今天我们来看下这安卓的四大组件的另外一个Service,
按套路应该先列点我们在探索过程需要注意的问题,不过现在一时没想到有什么,
让我们边看说解释,看下有什么需要注意的
起航—-开启服务
API : 23
我们启动服务一般有两种调用StartService
和BindService
,这里我们先从StartService开始。
首先去到ContextWrapper里面的startService函数
@Override
public ComponentName startService(Intent service) {
return mBase.startService(service);
}
这个我们在前一篇也分析广播时候也遇到过类似情况,这个mBase的具体实现是ContextImpl,我们继续看下
@Override
public ComponentName startService(Intent service) {
warnIfCallingFromSystemProcess();
return startServiceCommon(service, mUser);
}
private ComponentName startServiceCommon(Intent service, UserHandle user) {
try {
validateServiceIntent(service);
service.prepareToLeaveProcess();
ComponentName cn = ActivityManagerNative.getDefault().startService(
mMainThread.getApplicationThread(), service, service.resolveTypeIfNeeded(
getContentResolver()), getOpPackageName(), user.getIdentifier());
...
return cn;
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
}
好吧,看到这个AMN,最近我们都看到他,已经在熟悉不过了,他的实现是AMS,我们就跑去哪里再看下那个startService里面做了什么吧
@Override
public ComponentName startService(IApplicationThread caller, Intent service,
String resolvedType, String callingPackage, int userId)
throws TransactionTooLargeException {
enforceNotIsolatedCaller("startService");
...
synchronized(this) {
final int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
ComponentName res = mServices.startServiceLocked(caller, service,
resolvedType, callingPid, callingUid, callingPackage, userId);
Binder.restoreCallingIdentity(origId);
return res;
}
}
他在底层去调用了ActivityService.startServiceLocked()
,感觉这个命名格式也很有熟悉感啊,来我们继续看下他做了什么
ComponentName startServiceLocked(IApplicationThread caller, Intent service, String resolvedType,
int callingPid, int callingUid, String callingPackage, int userId)
throws TransactionTooLargeException {
ServiceLookupResult res =
retrieveServiceLocked(service, resolvedType, callingPackage,
callingPid, callingUid, userId, true, callerFg);
ServiceRecord r = res.record;
...
return startServiceInnerLocked(smap, service, r, callerFg, addToStarting);
}
经过一对的处理,他最后调用了startServiceInnerLocked();
ComponentName startServiceInnerLocked(ServiceMap smap, Intent service, ServiceRecord r,
boolean callerFg, boolean addToStarting) throws TransactionTooLargeException {
...
String error = bringUpServiceLocked(r, service.getFlags(), callerFg, false);
if (error != null) {
return new ComponentName("!!", error);
}
...
return r.name;
}
继续看下里面的内容
private final String bringUpServiceLocked(ServiceRecord r, int intentFlags, boolean execInFg,
boolean whileRestarting) throws TransactionTooLargeException {
...
app.addPackage(r.appInfo.packageName, r.appInfo.versionCode, mAm.mProcessStats);
realStartServiceLocked(r, app, execInFg);
...
}
哈,realStartServiceLocked
这名字看起来,前面都是骗人的启动过程,现在才开始干真活的样子
private final void realStartServiceLocked(ServiceRecord r,
ProcessRecord app, boolean execInFg) throws RemoteException {
...
try {
...
mAm.ensurePackageDexOpt(r.serviceInfo.packageName);
app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE);
app.thread.scheduleCreateService(r, r.serviceInfo,
mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),
app.repProcState);
r.postNotification();
created = true;
} catch (DeadObjectException e) {
...
}
requestServiceBindingsLocked(r, execInFg);
updateServiceClientActivitiesLocked(app, null, true);
// If the service is in the started state, and there are no
// pending arguments, then fake up one so its onStartCommand() will
// be called.
if (r.startRequested && r.callStart && r.pendingStarts.size() == 0) {
r.pendingStarts.add(new ServiceRecord.StartItem(r, false, r.makeNextStartId(),
null, null));
}
sendServiceArgsLocked(r, execInFg, true);
...
