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/*
* ====================================================================
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*
*/
package ch.boye.httpclientandroidlib.impl.client.cache;
import ch.boye.httpclientandroidlib.annotation.ThreadSafe;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
/**
* Implements a bounded failure cache. The oldest entries are discarded when
* the maximum size is exceeded.
*
* @since 4.3
*/
@ThreadSafe
public class DefaultFailureCache implements FailureCache {
static final int DEFAULT_MAX_SIZE = 1000;
static final int MAX_UPDATE_TRIES = 10;
private final int maxSize;
private final ConcurrentMap<String, FailureCacheValue> storage;
/**
* Create a new failure cache with the maximum size of
* {@link #DEFAULT_MAX_SIZE}.
*/
public DefaultFailureCache() {
this(DEFAULT_MAX_SIZE);
}
/**
* Creates a new failure cache with the specified maximum size.
* @param maxSize the maximum number of entries the cache should store
*/
public DefaultFailureCache(final int maxSize) {
this.maxSize = maxSize;
this.storage = new ConcurrentHashMap<String, FailureCacheValue>();
}
public int getErrorCount(final String identifier) {
if (identifier == null) {
throw new IllegalArgumentException("identifier may not be null");
}
final FailureCacheValue storedErrorCode = storage.get(identifier);
return storedErrorCode != null ? storedErrorCode.getErrorCount() : 0;
}
public void resetErrorCount(final String identifier) {
if (identifier == null) {
throw new IllegalArgumentException("identifier may not be null");
}
storage.remove(identifier);
}
public void increaseErrorCount(final String identifier) {
if (identifier == null) {
throw new IllegalArgumentException("identifier may not be null");
}
updateValue(identifier);
removeOldestEntryIfMapSizeExceeded();
}
private void updateValue(final String identifier) {
/**
* Due to concurrency it is possible that someone else is modifying an
* entry before we could write back our updated value. So we keep
* trying until it is our turn.
*
* In case there is a lot of contention on that identifier, a thread
* might starve. Thus it gives up after a certain number of failed
* update tries.
*/
for (int i = 0; i < MAX_UPDATE_TRIES; i++) {
final FailureCacheValue oldValue = storage.get(identifier);
if (oldValue == null) {
final FailureCacheValue newValue = new FailureCacheValue(identifier, 1);
if (storage.putIfAbsent(identifier, newValue) == null) {
return;
}
}
else {
final int errorCount = oldValue.getErrorCount();
if (errorCount == Integer.MAX_VALUE) {
return;
}
final FailureCacheValue newValue = new FailureCacheValue(identifier, errorCount + 1);
if (storage.replace(identifier, oldValue, newValue)) {
return;
}
}
}
}
private void removeOldestEntryIfMapSizeExceeded() {
if (storage.size() > maxSize) {
final FailureCacheValue valueWithOldestTimestamp = findValueWithOldestTimestamp();
if (valueWithOldestTimestamp != null) {
storage.remove(valueWithOldestTimestamp.getKey(), valueWithOldestTimestamp);
}
}
}
private FailureCacheValue findValueWithOldestTimestamp() {
long oldestTimestamp = Long.MAX_VALUE;
FailureCacheValue oldestValue = null;
for (final Map.Entry<String, FailureCacheValue> storageEntry : storage.entrySet()) {
final FailureCacheValue value = storageEntry.getValue();
final long creationTimeInNanos = value.getCreationTimeInNanos();
if (creationTimeInNanos < oldestTimestamp) {
oldestTimestamp = creationTimeInNanos;
oldestValue = storageEntry.getValue();
}
}
return oldestValue;
}
}
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