Android4.4——service之bindService
具体可参考“老罗的Android之旅”中的《Android应用程序绑定服务（bindService）的过程源代码分析》一文。
下面跟踪bindService流程。
Step 1、ContextWrapper::bindService()
代码位于frameworks/base/core/java/android/content/ContextWrapper.java。
public boolean bindService(Intent service, ServiceConnection conn,
int flags) {
return mBase.bindService(service, conn, flags);
} Context mBase;
class ContextImpl extends Context {
......
}其中mBase为一个ContextImpl对象（具体的分析过程请参考startService的文章）。
Step 2、ContextImpl::bindService()
代码位于frameworks/base/core/java/android/app/ContextImpl.java。
public boolean bindService(Intent service, ServiceConnection conn,
int flags) {
warnIfCallingFromSystemProcess();
return bindServiceCommon(service, conn, flags, Process.myUserHandle());
}
代码位于frameworks/base/core/java/android/app/ContextImpl.java。
private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags,
UserHandle user) {
IServiceConnection sd;
if (conn == null) {
throw new IllegalArgumentException("connection is null");
}
if (mPackageInfo != null) {
sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(),
mMainThread.getHandler(), flags);//作为ActivityManagerProxy::bindService的参数，将该IServiceConnection对象传递给AMS，后续AMS通过该IServiceConnection与ServiceConnection对象进行通信
} else {
throw new RuntimeException("Not supported in system context");
}
validateServiceIntent(service);
try {
IBinder token = getActivityToken();
if (token == null && (flags&BIND_AUTO_CREATE) == 0 && mPackageInfo != null
&& mPackageInfo.getApplicationInfo().targetSdkVersion
< android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
flags |= BIND_WAIVE_PRIORITY;
}
service.prepareToLeaveProcess();
int res = ActivityManagerNative.getDefault().bindService(
mMainThread.getApplicationThread(), getActivityToken(),
service, service.resolveTypeIfNeeded(getContentResolver()),
sd, flags, user.getIdentifier());
if (res < 0) {
throw new SecurityException(
"Not allowed to bind to service " + service);
}
return res != 0;
} catch (RemoteException e) {
return false;
}
}
ActivityManagerNative.getDefault().bindService通过binder机制，将调用ActivityManagerService::bindService()函数。
这里的mMainThread是一个ActivityThread实例，通过ActivityThread::getHandler()就可以获得一个Handler对象。有了该Handler对象就可以将消息发送到ActivityThread所在进程的消息队列中去。
随后调用了mPackageInfo.getServiceDispatcher函数。mPackageInfo的类型是LoadedApk，因此调用的是LoadedApk::getServiceDispatcher函数。该函数的代码位于frameworks/base/core/java/android/app/LoadedApk.java中。
final class LoadedApk {
......
public final IServiceConnection getServiceDispatcher(ServiceConnection c,
Context context, Handler handler, int flags) {
synchronized (mServices) {
LoadedApk.ServiceDispatcher sd = null;
HashMap map = mServices.get(context);
if (map != null) {
sd = map.get(c);
}
if (sd == null) {
sd = new ServiceDispatcher(c, context, handler, flags);
if (map == null) {
map = new HashMap();
mServices.put(context, map);
}
map.put(c, sd);
} else {
sd.validate(context, handler);
}
return sd.getIServiceConnection();
}
}
......
static final class ServiceDispatcher {
private final ServiceDispatcher.InnerConnection mIServiceConnection;
private final ServiceConnection mConnection;
private final Handler mActivityThread;
......
private static class InnerConnection extends IServiceConnection.Stub {
final WeakReference mDispatcher;
......
InnerConnection(LoadedApk.ServiceDispatcher sd) {
mDispatcher = new WeakReference(sd);
}
......
}
......
ServiceDispatcher(ServiceConnection conn,
Context context, Handler activityThread, int flags) {
mIServiceConnection = new InnerConnection(this);
mConnection = conn;
mActivityThread = activityThread;
......
}
......
