Android中的IPC方式——Binder（一）
Android中的IPC方式——Binder（二）
基于Android5.1.1分析，因为API26以后底层相关代码变动。
在client 中 通过bindservice来启动，来看下bindservice源码。
其具体是在
/frameworks/base/core/java/android/app/ContextImpl.java
@Override
public boolean bindService(Intent service, ServiceConnection conn,int flags) {
warnIfCallingFromSystemProcess();
return bindServiceCommon(service, conn, flags, mMainThread.getHandler(), getUser());
}
private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags,
UserHandle user) {
...
int res = ActivityManagerNative.getDefault().bindService(
mMainThread.getApplicationThread(), getActivityToken(),
service, service.resolveTypeIfNeeded(getContentResolver()),
sd, flags, user.getIdentifier());
...
}
/frameworks/base/core/java/android/app/ActivityManagerNative.java
public abstract class ActivityManagerNative extends Binder implements IActivityManager{
/**
* //最终返回的还是一个ActivityManagerProxy对象
*/
static public IActivityManager asInterface(IBinder obj) {
if (obj == null) {
return null;
}
IActivityManager in =
(IActivityManager)obj.queryLocalInterface(descriptor);
if (in != null) {
return in;
}
//这里面的Binder类型的obj参数会作为ActivityManagerProxy的成员变量保存为mRemote成员变量，负责进行IPC通信
return new ActivityManagerProxy(obj);
}
/**
* //从类声明上，我们可以看到ActivityManagerNative是Binder的一个子类，而且实现了IActivityManager接口
*/
static public IActivityManager getDefault() {
return gDefault.get();
}
//通过单例模式获取一个IActivityManager对象，这个对象通过asInterface(b)获得
private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>(){
protected IActivityManager create(){
IBinder b = ServiceManager.getService("activity");
if (false) {
Log.v("ActivityManager", "default service binder = " + b);
}
IActivityManager am = asInterface(b);
if (false) {
Log.v("ActivityManager", "default service = " + am);
}
return am;
}
};
}
/frameworks/base/core/java/android/app/IActivityManager.java
public interface IActivityManager extends IInterface {
...
public int bindService(IApplicationThread caller, IBinder token, Intent service, String resolvedType,IServiceConnection connection, int flags, int userId) throws RemoteException;
public boolean unbindService(IServiceConnection connection) throws RemoteException;
...
}
ActivityManagerNative.getDefault()获得IActivityManager,IActivitymanager继承于IInterface，这个结构是不是跟我们之前看的IStudentManager很像，那么IActivityManager.bindservice(),应该由它的静态内部类Proxy来实现。但是IActivityManager内部类并没有，其实是通过其他类来实现同样功能只是名称换了。这个类就是ActivityManagerNative。
public abstract class ActivityManagerNative extends Binder implements IActivityManager{
...
@Override
public boolean onTransact(int code, Parcel data, Parcel reply, int flags)throws RemoteException {
switch (code) {
case BIND_SERVICE_TRANSACTION:
data.enforceInterface(IActivityManager.descriptor);
IBinder b = data.readStrongBinder();
IApplicationThread app = ApplicationThreadNative.asInterface(b);
IBinder token = data.readStrongBinder();
Intent service = Intent.CREATOR.createFromParcel(data);
String resolvedType = data.readString();
b = data.readStrongBinder();
int fl = data.readInt();
int userId = data.readInt();
IServiceConnection conn = IServiceConnection.Stub.asInterface(b);
int res = bindService(app, token, service, resolvedType, conn, fl, userId);
reply.writeNoException();
reply.writeInt(res);
return true;
}
}
...
class ActivityManagerProxy implements IActivityManager{
...
public ActivityManagerProxy(IBinder remote){
mRemote = remote;
}
public IBinder asBinder()
{
return mRemote;
}
...
