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From: neykov <git@git.apache.org>
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References: <git-pr-520-brooklyn-server@git.apache.org>
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Subject: [GitHub] brooklyn-server pull request #520: Limit parallelism of start/stop steps on ...
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Message-Id: <20170125143807.D13DCDFA69@git1-us-west.apache.org>
Date: Wed, 25 Jan 2017 14:38:07 +0000 (UTC)
archived-at: Wed, 25 Jan 2017 14:38:09 -0000

Github user neykov commented on a diff in the pull request:

    https://github.com/apache/brooklyn-server/pull/520#discussion_r97790853
  
    --- Diff: core/src/main/java/org/apache/brooklyn/core/sensor/ReleaseableLatch.java ---
    @@ -0,0 +1,95 @@
    +/*
    + * 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.brooklyn.core.sensor;
    +
    +import java.util.concurrent.Semaphore;
    +
    +import org.apache.brooklyn.api.entity.Entity;
    +import org.apache.brooklyn.util.core.task.DeferredSupplier;
    +import org.apache.brooklyn.util.core.task.ImmediateSupplier;
    +import org.apache.brooklyn.util.exceptions.Exceptions;
    +import org.apache.brooklyn.util.guava.Maybe;
    +
    +// DeferredSupplier used as a marker interface to prevent coercion. When resolved it must evaluate to {@code Boolean.TRUE}.
    +public interface ReleaseableLatch extends DeferredSupplier<Boolean>, ImmediateSupplier<Boolean> {
    +    /**
    +     * Increment usage count for the {@code caller} entity
    +     */
    +    void acquire(Entity caller);
    +
    +    /**
    +     * Decrement usage count for the {@code caller} entity
    +     */
    +    void release(Entity caller);
    +
    +    static abstract class AbstractReleaseableLatch implements ReleaseableLatch {
    +        // Instances coerce to TRUE as they are non-null.
    +        @Override public Boolean get() {return Boolean.TRUE;}
    +        @Override public Maybe<Boolean> getImmediately() {return Maybe.of(Boolean.TRUE);}
    +    }
    +
    +    ReleaseableLatch NOP = new Factory.NopLatch();
    +
    +    static class Factory {
    +        private static class NopLatch extends AbstractReleaseableLatch {
    +            @Override public void acquire(Entity caller) {}
    +            @Override public void release(Entity caller) {}
    +        }
    +
    +        private static class MaxConcurrencyLatch extends AbstractReleaseableLatch {
    --- End diff --
    
    Two reasons:
      * Personal preference to inline small classes like this.
      * More importantly to hide the implementation and make it private.


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