IServiceConnection getIServiceConnection() {
return mIServiceConnection;
}
......
}
......
} 函数getServiceDispatcher最后就是返回了一个InnerConnection对象给ContextImpl.bindService函数。回到ContextImpl.bindService函数中，它接着就要调用ActivityManagerService的远程接口来进一步处理了。
Step 4、ActivityManagerService::bindService()
代码位于frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中。
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);
}
}
本函数的第二个参数token是由Step 3中ActivityManagerProxy::bindService参数中getActivityToken函数获得。第五个参数connection是通过LoadedApk::getServiceDispatcher函数得到的一个IServiceConnection接口。继续看看ActiveServices::bindServiceLocked函数。
Step 5、ActiveServices::bindServiceLocked()
代码位于frameworks/base/services/java/com/android/server/am/ActiveServices.java文件中。
int bindServiceLocked(IApplicationThread caller, IBinder token,
Intent service, String resolvedType,
IServiceConnection connection, int flags, int userId) {
if (DEBUG_SERVICE) Slog.v(TAG, "bindService: " + service
+ " type=" + resolvedType + " conn=" + connection.asBinder()
+ " flags=0x" + Integer.toHexString(flags));
final ProcessRecord callerApp = mAm.getRecordForAppLocked(caller);//根据IApplicationThread对象找到ProcessRecord对象
if (callerApp == null) {
throw new SecurityException(
"Unable to find app for caller " + caller
+ " (pid=" + Binder.getCallingPid()
+ ") when binding service " + service);
}
ActivityRecord activity = null;
if (token != null) {
activity = ActivityRecord.isInStackLocked(token);
if (activity == null) {
Slog.w(TAG, "Binding with unknown activity: " + token);
return 0;
}
}
int clientLabel = 0;
PendingIntent clientIntent = null;
if (callerApp.info.uid == Process.SYSTEM_UID) {
// Hacky kind of thing -- allow system stuff to tell us
// what they are, so we can report this elsewhere for
// others to know why certain services are running.
try {
clientIntent = (PendingIntent)service.getParcelableExtra(
Intent.EXTRA_CLIENT_INTENT);
} catch (RuntimeException e) {
}
if (clientIntent != null) {
clientLabel = service.getIntExtra(Intent.EXTRA_CLIENT_LABEL, 0);
if (clientLabel != 0) {
// There are no useful extras in the intent, trash them.
// System code calling with this stuff just needs to know
// this will happen.
service = service.cloneFilter();
}
}
}
final boolean callerFg = callerApp.setSchedGroup != Process.THREAD_GROUP_BG_NONINTERACTIVE;
ServiceLookupResult res =
retrieveServiceLocked(service, resolvedType,
Binder.getCallingPid(), Binder.getCallingUid(), userId, true, callerFg);//从AMS和PMS中，获取或者新建ServiceRecord，随后封装成ServiceLoolupResult对象并返回。
if (res == null) {
return 0;
}
if (res.record == null) {
return -1;
}
ServiceRecord s = res.record;
final long origId = Binder.clearCallingIdentity();
try {
if (unscheduleServiceRestartLocked(s)) {
if (DEBUG_SERVICE) Slog.v(TAG, "BIND SERVICE WHILE RESTART PENDING: "
+ s);
}
if ((flags&Context.BIND_AUTO_CREATE) != 0) {
s.lastActivity = SystemClock.uptimeMillis();
if (!s.hasAutoCreateConnections()) {
// This is the first binding, let the tracker know.