public int bindService(IApplicationThread caller, IBinder token,
Intent service, String resolvedType, IServiceConnection connection,int flags, int userId) throws RemoteException {
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(caller != null ? caller.asBinder() : null);
data.writeStrongBinder(token);
service.writeToParcel(data, 0);
data.writeString(resolvedType);
data.writeStrongBinder(connection.asBinder());
data.writeInt(flags);
data.writeInt(userId);
mRemote.transact(BIND_SERVICE_TRANSACTION, data, reply, 0);
reply.readException();
int res = reply.readInt();
data.recycle();
reply.recycle();
return res;
}
}
可以看到ActivityManagerNative继承Binder实现IActivityManager，ActivityManagerNative就相当于Stub。
ActivityManagerProxy就是Proxy。
通过调用到的mRemote.transact(BIND_SERVICE_TRANSACTION, data, reply, 0);调用到Stub中的onTranact(),而Stub的具体实现类则是Activity'ManagerService,最后就是在ActivityManagerService中的bindservice()。
/frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public final class ActivityManagerService extends ActivityManagerNative implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
final ActiveServices mServices;
public int bindService(IApplicationThread caller, IBinder token,Intent service, String resolvedType,IServiceConnection connection, int flags, int userId) {
enforceNotIsolatedCaller("bindService");
// Refuse possible leaked file descriptors
if (service != null && service.hasFileDescriptors() == true) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
synchronized(this) {
return mServices.bindServiceLocked(caller, token, service, resolvedType,
connection, flags, userId);
}
}
}
bindservice主要分为四种情况
- server整个进程都没有启动
- server进程启动了，但是里面的service没有创建
- server进程启动了，里面的service也创建了，但是没有绑定过，回调onBind()
- server进程启动了，里面的service创建了，也被绑定过，回调onRebind()
/frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
public final class ActiveServices {
...
int bindServiceLocked(IApplicationThread caller, IBinder token,Intent service, String resolvedType,IServiceConnection connection, int flags, int userId) {
...
if ((flags&Context.BIND_AUTO_CREATE) != 0) {
s.lastActivity = SystemClock.uptimeMillis();
if (bringUpServiceLocked(s, service.getFlags(), callerFg, false) != null) {
return 0;
}
}
...
//进程启动service也创建的情况下并且绑定了， 回调onRebind()
if (s.app != null && b.intent.received) {
// Service is already running, so we can immediately
// publish the connection.
try {
c.conn.connected(s.name, b.intent.binder);
} catch (Exception e) {
Slog.w(TAG, "Failure sending service " + s.shortName
+ " to connection " + c.conn.asBinder()
+ " (in " + c.binding.client.processName + ")", e);
}
// If this is the first app connected back to this binding,
// and the service had previously asked to be told when
// rebound, then do so.
if (b.intent.apps.size() == 1 && b.intent.doRebind) {
requestServiceBindingLocked(s, b.intent, callerFg, true);
}
} else if (!b.intent.requested) {
requestServiceBindingLocked(s, b.intent, callerFg, false);
}
...
}
...
//server整个进程都没有启动,server进程启动了，但是里面的service没有创建
private final String bringUpServiceLocked(ServiceRecord r,int intentFlags, boolean execInFg, boolean whileRestarting) {
if (!isolated) {
app = mAm.getProcessRecordLocked(procName, r.appInfo.uid, false);
if (DEBUG_MU) Slog.v(TAG_MU, "bringUpServiceLocked: appInfo.uid=" + r.appInfo.uid + " app=" + app);
if (app != null && app.thread != null) {//进程启动了service没有创建
try {
app.addPackage(r.appInfo.packageName, r.appInfo.versionCode, mAm.mProcessStats);
realStartServiceLocked(r, app, execInFg);
return null;
} catch (RemoteException e) {
Slog.w(TAG, "Exception when starting service " + r.shortName, e);
}
// If a dead object exception was thrown -- fall through to
// restart the application.
}
}
//进程未启动的情况
if (app == null) {
if ((app=mAm.startProcessLocked(procName, r.appInfo, true, intentFlags,
"service", r.name, false, isolated, false)) == null) {
String msg = "Unable to launch app "
+ r.appInfo.packageName + "/"
+ r.appInfo.uid + " for service "
+ r.intent.getIntent() + ": process is bad";
Slog.w(TAG, msg);
bringDownServiceLocked(r);
return msg;
}
if (isolated) {
r.isolatedProc = app;
}
}
}
private final void realStartServiceLocked(ServiceRecord r,
ProcessRecord app, boolean execInFg) throws RemoteException {
...
app.thread.scheduleCreateService(r, r.serviceInfo, mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),
...
