DropBoxManager

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[1]. service 实现接口并继承自Ixxx以用于通过IPC通信
[2]. 通过函数addService(String name, IBinder service)注册该服务
[3]. class DropBoxManager的成员变量为IDropBoxManagerService mService;
　　　　　DropBoxManager有封装了client的调用接口
[4]. getService获得service,
[5]. 调用service提供的接口

通过DropBoxManager的实现，加深对Binder，和基于Binder的IPC的理解

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frameworks/base/core/java/android/os/DropBoxManager.java
/**
 * Enqueues chunks of data (from various sources -- application crashes, kernel
 * log records, etc.).  The queue is size bounded and will drop old data if the
 * enqueued data exceeds the maximum size.  You can think of this as a
 * persistent, system-wide, blob-oriented "logcat".
 *
 * <p>You can obtain an instance of this class by calling
 * {@link android.content.Context#getSystemService}
 * with {@link android.content.Context#DROPBOX_SERVICE}.
 *
 * <p>DropBoxManager entries are not sent anywhere directly, but other system
 * services and debugging tools may scan and upload entries for processing.
 */


frameworks/base/core/java/android/content/Context.java
/**
     * Use with {@link #getSystemService} to retrieve a
     * {@link android.os.DropBoxManager} instance for recording
     * diagnostic logs.
     * @see #getSystemService
     */
    public static final String DROPBOX_SERVICE = "dropbox";


为什么getSystemService返回的是DropBoxManager，是因为下面的构造函数吗？
    private final IDropBoxManagerService mService;
    /** {@hide} */
    public DropBoxManager(IDropBoxManagerService service) { mService = service; }




    private final IAlarmManager mService;
    AlarmManager(IAlarmManager service, Context ctx) {mService = service;}
获得接口去请求服务


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以BootReceiver为例：
/**
 * Performs a number of miscellaneous, non-system-critical actions
 * after the system has finished booting.
 */
public class BootReceiver extends BroadcastReceiver {
    private static final String TAG = "BootReceiver";
    private static final File TOMBSTONE_DIR = new File("/data/tombstones");
    // Keep a reference to the observer so the finalizer doesn't disable it.
    private static FileObserver sTombstoneObserver = null;
        // Log boot events in the background to avoid blocking the main thread with I/O
        new Thread() {
            @Override
            public void run() {
                try {
                    logBootEvents(context);
                } catch (Exception e) {
                    Slog.e(TAG, "Can't log boot events", e);
                }
            }
        }.start();
    }


private void logBootEvents(Context ctx) throws IOException {
        final DropBoxManager db = (DropBoxManager) ctx.getSystemService(Context.DROPBOX_SERVICE);
        final String headers = new StringBuilder(512)
            .append("Build: ").append(Build.FINGERPRINT).append("\n")
            .append("Hardware: ").append(Build.BOARD).append("\n")
            .append("Revision: ")
            .append(SystemProperties.get("ro.revision", "")).append("\n")
            .append("Bootloader: ").append(Build.BOOTLOADER).append("\n")
            .append("Radio: ").append(Build.RADIO).append("\n")
            .append("Kernel: ")
            .append(FileUtils.readTextFile(new File("/proc/version"), 1024, "...\n"))
            .append("\n").toString();


if (db != null) db.addText("SYSTEM_BOOT", headers);


 
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3. DropBoxManager:
    /**
     * Stores human-readable text.  The data may be discarded eventually (or even
     * immediately) if space is limited, or ignored entirely if the tag has been
     * blocked (see {@link #isTagEnabled}).
     *
     * @param tag describing the type of entry being stored
     * @param data value to store
     */
    public void addText(String tag, String data) {
        try { mService.add(new Entry(tag, 0, data)); } catch (RemoteException e) {}
    }


