app
MainActivity.java:
startService(new Intent(this,TestService.class));
ContextWrapper.java
@Override
public @Nullable ComponentName startService(Intent service) {
return mBase.startService(service);
}
这里的mBase是代理模式，其对象是ContextImpl对象。
ContextImpl.java
@Override
public ComponentName startService(Intent service) {
warnIfCallingFromSystemProcess();
return startServiceCommon(service, false, mUser);
}
private ComponentName startServiceCommon(Intent service, boolean requireForeground,
UserHandle user) {
...
ComponentName cn = ActivityManager.getService().startService(
mMainThread.getApplicationThread(), service, service.resolveTypeIfNeeded(
getContentResolver()), requireForeground,
getOpPackageName(), user.getIdentifier());
...
}
ActivityManager.getService().startService 通过binder通信，会调用ActivityManagerService中的startService。
system_server
ActivityManagerService.java
@Override
public ComponentName startService(IApplicationThread caller, Intent service,
String resolvedType, boolean requireForeground, String callingPackage, int userId)
throws TransactionTooLargeException {
...
res = mServices.startServiceLocked(caller, service,
resolvedType, callingPid, callingUid,
requireForeground, callingPackage, userId);
...
}
mServices是类型为ActiveServices。
ActiveServices.java
ComponentName startServiceLocked(IApplicationThread caller, Intent service, String resolvedType,
int callingPid, int callingUid, boolean fgRequired, String callingPackage,
final int userId, boolean allowBackgroundActivityStarts)
throws TransactionTooLargeException {
...
ComponentName cmp = startServiceInnerLocked(smap, service, r, callerFg, addToStarting);
...
}
ComponentName startServiceInnerLocked(ServiceMap smap, Intent service, ServiceRecord r,
boolean callerFg, boolean addToStarting) throws TransactionTooLargeException {
...
String error = bringUpServiceLocked(r, service.getFlags(), callerFg, false, false);
...
return r.name;
}
它的返回值是ComponentName，与startService相同，在执行完bringUpServiceLocked之后就返回了，所以重点看下bringUpServiceLocked方法。
private String bringUpServiceLocked(ServiceRecord r, int intentFlags, boolean execInFg,
boolean whileRestarting, boolean permissionsReviewRequired)
throws TransactionTooLargeException {
// 第一种情况: 当进程存在，service存在
if (r.app != null && r.app.thread != null) {
sendServiceArgsLocked(r, execInFg, false);
return null;
}
// 第二种情况：当进程存在，service不存在
if (!isolated) {
if (app != null && app.thread != null) {
realStartServiceLocked(r, app, execInFg);
}
}
// 第三种情况：当进程不存在，service自然也不存在
if (app == null && !permissionsReviewRequired) {
if ((app=mAm.startProcessLocked(procName, r.appInfo, true, intentFlags,
hostingRecord, false, isolated, false)) == null) {
}
}
}
以上三种情形分别会调用不同的方法进行处理，现在就分别看下这三个方法的实现。
- sendServiceArgsLocked方法
private final void sendServiceArgsLocked(ServiceRecord r, boolean execInFg,
boolean oomAdjusted) throws TransactionTooLargeException {
bumpServiceExecutingLocked(r, execInFg, "start");
r.app.thread.scheduleServiceArgs(r, slice);
}
scheduleServiceArgs是发送应用的binder调用，对应应用中的onStartCommand方法。
- realStartServiceLocked方法
private final void realStartServiceLocked(ServiceRecord r,
ProcessRecord app, boolean execInFg) throws RemoteException {
bumpServiceExecutingLocked(r, execInFg, "create");
...
app.thread.scheduleCreateService(r, r.serviceInfo,
mAm.compatibilityInfoForPackage(r.serviceInfo.applicationInfo),
app.getReportedProcState());
...
requestServiceBindingsLocked(r, execInFg);
...
sendServiceArgsLocked(r, execInFg, true);
...
}
private final void requestServiceBindingsLocked(ServiceRecord r, boolean execInFg)
throws TransactionTooLargeException {
...
if (!requestServiceBindingLocked(r, ibr, execInFg, false)) {
...
}
private final boolean requestServiceBindingLocked(ServiceRecord r, IntentBindRecord i,
boolean execInFg, boolean rebind) throws TransactionTooLargeException {
...
bumpServiceExecutingLocked(r, execInFg, "bind");
...
r.app.thread.scheduleBindService(r, i.intent.getIntent(), rebind,
r.app.getReportedProcState());
...
}
realStartServiceLocked方法会执行三个主逻辑，并分别对应三个binder调用，分别是scheduleCreateService、scheduleBindService、scheduleServiceArgs，并分别对应binder对端，即app service组件的onCreate、onBind、onStartCommand方法。
- startProcessLocked方法
这里不再详述，但能想到它会做两件事情，第一件事情是创建进程，第二件事情就是执行realStartServiceLocked，因为realStartServiceLocked对应了“当进程存在，service不存在”这种场景。
app
ActivityThread.java
- scheduleCreateService
public final void scheduleCreateService(IBinder token,
ServiceInfo info, CompatibilityInfo compatInfo, int processState) {
...
sendMessage(H.CREATE_SERVICE, s);
}
- scheduleBindService
public final void scheduleBindService(IBinder token, Intent intent,
boolean rebind, int processState) {
...
sendMessage(H.BIND_SERVICE, s);
}
- scheduleServiceArgs
public final void scheduleServiceArgs(IBinder token, ParceledListSlice args) {
...
sendMessage(H.SERVICE_ARGS, s);
}
}
scheduleCreateService、scheduleBindService、scheduleServiceArgs三个方法其实运行在binder线程，这个时候需要通过消息机制的sendMessage让主线程去执行相应的操作。分别对应下面的三个case:
- CREATE_SERVICE
case CREATE_SERVICE:
handleCreateService((CreateServiceData)msg.obj);
break;
- BIND_SERVICE
case BIND_SERVICE:
handleBindService((BindServiceData)msg.obj);
break;
- SERVICE_ARGS
case SERVICE_ARGS:
handleServiceArgs((ServiceArgsData)msg.obj);
break;
三个case分别执行下面的三个方法
@UnsupportedAppUsage
private void handleCreateService(CreateServiceData data) {
...
service.onCreate();
...
ActivityManager.getService().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
...
}
private void handleBindService(BindServiceData data) {
Service s = mServices.get(data.token);
...
IBinder binder = s.onBind(data.intent);
...
ActivityManager.getService().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
...
}
private void handleServiceArgs(ServiceArgsData data) {
Service s = mServices.get(data.token);
...
res = s.onStartCommand(data.args, data.flags, data.startId);
...
ActivityManager.getService().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_START, data.startId, res);
...
}
可见handleCreateService、handleBindService、handleServiceArgs分别调用了Service组件的onCreate、onBind、onStartCommand，并且执行完成后通过调用binder方法serviceDoneExecuting告诉system_server操作已完成。
加油吧，少年！
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