前文
前言
我们知道Service有启动和绑定两种使用方式，本文根据两种情况分别解释（源码解析较长，不讲武德的同志可以直接拉最后看总结）
Service 的启动
Service的启动流程比较简单，在各版本中没什么大变动，本文代码为8.1截取，但在8-11版本也适用
ContextImpl到AMS的调用过程
我们调用startService其实调的是ContextWrapper的startService方法
frameworks/base/core/java/android/content/ContextWrapper.java
Context mBase;
@Override
public ComponentName startService(Intent service) {
return mBase.startService(service);
}
Context的具体实现是ContextImpl
frameworks/base/core/java/android/app/ContextImpl.java
@Override
public ComponentName startService(Intent service) {
warnIfCallingFromSystemProcess();
return startServiceCommon(service, false, mUser);
}
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();
}
}
根据Android系统揭秘（一）-Activity启动流程（上） 一节我们已经知道ActivityManager.getService()其实就是AMS
AMS通知ActivityThread
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
final ActiveServices mServices;
@Override
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;
}
}
frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
ComponentName startServiceLocked(IApplicationThread caller, Intent service, String resolvedType,
int callingPid, int callingUid, boolean fgRequired, String callingPackage, final int userId)
throws TransactionTooLargeException {
...
ComponentName cmp = startServiceInnerLocked(smap, service, r, callerFg, addToStarting);
return cmp;
}
ComponentName startServiceInnerLocked(ServiceMap smap, Intent service, ServiceRecord r,
boolean callerFg, boolean addToStarting) throws TransactionTooLargeException {
...
String error = bringUpServiceLocked(r, service.getFlags(), callerFg, false, false);
if (error != null) {
return new ComponentName("!!", error);
}
...
return r.name;
}
private String bringUpServiceLocked(ServiceRecord r, int intentFlags, boolean execInFg,
boolean whileRestarting, boolean permissionsReviewRequired)
throws TransactionTooLargeException {
// 发送Service参数
if (r.app != null && r.app.thread != null) {
sendServiceArgsLocked(r, execInFg, false);
return null;
}
...
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);
// 启动Service
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
...
}
// 如果Service进程不存在则创建
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;
}
}
...
return null;
}
bringUpServiceLocked方法会获取Service所在的进程，如果存在则通过realStartServiceLocked启动Service，否则先创建进程再启动Service
private final void realStartServiceLocked(ServiceRecord r,
ProcessRecord app, boolean execInFg) throws RemoteException {
...
boolean created = false;
try {
...
app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE);
app.thread.scheduleCreateService(r, r.serviceInfo,
mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),
app.repProcState);
r.postNotification();
created = true;
} catch (DeadObjectException e) {
...
} finally {
...
}
...
}
这里的app.thread指的是IApplicationThread,它的实现是ActivityThread的内部类ApplicationThread, 其中ApplicationThread继承了IApplicationThread.Stub
ActivityThread启动Service
frameworks/base/core/java/android/app/ActivityThread.java#ApplicationThread
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);
}
然后就是向mH发送CREATE_SERVICE命令，在H的handleMessage里面接收
frameworks/base/core/java/android/app/ActivityThread.java
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
switch (msg.what) {
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;
}
}
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();
// 获取包信息
LoadedApk packageInfo = getPackageInfoNoCheck(
data.info.applicationInfo, data.compatInfo);
Service service = null;
try {
// 获取类加载器
java.lang.ClassLoader cl = packageInfo.getClassLoader();
// 创建Service实例
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);
//创建上下文
ContextImpl context = ContextImpl.createAppContext(this, packageInfo);
context.setOuterContext(service);
// 创建或获取Application
Application app = packageInfo.makeApplication(false, mInstrumentation);
// 初始化Service
service.attach(context, this, data.info.name, data.token, app,
ActivityManager.getService());
// 回调通知开发者service创建完成
service.onCreate();
mServices.put(data.token, service);
try {
//通知AMS
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);
}
}
}
这一步主要做了以下事情：
- 获取包信息
- 获取类加载器
- 创建Service实例
- 创建上下文
- 创建或获取Application
- 初始化Service
- 回调通知开发者service创建完成
- 通知AMS
Service 的绑定
ContextImpl到AMS的调用过程
我们调用startService其实调的是ContextWrapper的startService方法
frameworks/base/core/java/android/content/ContextWrapper.java
Context mBase;
@Override
public boolean bindService(Intent service, ServiceConnection conn,
int flags) {
return mBase.bindService(service, conn, flags);
}
Context的具体实现是ContextImpl
frameworks/base/core/java/android/app/ContextImpl.java
@Override
public boolean bindService(Intent service, ServiceConnection conn,
int flags) {
warnIfCallingFromSystemProcess();
return bindServiceCommon(service, conn, flags, mMainThread.getHandler(),
Process.myUserHandle());
}
private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags, Handler
handler, UserHandle user) {
IServiceConnection sd;
...
