/*
 * Copyright (C) 2006 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.annotation.NonNull;
import android.annotation.Nullable;
import android.compat.annotation.UnsupportedAppUsage;
import android.ravenwood.annotation.RavenwoodKeepWholeClass;
import android.ravenwood.annotation.RavenwoodRedirect;
import android.ravenwood.annotation.RavenwoodRedirectionClass;
import android.util.TimeUtils;
import android.util.proto.ProtoOutputStream;

import com.android.internal.annotations.VisibleForTesting;

import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;

/**
 *
 * Defines a message containing a description and arbitrary data object that can be
 * sent to a {@link Handler}.  This object contains two extra int fields and an
 * extra object field that allow you to not do allocations in many cases.
 *
 * <p class="note">While the constructor of Message is public, the best way to get
 * one of these is to call {@link #obtain Message.obtain()} or one of the
 * {@link Handler#obtainMessage Handler.obtainMessage()} methods, which will pull
 * them from a pool of recycled objects.</p>
 */
@RavenwoodKeepWholeClass
@RavenwoodRedirectionClass("Message_ravenwood")
public final class Message implements Parcelable {

    /**
     * User-defined message code so that the recipient can identify
     * what this message is about. Each {@link Handler} has its own name-space
     * for message codes, so you do not need to worry about yours conflicting
     * with other handlers.
     *
     * If not specified, this value is 0.
     * Use values other than 0 to indicate custom message codes.
     */
    public int what;

    /**
     * arg1 and arg2 are lower-cost alternatives to using
     * {@link #setData(Bundle) setData()} if you only need to store a
     * few integer values.
     */
    public int arg1;

    /**
     * arg1 and arg2 are lower-cost alternatives to using
     * {@link #setData(Bundle) setData()} if you only need to store a
     * few integer values.
     */
    public int arg2;

    /**
     * An arbitrary object to send to the recipient.  When using
     * {@link Messenger} to send the message across processes this can only
     * be non-null if it contains a Parcelable of a framework class (not one
     * implemented by the application).   For other data transfer use
     * {@link #setData}.
     *
     * <p>Note that Parcelable objects here are not supported prior to
     * the {@link android.os.Build.VERSION_CODES#FROYO} release.
     */
    public Object obj;

    /**
     * Optional Messenger where replies to this message can be sent.  The
     * semantics of exactly how this is used are up to the sender and
     * receiver.
     */
    public Messenger replyTo;

    /**
     * Indicates that the uid is not set;
     *
     * @hide Only for use within the system server.
     */
    public static final int UID_NONE = -1;

    /**
     * Optional field indicating the uid that sent the message.  This is
     * only valid for messages posted by a {@link Messenger}; otherwise,
     * it will be -1.
     */
    public int sendingUid = UID_NONE;

    /**
     * Optional field indicating the uid that caused this message to be enqueued.
     *
     * @hide Only for use within the system server.
     */
    public int workSourceUid = UID_NONE;

    /**
     * Name of the thread that sent the message.
     */
    /*package*/ String sendingThreadName;

    /** If set message is in use.
     * This flag is set when the message is enqueued and remains set while it
     * is delivered and afterwards when it is recycled.  The flag is only cleared
     * when a new message is created or obtained since that is the only time that
     * applications are allowed to modify the contents of the message.
     *
     * It is an error to attempt to enqueue or recycle a message that is already in use.
     */
    /*package*/ static final int FLAG_IN_USE = 1 << 0;

    /** If set message is asynchronous */
    /*package*/ static final int FLAG_ASYNCHRONOUS = 1 << 1;

    /** If the message is marked for removal */
    /* package*/ static final int FLAG_REMOVED = 1 << 2;

    /** Flags to clear in the copyFrom method */
    /*package*/ static final int FLAGS_TO_CLEAR_ON_COPY_FROM = FLAG_IN_USE | FLAG_REMOVED;

