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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
*
* 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.
*
*/
package org.apache.cassandra.utils.concurrent;
import java.util.*;
import javax.annotation.Nullable;
import com.google.common.base.Function;
import com.google.common.collect.Iterables;
import com.google.common.collect.Iterators;
import static org.apache.cassandra.utils.Throwables.maybeFail;
import static org.apache.cassandra.utils.Throwables.merge;
/**
* A collection of managed Ref references to RefCounted objects, and the objects they are referencing.
* Care MUST be taken when using this collection, as if a permanent reference to it leaks we will not
* be alerted to a lack of reference release.
*
* All of the java.util.Collection operations that modify the collection are unsupported.
*/
public final class Refs> extends AbstractCollection implements AutoCloseable
{
private final Map> references;
public Refs()
{
this.references = new HashMap<>();
}
public Refs(Map> references)
{
this.references = new HashMap<>(references);
}
/**
* Release ALL of the references held by this Refs collection
*/
public void release()
{
try
{
release(references.values());
}
finally
{
references.clear();
}
}
/**
* See {@link Refs#release()}
*/
public void close()
{
release();
}
/**
* @param referenced the object we have a Ref to
* @return the Ref to said object
*/
public Ref get(T referenced)
{
return references.get(referenced);
}
/**
* @param referenced the object we have a Ref to
*/
public void release(T referenced)
{
Ref ref = references.remove(referenced);
if (ref == null)
throw new IllegalStateException("This Refs collection does not hold a reference to " + referenced);
ref.release();
}
/**
* Release the retained Ref to the provided object, if held, return false otherwise
* @param referenced the object we retain a Ref to
* @return return true if we held a reference to the object, and false otherwise
*/
public boolean releaseIfHolds(T referenced)
{
Ref ref = references.remove(referenced);
if (ref != null)
ref.release();
return ref != null;
}
public void relaseAllExcept(Collection keep)
{
Collection release = new ArrayList<>(references.keySet());
release.retainAll(keep);
release(release);
}
/**
* Release a retained Ref to all of the provided objects; if any is not held, an exception will be thrown
* @param release
*/
public void release(Collection release)
{
List> refs = new ArrayList<>();
List notPresent = null;
for (T obj : release)
{
Ref ref = references.remove(obj);
if (ref == null)
{
if (notPresent == null)
notPresent = new ArrayList<>();
notPresent.add(obj);
}
else
{
refs.add(ref);
}
}
IllegalStateException notPresentFail = null;
if (notPresent != null)
{
notPresentFail = new IllegalStateException("Could not release references to " + notPresent
+ " as references to these objects were not held");
notPresentFail.fillInStackTrace();
}
try
{
release(refs);
}
catch (Throwable t)
{
if (notPresentFail != null)
t.addSuppressed(notPresentFail);
}
if (notPresentFail != null)
throw notPresentFail;
}
/**
* Attempt to take a reference to the provided object; if it has already been released, null will be returned
* @param t object to acquire a reference to
* @return true iff success
*/
public boolean tryRef(T t)
{
Ref ref = t.tryRef();
if (ref == null)
return false;
ref = references.put(t, ref);
if (ref != null)
ref.release(); // release dup
return true;
}
public Iterator iterator()
{
return Iterators.unmodifiableIterator(references.keySet().iterator());
}
public int size()
{
return references.size();
}
/**
* Merge two sets of references, ensuring only one reference is retained between the two sets
*/
public Refs addAll(Refs add)
{
List> overlap = new ArrayList<>();
for (Map.Entry> e : add.references.entrySet())
{
if (this.references.containsKey(e.getKey()))
overlap.add(e.getValue());
else
this.references.put(e.getKey(), e.getValue());
}
add.references.clear();
release(overlap);
return this;
}
/**
* Acquire a reference to all of the provided objects, or none
*/
public static > Refs tryRef(Iterable reference)
{
HashMap> refs = new HashMap<>();
for (T rc : reference)
{
Ref ref = rc.tryRef();
if (ref == null)
{
release(refs.values());
return null;
}
refs.put(rc, ref);
}
return new Refs(refs);
}
public static > Refs ref(Iterable reference)
{
Refs refs = tryRef(reference);
if (refs != null)
return refs;
throw new IllegalStateException();
}
public static void release(Iterable> refs)
{
maybeFail(release(refs, null));
}
public static Throwable release(Iterable> refs, Throwable accumulate)
{
for (Ref ref : refs)
{
try
{
ref.release();
}
catch (Throwable t)
{
accumulate = merge(accumulate, t);
}
}
return accumulate;
}
public static > Iterable> selfRefs(Iterable refs)
{
return Iterables.transform(refs, new Function>()
{
@Nullable
public Ref apply(T t)
{
return t.selfRef();
}
});
}
}