Android-Framework学习笔记（八）Service的启动-绑定过程

ActiveServices#bringUpServiceLocked()

private String bringUpServiceLocked(ServiceRecord r, int intentFlags, boolean execInFg,
boolean whileRestarting, boolean permissionsReviewRequired)
throws TransactionTooLargeException {
…
final String procName = r.processName;//1
ProcessRecord app;
if (!isolated) {
app = mAm.getProcessRecordLocked(procName, r.appInfo.uid, false);//2
if (DEBUG_MU) Slog.v(TAG_MU, “bringUpServiceLocked: appInfo.uid=” + r.appInfo.uid

• " app=" + app);
  if (app != null && app.thread != null) {//3
  try {
  app.addPackage(r.appInfo.packageName, r.appInfo.versionCode,
  mAm.mProcessStats);
  realStartServiceLocked(r, app, execInFg);//4
  return null;
  } catch (TransactionTooLargeException e) {
  throw e;
  } catch (RemoteException e) {
  Slog.w(TAG, "Exception when starting service " + r.shortName, e);
  }
  }
  } else {
  app = r.isolatedProc;
  }
  if (app == null && !permissionsReviewRequired) {//5
  if ((app=mAm.startProcessLocked(procName, r.appInfo, true, intentFlags,
  “service”, r.name, false, isolated, false)) == null) {//6
  …
  }
  if (isolated) {
  r.isolatedProc = app;
  }
  }
  …
  }

和应用程序启动流程基本一致。
注释1处得到ServiceRecord的processName的值赋值给procName ，其中ServiceRecord用来描述Service的android:process属性。
注释2处将procName和Service的uid传入到AMS的getProcessRecordLocked方法中，来查询是否存在一个与Service对应的ProcessRecord类型的对象app，ProcessRecord主要用来记录运行的应用程序进程的信息。
注释5处判断Service对应的app为null则说明用来运行Service的应用程序进程不存在，则调用注释6处的AMS的startProcessLocked方法来创建对应的应用程序进程，具体创建过程参考Framework学习（六）应用程序进程启动过程。
注释3处表示Service的应用程序进程已经存在，则执行注释4的realStartServiceLocked方法。

ActiveServices#realStartServiceLocked()

private final void realStartServiceLocked(ServiceRecord r,
ProcessRecord app, boolean execInFg) throws RemoteException {
…
try {
…
//1
app.thread.scheduleCreateService(r, r.serviceInfo,
mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),
app.repProcState);
r.postNotification();
created = true;
} catch (DeadObjectException e) {
…
}
…
}

注释1调用了app.thread的scheduleCreateService方法。其中app.thread是IApplicationThread类型的，它的实现是ActivityThread的内部类ApplicationThread，其中ApplicationThread继承了ApplicationThreadNative，而ApplicationThreadNative继承了Binder并实现了IApplicationThread接口。

ActivityThread启动Service
frameworks/base/core/java/android/app/ActivityThread.java

ApplicationThread#scheduleCreateService()

public final void scheduleCreateService(IBinder token,
ServiceInfo info, CompatibilityInfo compatInfo, int processState) {
updateProcessState(processState, false);
CreateServiceData s = new CreateServiceData(); //1
s.token = token;
s.info = info;
s.compatInfo = compatInfo;

sendMessage(H.CREATE_SERVICE, s); //2
}

注释1将要启动的信息封装成CreateServiceData对象。
注释2将CreateServiceData对象通过sendMessage方法向H发送CREATE_SERVICE消息。

ApplicationThread#sendMessage()

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) {
if (DEBUG_MESSAGES) Slog.v(
TAG, "SCHEDULE " + what + " " + mH.codeToString(what)

• ": " + arg1 + " / " + obj);
  Message msg = Message.obtain();
  msg.what = what;
  msg.obj = obj;
  msg.arg1 = arg1;
  msg.arg2 = arg2;
  if (async) {
  msg.setAsynchronous(true);