}
}
对应的上述四种情况
-
server整个进程都没有启动
bindServiceLocked()->bringUpServiceLocked()通过mAm.startProcessLocked()启动进程，bringDownServiceLocked(r);来启动服务。 -
server进程启动了，但是里面的service没有创建
bindServiceLocked()->bringUpServiceLocked()->realStartServiceLocked(r, app, execInFg);后续跟一下 -
server进程启动了，里面的service也创建了，但是没有绑定过，回调onBind()
bindServiceLocked()->requestServiceBindingLocked(s, b.intent, callerFg, false); -
server进程启动了，里面的service创建了，也被绑定过，回调onRebind()
bindServiceLocked()->requestServiceBindingLocked(s, b.intent, callerFg, true);
第一种情况没什么好说的，看一下第二种情况，从上面代码看到realStartServiceLocked()调用了scheduleCreateService()
/frameworks/base/core/java/android/app/ActivityThread.java
public final void scheduleCreateService(IBinder token,
ServiceInfo info, CompatibilityInfo compatInfo, int processState) {
updateProcessState(processState, false);
CreateServiceData s = new CreateServiceData();
s.token = token;
s.info = info;
s.compatInfo = compatInfo;
sendMessage(H.CREATE_SERVICE, s);
}
public void handleMessage(Message msg) {
...
case CREATE_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceCreate");
handleCreateService((CreateServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
...
}
private void handleCreateService(CreateServiceData data) {
...
try {
java.lang.ClassLoader cl = packageInfo.getClassLoader();
service = (Service) cl.loadClass(data.info.name).newInstance();
} catch (Exception e) {
if (!mInstrumentation.onException(service, e)) {
throw new RuntimeException(
"Unable to instantiate service " + data.info.name
+ ": " + e.toString(), e);
}
}
...
}
这里可以看到最后通过反射来创建service。
第三、四种情况，都是调用的从ActiveService中requestServiceBindingLocked()只是最后一个参数不一样。
/frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
private final boolean requestServiceBindingLocked(ServiceRecord r,
IntentBindRecord i, boolean execInFg, boolean rebind) {
if (r.app == null || r.app.thread == null) {
// If service is not currently running, can't yet bind.
return false;
}
if ((!i.requested || rebind) && i.apps.size() > 0) {
try {
bumpServiceExecutingLocked(r, execInFg, "bind");
r.app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE);
r.app.thread.scheduleBindService(r, i.intent.getIntent(), rebind,
r.app.repProcState);
if (!rebind) {
i.requested = true;
}
i.hasBound = true;
i.doRebind = false;
} catch (RemoteException e) {
if (DEBUG_SERVICE) Slog.v(TAG, "Crashed while binding " + r);
return false;
}
}
return true;
}
发现跟调用到ActivityThread.java的scheduleBindService()
public final void scheduleBindService(IBinder token, Intent intent,
boolean rebind, int processState) {
updateProcessState(processState, false);
BindServiceData s = new BindServiceData();
s.token = token;
s.intent = intent;
s.rebind = rebind;
if (DEBUG_SERVICE)
Slog.v(TAG, "scheduleBindService token=" + token + " intent=" + intent + " uid="
+ Binder.getCallingUid() + " pid=" + Binder.getCallingPid());
sendMessage(H.BIND_SERVICE, s);
}
public void handleMessage(Message msg) {
...
case BIND_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind");
handleBindService((BindServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
...
}
private void handleBindService(BindServiceData data) {
Service s = mServices.get(data.token);
if (DEBUG_SERVICE)
Slog.v(TAG, "handleBindService s=" + s + " rebind=" + data.rebind);
if (s != null) {
try {
data.intent.setExtrasClassLoader(s.getClassLoader());
data.intent.prepareToEnterProcess();
try {
if (!data.rebind) {
IBinder binder = s.onBind(data.intent);
//重点
ActivityManagerNative.getDefault().publishService(
data.token, data.intent, binder);
} else {
s.onRebind(data.intent);
ActivityManagerNative.getDefault().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
}
ensureJitEnabled();
} catch (RemoteException ex) {
}
} catch (Exception e) {
if (!mInstrumentation.onException(s, e)) {
throw new RuntimeException(
"Unable to bind to service " + s
+ " with " + data.intent + ": " + e.toString(), e);
}
}
}
}
最后调用handleBindService()首先从mServices在这个map去取服务，服务不为空后,根据flag来判断调用onBind()还是 onReind()，s.onBind(data.intent)返回Binder。这个可以根据前面aidl使用的部分，service在OnBind()方法需要返回一个IBineder，而这个IBinder是 IStudentManager.Stub,由Service实现。
/frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
public void publishService(IBinder token, Intent intent, IBinder service) {
// Refuse possible leaked file descriptors
if (intent != null && intent.hasFileDescriptors() == true) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
synchronized(this) {
if (!(token instanceof ServiceRecord)) {
throw new IllegalArgumentException("Invalid service token");
}
mServices.publishServiceLocked((ServiceRecord)token, intent, service);
}
}
/frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public void publishService(IBinder token, Intent intent, IBinder service) {
// Refuse possible leaked file descriptors
if (intent != null && intent.hasFileDescriptors() == true) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
synchronized(this) {
if (!(token instanceof ServiceRecord)) {
throw new IllegalArgumentException("Invalid service token");
}
mServices.publishServiceLocked((ServiceRecord)token, intent, service);
}
}
/frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service) {
ArrayList<ConnectionRecord> clist = r.connections.valueAt(conni);
ConnectionRecord c = clist.get(i);
...
