com.facebook.buck.util.concurrent.AssertScopeExclusiveAccess.java Source code

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Here is the source code for com.facebook.buck.util.concurrent.AssertScopeExclusiveAccess.java

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/*
 * Copyright 2016-present Facebook, Inc.
 *
 * 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.buck.util.concurrent;

import com.facebook.buck.log.Logger;
import com.google.common.base.Optional;

import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Makes it simple to assert that access to a piece of code should be done from one thread
 * at a time in a non-reentrant manner.
 */
public class AssertScopeExclusiveAccess {
    private static final Logger LOG = Logger.get(AssertScopeExclusiveAccess.class);

    private final AtomicBoolean inScope;
    private Optional<Throwable> inScopeStack;

    public AssertScopeExclusiveAccess() {
        inScope = new AtomicBoolean();
        inScopeStack = Optional.absent();
    }

    public Scope scope() {
        final boolean firstOneInScope = inScope.compareAndSet(false, true);
        if (firstOneInScope && LOG.isVerboseEnabled()) {
            inScopeStack = Optional.of(new Throwable());
        }

        if (!firstOneInScope) {
            LOG.verbose(inScopeStack.get(), "Indicating previous access to single threaded scope.");

            throw new IllegalStateException("More than one thread attempting access to single-threaded scope.");
        }

        return new Scope() {
            @Override
            public void close() {
                if (firstOneInScope) {
                    inScope.set(false);
                }
            }
        };
    }

    public interface Scope extends AutoCloseable {
        @Override
        void close();
    }
}