMappings, expires, policy);
  Set<K> result = Sets.newHashSetWithExpectedSize(rawResult.size());
  for (TaggedKey<K> key : rawResult) {
    result.add(key.getKey());
  }
  return result;
}
 

import com.google.appengine.api.memcache.MemcacheService.SetPolicy; //导入依赖的package包/类
/**
 * Returns and maybe creates a mapping to a server for the given object id.
 *
 * @return the mapped server, and true if that mapping already existed, false
 *         if it was created by this method.
 *
 *         WARNING: if a mapping could not be established, returns null.
 */
@Nullable
private Pair<Boolean, Integer> serverFor(SlobId objectId) {
  boolean wasMapped;
  int serverId;

  Integer maybeServerId = objectServerMappings.get(objectId);
  if (maybeServerId != null) {
    wasMapped = true;
    serverId = maybeServerId;
    monitoring.incrementCounter("affinity-mapping-found");
  } else {
    int newServerId = random.nextInt(numStoreServers);
    int expiration = AFFINITY_MIN_EXPIRATION_SECONDS
        + random.nextInt(AFFINITY_EXPIRATION_SPREAD_SECONDS);
    log.info("No mapping for " + objectId + ", generated " + newServerId +
      ", expiration " + expiration);
    boolean putSucceeded = objectServerMappings.put(objectId, newServerId,
        Expiration.byDeltaSeconds(expiration),
        SetPolicy.ADD_ONLY_IF_NOT_PRESENT);
    if (putSucceeded) {
      serverId = newServerId;
      wasMapped = false;
      monitoring.incrementCounter("affinity-mapping-generated");
    } else {
      log.warning("Mapping was generated concurrently");
      maybeServerId = objectServerMappings.get(objectId);
      if (maybeServerId != null) {
        serverId = maybeServerId;
        wasMapped = true;
        monitoring.incrementCounter("affinity-mapping-generated-but-overwritten");
      } else {
        log.warning("Concurrently generated mapping promptly disappeared!");
        monitoring.incrementCounter("affinity-mapping-generated-but-lost");
        return null;
      }
    }
  }

 return Pair.of(wasMapped, serverId);
}
 

import com.google.appengine.api.memcache.MemcacheService.SetPolicy; //导入依赖的package包/类
/**
 * Returns and maybe creates a mapping to a server for the given object id.
 * 
 * @return the mapped server, and true if that mapping already existed, false if it was created by
 *         this method.
 * 
 *         WARNING: if a mapping could not be established, returns null.
 */
@Nullable
private Pair<Boolean, Integer> serverFor(ObjectId objectId) {
  boolean wasMapped;
  int serverId;

  Integer maybeServerId = objectServerMappings.get(objectId);
  if (maybeServerId != null) {
    wasMapped = true;
    serverId = maybeServerId;
    monitoring.incrementCounter("affinity-mapping-found");
  } else {
    int newServerId = random.nextInt(numStoreServers);
    int expiration =
        AFFINITY_MIN_EXPIRATION_SECONDS + random.nextInt(AFFINITY_EXPIRATION_SPREAD_SECONDS);
    log.info("No mapping for " + objectId + ", generated " + newServerId + ", expiration "
        + expiration);
    boolean putSucceeded =
        objectServerMappings.put(objectId, newServerId, Expiration.byDeltaSeconds(expiration),
            SetPolicy.ADD_ONLY_IF_NOT_PRESENT);
    if (putSucceeded) {
      serverId = newServerId;
      wasMapped = false;
      monitoring.incrementCounter("affinity-mapping-generated");
    } else {
      log.warning("Mapping was generated concurrently");
      maybeServerId = objectServerMappings.get(objectId);
      if (maybeServerId != null) {
        serverId = maybeServerId;
        wasMapped = true;
        monitoring.incrementCounter("affinity-mapping-generated-but-overwritten");
      } else {
        log.warning("Concurrently generated mapping promptly disappeared!");
        monitoring.incrementCounter("affinity-mapping-generated-but-lost");
        return null;
      }
    }
  }

  return Pair.of(wasMapped, serverId);
}