Android系統匿名共享記憶體Ashmem（Anonymous Shared Memory）簡要介紹和學習計劃 (二)

這裡要用到的Binder程式間通訊介面定義在src/shy/luo/ashmem/IMemoryService.java檔案中：

package shy.luo.ashmem;

import android.util.Log;
import android.os.IInterface;
import android.os.Binder;
import android.os.IBinder;
import android.os.Parcel;
import android.os.ParcelFileDescriptor;
import android.os.RemoteException;

public interface IMemoryService extends IInterface {
	public static abstract class Stub extends Binder implements IMemoryService {
		private static final String DESCRIPTOR = "shy.luo.ashmem.IMemoryService";

		public Stub() {
			attachInterface(this, DESCRIPTOR);
		}

		public static IMemoryService asInterface(IBinder obj) {
			if (obj == null) {
				return null;
			}

			IInterface iin = (IInterface)obj.queryLocalInterface(DESCRIPTOR);
			if (iin != null && iin instanceof IMemoryService) {
				return (IMemoryService)iin;
			}

			return new IMemoryService.Stub.Proxy(obj);
		}

		public IBinder asBinder() {
			return this;
		}

		@Override 
		public boolean onTransact(int code, Parcel data, Parcel reply, int flags) throws android.os.RemoteException {
			switch (code) {
			case INTERFACE_TRANSACTION: {
				reply.writeString(DESCRIPTOR);
				return true;
			}
			case TRANSACTION_getFileDescriptor: {
				data.enforceInterface(DESCRIPTOR);
				
				ParcelFileDescriptor result = this.getFileDescriptor();
				
				reply.writeNoException();
				
				if (result != null) {
					reply.writeInt(1);
					result.writeToParcel(reply, 0);
				} else {
					reply.writeInt(0);
				}

				return true;
			}
			case TRANSACTION_setValue: {
				data.enforceInterface(DESCRIPTOR);
				
				int val = data.readInt();
				setValue(val);
				
				reply.writeNoException();
				
				return true;
			}
			}

			return super.onTransact(code, data, reply, flags);
		}

		private static class Proxy implements IMemoryService {
			private IBinder mRemote;

			Proxy(IBinder remote) {
				mRemote = remote;
			}

			public IBinder asBinder() {
				return mRemote;
			}

			public String getInterfaceDescriptor() {
				return DESCRIPTOR;
			}

			public ParcelFileDescriptor getFileDescriptor() throws RemoteException {
				Parcel data = Parcel.obtain();
				Parcel reply = Parcel.obtain();

				ParcelFileDescriptor result;
	
				try {
					data.writeInterfaceToken(DESCRIPTOR);

					mRemote.transact(Stub.TRANSACTION_getFileDescriptor, data, reply, 0);
		
					reply.readException();
					if (0 != reply.readInt()) {
						result = ParcelFileDescriptor.CREATOR.createFromParcel(reply);
					} else {
						result = null;
					}
				} finally {
					reply.recycle();
					data.recycle();
				}
	
				return result;
			}

			public void setValue(int val) throws RemoteException {
				Parcel data = Parcel.obtain();
				Parcel reply = Parcel.obtain();

				try {
					data.writeInterfaceToken(DESCRIPTOR);
					data.writeInt(val);

					mRemote.transact(Stub.TRANSACTION_setValue, data, reply, 0);
					
					reply.readException();
				} finally {
					reply.recycle();
					data.recycle();
				}
			}
		}

		static final int TRANSACTION_getFileDescriptor = IBinder.FIRST_CALL_TRANSACTION + 0;
		static final int TRANSACTION_setValue = IBinder.FIRST_CALL_TRANSACTION + 1;

	}

	public ParcelFileDescriptor getFileDescriptor() throws RemoteException;
	public void setValue(int val) throws RemoteException;
}

        這裡主要是定義了IMemoryService介面，它裡面有兩個呼叫介面：

	public ParcelFileDescriptor getFileDescriptor() throws RemoteException;
	public void setValue(int val) throws RemoteException;

        同時，還分別定義了用於Server端實現的IMemoryService.Stub基類和用於Client端使用的代理IMemoryService.Stub.Proxy類。關於Binder程式間通訊機制在應用程式框架層的Java介面定義，請參考前面Android系統程式間通訊Binder機制在應用程式框架層的Java介面原始碼分析一文。