try {
c.conn.connected(r.name, service);
} catch (Exception e) {
Slog.w(TAG, "Failure sending service " + r.name +
" to connection " + c.conn.asBinder() +
" (in " + c.binding.client.processName + ")", e);
}
....
}
到这里可以看到我们在service实现的onBind方法返回的 IBinder对象通过publishService()->publishServiceLocked()传递。
ConnectionRecord.java
final class ConnectionRecord {
final AppBindRecord binding; // The application/service binding.
final ActivityRecord activity; // If non-null, the owning activity.
final IServiceConnection conn;
...
}
c.conn.connected(r.name, service);传递的service 就是我们刚刚的IBinder,c.conn最终指的是IServiceConnection,具体实现为
/frameworks/base/core/java/android/app/LoadedApk.javaLoadedApk.ServiceDispatcher.InnerConnection
static final class ServiceDispatcher {
...
private static class InnerConnection extends IServiceConnection.Stub {
final WeakReference<LoadedApk.ServiceDispatcher> mDispatcher;
InnerConnection(LoadedApk.ServiceDispatcher sd) {
mDispatcher = new WeakReference<LoadedApk.ServiceDispatcher>(sd);
}
public void connected(ComponentName name, IBinder service) throws RemoteException {
LoadedApk.ServiceDispatcher sd = mDispatcher.get();
if (sd != null) {
sd.connected(name, service);
}
}
}
...
public void connected(ComponentName name, IBinder service) {
if (mActivityThread != null) {
mActivityThread.post(new RunConnection(name, service, 0));
} else {
doConnected(name, service);
}
}
}
private final class RunConnection implements Runnable {
RunConnection(ComponentName name, IBinder service, int command) {
mName = name;
mService = service;
mCommand = command;
}
public void run() {
if (mCommand == 0) {
doConnected(mName, mService);
} else if (mCommand == 1) {
doDeath(mName, mService);
}
}
final ComponentName mName;
final IBinder mService;
final int mCommand;
}
public void doConnected(ComponentName name, IBinder service) {
...
// If there was an old service, it is not disconnected.
if (old != null) {
mConnection.onServiceDisconnected(name);
}
// If there is a new service, it is now connected.
if (service != null) {
mConnection.onServiceConnected(name, service);
}
}
mActivityThread.post(new RunConnection(name, service, 0));在RunConnection的run方法中调用了doConnected方法，doConnected()中调用了onServiceDisconnected() 和onServiceConnected()
这个就是由我们client端创建serviceConnetion时需要实现的方法。这样最终在客户端的onServiceConnected()获取了由service实现的IBinder。
整个的流程走完了，在我们刚刚分析中无论是AMS 还是 后面的IService 基本上都看到了类似 Binder的 方式。
| AIDL接口 | Stub | Proxy | Stub实现类 |
|---|---|---|---|
| IStudentManager.aidl | IStudentManager.Stub | IStudentManager.Proxy | StudentManagerService |
| IActivityManager | ActivityManagerNative | ActivityManagerProxy | ActivityManagerService |
在我们的实际项目中会使用到非常多的系统服务，这时候也是需要进行进程间通信，他们都存在不同的进程中，如果都通过aidl方式来调用就会很繁琐。所以Android给我提供了ServiceManager来统一管理。
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