    @UnsupportedAppUsage
    /*package*/ volatile int flags;
    /*package*/ static final VarHandle sFlags;
    static {
        try {
            MethodHandles.Lookup l = MethodHandles.lookup();
            sFlags = l.findVarHandle(Message.class, "flags", int.class);
        } catch (ReflectiveOperationException e) {
            throw new ExceptionInInitializerError(e);
        }
    }

    /**
     * CAS flags with FLAG_REMOVED to indicate that this message should be removed. Returns false if
     * the message has already been marked for removal.
     *
     * The CAS loop shouldn't fail due to FLAG_IN_USE or FLAG_ASYNCHRONOUS being set because those
     * are only changed when a message is initially created and enqueued. However, we loop anyways
     * in case additional flags that can be modified are added in the future.
     *
     * @hide
     */
    @VisibleForTesting
    public boolean markRemoved() {
        int localFlags;
        do {
            localFlags = this.flags;
            if ((localFlags & FLAG_REMOVED) != 0) {
                return false;
            }
        } while (!sFlags.compareAndSet(this, localFlags, localFlags | FLAG_REMOVED));
        return true;
    }

    boolean isRemoved() {
       return (this.flags & FLAG_REMOVED) != 0;
    }

    /**
     * The targeted delivery time of this message. The time-base is
     * {@link SystemClock#uptimeMillis}.
     * @hide Only for use within the tests.
     */
    @UnsupportedAppUsage
    @VisibleForTesting(visibility = VisibleForTesting.Visibility.PACKAGE)
    public long when;

    /** @hide */
    public long insertSeq;

    /** @hide */
    public int heapIndex = -1;

    /*package*/ Bundle data;

    @UnsupportedAppUsage
    /*package*/ Handler target;

    @UnsupportedAppUsage
    /*package*/ Runnable callback;

    // sometimes we store linked lists of these things
    @UnsupportedAppUsage
    /*package*/ Message next;

    // only used in MessageStack
    /*package*/ Message prev;
    /*package*/ Message nextFree;

    /**
     * For trace flows, if tracing is enabled.
     */
    /*package*/ volatile long eventId;

    /** @hide */
    public static final Object sPoolSync = new Object();
    private static Message sPool;
    private static int sPoolSize = 0;

    private static final int MAX_POOL_SIZE = 50;

    /**
     * Return a new Message instance from the global pool. Allows us to
     * avoid allocating new objects in many cases.
     */
    public static Message obtain() {
        if (!MessageQueue.getUseConcurrent()) {
            synchronized (sPoolSync) {
                if (sPool != null) {
                    Message m = sPool;
                    sPool = m.next;
                    m.next = null;
                    m.flags = 0; // clear in-use flag
                    sPoolSize--;
                    return m;
                }
            }
        }
        return new Message();
    }

    /**
     * Same as {@link #obtain()}, but copies the values of an existing
     * message (including its target) into the new one.
     * @param orig Original message to copy.
     * @return A Message object from the global pool.
     */
    public static Message obtain(Message orig) {
        Message m = obtain();
        m.what = orig.what;
        m.arg1 = orig.arg1;
        m.arg2 = orig.arg2;
        m.obj = orig.obj;
        m.replyTo = orig.replyTo;
        m.sendingUid = orig.sendingUid;
        m.workSourceUid = orig.workSourceUid;
        if (orig.data != null) {
            m.data = new Bundle(orig.data);
        }
        m.target = orig.target;
        m.callback = orig.callback;

        return m;
    }

    /**
     * Same as {@link #obtain()}, but sets the value for the <em>target</em> member on the Message returned.
     * @param h  Handler to assign to the returned Message object's <em>target</em> member.
     * @return A Message object from the global pool.
     */
    public static Message obtain(Handler h) {
        Message m = obtain();
        m.target = h;

        return m;
    }

    /**
     * Same as {@link #obtain(Handler)}, but assigns a callback Runnable on
     * the Message that is returned.
     * @param h  Handler to assign to the returned Message object's <em>target</em> member.
     * @param callback Runnable that will execute when the message is handled.
     * @return A Message object from the global pool.
     */
    public static Message obtain(Handler h, Runnable callback) {
        Message m = obtain();
        m.target = h;
        m.callback = callback;

