Android 进阶8：进程通信之 Binder 机制浅析

public class Binder implements IBinder {...}
public interface IBinder {...}

public boolean transact(int code, Parcel data, Parcel reply, int flags)
    throws RemoteException;

protected boolean onTransact(int code, Parcel data, Parcel reply,
        int flags) throws RemoteException {...}

/**
 * 检查远程 Binder 对象是否存在
 * 
 * 当不存在时返回 false
 */
public boolean pingBinder();
/**
 * 注册一个 Binder 销毁的监听
   如果一个 Binder 被销毁（通常是它所在的进程被关闭），会回调 DeathRecipient 的 BinderDied 方法
 * 注意，只会监听远程的 Binder，本地 Binder 一般不会销毁，除非当前进程退出
 * 
 * 如果要注册的 Binder 进程已经销毁，就抛出 RemoteException 
 */
public void linkToDeath(DeathRecipient recipient, int flags)
        throws RemoteException;

/**
 * linkToDeath 注册监听回调的接口
 */
public interface DeathRecipient {
    public void binderDied();
}

public final boolean transact(int code, Parcel data, Parcel reply,
        int flags) throws RemoteException {
    if (false) Log.v("Binder", "Transact: " + code + " to " + this);

    if (data != null) {
        data.setDataPosition(0);
    }
    boolean r = onTransact(code, data, reply, flags);
    if (reply != null) {
        reply.setDataPosition(0);
    }
    return r;
}

protected boolean onTransact(int code, Parcel data, Parcel reply,
        int flags) throws RemoteException {
    if (code == INTERFACE_TRANSACTION) {    //获取接口描述
        reply.writeString(getInterfaceDescriptor());
        return true;
    } else if (code == DUMP_TRANSACTION) {    //获取当前状态
        ParcelFileDescriptor fd = data.readFileDescriptor();
        String[] args = data.readStringArray();
        if (fd != null) {
            try {
                dump(fd.getFileDescriptor(), args);
            } finally {
                IoUtils.closeQuietly(fd);
            }
        }
        // Write the StrictMode header.
        if (reply != null) {
            reply.writeNoException();
        } else {
            StrictMode.clearGatheredViolations();
        }
        return true;
    } else if (code == SHELL_COMMAND_TRANSACTION) {    //执行 shell 脚本
        ParcelFileDescriptor in = data.readFileDescriptor();
        ParcelFileDescriptor out = data.readFileDescriptor();
        ParcelFileDescriptor err = data.readFileDescriptor();
        String[] args = data.readStringArray();
        ResultReceiver resultReceiver = ResultReceiver.CREATOR.createFromParcel(data);
        try {
            if (out != null) {
                shellCommand(in != null ? in.getFileDescriptor() : null,
                        out.getFileDescriptor(),
                        err != null ? err.getFileDescriptor() : out.getFileDescriptor(),
                        args, resultReceiver);
            }
        } finally {
            IoUtils.closeQuietly(in);
            IoUtils.closeQuietly(out);
            IoUtils.closeQuietly(err);
            // Write the StrictMode header.
            if (reply != null) {
                reply.writeNoException();
            } else {
                StrictMode.clearGatheredViolations();
            }
        }
        return true;
    }
    return false;
}

public void attachInterface(IInterface owner, String descriptor) {
    mOwner = owner;
    mDescriptor = descriptor;
}
/* mObject is used by native code, do not remove or rename */
private long mObject;
private IInterface mOwner;
private String mDescriptor;

public interface IInterface
{
    /**
     * Retrieve the Binder object associated with this interface.
     * You must use this instead of a plain cast, so that proxy objects
     * can return the correct result.
     */
    public IBinder asBinder();
}

public final class ServiceManager {
    private static final String TAG = "ServiceManager";

    private static IServiceManager sServiceManager;
    private static HashMap<String, IBinder> sCache = new HashMap<String, IBinder>();

    private static IServiceManager getIServiceManager() {
        if (sServiceManager != null) {
            return sServiceManager;
        }

        // Find the service manager
        sServiceManager = ServiceManagerNative.asInterface(BinderInternal.getContextObject());
        return sServiceManager;
    }

    /**
     * 根据 Service 名称获取 Service
     */
    public static IBinder getService(String name) {
        try {
            IBinder service = sCache.get(name);
            if (service != null) {
                return service;
            } else {
                //如果不存在就去 IServiceManager 中找，这时可能会阻塞
                return getIServiceManager().getService(name);
            }
        } catch (RemoteException e) {
            Log.e(TAG, "error in getService", e);
        }
        return null;
    }

    /**
     * 添加一个 Service 到 Manager 中
     */
    public static void addService(String name, IBinder service) {
        try {
            getIServiceManager().addService(name, service, false);
        } catch (RemoteException e) {
            Log.e(TAG, "error in addService", e);
        }
    }

    /**
     * 添加一个 Service 到 Manager 中,如果 allowIsolated 为 true 表示运行在沙盒中的进程也可以访问这个 Service

     */
    public static void addService(String name, IBinder service, boolean allowIsolated) {
        try {
            getIServiceManager().addService(name, service, allowIsolated);
        } catch (RemoteException e) {
            Log.e(TAG, "error in addService", e);
        }
    }

    /**
     * Retrieve an existing service called @a name from the
     * service manager.  Non-blocking.
     */
    public static IBinder checkService(String name) {
        try {
            IBinder service = sCache.get(name);
            if (service != null) {
                return service;
            } else {
                return getIServiceManager().checkService(name);
            }
        } catch (RemoteException e) {
            Log.e(TAG, "error in checkService", e);
            return null;
        }
    }

    /**
     * 获取 Service 列表
     */
    public static String[] listServices() {
        try {
            return getIServiceManager().listServices();
        } catch (RemoteException e) {
            Log.e(TAG, "error in listServices", e);
            return null;
        }
    }

    /**
     * 当前进程首次被 activity manager 创建时调用这个方法 
     */
    public static void initServiceCache(Map<String, IBinder> cache) {
        if (sCache.size() != 0) {
            throw new IllegalStateException("setServiceCache may only be called once");
        }
        sCache.putAll(cache);
    }
}

public interface IServiceManager extends IInterface
{
    /**
     * 获取一个 Service，不存在就会阻塞几秒
     */
    public IBinder getService(String name) throws RemoteException;

    /**
     * 不阻塞的获取 Service
     */
    public IBinder checkService(String name) throws RemoteException;

    public void addService(String name, IBinder service, boolean allowIsolated)
                throws RemoteException;

    public String[] listServices() throws RemoteException;

    /**
     * 为 Service Manager 添加权限，具体作用暂不追究
     */
    public void setPermissionController(IPermissionController controller)
            throws RemoteException;

    static final String descriptor = "android.os.IServiceManager";

    //定义了一些用于调用 transact() 方法的 code
    int GET_SERVICE_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION;
    int CHECK_SERVICE_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION+1;
    int ADD_SERVICE_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION+2;
    int LIST_SERVICES_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION+3;
    int CHECK_SERVICES_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION+4;
    int SET_PERMISSION_CONTROLLER_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION+5;
}