ContextImpl到AMS的过程
流程图：
要启动Service，我们会先调用startService方法。
@Override
public ComponentName startService(Intent service) {
return mBase.startService(service);
}
@Override
public ComponentName startService(Intent service) {
warnIfCallingFromSystemProcess();
return startServiceCommon(service, false, mUser);
}
我们最终会调用ContextImpl中的startService方法，在这个方法中会调用startServiceCommon方法
private ComponentName startServiceCommon(Intent service, boolean requireForeground,
UserHandle user) {
try {
validateServiceIntent(service);
service.prepareToLeaveProcess(this);
ComponentName cn = ActivityManager.getService().startService(
mMainThread.getApplicationThread(), service, service.resolveTypeIfNeeded(
getContentResolver()), requireForeground,
getOpPackageName(), user.getIdentifier());
if (cn != null) {
if (cn.getPackageName().equals("!")) {
throw new SecurityException(
"Not allowed to start service " + service
+ " without permission " + cn.getClassName());
} else if (cn.getPackageName().equals("!!")) {
throw new SecurityException(
"Unable to start service " + service
+ ": " + cn.getClassName());
} else if (cn.getPackageName().equals("?")) {
throw new IllegalStateException(
"Not allowed to start service " + service + ": " + cn.getClassName());
}
}
return cn;
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
在方法中会调用ActivityManager的getService方法获取AMS的代理IActivityManager，然后调用startService方法，最终会调用到AMS的startService方法。
ActivityThread启动Service
时序图：
上面说到最终调用了AMS的startService方法，下面我们来看看
public ComponentName startService(IApplicationThread caller, Intent service,
String resolvedType, boolean requireForeground, String callingPackage, int userId)
throws TransactionTooLargeException {
...
synchronized(this) {
final int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
ComponentName res;
try {
res = mServices.startServiceLocked(caller, service,
resolvedType, callingPid, callingUid,
requireForeground, callingPackage, userId);
} finally {
Binder.restoreCallingIdentity(origId);
}
return res;
}
}
我们可以看到这里调用了mServices的startServiceLocked方法。这里的mService是ActiveServices类，接下来我们看一下ActiveServices的startServiceLocked方法
ComponentName startServiceLocked(IApplicationThread caller, Intent service, String resolvedType,
int callingPid, int callingUid, boolean fgRequired, String callingPackage, final int userId)
throws TransactionTooLargeException {
...
ServiceLookupResult res =
retrieveServiceLocked(service, resolvedType, callingPackage,
callingPid, callingUid, userId, true, callerFg, false);
if (res == null) {
return null;
}
if (res.record == null) {
return new ComponentName("!", res.permission != null
? res.permission : "private to package");
}
ServiceRecord r = res.record;
...
ComponentName cmp = startServiceInnerLocked(smap, service, r, callerFg, addToStarting);
return cmp;
}
在方法中先通过retrieveServiceLocked查找是否有与要启动的Service对应的ServiceRecord，这里的ServiceRecord是Service的描述类。如果没有，就会调用PackageManagerService去获取Service的信息，并封装到ServiceRecord中，然后将ServiceRecord封装成ServiceLookupResult。然后将获取到的ServiceRecord赋值给r，并在调用startServiceInnerLocked方法的时候传入。
下面来看看startServiceInnerLocked是怎么实现的
ComponentName startServiceInnerLocked(ServiceMap smap, Intent service, ServiceRecord r,
boolean callerFg, boolean addToStarting) throws TransactionTooLargeException {
ServiceState stracker = r.getTracker();
if (stracker != null) {
stracker.setStarted(true, mAm.mProcessStats.getMemFactorLocked(), r.lastActivity);
}
r.callStart = false;
synchronized (r.stats.getBatteryStats()) {
r.stats.startRunningLocked();
}
String error = bringUpServiceLocked(r, service.getFlags(), callerFg, false, false);
if (error != null) {
return new ComponentName("!!", error);
}
...
return r.name;
}
方法中调用了bringUpServiceLocked方法
private String bringUpServiceLocked(ServiceRecord r, int intentFlags, boolean execInFg,
boolean whileRestarting, boolean permissionsReviewRequired)
throws TransactionTooLargeException {
...
final boolean isolated = (r.serviceInfo.flags&ServiceInfo.FLAG_ISOLATED_PROCESS) != 0;
final String procName = r.processName;
String hostingType = "service";
ProcessRecord app;
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) {
try {
app.addPackage(r.appInfo.packageName, r.appInfo.versionCode, mAm.mProcessStats);
realStartServiceLocked(r, app, execInFg);
return null;
} catch (TransactionTooLargeException e) {
throw e;
} 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.