}
好了,截取掉一部分不相干的消息,我们现在看下他实际做了什么,我们看到了他是去调用app.thread.scheduleCreateService()函数去执行service的,这个我们前篇文章有看到过这个app.thread,最终干活的是ActivityThread里的一个ApplicationThread。让我们去看下他实际干了什么。
另外结尾也有注释,如果service已启动且没Pending arguments,那是去调用了他onStartCommand()
好了,还是就像去看下主线任务吧
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);
}
我们的”H“显示似乎又要登场了,靠他来发送一个创建服务的消息来干活。
private void sendMessage(int what, Object obj) {
sendMessage(what, obj, 0, 0, false);
}
private void sendMessage(int what, Object obj, int arg1, int arg2, boolean async) {
Message msg = Message.obtain();
msg.what = what;
msg.obj = obj;
msg.arg1 = arg1;
msg.arg2 = arg2;
if (async) {
msg.setAsynchronous(true);
}
mH.sendMessage(msg);
}
确实是去调用我们的H朋友去发送消息去了,我们看下消息里面调用的handleCreateService((CreateServiceData)msg.obj)
具体做了什么
private void handleCreateService(CreateServiceData data) {
LoadedApk packageInfo = getPackageInfoNoCheck(
data.info.applicationInfo, data.compatInfo);
Service service = null;
java.lang.ClassLoader cl = packageInfo.getClassLoader();
service = (Service) cl.loadClass(data.info.name).newInstance();
ContextImpl context = ContextImpl.createAppContext(this, packageInfo);
context.setOuterContext(service);
Application app = packageInfo.makeApplication(false, mInstrumentation);
service.attach(context, this, data.info.name, data.token, app,
ActivityManagerNative.getDefault());
service.onCreate();
mServices.put(data.token, service);
ActivityManagerNative.getDefault().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
}
为何方便看,精简了下代码,从上面的代码可以看到,到这里用ClassLoader去启动了服务,配置了下Context,这个就是我们然后调用了服务的onCreate方法。好了,这样我们的启动过程基本就到这里了。
另外,我们知道onCreate函数执行完后,就是到了onStartCommand()啦,不过这个过程好像没看到啊?跑去哪里了呢?
这是因为还有一部分代码没说,重新回到我们的 真 · 干活的realStartServiceLocked
函数的地步,有这么一个函数我留着 sendServiceArgsLocked(r, execInFg, true);
,他的作用就是发送参数,让我们看下这部分内容
private final void sendServiceArgsLocked(ServiceRecord r, boolean execInFg,
boolean oomAdjusted) throws TransactionTooLargeException {
...
r.app.thread.scheduleServiceArgs(r, si.taskRemoved, si.id, flags, si.intent);
...
}
只留下最重要的一句话,就是调度发送service的参数
public final void scheduleServiceArgs(IBinder token, boolean taskRemoved, int startId,
int flags ,Intent args) {
ServiceArgsData s = new ServiceArgsData();
s.token = token;
s.taskRemoved = taskRemoved;
s.startId = startId;
s.flags = flags;
s.args = args;
sendMessage(H.SERVICE_ARGS, s);
}
这个复杂发送了一个消息回去,代码在下面
private void handleServiceArgs(ServiceArgsData data) {
Service s = mServices.get(data.token);
if (s != null) {
if (data.args != null) {
data.args.setExtrasClassLoader(s.getClassLoader());
data.args.prepareToEnterProcess();
}
int res;
if (!data.taskRemoved) {
res = s.onStartCommand(data.args, data.flags, data.startId);
} else {
s.onTaskRemoved(data.args);
res = Service.START_TASK_REMOVED_COMPLETE;
}
...
}
}
好了,这样我们的onStartCommannd也就集齐了。
整个流程算跑完一半了。
前进— — 停止服务
在开始看过程前,我们来猜下他打开的过程,应该最后也是跑回到H里面执行一个什么STOP_SERVICE
消息。带着这个猜想,我们偷下懒,直接从我们的H先生哪里看下消息列表,看下有没我们想要的
case CREATE_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceCreate");
handleCreateService((CreateServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case BIND_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind");
handleBindService((BindServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case UNBIND_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceUnbind");
handleUnbindService((BindServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case SERVICE_ARGS:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceStart");
handleServiceArgs((ServiceArgsData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case STOP_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceStop");
handleStopService((IBinder)msg.obj);
maybeSnapshot();
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
哈哈,真的中了,我们看到还有BIND_SERVICE
和UNBIND_SERVICE
,全部在这里,那么中间过程我们就可以猜想啦
private void handleStopService(IBinder token) {
Service s = mServices.remove(token);
if (s != null) {
try {
s.onDestroy();
Context context = s.getBaseContext();
if (context instanceof ContextImpl) {
final String who = s.getClassName();
((ContextImpl) context).scheduleFinalCleanup(who, "Service");
}
QueuedWork.waitToFinish();
ActivityManagerNative.getDefault().serviceDoneExecuting(
token, SERVICE_DONE_EXECUTING_STOP, 0, 0);
} catch (Exception e) {
...
