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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.os;
import android.os.ICancellationSignal;
/**
* Provides the ability to cancel an operation in progress.
*/
public final class CancellationSignal {
private boolean mIsCanceled;
private OnCancelListener mOnCancelListener;
private ICancellationSignal mRemote;
private boolean mCancelInProgress;
/**
* Creates a cancellation signal, initially not canceled.
*/
public CancellationSignal() {
}
/**
* 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 cancellation listener.
* If the operation has not yet started, then it will be canceled as soon as it does.
*/
public void cancel() {
final OnCancelListener listener;
final ICancellationSignal remote;
synchronized (this) {
if (mIsCanceled) {
return;
}
mIsCanceled = true;
mCancelInProgress = true;
listener = mOnCancelListener;
remote = mRemote;
}
try {
if (listener != null) {
listener.onCancel();
}
if (remote != null) {
try {
remote.cancel();
} catch (RemoteException ex) {
}
}
} finally {
synchronized (this) {
mCancelInProgress = false;
notifyAll();
}
}
}
/**
* Sets the cancellation listener to be called when canceled.
*
* This method is intended to be used by the recipient of a cancellation signal
* such as a database or a content provider to handle cancellation requests
* while performing a long-running operation. This method is not intended to be
* used by applications themselves.
*
* If {@link CancellationSignal#cancel} has already been called, then the provided
* listener is invoked immediately.
*
* This method is guaranteed that the listener will not be called after it
* has been removed.
*
* @param listener The cancellation listener, or null to remove the current listener.
*/
public void setOnCancelListener(OnCancelListener listener) {
synchronized (this) {
waitForCancelFinishedLocked();
if (mOnCancelListener == listener) {
return;
}
mOnCancelListener = listener;
if (!mIsCanceled || listener == null) {
return;
}
}
listener.onCancel();
}
/**
* Sets the remote transport.
*
* If {@link CancellationSignal#cancel} has already been called, then the provided
* remote transport is canceled immediately.
*
* This method is guaranteed that the remote transport will not be called after it
* has been removed.
*
* @param remote The remote transport, or null to remove.
*
* @hide
*/
public void setRemote(ICancellationSignal remote) {
synchronized (this) {
waitForCancelFinishedLocked();
if (mRemote == remote) {
return;
}
mRemote = remote;
if (!mIsCanceled || remote == null) {
return;
}
}
try {
remote.cancel();
} catch (RemoteException ex) {
}
}
private void waitForCancelFinishedLocked() {
while (mCancelInProgress) {
try {
wait();
} catch (InterruptedException ex) {
}
}
}
/**
* Creates a transport that can be returned back to the caller of
* a Binder function and subsequently used to dispatch a cancellation signal.
*
* @return The new cancellation signal transport.
*
* @hide
*/
public static ICancellationSignal createTransport() {
return new Transport();
}
/**
* Given a locally created transport, returns its associated cancellation signal.
*
* @param transport The locally created transport, or null if none.
* @return The associated cancellation signal, or null if none.
*
* @hide
*/
public static CancellationSignal fromTransport(ICancellationSignal transport) {
if (transport instanceof Transport) {
return ((Transport)transport).mCancellationSignal;
}
return null;
}
/**
* Listens for cancellation.
*/
public interface OnCancelListener {
/**
* Called when {@link CancellationSignal#cancel} is invoked.
*/
void onCancel();
}
private static final class Transport extends ICancellationSignal.Stub {
final CancellationSignal mCancellationSignal = new CancellationSignal();
@Override
public void cancel() throws RemoteException {
mCancellationSignal.cancel();
}
}
}
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