Copyright (c) 2016-present, RxJava Contributors.
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 (c) 2016-present, RxJava Contributors.
 *
 * 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 io.reactivex.internal.observers;

import java.util.concurrent.CountDownLatch;

import io.reactivex.Observer;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.util.*;

public abstract class BlockingBaseObserver<T> extends CountDownLatch
implements Observer<T>, Disposable {

    T value;
    Throwable error;

    Disposable upstream;

    volatile boolean cancelled;

    public BlockingBaseObserver() {
        super(1);
    }

    @Override
    public final void onSubscribe(Disposable d) {
        this.upstream = d;
        if (cancelled) {
            d.dispose();
        }
    }

    @Override
    public final void onComplete() {
        countDown();
    }

    @Override
    public final void dispose() {
        cancelled = true;
        Disposable d = this.upstream;
        if (d != null) {
            d.dispose();
        }
    }

    @Override
    public final boolean isDisposed() {
        return cancelled;
    }

    
Block until the first value arrives and return it, otherwise
return null for an empty source and rethrow any exception.
Returns:
the first value or null if the source is empty/**
     * Block until the first value arrives and return it, otherwise
     * return null for an empty source and rethrow any exception.
     * @return the first value or null if the source is empty
     */
    public final T blockingGet() {
        if (getCount() != 0) {
            try {
                BlockingHelper.verifyNonBlocking();
                await();
            } catch (InterruptedException ex) {
                dispose();
                throw ExceptionHelper.wrapOrThrow(ex);
            }
        }

        Throwable e = error;
        if (e != null) {
            throw ExceptionHelper.wrapOrThrow(e);
        }
        return value;
    }
}