}
}
}
大跃进— — 绑定服务
现在我们直接来看下绑定服务是怎么回事
@Override
public boolean bindService(Intent service, ServiceConnection conn,
int flags) {
return mBase.bindService(service, conn, flags);
}
老套路,我们继续看下ContextImpl的内容
@Override
public boolean bindService(Intent service, ServiceConnection conn,
int flags) {
warnIfCallingFromSystemProcess();
return bindServiceCommon(service, conn, flags, Process.myUserHandle());
}
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);
} 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, getOpPackageName(), user.getIdentifier());
if (res < 0) {
throw new SecurityException(
"Not allowed to bind to service " + service);
}
return res != 0;
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
}
我们这里看到,最重要的一句还是上面第十行的位置,跑去调用AMS的bindService
了。
另外这里有点要补充的内容就是,我们的这个绑定可能是跨进程的情况啊,所以我们看到上面,他把我们的
ServiceConnection被再次打包了一下,弄成了IServiceConnection
,显然这个是一个Binder
,和我们的广播类似啊,被打包成了IIntentReceiver
,从而达到能够跨进程的效果。这个IServiceConnection也是在LoadedApk里面啊,保存着一个map,存储两者的关系,这里就不细细去看了,继续看我们的主线吧。
public int bindService(IApplicationThread caller, IBinder token, Intent service,
String resolvedType, IServiceConnection connection, int flags, String callingPackage,
int userId) throws TransactionTooLargeException {
enforceNotIsolatedCaller("bindService");
// Refuse possible leaked file descriptors
if (service != null && service.hasFileDescriptors() == true) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
if (callingPackage == null) {
throw new IllegalArgumentException("callingPackage cannot be null");
}
synchronized(this) {
return mServices.bindServiceLocked(caller, token, service,
resolvedType, connection, flags, callingPackage, userId);
}
}
我们看到结尾这里,继续调用了ActiveServices的bindServiceLocked()。想说的是,这个ActivityService是负责给AMS打工,管理Service的启动,绑定,解绑和停止等工作的,终于想说这个AMS里面有点像组合模型的地方,把一些业务分割出去了。应该在分割出去点的,虽然很多都是判断和处理语句,太庞大了,整个AMS类
我们继续看下那个bindServiceLock
,他和我们启动任务的时候类似,去调用了bringUpServiceLocked
,调用完后就去realStartServiceLocked
,后面流程类似,就不重复,唯一看完全部,不一样的地方当然是我们是绑定啊,要返回连接的啊!
在RealStartServiceLock
里面,他继续去执行了函数结尾处的下面的函数
requestServiceBindingsLocked(r, execInFg);
updateServiceClientActivitiesLocked(app, null, true);
private final boolean requestServiceBindingLocked(ServiceRecord r, IntentBindRecord i,
boolean execInFg, boolean rebind) throws TransactionTooLargeException {
...
if ((!i.requested || rebind) && i.apps.size() > 0) {
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;
}
...
return true;
}
这样我们就看到他去调用多了ApplicationThread里面的scheduleBindService去绑定多服务!
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);
}
通过这里去绑定我们的服务
private void handleBindService(BindServiceData data) {
Service s = mServices.get(data.token);
if (s != null) {
data.intent.setExtrasClassLoader(s.getClassLoader());
data.intent.prepareToEnterProcess();
try {
if (!data.rebind) {
IBinder binder = s.onBind(data.intent);
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) {
}
}
}
在这里我们看到,对于多次绑定,他调用了我们服务的onRebind函数!而对于第一次绑定,我们是调用了我们的服务的onBind函数,这和我们以前的开发经验也很对,不过好像缺少了跑到回调去的步骤啊,
看下去,嗯,应该是用AMS的publishService
去做的,让我们探索下去吧!。
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);
}
}
你看,我们的小助手mService又出现了,真的是管理Service的好助手啊
void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service) {
final long origId = Binder.clearCallingIdentity();
if (r != null) {
Intent.FilterComparison filter
= new Intent.FilterComparison(intent);
IntentBindRecord b = r.bindings.get(filter);
if (b != null && !b.received) {
for (int conni=r.connections.size()-1; conni>=0; conni--) {
ArrayList<ConnectionRecord> clist =
r.connections.valueAt(conni);
for (int i=0; i<clist.size(); i++) {
ConnectionRecord c = clist.get(i);
...
c.conn.connected(r.name, service);
}
}
}
serviceDoneExecutingLocked(r, mDestroyingServices.contains(r), false);
}
}
看到这里,需要解释下,还记得前面说,我们的ServiceConnection是被打包起来,弄成了IServiceConnection
,才来达到跨进程的效果的,这里的c.conn
就是原来那个iServiceConnection。
很显然他的这个connected方法就是回调,像前面说的广播一样,再在里面去执行我们的方法的回调。
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);
}
}
}
这个我们看到跑到了sd.connected();
不小心看成了连接sb.
public void connected(ComponentName name, IBinder service) {
if (mActivityThread != null) {
mActivityThread.post(new RunConnection(name, service, 0));
} else {
doConnected(name, service);
}
}
好了,这里有看到一些熟悉的内容啦!!!
这个坑爹的mActivyThread!!实际上就是那个“H”先生!!,这里就不解释了!通过他来运行回主线程!既然是调用它的post方法去执行,继续看下那个RunConnection里面的内容吧
public void run() {
if (mCommand == 0) {
doConnected(mName, mService);
} else if (mCommand == 1) {
doDeath(mName, mService);
}
}
好了,我们去看下doConencted的内容把
public void doConnected(ComponentName name, IBinder service) {
...
if (service != null) {
mConnection.onServiceConnected(name, service);
}
}
到这里我们就回调到我们绑定的时候的的回调接口去。
好了,贴了这么多代码,终于进入尾声了,我们的整个绑定过程!
后记
偷下懒,别的过程就先不写了。其余的过程基本最后也是跑回到那个H先生那里去执行下的,没什么大的问题的。
另外,说到Service,都会想到他的朋友IntentService,为何它可以执行一些耗时的操作呢?
这部分没写下来。
这样就剩下最后一个金刚没写他的故事啦,今晚抽空写下,就算对四大金刚有一个进一步的了解了!