        return m;
    }

    /**
     * Same as {@link #obtain()}, but sets the values for both <em>target</em> and
     * <em>what</em> members on the Message.
     * @param h  Value to assign to the <em>target</em> member.
     * @param what  Value to assign to the <em>what</em> member.
     * @return A Message object from the global pool.
     */
    public static Message obtain(Handler h, int what) {
        Message m = obtain();
        m.target = h;
        m.what = what;

        return m;
    }

    /**
     * Same as {@link #obtain()}, but sets the values of the <em>target</em>, <em>what</em>, and <em>obj</em>
     * members.
     * @param h  The <em>target</em> value to set.
     * @param what  The <em>what</em> value to set.
     * @param obj  The <em>object</em> method to set.
     * @return  A Message object from the global pool.
     */
    public static Message obtain(Handler h, int what, Object obj) {
        Message m = obtain();
        m.target = h;
        m.what = what;
        m.obj = obj;

        return m;
    }

    /**
     * Same as {@link #obtain()}, but sets the values of the <em>target</em>, <em>what</em>,
     * <em>arg1</em>, and <em>arg2</em> members.
     *
     * @param h  The <em>target</em> value to set.
     * @param what  The <em>what</em> value to set.
     * @param arg1  The <em>arg1</em> value to set.
     * @param arg2  The <em>arg2</em> value to set.
     * @return  A Message object from the global pool.
     */
    public static Message obtain(Handler h, int what, int arg1, int arg2) {
        Message m = obtain();
        m.target = h;
        m.what = what;
        m.arg1 = arg1;
        m.arg2 = arg2;

        return m;
    }

    /**
     * Same as {@link #obtain()}, but sets the values of the <em>target</em>, <em>what</em>,
     * <em>arg1</em>, <em>arg2</em>, and <em>obj</em> members.
     *
     * @param h  The <em>target</em> value to set.
     * @param what  The <em>what</em> value to set.
     * @param arg1  The <em>arg1</em> value to set.
     * @param arg2  The <em>arg2</em> value to set.
     * @param obj  The <em>obj</em> value to set.
     * @return  A Message object from the global pool.
     */
    public static Message obtain(Handler h, int what,
            int arg1, int arg2, Object obj) {
        Message m = obtain();
        m.target = h;
        m.what = what;
        m.arg1 = arg1;
        m.arg2 = arg2;
        m.obj = obj;

        return m;
    }

    /**
     * Return a Message instance to the global pool.
     * <p>
     * You MUST NOT touch the Message after calling this function because it has
     * effectively been freed.  It is an error to recycle a message that is currently
     * enqueued or that is in the process of being delivered to a Handler.
     * </p>
     */
    public void recycle() {
        if (isInUse()) {
            throw new IllegalStateException("This message cannot be recycled because it "
                    + "is still in use.");
        }
        recycleUnchecked();
    }

    /**
     * Recycles a Message that may be in-use.
     * Used internally by the MessageQueue and Looper when disposing of queued Messages.
     */
    @UnsupportedAppUsage
    void recycleUnchecked() {
        clear();
        if (!MessageQueue.getUseConcurrent()) {
            synchronized (sPoolSync) {
                if (sPoolSize < MAX_POOL_SIZE) {
                    next = sPool;
                    sPool = this;
                    sPoolSize++;
                }
            }
        }
    }

    /**
     * Clears all Message contents.
     */
    void clear() {
        // Prevent accidental reuse such as if this Message is recycled.
        flags = FLAG_IN_USE;
        what = 0;
        arg1 = 0;
        arg2 = 0;
        obj = null;
        replyTo = null;
        sendingUid = UID_NONE;
        workSourceUid = UID_NONE;
        when = 0;
        target = null;
        callback = null;
        data = null;
        this.onClear();
    }