if (mPackageInfo != null) {
sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(), handler, flags);
} else {
throw new RuntimeException("Not supported in system context");
}
...
validateServiceIntent(service);
try {
...
int res = ActivityManager.getService().bindService(
mMainThread.getApplicationThread(), getActivityToken(), service,
service.resolveTypeIfNeeded(getContentResolver()),
sd, flags, getOpPackageName(), user.getIdentifier());
if (res < 0) {
throw new SecurityException(
"Not allowed to bind to service " + service);
}
return res != 0;
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
AMS通知ActivityThread
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
final ActiveServices mServices;
public int bindService(IApplicationThread caller, IBinder token, Intent service,
String resolvedType, IServiceConnection connection, int flags, String callingPackage,
int userId) throws TransactionTooLargeException {
...
synchronized(this) {
return mServices.bindServiceLocked(caller, token, service,
resolvedType, connection, flags, callingPackage, userId);
}
}
(Android 10 之后会跳转bindIsolatedService方法先)
public int bindService(IApplicationThread caller, IBinder token, Intent service,
String resolvedType, IServiceConnection connection, int flags,
String callingPackage, int userId) throws TransactionTooLargeException {
return bindIsolatedService(caller, token, service, resolvedType, connection, flags,
null, callingPackage, userId);
}
public int bindIsolatedService(IApplicationThread caller, IBinder token, Intent service,
String resolvedType, IServiceConnection connection, int flags, String instanceName,
String callingPackage, int userId) throws TransactionTooLargeException {
...
synchronized(this) {
return mServices.bindServiceLocked(caller, token, service,
resolvedType, connection, flags, instanceName, callingPackage, userId);
}
}
frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
int bindServiceLocked(IApplicationThread caller, IBinder token, Intent service,
String resolvedType, final IServiceConnection connection, int flags,
String callingPackage, final int userId) throws TransactionTooLargeException {
...
// 记录进程信息
final ProcessRecord callerApp = mAm.getRecordForAppLocked(caller);
...
// Activity信息
ActivityRecord activity = null;
if (token != null) {
activity = ActivityRecord.isInStackLocked(token);
if (activity == null) {
Slog.w(TAG, "Binding with unknown activity: " + token);
return 0;
}
}
...
try {
...
// Service与应用程序的关系
AppBindRecord b = s.retrieveAppBindingLocked(service, callerApp);
ConnectionRecord c = new ConnectionRecord(b, activity,
connection, flags, clientLabel, clientIntent);
IBinder binder = connection.asBinder();
ArrayList<ConnectionRecord> clist = s.connections.get(binder);
...
// 如果设置了BIND_AUTO_CREATE标志，则启动bringUpServiceLocked方法，后面参考Service启动
if ((flags&Context.BIND_AUTO_CREATE) != 0) {
s.lastActivity = SystemClock.uptimeMillis();
if (bringUpServiceLocked(s, service.getFlags(), callerFg, false,
permissionsReviewRequired) != null) {
return 0;
}
}
....
if (s.app != null && b.intent.received) {
try {
c.conn.connected(s.name, b.intent.binder, false);
} catch (Exception e) {
...
}
if (b.intent.apps.size() == 1 && b.intent.doRebind) {
requestServiceBindingLocked(s, b.intent, callerFg, true);
}
} else if (!b.intent.requested) {
requestServiceBindingLocked(s, b.intent, callerFg, false);
}
getServiceMapLocked(s.userId).ensureNotStartingBackgroundLocked(s);
} finally {
Binder.restoreCallingIdentity(origId);
}
return 1;
}
这个方法会先获取进程与Activity等信息，然后获取Service与应用程序的关系，
（注意的是，如果存在设置了BIND_AUTO_CREATE的连接，就不销毁服务直接返回，启动bringUpServiceLocked方法，后面参考Service启动）
后面调用requestServiceBindingLocked方法
private final boolean requestServiceBindingLocked(ServiceRecord r, IntentBindRecord i,
boolean execInFg, boolean rebind) throws TransactionTooLargeException {
...
if ((!i.requested || rebind) && i.apps.size() > 0) {
try {
bumpServiceExecutingLocked(r, execInFg, "bind");
r.app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE);
r.app.thread.scheduleBindService(r, i.intent.getIntent(), rebind,
r.app.repProcState);
if (!rebind) {
i.requested = true;
}
i.hasBound = true;
i.doRebind = false;
} catch (TransactionTooLargeException e) {
..
