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rxjava3-flowable developed by David Karnok

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/**
 * 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.flowable.internal.operators;

import java.util.concurrent.Callable;

import org.reactivestreams.Subscriber;

import io.reactivex.common.exceptions.Exceptions;
import io.reactivex.common.internal.functions.ObjectHelper;
import io.reactivex.flowable.Flowable;
import io.reactivex.flowable.internal.subscriptions.DeferredScalarSubscription;

public final class FlowableFromCallable extends Flowable implements Callable {
    final Callable callable;
    public FlowableFromCallable(Callable callable) {
        this.callable = callable;
    }
    @Override
    public void subscribeActual(Subscriber s) {
        DeferredScalarSubscription deferred = new DeferredScalarSubscription(s);
        s.onSubscribe(deferred);

        T t;
        try {
            t = ObjectHelper.requireNonNull(callable.call(), "The callable returned a null value");
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);
            s.onError(ex);
            return;
        }

        deferred.complete(t);
    }

    @Override
    public T call() throws Exception {
        return ObjectHelper.requireNonNull(callable.call(), "The callable returned a null value");
    }
}