    @RavenwoodRedirect
    private void onClear() {
    }

    // Sentinel values used to clear reference fields with a valid 'null' value, to avoid grabbing a
    // removed message when matching for 'null' in these fields.
    private static final Object NULL_OBJECT = new Object();
    private static final Runnable NULL_RUNNABLE = () -> {};

    /**
     * Clear reference fields to avoid retaining any objects. This is used in MessageStack's message
     * removal functions, and differs from clear() in that 'flags' and links (next, prev, nextFree)
     * are not cleared, as they are still needed to indicate that a message is removed and to
     * traverse the stack.
     */
    void clearReferenceFields() {
        obj = NULL_OBJECT;
        replyTo = null;
        sendingThreadName = null;
        data = null;
        callback = NULL_RUNNABLE;
    }

    /**
     * Make this message like o.  Performs a shallow copy of the data field.
     * Does not copy the linked list fields, nor the timestamp or
     * target/callback of the original message.
     */
    public void copyFrom(Message o) {
        this.flags = o.flags & ~FLAGS_TO_CLEAR_ON_COPY_FROM;
        this.what = o.what;
        this.arg1 = o.arg1;
        this.arg2 = o.arg2;
        this.obj = o.obj;
        this.replyTo = o.replyTo;
        this.sendingUid = o.sendingUid;
        this.workSourceUid = o.workSourceUid;

        if (o.data != null) {
            this.data = (Bundle) o.data.clone();
        } else {
            this.data = null;
        }
    }

    /**
     * Return the targeted delivery time of this message, in milliseconds.
     */
    public long getWhen() {
        return when;
    }

    public void setTarget(Handler target) {
        this.target = target;
    }

    /**
     * Retrieve the {@link android.os.Handler Handler} implementation that
     * will receive this message. The object must implement
     * {@link android.os.Handler#handleMessage(android.os.Message)
     * Handler.handleMessage()}. Each Handler has its own name-space for
     * message codes, so you do not need to
     * worry about yours conflicting with other handlers.
     */
    public Handler getTarget() {
        return target;
    }

    /**
     * Retrieve callback object that will execute when this message is handled.
     * This object must implement Runnable. This is called by
     * the <em>target</em> {@link Handler} that is receiving this Message to
     * dispatch it.  If
     * not set, the message will be dispatched to the receiving Handler's
     * {@link Handler#handleMessage(Message)}.
     */
    public Runnable getCallback() {
        // We assign this first to avoid a data race that could potentially expose NULL_RUNNABLE.
        final Runnable ret = callback;
        return ret == NULL_RUNNABLE ? null : ret;
    }

    /** @hide */
    @UnsupportedAppUsage
    public Message setCallback(Runnable r) {
        callback = r;
        return this;
    }

    /**
     * Obtains a Bundle of arbitrary data associated with this
     * event, lazily creating it if necessary. Set this value by calling
     * {@link #setData(Bundle)}.  Note that when transferring data across
     * processes via {@link Messenger}, you will need to set your ClassLoader
     * on the Bundle via {@link Bundle#setClassLoader(ClassLoader)
     * Bundle.setClassLoader()} so that it can instantiate your objects when
     * you retrieve them.
     * @see #peekData()
     * @see #setData(Bundle)
     */
    public Bundle getData() {
        if (data == null) {
            data = new Bundle();
        }

        return data;
    }

    /**
     * Like getData(), but does not lazily create the Bundle.  A null
     * is returned if the Bundle does not already exist.  See
     * {@link #getData} for further information on this.
     * @see #getData()
     * @see #setData(Bundle)
     */
    @Nullable
    public Bundle peekData() {
        return data;
    }

    /**
     * Sets a Bundle of arbitrary data values. Use arg1 and arg2 members
     * as a lower cost way to send a few simple integer values, if you can.
     * @see #getData()
     * @see #peekData()
     */
    public void setData(Bundle data) {
        this.data = data;
    }

    /**
     * Chainable setter for {@link #what}
     *
     * @hide
     */
    public Message setWhat(int what) {
        this.what = what;
        return this;
    }

