/*
* 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.facebook.presto.operator;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.SettableFuture;
import javax.annotation.concurrent.GuardedBy;
import javax.annotation.concurrent.ThreadSafe;
import static com.google.common.base.Preconditions.checkState;
@ThreadSafe
public class ReferenceCount
{
private final SettableFuture<Void> freeFuture = SettableFuture.create();
@GuardedBy("this")
private int count = 1;
public ListenableFuture<Void> getFreeFuture()
{
return freeFuture;
}
public synchronized void retain()
{
checkState(!freeFuture.isDone(), "Reference has already been freed");
count++;
}
public synchronized void release()
{
checkState(!freeFuture.isDone(), "Reference has already been freed");
count--;
if (count == 0) {
freeFuture.set(null);
}
}
}