/*
 * 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.
/**
 * 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.
/**
     * Creates a cancellation signal, initially not canceled.
     */
    public CancellationSignal() {
    }

    
Returns true if the operation has been canceled.
Returns:
True if the operation has been canceled./**
     * Returns true if the operation has been canceled.
     *
     * @return True if the operation has been canceled.
     */
    public boolean isCanceled() {
        synchronized (this) {
            return mIsCanceled;
        }
    }

    
Throws OperationCanceledException if the operation has been canceled. 
Throws:
OperationCanceledException – if the operation has been canceled./**
     * 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.
/**
     * 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 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. 
Params:
listener – The cancellation listener, or null to remove the current listener./**
     * 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 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. 
Params:
remote – The remote transport, or null to remove.
@hide
/**
     * 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.
Returns:
The new cancellation signal transport.
@hide
/**
     * 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.
Params:
transport – The locally created transport, or null if none.
Returns:
The associated cancellation signal, or null if none.
@hide
/**
     * 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.
/**
     * Listens for cancellation.
     */
    public interface OnCancelListener {
        
Called when CancellationSignal.cancel is invoked. /**
         * 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();
        }
    }
}