    /**
     * Sends this Message to the Handler specified by {@link #getTarget}.
     * Throws a null pointer exception if this field has not been set.
     */
    public void sendToTarget() {
        // We have no use for the return value, so ignore it.
        boolean unused = target.sendMessage(this);
    }

    /**
     * Returns true if the message is asynchronous, meaning that it is not
     * subject to {@link Looper} synchronization barriers.
     *
     * @return True if the message is asynchronous.
     *
     * @see #setAsynchronous(boolean)
     */
    public boolean isAsynchronous() {
        return (flags & FLAG_ASYNCHRONOUS) != 0;
    }

    /**
     * Sets whether the message is asynchronous, meaning that it is not
     * subject to {@link Looper} synchronization barriers.
     * <p>
     * Certain operations, such as view invalidation, may introduce synchronization
     * barriers into the {@link Looper}'s message queue to prevent subsequent messages
     * from being delivered until some condition is met.  In the case of view invalidation,
     * messages which are posted after a call to {@link android.view.View#invalidate}
     * are suspended by means of a synchronization barrier until the next frame is
     * ready to be drawn.  The synchronization barrier ensures that the invalidation
     * request is completely handled before resuming.
     * </p><p>
     * Asynchronous messages are exempt from synchronization barriers.  They typically
     * represent interrupts, input events, and other signals that must be handled independently
     * even while other work has been suspended.
     * </p><p>
     * Note that asynchronous messages may be delivered out of order with respect to
     * synchronous messages although they are always delivered in order among themselves.
     * If the relative order of these messages matters then they probably should not be
     * asynchronous in the first place.  Use with caution.
     * </p>
     *
     * @param async True if the message is asynchronous.
     *
     * @see #isAsynchronous()
     */
    public void setAsynchronous(boolean async) {
        if (async) {
            flags |= FLAG_ASYNCHRONOUS;
        } else {
            flags &= ~FLAG_ASYNCHRONOUS;
        }
    }

    /*package*/ boolean isInUse() {
        return ((flags & FLAG_IN_USE) == FLAG_IN_USE);
    }

    @UnsupportedAppUsage
    /*package*/ void markInUse() {
        flags |= FLAG_IN_USE;
    }

    /** Constructor (but the preferred way to get a Message is to call {@link #obtain() Message.obtain()}).
    */
    public Message() {
    }

    /*package*/ static int compareMessages(@NonNull Message m1, @NonNull Message m2) {
        // Implement the comparison with branchless logic.
        final long when1 = m1.when;
        final long when2 = m2.when;
        final long insertSeq1 = m1.insertSeq;
        final long insertSeq2 = m2.insertSeq;
        final int whenSign = Long.signum(when1 - when2);
        final int insertSeqSign = Long.signum(insertSeq1 - insertSeq2);
        // whenSign takes precedence over insertSeqSign, so the formula below is such that
        // insertSeqSign
        // only matters as a tie-breaker if whenSign is 0.
        return whenSign * 2 + insertSeqSign;
    }

    @Override
    public String toString() {
        return toString(SystemClock.uptimeMillis());
    }

    @UnsupportedAppUsage
    String toString(long now) {
        StringBuilder b = new StringBuilder();
        b.append("{ when=");
        TimeUtils.formatDuration(when - now, b);

        if (target != null) {
            if (callback != null) {
                b.append(" callback=");
                b.append(callback.getClass().getName());
            } else {
                b.append(" what=");
                b.append(what);
            }

            if (arg1 != 0) {
                b.append(" arg1=");
                b.append(arg1);
            }

            if (arg2 != 0) {
                b.append(" arg2=");
                b.append(arg2);
            }

            if (obj != null) {
                b.append(" obj=");
                b.append(obj);
            }

            b.append(" target=");
            b.append(target.getClass().getName());
        } else {
            b.append(" barrier=");
            b.append(arg1);
        }

