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LimitingTopicBacklogReader.java
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LimitingTopicBacklogReader.java
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/*
* Copyright 2020 Google LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.cloud.pubsublite.beam;
import static com.google.cloud.pubsublite.internal.ExtractStatus.toCanonical;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.api.gax.rpc.ApiException;
import com.google.cloud.pubsublite.Offset;
import com.google.cloud.pubsublite.proto.ComputeMessageStatsResponse;
import com.google.common.base.Ticker;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.errorprone.annotations.concurrent.GuardedBy;
import java.util.concurrent.TimeUnit;
import javax.annotation.Nullable;
final class LimitingTopicBacklogReader implements TopicBacklogReader {
private final TopicBacklogReader underlying;
private final LoadingCache<String, ComputeMessageStatsResponse> backlogCache;
@GuardedBy("this")
@Nullable
private Offset currentRequestOffset = null;
@SuppressWarnings("method.invocation.invalid")
LimitingTopicBacklogReader(TopicBacklogReader underlying, Ticker ticker) {
this.underlying = underlying;
backlogCache =
CacheBuilder.newBuilder()
.ticker(ticker)
.maximumSize(1)
.expireAfterWrite(1, TimeUnit.MINUTES)
.refreshAfterWrite(10, TimeUnit.SECONDS)
.build(
new CacheLoader<String, ComputeMessageStatsResponse>() {
@Override
public ComputeMessageStatsResponse load(String val) {
return loadFromUnderlying();
}
});
}
@SuppressWarnings("argument.type.incompatible")
private synchronized ComputeMessageStatsResponse loadFromUnderlying() {
return underlying.computeMessageStats(checkNotNull(currentRequestOffset));
}
@Override
public synchronized ComputeMessageStatsResponse computeMessageStats(Offset offset)
throws ApiException {
currentRequestOffset = offset;
try {
// There is only a single entry in the cache.
return backlogCache.get("cache");
} catch (Throwable t) {
throw toCanonical(t).underlying;
}
}
@Override
public void close() {
underlying.close();
}
}