Copyright 2018 Netflix, 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.
/**
 * Copyright 2018 Netflix, 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.netflix.concurrency.limits.executors;

import com.netflix.concurrency.limits.Limiter;
import com.netflix.concurrency.limits.Limiter.Listener;
import com.netflix.concurrency.limits.limiter.BlockingLimiter;

import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.RejectedExecutionException;

Executor which uses a Limiter to determine the size of the thread pool. Any Runnable executed once the limit has been reached will block the calling thread until the limit is released. Operations submitted to this executor should be homogeneous and have similar long term latency characteristics. RTT samples will only be taken from successful operations. The Runnable should throw a RejectedExecutionException if a request timed out or some external limit was reached. All other exceptions will be ignored. /**
 * {@link Executor} which uses a {@link Limiter} to determine the size of the thread pool.
 * Any {@link Runnable} executed once the limit has been reached will block the calling
 * thread until the limit is released.
 * 
 * Operations submitted to this executor should be homogeneous and have similar
 * long term latency characteristics.  RTT samples will only be taken from successful 
 * operations.  The {@link Runnable} should throw a {@link RejectedExecutionException} if 
 * a request timed out or some external limit was reached.  All other exceptions will be
 * ignored.
 */
public final class BlockingAdaptiveExecutor implements Executor {
    private final Limiter<Void> limiter;
    private final Executor executor;

    public BlockingAdaptiveExecutor(Limiter<Void> limiter) {
        this(limiter, Executors.newCachedThreadPool());
    }

    public BlockingAdaptiveExecutor(Limiter<Void> limiter, Executor executor) {
        this.limiter = BlockingLimiter.wrap(limiter);
        this.executor = executor;
    }

    @Override
    public void execute(Runnable command) {
        Listener token = limiter.acquire(null).orElseThrow(() -> new RejectedExecutionException());
        executor.execute(() -> {
            try {
                command.run();
                token.onSuccess();
            } catch (RejectedExecutionException e) {
                token.onDropped();
            } catch (Exception e) {
                token.onIgnore();
            }
        });
    }
}