}
} else {
// If this service runs in an isolated process, then each time
// we call startProcessLocked() we will get a new isolated
// process, starting another process if we are currently waiting
// for a previous process to come up. To deal with this, we store
// in the service any current isolated process it is running in or
// waiting to have come up.
app = r.isolatedProc;
if (WebViewZygote.isMultiprocessEnabled()
&& r.serviceInfo.packageName.equals(WebViewZygote.getPackageName())) {
hostingType = "webview_service";
}
}
// Not running -- get it started, and enqueue this service record
// to be executed when the app comes up.
if (app == null && !permissionsReviewRequired) {
if ((app=mAm.startProcessLocked(procName, r.appInfo, true, intentFlags,
hostingType, 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;
}
}
if (!mPendingServices.contains(r)) {
mPendingServices.add(r);
}
if (r.delayedStop) {
// Oh and hey we've already been asked to stop!
r.delayedStop = false;
if (r.startRequested) {
if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE,
"Applying delayed stop (in bring up): " + r);
stopServiceLocked(r);
}
}
return null;
}
方法中会调用ServiceRecord的processName参数，获取Service想要启动的进程，然后调用ActivityManagerService的getProcessRecordLocked方法获取和Service匹配的进程。接着判断这个进程是否为已经启动，如果启动了，会调用realStartServiceLocked方法，如果没有启动，会调用ActivityManagerService的startProcessLocked来启动这个进程。
接下来我们看看realStartServiceLocked方法
private final void realStartServiceLocked(ServiceRecord r,
ProcessRecord app, boolean execInFg) throws RemoteException {
...
try {
...
app.thread.scheduleCreateService(r, r.serviceInfo,
mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),
app.repProcState);
r.postNotification();
created = true;
} catch (DeadObjectException e) {
Slog.w(TAG, "Application dead when creating service " + r);
mAm.appDiedLocked(app);
throw e;
} finally {
if (!created) {
// Keep the executeNesting count accurate.
final boolean inDestroying = mDestroyingServices.contains(r);
serviceDoneExecutingLocked(r, inDestroying, inDestroying);
// Cleanup.
if (newService) {
app.services.remove(r);
r.app = null;
}
// Retry.
if (!inDestroying) {
scheduleServiceRestartLocked(r, false);
}
}
}
...
}
方法中最后调用了app.thread的scheduleCreateService。我们知道app.thread其实是IApplicationThread类型的，实现类是ActivityThread的内部类AppliationThread。
接着来看看AppliationThread中的scheduleCreateService方法
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);
}
这个方法是给H这个Handler发送一个消息，消息类型为CREATE_SERVICE。这个和启动Activity有点类似，下面我们来看看H中对应的实现
case CREATE_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, ("serviceCreate: " + String.valueOf(msg.obj)));
handleCreateService((CreateServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
这里会调用handleCreateService方法
private void handleCreateService(CreateServiceData data) {
// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
//线获取到LoadedApk类，这个是描述apk的类
LoadedApk packageInfo = getPackageInfoNoCheck(
data.info.applicationInfo, data.compatInfo);
Service service = null;
try {
//获取到classLoader，并通过CreateServiceData的参数创建Service实例
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);
}
}
try {
if (localLOGV) Slog.v(TAG, "Creating service " + data.info.name);
//创建Context的实现类ContextImpl
ContextImpl context = ContextImpl.createAppContext(this, packageInfo);
context.setOuterContext(service);
//创建Application，如果已经创建了Application，则直接返回
Application app = packageInfo.makeApplication(false, mInstrumentation);
//调用attach方法初始化Service的一些变量，context等
service.attach(context, this, data.info.name, data.token, app,
ActivityManager.getService());
//调用Service的onCreate方法，这样一个Service就启动了。
service.onCreate();
//将service加入到mServices这个map中，mServices是ArrayMap<IBinder, Service>
mServices.put(data.token, service);
try {
ActivityManager.getService().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
} catch (Exception e) {
if (!mInstrumentation.onException(service, e)) {
throw new RuntimeException(
"Unable to create service " + data.info.name
+ ": " + e.toString(), e);
}
}
}
代码中已经加入了注释，到这里，Service的启动就完成了。
