android 进程间通信---Service Manager（2）

关于servicemanager的设计：

还是这张结构图，由于ProcessState & IPCThreadState是与binder deriver交互的，

所以对于client端来说BpBinder以下的部分是透明的。

我们从Activity的getsystemservice来一步步分析整个servicemanager提供服务的过程。

在contextImple.java 中

        registerService(ALARM_SERVICE, new ServiceFetcher() {
                public Object createService(ContextImpl ctx) {
                    IBinder b = ServiceManager.getService(ALARM_SERVICE);
                    IAlarmManager service = IAlarmManager.Stub.asInterface(b);
                    return new AlarmManager(service, ctx);
                }});

注册的代码是static block的形式。

    @Override
    public Object getSystemService(String name) {
        ServiceFetcher fetcher = SYSTEM_SERVICE_MAP.get(name);
        return fetcher == null ? null : fetcher.getService(this);
    }

getservice：

public Object getService(ContextImpl ctx) {
            ArrayList<Object> cache = ctx.mServiceCache;
            Object service;
            synchronized (cache) {
                if (cache.size() == 0) {
                    // Initialize the cache vector on first access.
                    // At this point sNextPerContextServiceCacheIndex
                    // is the number of potential services that are
                    // cached per-Context.
                    for (int i = 0; i < sNextPerContextServiceCacheIndex; i++) {
                        cache.add(null);
                    }
                } else {
                    service = cache.get(mContextCacheIndex);
                    if (service != null) {
                        return service;
                    }
                }
                service = createService(ctx);
                cache.set(mContextCacheIndex, service);
                return service;
            }
        }

所以可以看到最终调用就是注册函数的内容

 IBinder b = ServiceManager.getService(ALARM_SERVICE);

ServiceManager.java:

    public static IBinder getService(String name) {
        try {
            IBinder service = sCache.get(name);
            if (service != null) {
                return service;
            } else {
                return getIServiceManager().getService(name);
            }
        } catch (RemoteException e) {
            Log.e(TAG, "error in getService", e);
        }
        return null;
    }

我们应用层看到的service对象是IBinder。

然后我们看看IServiceManager

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

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

    /**
     * Return the global "context object" of the system.  This is usually
     * an implementation of IServiceManager, which you can use to find
     * other services.
     */
    public static final native IBinder getContextObject();

可以看到注释说明，返回的就是全局唯一的ServiceManager对象。

class ServiceManagerProxy implements IServiceManager {
    public ServiceManagerProxy(IBinder remote) {
        mRemote = remote;
    }
    
    public IBinder asBinder() {
        return mRemote;
    }
    
    public IBinder getService(String name) throws RemoteException {
        Parcel data = Parcel.obtain();
        Parcel reply = Parcel.obtain();
        data.writeInterfaceToken(IServiceManager.descriptor);
        data.writeString(name);
        mRemote.transact(GET_SERVICE_TRANSACTION, data, reply, 0);
        IBinder binder = reply.readStrongBinder();
        reply.recycle();
        data.recycle();
        return binder;
    }

AIDL的实现：

网上有很多关于AIDL的讨论，解释等等。

AIDL是什么？

Android Interface definition language:

所以aidl是google为了便利的实现binder机制，而创建的一种语言。

AIDL的目的是为了便于开发者可以快速书写创建进程间通信的一种语言，或者代码。

package com.htc.globalsearch.imagesearch.service.aidl;
import com.htc.globalsearch.imagesearch.service.aidl.PersonImageItem;
import com.htc.globalsearch.imagesearch.service.aidl.ICallBack;

interface IBuildService{
    int getServiceStatus();
    int findPerson(String path,int filter);
    void registerCallback(ICallBack cb);     
    void unregisterCallback(ICallBack cb);  
}

