service启动流程

1、以start方式启动

（1）原应用进程---AMS

startService

 1 public class ContextWrapper extends Context {
 2       Context mBase;
 3       ......
 4       protected void attachBaseContext(Context base) {
 5           if (mBase != null) {
 6               throw new IllegalStateException("Base context already set");
 7           }
 8           mBase = base;
 9        }
10        ......
11        @Override
12        public ComponentName startService(Intent service) {
13           return mBase.startService(service);
14        }
15        ......
16 }

mBase来历

 1 //====ActivityThread.java=====
 2 private Activity performLaunchActivity(...){
 3     ......
 4     ContextImpl appContext = createBaseContextForActivity(r); //代码①
 5     Activity activity = null;
 6     ......
 7     activity.attach(appContext,...);//代码②
 8     ......
 9 }
10 
11 //跟进代码①
12 private ContextImpl createBaseContextForActivity(ActivityClientRecord r) {
13     ......
14     ContextImpl appContext = ContextImpl.createActivityContext(
15             this, r.packageInfo, r.activityInfo, r.token, displayId, r.overrideConfig);
16     ......
17     return appContext;
18 }
19 
20 //==========ContextImpl.java=======
21 static ContextImpl createActivityContext(...){
22      ......
23      ContextImpl context = new ContextImpl(...);
24      .....
25      return context;
26 }
27 
28 //跟进代码②
29 //======Activity.java extends ContextThemeWrapper extends ContextThemeWrapper extends ContextWrapper extends Context===
30 final void attach(Context context,...){
31      attachBaseContext(context);
32      ......
33 }
34 
35 protected void attachBaseContext(Context newBase) {
36     super.attachBaseContext(newBase);
37     ......
38 }
39 
40 //======ContextThemeWrapper.java======
41 @Override
42 protected void attachBaseContext(Context newBase) {
43     super.attachBaseContext(newBase);
44 }
45 //========ContextWrapper.java=====
46 protected void attachBaseContext(Context base) {
47     if (mBase != null) {
48         throw new IllegalStateException("Base context already set");
49     }
50     mBase = base;
51 }

所以mBase就是ContextImpl的实例。

1 class ContextImpl extends Context {
2      ......
3 }

 1 @Override
 2 public ComponentName startService(Intent service) {
 3     warnIfCallingFromSystemProcess();
 4     return startServiceCommon(service, false, mUser);
 5 }
 6 
 7 private ComponentName startServiceCommon(Intent service, boolean requireForeground,
 8         UserHandle user) {
 9     try {
10         ......
11         ComponentName cn = ActivityManager.getService().startService(
12             mMainThread.getApplicationThread(), service, service.resolveTypeIfNeeded(
13                         getContentResolver()), requireForeground,
14                         getOpPackageName(), user.getIdentifier());
15         ......
16         return cn;
17     } catch (RemoteException e) {
18         throw e.rethrowFromSystemServer();
19     }
20 }

在上一篇文章中提到过，ActivityManager.getService()实际上就是获取AMS在当前进程的远程代理Proxy，这里不赘述了。

 1 //=========ActivityManagerService.java============
 2 ......
 3 final ActiveServices mServices;
 4 ......
 5 @Override
 6 public ComponentName startService(IApplicationThread caller, Intent service,
 7         String resolvedType, boolean requireForeground, String callingPackage, int userId)
 8         throws TransactionTooLargeException {
 9     ......
10     synchronized(this) {
11         final int callingPid = Binder.getCallingPid(); //调用者进程id
12         final int callingUid = Binder.getCallingUid();//调用者用户id
13         final long origId = Binder.clearCallingIdentity();
14         ComponentName res;
15         try {
16             res = mServices.startServiceLocked(caller, service,
17                     resolvedType, callingPid, callingUid,
18                     requireForeground, callingPackage, userId);
19         } finally {
20             Binder.restoreCallingIdentity(origId);
21         }
22         return res;
23     }
24 }

（2）AMS到ApplicationThread

2、以bindService方式启动