ProcessStats.ServiceState stracker = s.getTracker();
if (stracker != null) {
stracker.setBound(true, mAm.mProcessStats.getMemFactorLocked(),
s.lastActivity);
}
}
}
AppBindRecord b = s.retrieveAppBindingLocked(service, callerApp);//在ServiceRecord的IntentBindRecord列表，AppBindRecord列表中检索AppBindRecor，若没有，则new AppBindRecord并返回
ConnectionRecord c = new ConnectionRecord(b, activity,
connection, flags, clientLabel, clientIntent);
IBinder binder = connection.asBinder();
ArrayList clist = s.connections.get(binder);
if (clist == null) {
clist = new ArrayList();
s.connections.put(binder, clist);//将ConnectionRecor放入ServiceRecord.connections列表中，在之后的publishService中依次取出。
}
clist.add(c);
b.connections.add(c);
if (activity != null) {
if (activity.connections == null) {
activity.connections = new HashSet();
}
activity.connections.add(c);
}
b.client.connections.add(c);
if ((c.flags&Context.BIND_ABOVE_CLIENT) != 0) {
b.client.hasAboveClient = true;
}
clist = mServiceConnections.get(binder);
if (clist == null) {
clist = new ArrayList();
mServiceConnections.put(binder, clist);
}
clist.add(c);
if ((flags&Context.BIND_AUTO_CREATE) != 0) {//若应用程序使用bindService时传入的参数为该标志时直接调用bringUpServiceLocked
s.lastActivity = SystemClock.uptimeMillis();
if (bringUpServiceLocked(s, service.getFlags(), callerFg, false) != null) {
return 0;
}
}
if (s.app != null) {
// This could have made the service more important.
mAm.updateOomAdjLocked(s.app);
}
if (DEBUG_SERVICE) Slog.v(TAG, "Bind " + s + " with " + b
+ ": received=" + b.intent.received
+ " apps=" + b.intent.apps.size()
+ " doRebind=" + b.intent.doRebind);
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);
}
getServiceMap(s.userId).ensureNotStartingBackground(s);
} finally {
Binder.restoreCallingIdentity(origId);
}
return 1;
}
倘若应用程序中bindService时传入的参数为BIND_AUTO_CREATE时，执行bringUpServiceLocked；这里分析另外一种情况——参数flags不为BIND_AUTO_CREATE的情况。
Step 6、ActiveServices::requestServiceBindingLocked
代码位于frameworks/base/services/java/com/android/am/ActiveServices.java文件中。
private final boolean requestServiceBindingLocked(ServiceRecord r,
IntentBindRecord i, boolean execInFg, boolean rebind) {
if (r.app == null || r.app.thread == null) {//若service未运行，直接返回，不做任何操作
// If service is not currently running, can't yet bind.
return false;
}
if ((!i.requested || rebind) && i.apps.size() > 0) {//rebind表示是否重新绑定service，requested表示是否已绑定service？
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;
}
这里app.thread是ApplicationThread的代理对象，类型是AppllicationThreadProxy。
Step 7、ApplicationThreadProxy::scheduleBindService
代码位于frameworks/base/core/java/android/app/ActvityThread.java文件中。
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);
}
Step 8、H::handleMessage
代码位于frameworks/base/core/java/android/app/ActvityThread.java文件中。
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
switch (msg.what) {
......
case BIND_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind");
handleBindService((BindServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
......