看看生成后变成什么？

/*
 * This file is auto-generated.  DO NOT MODIFY.
 * Original file: D:\AndroidDev\github\Example\Examples\ImageSearch\src\com\htc\globalsearch\imagesearch\service\aidl\IBuildService.aidl
 */
package com.htc.globalsearch.imagesearch.service.aidl;
public interface IBuildService extends android.os.IInterface
{
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder implements com.htc.globalsearch.imagesearch.service.aidl.IBuildService
{
private static final java.lang.String DESCRIPTOR = "com.htc.globalsearch.imagesearch.service.aidl.IBuildService";
/** Construct the stub at attach it to the interface. */
public Stub()
{
this.attachInterface(this, DESCRIPTOR);
}
/**
 * Cast an IBinder object into an com.htc.globalsearch.imagesearch.service.aidl.IBuildService interface,
 * generating a proxy if needed.
 */
public static com.htc.globalsearch.imagesearch.service.aidl.IBuildService asInterface(android.os.IBinder obj)
{
if ((obj==null)) {
return null;
}
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (((iin!=null)&&(iin instanceof com.htc.globalsearch.imagesearch.service.aidl.IBuildService))) {
return ((com.htc.globalsearch.imagesearch.service.aidl.IBuildService)iin);
}
return new com.htc.globalsearch.imagesearch.service.aidl.IBuildService.Stub.Proxy(obj);
}
@Override public android.os.IBinder asBinder()
{
return this;
}
@Override public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException
{
switch (code)
{
case INTERFACE_TRANSACTION:
{
reply.writeString(DESCRIPTOR);
return true;
}
case TRANSACTION_getServiceStatus:
{
data.enforceInterface(DESCRIPTOR);
int _result = this.getServiceStatus();
reply.writeNoException();
reply.writeInt(_result);
return true;
}
case TRANSACTION_findPerson:
{
data.enforceInterface(DESCRIPTOR);
java.lang.String _arg0;
_arg0 = data.readString();
int _arg1;
_arg1 = data.readInt();
int _result = this.findPerson(_arg0, _arg1);
reply.writeNoException();
reply.writeInt(_result);
return true;
}
case TRANSACTION_registerCallback:
{
data.enforceInterface(DESCRIPTOR);
com.htc.globalsearch.imagesearch.service.aidl.ICallBack _arg0;
_arg0 = com.htc.globalsearch.imagesearch.service.aidl.ICallBack.Stub.asInterface(data.readStrongBinder());
this.registerCallback(_arg0);
reply.writeNoException();
return true;
}
case TRANSACTION_unregisterCallback:
{
data.enforceInterface(DESCRIPTOR);
com.htc.globalsearch.imagesearch.service.aidl.ICallBack _arg0;
_arg0 = com.htc.globalsearch.imagesearch.service.aidl.ICallBack.Stub.asInterface(data.readStrongBinder());
this.unregisterCallback(_arg0);
reply.writeNoException();
return true;
}
}
return super.onTransact(code, data, reply, flags);
}
private static class Proxy implements com.htc.globalsearch.imagesearch.service.aidl.IBuildService
{
private android.os.IBinder mRemote;
Proxy(android.os.IBinder remote)
{
mRemote = remote;
}
@Override public android.os.IBinder asBinder()
{
return mRemote;
}
public java.lang.String getInterfaceDescriptor()
{
return DESCRIPTOR;
}
@Override public int getServiceStatus() throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
int _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
mRemote.transact(Stub.TRANSACTION_getServiceStatus, _data, _reply, 0);
_reply.readException();
_result = _reply.readInt();
}
finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
@Override public int findPerson(java.lang.String path, int filter) throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
int _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
_data.writeString(path);
_data.writeInt(filter);
mRemote.transact(Stub.TRANSACTION_findPerson, _data, _reply, 0);
_reply.readException();
_result = _reply.readInt();
}
finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
@Override public void registerCallback(com.htc.globalsearch.imagesearch.service.aidl.ICallBack cb) throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
try {
_data.writeInterfaceToken(DESCRIPTOR);
_data.writeStrongBinder((((cb!=null))?(cb.asBinder()):(null)));
mRemote.transact(Stub.TRANSACTION_registerCallback, _data, _reply, 0);
_reply.readException();
}
finally {
_reply.recycle();
_data.recycle();
}
}
@Override public void unregisterCallback(com.htc.globalsearch.imagesearch.service.aidl.ICallBack cb) throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
try {
_data.writeInterfaceToken(DESCRIPTOR);
_data.writeStrongBinder((((cb!=null))?(cb.asBinder()):(null)));
mRemote.transact(Stub.TRANSACTION_unregisterCallback, _data, _reply, 0);
_reply.readException();
}
finally {
_reply.recycle();
_data.recycle();
}
}
}
static final int TRANSACTION_getServiceStatus = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
static final int TRANSACTION_findPerson = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);
static final int TRANSACTION_registerCallback = (android.os.IBinder.FIRST_CALL_TRANSACTION + 2);
static final int TRANSACTION_unregisterCallback = (android.os.IBinder.FIRST_CALL_TRANSACTION + 3);
}
public int getServiceStatus() throws android.os.RemoteException;
public int findPerson(java.lang.String path, int filter) throws android.os.RemoteException;
public void registerCallback(com.htc.globalsearch.imagesearch.service.aidl.ICallBack cb) throws android.os.RemoteException;
public void unregisterCallback(com.htc.globalsearch.imagesearch.service.aidl.ICallBack cb) throws android.os.RemoteException;
}

public static abstract class Stub extends android.os.Binder implements com.htc.globalsearch.imagesearch.service.aidl.IBuildService

关键是这个class，stub继承自binder，而且实现了IbuildService的接口。

在看service

private class ImageSearchBuildServiceImpl extends IBuildService.Stub{

所以，service是实现了Stub的内容，进而可以实现这个方法。

而service的onbind就是返回这个stub

    @Override
    public IBinder onBind(Intent intent) {
        mCurrentCookie = intent.getLongExtra("cookie",-1);
        Log.i(TAG, "[onBind] mCurrentCookie:"+mCurrentCookie);
        iServiceImpl = new ImageSearchBuildServiceImpl(mImageSearchOperator);
        return iServiceImpl;
    }

通过bindservice，会把这个Ibinder对象返回给client端。