    /** Create a new Entry with plain text contents. */
    public Entry(String tag, long millis, String text) {
            if (tag == null) throw new NullPointerException("tag == null");
            if (text == null) throw new NullPointerException("text == null");


            mTag = tag;
            mTimeMillis = millis;
            mData = text.getBytes();
            mFileDescriptor = null;
            mFlags = IS_TEXT;
     }
DropBoxManager又封装了一层：has a: mService.add
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frameworks/base/core/java/com/android/internal/os/IDropBoxManagerService.aidl

make framework

/**
 * "Backend" interface used by {@link android.os.DropBoxManager} to talk to the
 * DropBoxManagerService that actually implements the drop box functionality.
 *
 * @see DropBoxManager
 * @hide
 */
interface IDropBoxManagerService {
    /**
     * @see DropBoxManager#addText
     * @see DropBoxManager#addData
     * @see DropBoxManager#addFile
     */
    void add(in DropBoxManager.Entry entry);


    /** @see DropBoxManager#getNextEntry */
    boolean isTagEnabled(String tag);


    /** @see DropBoxManager#getNextEntry */
    DropBoxManager.Entry getNextEntry(String tag, long millis);
/*生成的对应文件*/
out/target/common/obj/JAVA_LIBRARIES/framework-full_intermediates/src/core/java/com/android/internal/os/IDropBoxManagerService.java
@Override 
public void add(android.os.DropBoxManager.Entry entry) throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
try {
_data.writeInterfaceToken(DESCRIPTOR);
if ((entry!=null)) {
   _data.writeInt(1);
   entry.writeToParcel(_data, 0);
}
else {
   _data.writeInt(0);
}
mRemote.transact(Stub.TRANSACTION_add, _data, _reply, 0);
_reply.readException();
}
finally {
_reply.recycle();
_data.recycle();
}
}


Parcel是用于IPC的传输通道：client端把数据写到这里
public void writeToParcel(Parcel out, int flags) {
            out.writeString(mTag);
            out.writeLong(mTimeMillis);
            if (mFileDescriptor != null) {
                out.writeInt(mFlags & ~HAS_BYTE_ARRAY);  // Clear bit just to be safe
                mFileDescriptor.writeToParcel(out, flags);
            } else {
                out.writeInt(mFlags | HAS_BYTE_ARRAY);
                out.writeByteArray(mData);
            }
        }
}


@Override 
public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException
{
switch (code)
{
case TRANSACTION_add:
{
　　data.enforceInterface(DESCRIPTOR);
　　android.os.DropBoxManager.Entry _arg0;
　　if ((0!=data.readInt())) {
　　　　_arg0 = android.os.DropBoxManager.Entry.CREATOR.createFromParcel(data);
　　}
　　else {
　　_arg0 = null;
　　}
　 this.add(_arg0);
　 reply.writeNoException();
　 return true;
}
}
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看到这里找不到this.add这里的add是怎么实现的
frameworks/base/services/core/java/com/android/server/DropBoxManagerService.java
public final class DropBoxManagerService extends IDropBoxManagerService.Stub{
}
这里的IDropBoxManagerService.Stub说的是类IDropBoxManagerService的内部类Stub
/**
 * Implementation of {@link IDropBoxManagerService} using the filesystem.
 * Clients use {@link DropBoxManager} to access this service.
 */
    @Override
    public void add(DropBoxManager.Entry entry) {
        File temp = null;
        OutputStream output = null;
        final String tag = entry.getTag();
long time = createEntry(temp, tag, flags);
}


EntryFile:
this.file = new File(dir, Uri.encode(tag) + "@" + timestampMillis +
    ((flags & DropBoxManager.IS_TEXT) != 0 ? ".txt" : ".dat") +
    ((flags & DropBoxManager.IS_GZIPPED) != 0 ? ".gz" : ""));


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    /**
     * Place a new @a service called @a name into the service
     * manager.
     *
     * @param name the name of the new service
     * @param service the service object
     */
    public static void addService(String name, IBinder service) {
        try {
            getIServiceManager().addService(name, service, false);
        } catch (RemoteException e) {
            Log.e(TAG, "error in addService", e);
        }
    }


从类的继承关系，可知向上转型
public final class DropBoxManagerService extends IDropBoxManagerService.Stub {}