Copyright 2015 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 2015 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.hystrix.metric;

import com.netflix.hystrix.HystrixCommandKey;
import rx.Observable;
import rx.subjects.PublishSubject;
import rx.subjects.SerializedSubject;
import rx.subjects.Subject;

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

Per-Command stream of HystrixCommandExecutionStarteds. This gets written to by HystrixThreadEventStreams. Events are emitted synchronously in the same thread that performs the command execution. /**
 * Per-Command stream of {@link HystrixCommandExecutionStarted}s.  This gets written to by {@link HystrixThreadEventStream}s.
 * Events are emitted synchronously in the same thread that performs the command execution.
 */
public class HystrixCommandStartStream implements HystrixEventStream<HystrixCommandExecutionStarted> {
    private final HystrixCommandKey commandKey;

    private final Subject<HystrixCommandExecutionStarted, HystrixCommandExecutionStarted> writeOnlySubject;
    private final Observable<HystrixCommandExecutionStarted> readOnlyStream;

    private static final ConcurrentMap<String, HystrixCommandStartStream> streams = new ConcurrentHashMap<String, HystrixCommandStartStream>();

    public static HystrixCommandStartStream getInstance(HystrixCommandKey commandKey) {
        HystrixCommandStartStream initialStream = streams.get(commandKey.name());
        if (initialStream != null) {
            return initialStream;
        } else {
            synchronized (HystrixCommandStartStream.class) {
                HystrixCommandStartStream existingStream = streams.get(commandKey.name());
                if (existingStream == null) {
                    HystrixCommandStartStream newStream = new HystrixCommandStartStream(commandKey);
                    streams.putIfAbsent(commandKey.name(), newStream);
                    return newStream;
                } else {
                    return existingStream;
                }
            }
        }
    }

    HystrixCommandStartStream(final HystrixCommandKey commandKey) {
        this.commandKey = commandKey;

        this.writeOnlySubject = new SerializedSubject<HystrixCommandExecutionStarted, HystrixCommandExecutionStarted>(PublishSubject.<HystrixCommandExecutionStarted>create());
        this.readOnlyStream = writeOnlySubject.share();
    }

    public static void reset() {
        streams.clear();
    }

    public void write(HystrixCommandExecutionStarted event) {
        writeOnlySubject.onNext(event);
    }

    @Override
    public Observable<HystrixCommandExecutionStarted> observe() {
        return readOnlyStream;
    }

    @Override
    public String toString() {
        return "HystrixCommandStartStream(" + commandKey.name() + ")";
    }
}