안드로이드 Message 소스 분석 (Android Message.java)

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Source Path : Message.java (frameworks\base\core\java\android\os)

/*
 * 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.util.TimeUtils;

/**
 * 
 * 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. 
 *
 * 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.
 */
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.
 */
 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}.
 * 
 * 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;

/** If set message is in use */
 /*package*/ static final int FLAG_IN_USE = 1 << 0;

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

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

/*package*/ int flags;

/*package*/ long when;
    
    /*package*/ Bundle data;
    
    /*package*/ Handler target;     
    
    /*package*/ Runnable callback;   
    
    // sometimes we store linked lists of these things
    /*package*/ Message next;

private 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() {
        synchronized (sPoolSync) {
			/** 
			 *  Message Pool로부터 Message 객체 반환
			 *  Messsage Pool?

*  현재 사용되지 않는 메시지들이 보관되는 장소이다.
			 *  Message의 링크드 리스트 형태로 메시지를 보관하고, 
			 *  Message를 필요로 하는 객체에 제공하고, 링크드 리스트의 메시지를 삭제한다.
			 **/
            if (sPool != null) {
                Message m = sPool;
                sPool = m.next;
                m.next = null;
                sPoolSize--;
                return m;
            }
        }
		
		/**
		 * Message Pool에 메시지가 없다면, 새로운 Message 객체를 생성 후 반환 
		 **/
        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;
        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 target member on the Message returned.
 * @param h Handler to assign to the returned Message object's target 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 target 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 target and
 * what members on the Message.
 * @param h Value to assign to the target member.
 * @param what Value to assign to the what 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 target, what, and obj
 * members.
 * @param h The target value to set.
 * @param what The what value to set.
 * @param obj The object 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 target, what, 
 * arg1, and arg2 members.
 * 
 * @param h The target value to set.
 * @param what The what value to set.
 * @param arg1 The arg1 value to set.
 * @param arg2 The arg2 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 target, what, 
 * arg1, arg2, and obj members.
 * 
 * @param h The target value to set.
 * @param what The what value to set.
 * @param arg1 The arg1 value to set.
 * @param arg2 The arg2 value to set.
 * @param obj The obj 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.  You MUST NOT touch
     * the Message after calling this function -- it has effectively been
     * freed.
     */
    public void recycle() {
    	/**
    	 * 사용한 메시지의 모든 멤버 변수를 초기화
    	 **/
        clearForRecycle();

synchronized (sPoolSync) {
	 	/**
	 	 * Message Pool에 존재하는 객체수를 비교
	 	 * MAX_POOL_SIZE보다 Message 객체가 더 존재하는 경우, Message Pool에 유지되지 않는다.
	 	 * MAX_POOL_SIZE = 50
	 	 **/			
 if (sPoolSize < MAX_POOL_SIZE) {
				/**
				 * 현재의 Message Pool을 다음 Linked List로 넘긴다.
				 **/
 next = sPool;
				/**
				 * 사용한 메시지는 풀에 반납한다.
				 **/				
 sPool = this;
				/**
				 * 재 사용가능한 Message의 객체가 증가
				 **/				
 sPoolSize++;
 }
 }
 }

/**
     * 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;

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 a {@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 target {@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 Handler.handleMessage())}.
 */
 public Runnable getCallback() {
 return callback;
 }
 
 /** 
 * 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)
     */
    public Bundle peekData() {
        return data;
    }

/**
     * Sets a Bundle of arbitrary data values. Use arg1 and arg1 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;
    }

/**
     * 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() {
        target.sendMessage(this);
    }

/**
     * Returns true if the message is asynchronous.
     *
     * Asynchronous messages represent interrupts or events that do not require global ordering
     * with represent to synchronous messages.  Asynchronous messages are not subject to
     * the synchronization barriers introduced by {@link MessageQueue#enqueueSyncBarrier(long)}.
     *
     * @return True if the message is asynchronous.
     *
     * @see #setAsynchronous(boolean)
     * @see MessageQueue#enqueueSyncBarrier(long)
     * @see MessageQueue#removeSyncBarrier(int)
     *
     * @hide
     */
    public boolean isAsynchronous() {
        return (flags & FLAG_ASYNCHRONOUS) != 0;
    }

/**
     * Sets whether the message is asynchronous.
     *
     * Asynchronous messages represent interrupts or events that do not require global ordering
     * with represent to synchronous messages.  Asynchronous messages are not subject to
     * the synchronization barriers introduced by {@link MessageQueue#enqueueSyncBarrier(long)}.
     *
     * @param async True if the message is asynchronous.
     *
     * @see #isAsynchronous()
     * @see MessageQueue#enqueueSyncBarrier(long)
     * @see MessageQueue#removeSyncBarrier(int)
     *
     * @hide
     */
    public void setAsynchronous(boolean async) {
        if (async) {
            flags |= FLAG_ASYNCHRONOUS;
        } else {
            flags &= ~FLAG_ASYNCHRONOUS;
        }
    }

/*package*/ void clearForRecycle() {
        flags = 0;
        what = 0;
        arg1 = 0;
        arg2 = 0;
        obj = null;
        replyTo = null;
        when = 0;
        target = null;
        callback = null;
        data = null;
    }

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

/*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() {
    }

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

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(" }");
        return b.toString();
    }

public static final 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);
    }

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

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