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.MetricRegistry;
import com.netflix.concurrency.limits.internal.EmptyMetricRegistry;
import com.netflix.concurrency.limits.limit.AIMDLimit;
import com.netflix.concurrency.limits.limiter.BlockingLimiter;
import com.netflix.concurrency.limits.limiter.SimpleLimiter;

import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;

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 UncheckedTimeoutException 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 UncheckedTimeoutException} if
 * a request timed out or some external limit was reached.  All other exceptions will be
 * ignored.
 */
public final class BlockingAdaptiveExecutor implements Executor {
    public static class Builder {
        private static AtomicInteger idCounter = new AtomicInteger();

        private MetricRegistry metricRegistry = EmptyMetricRegistry.INSTANCE;
        private Executor executor;
        private Limiter<Void> limiter;
        private String name;

        public Builder metricRegistry(MetricRegistry metricRegistry) {
            this.metricRegistry = metricRegistry;
            return this;
        }

        public Builder executor(Executor executor) {
            this.executor = executor;
            return this;
        }

        public Builder limiter(Limiter<Void> limiter) {
            this.limiter = limiter;
            return this;
        }

        public Builder name(String name) {
            this.name = name;
            return this;
        }

        public BlockingAdaptiveExecutor build() {
            if (name == null) {
                name = "unnamed-" + idCounter.incrementAndGet();
            }

            if (executor == null) {
                executor = Executors.newCachedThreadPool(new ThreadFactory() {
                    @Override
                    public Thread newThread(Runnable r) {
                        Thread thread = new Thread(r);
                        thread.setDaemon(true);
                        return thread;
                    }
                });
            }

            if (limiter == null) {
                limiter = SimpleLimiter.newBuilder()
                        .metricRegistry(metricRegistry)
                        .limit(AIMDLimit.newBuilder().build())
                        .build();
            }

            return new BlockingAdaptiveExecutor(this);
        }
    }

    public static Builder newBuilder() {
        return new Builder();
    }

    private final Limiter<Void> limiter;
    private final Executor executor;

    private BlockingAdaptiveExecutor(Builder builder) {
        this.limiter = builder.limiter;
        this.executor = builder.executor;
    }

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

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

    @Override
    public void execute(Runnable command) {
        Listener listener = limiter.acquire(null).orElseThrow(() -> new RejectedExecutionException());
        try {
            executor.execute(() -> {
                try {
                    command.run();
                    listener.onSuccess();
                } catch (UncheckedTimeoutException e) {
                    listener.onDropped();
                } catch (RejectedExecutionException e) {
                    // TODO: Remove support for RejectedExecutionException here.
                    listener.onDropped();
                } catch (Exception e) {
                    // We have no idea what caused the exception.  It could be an NPE thrown immediately on the client
                    // or some remote call failure.  The only sane thing to do here is just ignore this request
                    listener.onIgnore();
                }
            });
        } catch (Exception e) {
            listener.onIgnore();
            throw e;
        }
    }
}