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/**
* Copyright 2013 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 rx;
import java.util.Date;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import rx.subscriptions.CompositeSubscription;
import rx.subscriptions.MultipleAssignmentSubscription;
import rx.subscriptions.Subscriptions;
import rx.util.functions.Action0;
import rx.util.functions.Action1;
import rx.util.functions.Func2;
/**
* Represents an object that schedules units of work.
* <p>
* The methods left to implement are:
* <ul>
* <li>{@code <T> Subscription schedule(T state, Func2<Scheduler, T, Subscription> action, long delayTime, TimeUnit unit)}</li>
* <li>{@code <T> Subscription schedule(T state, Func2<Scheduler, T, Subscription> action)}</li>
* </ul>
* <p>
* Why is this an abstract class instead of an interface?
* <p>
* <ol>
* <li>Java doesn't support extension methods and there are many overload methods needing default implementations.</li>
* <li>Virtual extension methods aren't available until Java8 which RxJava will not set as a minimum target for a long time.</li>
* <li>If only an interface were used Scheduler implementations would then need to extend from an AbstractScheduler pair that gives all of the functionality unless they intend on copy/pasting the
* functionality.</li>
* <li>Without virtual extension methods even additive changes are breaking and thus severely impede library maintenance.</li>
* </ol>
*/
public abstract class Scheduler {
/**
* Schedules a cancelable action to be executed.
*
* @param state
* State to pass into the action.
* @param action
* Action to schedule.
* @return a subscription to be able to unsubscribe from action.
*/
public abstract <T> Subscription schedule(T state, Func2<? super Scheduler, ? super T, ? extends Subscription> action);
/**
* Schedules a cancelable action to be executed in delayTime.
*
* @param state
* State to pass into the action.
* @param action
* Action to schedule.
* @param delayTime
* Time the action is to be delayed before executing.
* @param unit
* Time unit of the delay time.
* @return a subscription to be able to unsubscribe from action.
*/
public abstract <T> Subscription schedule(T state, Func2<? super Scheduler, ? super T, ? extends Subscription> action, long delayTime, TimeUnit unit);
/**
* Schedules a cancelable action to be executed periodically.
* This default implementation schedules recursively and waits for actions to complete (instead of potentially executing
* long-running actions concurrently). Each scheduler that can do periodic scheduling in a better way should override this.
*
* @param state
* State to pass into the action.
* @param action
* The action to execute periodically.
* @param initialDelay
* Time to wait before executing the action for the first time.
* @param period
* The time interval to wait each time in between executing the action.
* @param unit
* The time unit the interval above is given in.
* @return A subscription to be able to unsubscribe from action.
*/
public <T> Subscription schedulePeriodically(T state, final Func2<? super Scheduler, ? super T, ? extends Subscription> action, long initialDelay, long period, TimeUnit unit) {
final long periodInNanos = unit.toNanos(period);
final AtomicBoolean complete = new AtomicBoolean();
final Func2<Scheduler, T, Subscription> recursiveAction = new Func2<Scheduler, T, Subscription>() {
@Override
public Subscription call(Scheduler scheduler, T state0) {
if (!complete.get()) {
long startedAt = now();
final Subscription sub1 = action.call(scheduler, state0);
long timeTakenByActionInNanos = TimeUnit.MILLISECONDS.toNanos(now() - startedAt);
final Subscription sub2 = schedule(state0, this, periodInNanos - timeTakenByActionInNanos, TimeUnit.NANOSECONDS);
return Subscriptions.create(new Action0() {
@Override
public void call() {
sub1.unsubscribe();
sub2.unsubscribe();
}
});
}
return Subscriptions.empty();
}
};
final Subscription sub = schedule(state, recursiveAction, initialDelay, unit);
return Subscriptions.create(new Action0() {
@Override
public void call() {
complete.set(true);
sub.unsubscribe();
}
});
}
/**
* Schedules a cancelable action to be executed at dueTime.
*
* @param state
* State to pass into the action.
* @param action
* Action to schedule.
* @param dueTime
* Time the action is to be executed. If in the past it will be executed immediately.
* @return a subscription to be able to unsubscribe from action.
*/
public <T> Subscription schedule(T state, Func2<? super Scheduler, ? super T, ? extends Subscription> action, Date dueTime) {
long scheduledTime = dueTime.getTime();
long timeInFuture = scheduledTime - now();
if (timeInFuture <= 0) {
return schedule(state, action);
} else {
return schedule(state, action, timeInFuture, TimeUnit.MILLISECONDS);
}
}
/**
* Schedules an action and receives back an action for recursive execution.
*
* @param action
* action
* @return a subscription to be able to unsubscribe from action.
*/
public Subscription schedule(final Action1<Action0> action) {
final CompositeSubscription parentSubscription = new CompositeSubscription();
final MultipleAssignmentSubscription childSubscription = new MultipleAssignmentSubscription();
parentSubscription.add(childSubscription);
final Func2<Scheduler, Func2, Subscription> parentAction = new Func2<Scheduler, Func2, Subscription>() {
@Override
public Subscription call(final Scheduler scheduler, final Func2 parentAction) {
action.call(new Action0() {
@Override
public void call() {
if (!parentSubscription.isUnsubscribed()) {
childSubscription.setSubscription(scheduler.schedule(parentAction, parentAction));
}
}
});
return childSubscription;
}
};
parentSubscription.add(schedule(parentAction, parentAction));
return parentSubscription;
}
/**
* Schedules an action to be executed.
*
* @param action
* action
* @return a subscription to be able to unsubscribe from action.
*/
public Subscription schedule(final Action0 action) {
return schedule(null, new Func2<Scheduler, Void, Subscription>() {
@Override
public Subscription call(Scheduler scheduler, Void state) {
action.call();
return Subscriptions.empty();
}
});
}
/**
* Schedules an action to be executed in delayTime.
*
* @param action
* action
* @return a subscription to be able to unsubscribe from action.
*/
public Subscription schedule(final Action0 action, long delayTime, TimeUnit unit) {
return schedule(null, new Func2<Scheduler, Void, Subscription>() {
@Override
public Subscription call(Scheduler scheduler, Void state) {
action.call();
return Subscriptions.empty();
}
}, delayTime, unit);
}
/**
* Schedules an action to be executed periodically.
*
* @param action
* The action to execute periodically.
* @param initialDelay
* Time to wait before executing the action for the first time.
* @param period
* The time interval to wait each time in between executing the action.
* @param unit
* The time unit the interval above is given in.
* @return A subscription to be able to unsubscribe from action.
*/
public Subscription schedulePeriodically(final Action0 action, long initialDelay, long period, TimeUnit unit) {
return schedulePeriodically(null, new Func2<Scheduler, Void, Subscription>() {
@Override
public Subscription call(Scheduler scheduler, Void state) {
action.call();
return Subscriptions.empty();
}
}, initialDelay, period, unit);
}
/**
* @return the scheduler's notion of current absolute time in milliseconds.
*/
public long now() {
return System.currentTimeMillis();
}
/**
* Parallelism available to a Scheduler.
* <p>
* This defaults to {@code Runtime.getRuntime().availableProcessors()} but can be overridden for use cases such as scheduling work on a computer cluster.
*
* @return the scheduler's available degree of parallelism.
*/
public int degreeOfParallelism() {
return Runtime.getRuntime().availableProcessors();
}
}