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136 lines
4.1 KiB
136 lines
4.1 KiB
---
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Service 的启动原理
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---
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1. Service 启动有哪几种方式？
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2. Service 启动过程中主要流程有哪些？
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3. Service 启动过程涉及哪些参与者，通信过程是怎样的？
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```java
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@Override
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public ComponentName startService(Intent service) {
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return startServiceCommon(service, mUser);
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}
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```
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```java
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ComponentName startServiceCommon(Intent service, ...) {
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ComponentName cn = ActivityManagerNative.getDefault().startService(mMainThread.getApplicationThread(), service, ...);
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return cn;
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}
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```
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```java
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// ASM#startService
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ComponentName startService(IApplicationThread caller, Intent service, ...) {
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ComponentName res = mService.startServiceLocked(caller, service, ...);
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return res;
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}
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ComponentName startServiceLocked(Intent service, ...){
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ServiceLookupResult res = retrieveServiceLocked(service, ...);
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ServiceRecord r = res.record;
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//...
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r.pendingStarts.add(new ServiceRecord.StartItem(r, ...));
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return startServiceInnerLocked(smap, service, r, ...);
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}
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ComponentName startServiceInnerLocked(ServiceMap smap, Intent service, ...){
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bringUpServiceLocked(r, service.getFlags(), callerFg, false);
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}
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final String bringUpServiceLocked(ServiceRecord r, ...) {
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if(r.app != null && r.app.thread != null){
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// 如果 Service 已经启动，就执行 Service#onStartCommand
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sendServiceArgsLocked(r, ...);
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return null;
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}
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ProcessRecord app = mAm.getProcessRecordLocked(procName, ...);
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if(app != null && app.thread != null) {
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realStartServiceLocked(r, app, execlnFg);
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return null;
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}
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if(app == null){
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app = mAm.startProcessLocked(procName, ...);
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}
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if(!mPendingService.contains(r)){
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mPendingService.add(r);
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}
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}
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```
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```java
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//ASM#attachApplicationLocked
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boolean attachApplicationLocked(IApplicationThread thread, ...) {
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// 处理 Pending 的 Service
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mService.attachApplicationLocked(app, processName);
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return true;
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}
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boolean attachApplicationLocked(ProcessRecord proc, ...) {
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for(int i=0;i<mPendingService.size();i++) {
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sr = mPendingService.get(i);
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//...
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mPendingServices.remove(i--);
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realStartServiceLocked(sr, proc, ...);
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}
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}
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void realStartServiceLocked(ServiceRecord r, ProcessRecord app, ...) {
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r.app = app;
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// scheduleCreateService: 向应用端发起 IPC 调用
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// 应用端收到之后就会去创建 Service，并执行 onCreate 回调
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// r: class ServiceRecord extends Binder{}
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app.thread.scheduleCreateService(r, r.serviceInfo, ...);
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// 触发 Service 的 onStartCommand 回调
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sendServiceArgsLocked(r, ...);
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}
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// 应用端处理 CreateService 请求，运行在主线程
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private void handleCreateService(CreateServiceData data) {
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LoadedApk = packageInfo = getPackageInfoNoCheck(...);
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Service service = (Service)cl.loadClass(data.info.name).newInstance();
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ContextImpl context = ContextImpl.createAppContext(this, ...);
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Application app = packageInfo.makeApplication(false, ...);
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service.attach(context, this, ...);
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service.onCreate();
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// mService: ArrayMap<IBinder, Service>,key: ServiceRecord
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mService.put(data.token, service);
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}
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private final void sendServiceArgsLocked(ServiceRecord r, ){
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while(r.pendingStarts.size() > 0){
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StartItem si = r.pendingStarts.remove(0);
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// 调到应用端
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r.app.thread.scheduleServiceArgs(r, ...);
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}
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}
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public final void scheduleServiceArgs(IBinder token, ...) {
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ServiceArgsData s = new ServiceArgsData();
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//...
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sendMessage(H.SERVICE_ARGS, s);
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}
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private void handleServiceArgs(ServiceArgsData data) {
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Service s = mService.get(data, token);
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if(s != null){
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s.onStartCommand(data.args, data.flags, data.startId);
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}
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}
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```
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**总结**
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绑定服务：
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```java
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int bindServiceLocked(IApplicationThread caller, ...) {
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//...
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if((flags & Context.BIND_AUTO_CREATE)!=0){
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bringUpServiceLocked(s, ...);
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}
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}
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```
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BindService 并不会触发 onStartCommand，因为 bind service 它没有给 ServiceRecord 加到 pendingStarts 队列里面。 |