        b.append(" async=");
        b.append(isAsynchronous());
        b.append(" heapIndex=");
        b.append(heapIndex);
        b.append(" }");
        return b.toString();
    }

    void dumpDebug(ProtoOutputStream proto, long fieldId) {
        final long messageToken = proto.start(fieldId);
        proto.write(MessageProto.WHEN, when);

        if (target != null) {
            if (callback != null) {
                proto.write(MessageProto.CALLBACK, callback.getClass().getName());
            } else {
                proto.write(MessageProto.WHAT, what);
            }

            if (arg1 != 0) {
                proto.write(MessageProto.ARG1, arg1);
            }

            if (arg2 != 0) {
                proto.write(MessageProto.ARG2, arg2);
            }

            if (obj != null) {
                proto.write(MessageProto.OBJ, obj.toString());
            }

            proto.write(MessageProto.TARGET, target.getClass().getName());
        } else {
            proto.write(MessageProto.BARRIER, arg1);
        }

        proto.end(messageToken);
    }

    public static final @NonNull Parcelable.Creator<Message> CREATOR
            = new Parcelable.Creator<Message>() {
        public Message createFromParcel(Parcel source) {
            Message msg = Message.obtain();
            msg.readFromParcel(source);
            return msg;
        }

        public Message[] newArray(int size) {
            return new Message[size];
        }
    };

    public int describeContents() {
        return 0;
    }

    public void writeToParcel(Parcel dest, int flags) {
        if (callback != null) {
            throw new RuntimeException(
                "Can't marshal callbacks across processes.");
        }
        dest.writeInt(what);
        dest.writeInt(arg1);
        dest.writeInt(arg2);
        if (obj != null) {
            try {
                Parcelable p = (Parcelable)obj;
                dest.writeInt(1);
                dest.writeParcelable(p, flags);
            } catch (ClassCastException e) {
                throw new RuntimeException(
                    "Can't marshal non-Parcelable objects across processes.");
            }
        } else {
            dest.writeInt(0);
        }
        dest.writeLong(when);
        dest.writeBundle(data);
        Messenger.writeMessengerOrNullToParcel(replyTo, dest);
        dest.writeInt(sendingUid);
        dest.writeInt(workSourceUid);
    }

    private void readFromParcel(Parcel source) {
        what = source.readInt();
        arg1 = source.readInt();
        arg2 = source.readInt();
        if (source.readInt() != 0) {
            obj = source.readParcelable(getClass().getClassLoader(), java.lang.Object.class);
        }
        when = source.readLong();
        data = source.readBundle();
        replyTo = Messenger.readMessengerOrNullFromParcel(source);
        sendingUid = source.readInt();
        workSourceUid = source.readInt();
    }

    /*
     * This class is used to find matches for MessageQueue.hasMessages() and
     * MessageQueue.removeMessages()
     */
    abstract static class MessageCompare {
        public abstract boolean compareMessage(Message m, Handler h, int what, Object object,
                Runnable r, long when);
    }

    /**
     * Matches handler, what, and object if non-null.
     *
     * @hide
     */
    public static final class MatchHandlerWhatAndObject extends MessageCompare {
        @Override
        public boolean compareMessage(Message m, Handler h, int what, Object object, Runnable r,
                long when) {
            if (m.target == h && m.what == what && (object == null || m.obj == object)) {
                return true;
            }
            return false;
        }
    }
    /** @hide */
    public static final MatchHandlerWhatAndObject sMatchHandlerWhatAndObject =
            new MatchHandlerWhatAndObject();

    /**
     * Matches handler, what, and object.equals() if non-null.
     */
    static final class MatchHandlerWhatAndObjectEquals extends MessageCompare {
        @Override
        public boolean compareMessage(Message m, Handler h, int what, Object object, Runnable r,
                long when) {
            if (m.target == h && m.what == what && (object == null || object.equals(m.obj))) {
                return true;
            }
            return false;
        }
    }

    static final MatchHandlerWhatAndObjectEquals sMatchHandlerWhatAndObjectEquals =
            new MatchHandlerWhatAndObjectEquals();

