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/*
* Copyright (C) 2012 The Android Open Source Project
*
* 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 android.content;
import android.os.RemoteException;
/**
* Provides the ability to cancel an operation in progress.
*/
public final class CancelationSignal {
private boolean mIsCanceled;
private OnCancelListener mOnCancelListener;
private ICancelationSignal mRemote;
/**
* Creates a cancelation signal, initially not canceled.
*/
public CancelationSignal() {
}
/**
* Returns true if the operation has been canceled.
*
* @return True if the operation has been canceled.
*/
public boolean isCanceled() {
synchronized (this) {
return mIsCanceled;
}
}
/**
* Throws {@link OperationCanceledException} if the operation has been canceled.
*
* @throws OperationCanceledException if the operation has been canceled.
*/
public void throwIfCanceled() {
if (isCanceled()) {
throw new OperationCanceledException();
}
}
/**
* Cancels the operation and signals the cancelation listener.
* If the operation has not yet started, then it will be canceled as soon as it does.
*/
public void cancel() {
synchronized (this) {
if (!mIsCanceled) {
mIsCanceled = true;
if (mOnCancelListener != null) {
mOnCancelListener.onCancel();
}
if (mRemote != null) {
try {
mRemote.cancel();
} catch (RemoteException ex) {
}
}
}
}
}
/**
* Sets the cancelation listener to be called when canceled.
* If {@link CancelationSignal#cancel} has already been called, then the provided
* listener is invoked immediately.
*
* The listener is called while holding the cancelation signal's lock which is
* also held while registering or unregistering the listener. Because of the lock,
* it is not possible for the listener to run after it has been unregistered.
* This design choice makes it easier for clients of {@link CancelationSignal} to
* prevent race conditions related to listener registration and unregistration.
*
* @param listener The cancelation listener, or null to remove the current listener.
*/
public void setOnCancelListener(OnCancelListener listener) {
synchronized (this) {
mOnCancelListener = listener;
if (mIsCanceled && listener != null) {
listener.onCancel();
}
}
}
/**
* Sets the remote transport.
*
* @param remote The remote transport, or null to remove.
*
* @hide
*/
public void setRemote(ICancelationSignal remote) {
synchronized (this) {
mRemote = remote;
if (mIsCanceled && remote != null) {
try {
remote.cancel();
} catch (RemoteException ex) {
}
}
}
}
/**
* Creates a transport that can be returned back to the caller of
* a Binder function and subsequently used to dispatch a cancelation signal.
*
* @return The new cancelation signal transport.
*
* @hide
*/
public static ICancelationSignal createTransport() {
return new Transport();
}
/**
* Given a locally created transport, returns its associated cancelation signal.
*
* @param transport The locally created transport, or null if none.
* @return The associated cancelation signal, or null if none.
*
* @hide
*/
public static CancelationSignal fromTransport(ICancelationSignal transport) {
if (transport instanceof Transport) {
return ((Transport)transport).mCancelationSignal;
}
return null;
}
/**
* Listens for cancelation.
*/
public interface OnCancelListener {
/**
* Called when {@link CancelationSignal#cancel} is invoked.
*/
void onCancel();
}
private static final class Transport extends ICancelationSignal.Stub {
final CancelationSignal mCancelationSignal = new CancelationSignal();
@Override
public void cancel() throws RemoteException {
mCancelationSignal.cancel();
}
}
}
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