}
if (DEBUG_MESSAGES) Slog.v(TAG, "<<< done: " + codeToString(msg.what));
}
代码位于frameworks/base/core/java/android/app/ActvityThread.java文件中。
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());
try {
if (!data.rebind) {
IBinder binder = s.onBind(data.intent);//获取service的一个Binder对象，然后连同service实例传入AMS
ActivityManagerNative.getDefault().publishService(
data.token, data.intent, binder);
} else {
s.onRebind(data.intent);
ActivityManagerNative.getDefault().serviceDoneExecuting(
data.token, 0, 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);
}
}
}
}
这里的data是一个BindServiceData对象，之前是通过ApllicationThreadProxy的scheduleBindService经由Binder机制传入，通过data.token获取之前已启动了的service实例，即s。
Step 10、ActivityManagerService::publishService
代码位于frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中。
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);
}
}
Setp 11、ActiveServices::publishServiceLocked
代码位于frameworks/base/services/java/com/android/server/am/ActiveServices.java文件中。
void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service) {
final long origId = Binder.clearCallingIdentity();
try {
if (DEBUG_SERVICE) Slog.v(TAG, "PUBLISHING " + r
+ " " + intent + ": " + service);
if (r != null) {
Intent.FilterComparison filter
= new Intent.FilterComparison(intent);
IntentBindRecord b = r.bindings.get(filter);
if (b != null && !b.received) {
b.binder = service;
b.requested = true;
b.received = true;
for (int conni=r.connections.size()-1; conni>=0; conni--) {
ArrayList clist = r.connections.valueAt(conni);
for (int i=0; i 每一个ConnectionRecord里面都有一个成员变量conn，它的类型是IServiceConnection，是一个Binder对象的远程接口。函数中体现为c.conn，它是在Step 3中通过LoadedApk::getServiceDispatch创建的LoadedApk.ServiceDispatcher.InnerConnection对象。因此，在调用c.conn.connected(r.name, service)时，进入到了LoadedApk.ServiceDispatcher.InnerConnection.connected函数中去了。
Step 12、InnerConnection::connected
代码位于frameworks/base/core/java/android/app/LoadedApk.java文件中。
final class LoadedApk {
......
static final class ServiceDispatcher {
......
private static class InnerConnection extends IServiceConnection.Stub {
......
public void connected(ComponentName name, IBinder service) throws RemoteException {
LoadedApk.ServiceDispatcher sd = mDispatcher.get();
if (sd != null) {
sd.connected(name, service);
}
}
......
}
......
}
......
}Step 13、ServiceDspatcher::connected
这个函数定义在frameworks/base/core/java/android/app/LoadedApk.java文件中。
final class LoadedApk {
......
static final class ServiceDispatcher {
......
public void connected(ComponentName name, IBinder service) {
if (mActivityThread != null) {
mActivityThread.post(new RunConnection(name, service, 0));
} else {
......
}
}
......
}
......
}Step 14、Handler::post
这个函数定义在frameworks/base/core/java/android/os/Handler.java文件中。
public class Handler {
……
public final boolean post(Runnable r)
{
return sendMessageDelayed(getPostMessage(r), 0);
}
……
}
调用了这个函数之后，这个消息就真正地进入到ActivityThread的消息队列去了，与sendMessage把消息放在消息队列不一样的地方是，post方式发送的消息不是由这个Handler的handleMessage函数来处理的，而是由post的参数Runnable的run函数来处理的。这里传给post的参数是一个RunConnection类型的参数，它继承了Runnable类，因此，最终会调用RunConnection.run函数来处理这个消息。
Step 15、RunConnection::run
这个函数定义在frameworks/base/core/java/android/app/LoadedApk.java文件中。
final class LoadedApk {
......
static final class ServiceDispatcher {
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;
}
......
}
......
}
Step 14、ServiceDispatcher::doConnected
这个函数定义在frameworks/base/core/java/android/app/LoadedApk.java文件中。
final class LoadedApk {
......
static final class ServiceDispatcher {
......
public void doConnected(ComponentName name, IBinder service) {
ServiceDispatcher.ConnectionInfo old;
ServiceDispatcher.ConnectionInfo info;
synchronized (this) {
if (mForgotten) {
// We unbound before receiving the connection; ignore
// any connection received.
return;
}
old = mActiveConnections.get(name);
if (old != null && old.binder == service) {
// Huh, already have this one. Oh well!
return;
}
if (service != null) {
// A new service is being connected... set it all up.
mDied = false;
info = new ConnectionInfo();
info.binder = service;
info.deathMonitor = new DeathMonitor(name, service);
try {
service.linkToDeath(info.deathMonitor, 0);
mActiveConnections.put(name, info);
} catch (RemoteException e) {
// This service was dead before we got it... just
// don't do anything with it.
mActiveConnections.remove(name);
return;
}
} else {
// The named service is being disconnected... clean up.
mActiveConnections.remove(name);
}
if (old != null) {
old.binder.unlinkToDeath(old.deathMonitor, 0);
}
}
// 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);
}
}
......
}
......
}