    /**
     * Matches handler, runnable, and object if non-null.
     */
    static final class MatchHandlerRunnableAndObject extends MessageCompare {
        @Override
        public boolean compareMessage(Message m, Handler h, int what, Object object, Runnable r,
                long when) {
            if (m.target == h && m.callback == r && (object == null || m.obj == object)) {
                return true;
            }
            return false;
        }
    }
    static final MatchHandlerRunnableAndObject sMatchHandlerRunnableAndObject =
            new MatchHandlerRunnableAndObject();

    /**
     * Matches handler.
     */
    static final class MatchHandler extends MessageCompare {
        @Override
        public boolean compareMessage(Message m, Handler h, int what, Object object, Runnable r,
                long when) {
            return m.target == h;
        }
    }
    static final MatchHandler sMatchHandler = new MatchHandler();

    /**
     * Matches handler, runnable, and object.equals() if non-null.
     */
    static final class MatchHandlerRunnableAndObjectEquals extends MessageCompare {
        @Override
        public boolean compareMessage(Message m, Handler h, int what, Object object, Runnable r,
                long when) {
            if (m.target == h && m.callback == r && (object == null || object.equals(m.obj))) {
                return true;
            }
            return false;
        }
    }
    static final MatchHandlerRunnableAndObjectEquals sMatchHandlerRunnableAndObjectEquals =
            new MatchHandlerRunnableAndObjectEquals();

    /**
     * Matches handler, and object if non-null.
     */
    static final class MatchHandlerAndObject extends MessageCompare {
        @Override
        public boolean compareMessage(Message m, Handler h, int what, Object object, Runnable r,
                long when) {
            if (m.target == h && (object == null || m.obj == object)) {
                return true;
            }
            return false;
        }
    }
    static final MatchHandlerAndObject sMatchHandlerAndObject = new MatchHandlerAndObject();

    /**
     * Matches handler, and object.equals() if non-null.
     */
    static final class MatchHandlerAndObjectEquals extends MessageCompare {
        @Override
        public boolean compareMessage(Message m, Handler h, int what, Object object, Runnable r,
                long when) {
            if (m.target == h && (object == null || object.equals(m.obj))) {
                return true;
            }
            return false;
        }
    }
    static final MatchHandlerAndObjectEquals sMatchHandlerAndObjectEquals =
            new MatchHandlerAndObjectEquals();

    /**
     * Matches all messages.
     */
    static final class MatchAllMessages extends MessageCompare {
        @Override
        public boolean compareMessage(Message m, Handler h, int what, Object object, Runnable r,
                long when) {
            return true;
        }
    }
    static final MatchAllMessages sMatchAllMessages = new MatchAllMessages();

    /**
     * Matches all messages whose when is greater than the when parameter passed in.
     */
    static final class MatchAllFutureMessages extends MessageCompare {
        @Override
        public boolean compareMessage(Message m, Handler h, int what, Object object, Runnable r,
                long when) {
            return m.when > when;
        }
    }
    static final MatchAllFutureMessages sMatchAllFutureMessages =
            new MatchAllFutureMessages();

    /**
     * For use with removeSyncBarrier. Matches the barrier with passed token.
     */
    static final class MatchBarrierToken extends MessageCompare {
        final int mBarrierToken;

        MatchBarrierToken(int token) {
            mBarrierToken = token;
        }

        @Override
        public boolean compareMessage(Message m, Handler h, int what, Object object, Runnable r,
                long when) {
            return m.target == null && m.arg1 == mBarrierToken;
        }
    }

    /**
     * Matches any messages that come at or before when.
     */
    static final class MatchDeliverableMessages extends MessageCompare {
        @Override
        public boolean compareMessage(Message m, Handler h, int what, Object object, Runnable r,
                long when) {
            return m.when <= when;
        }
    }
    static final MatchDeliverableMessages sMatchDeliverableMessages =
            new MatchDeliverableMessages();
}