} catch (RemoteException e) {
...
}
}
return true;
}
这里的app.thread指的是IApplicationThread,它的实现是ActivityThread的内部类ApplicationThread, 其中ApplicationThread继承了IApplicationThread.Stub
ActivityThread绑定Service
frameworks/base/core/java/android/app/ActivityThread.java#ApplicationThread
public final void scheduleBindService(IBinder token, Intent intent,
boolean rebind, int processState) {
updateProcessState(processState, false);
BindServiceData s = new BindServiceData();
s.token = token;
s.intent = intent;
s.rebind = rebind;
if (DEBUG_SERVICE)
Slog.v(TAG, "scheduleBindService token=" + token + " intent=" + intent + " uid="
+ Binder.getCallingUid() + " pid=" + Binder.getCallingPid());
sendMessage(H.BIND_SERVICE, s);
}
然后就是向mH发送BIND_SERVICE命令，在H的handleMessage里面接收
frameworks/base/core/java/android/app/ActivityThread.java
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
switch (msg.what) {
case BIND_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind");
handleBindService((BindServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
}
}
final ArrayMap<IBinder, Service> mServices = new ArrayMap<>();
private void handleBindService(BindServiceData data) {
Service s = mServices.get(data.token);
if (DEBUG_SERVICE)
Slog.v(TAG, "handleBindService s=" + s + " rebind=" + data.rebind);
if (s != null) {
try {
data.intent.setExtrasClassLoader(s.getClassLoader());
data.intent.prepareToEnterProcess();
try {
if (!data.rebind) {
IBinder binder = s.onBind(data.intent);
ActivityManager.getService().publishService(
data.token, data.intent, binder);
} else {
s.onRebind(data.intent);
ActivityManager.getService().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
}
ensureJitEnabled();
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
} catch (Exception e) {
if (!mInstrumentation.onException(s, e)) {
throw new RuntimeException(
"Unable to bind to service " + s
+ " with " + data.intent + ": " + e.toString(), e);
}
}
}
}
mService是一个存着token与Server关系的Map，先从中获取要绑定的Service，再判断Service是否初次绑定， 是的话回调onBind方法并调用AMS的publishService方法；否则回调onRebind并调用AMS的serviceDoneExecuting方法
我们先看下publishService方法
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public void publishService(IBinder token, Intent intent, IBinder service) {
// Refuse possible leaked file descriptors
if (intent != null && intent.hasFileDescriptors() == true) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
synchronized(this) {
if (!(token instanceof ServiceRecord)) {
throw new IllegalArgumentException("Invalid service token");
}
mServices.publishServiceLocked((ServiceRecord)token, intent, service);
}
}
frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service) {
final long origId = Binder.clearCallingIdentity();
try {
...
if (r != null) {
Intent.FilterComparison filter
= new Intent.FilterComparison(intent);
IntentBindRecord b = r.bindings.get(filter);
if (b != null && !b.received) {
b.binder = service;
b.requested = true;
b.received = true;
for (int conni=r.connections.size()-1; conni>=0; conni--) {
ArrayList<ConnectionRecord> clist = r.connections.valueAt(conni);
for (int i=0; i<clist.size(); i++) {
ConnectionRecord c = clist.get(i);
...
try {
c.conn.connected(r.name, service, false);
} catch (Exception e) {
...
}
}
}
}
...
serviceDoneExecutingLocked(r, mDestroyingServices.contains(r), false);
}
} finally {
Binder.restoreCallingIdentity(origId);
}
}
可知后面也是走到serviceDoneExecutingLocked方法,我们继续看下c.conn.connected
frameworks/base/services/core/java/com/android/server/am/ConnectionRecord.java
final IServiceConnection conn; // The client connection.
IServiceConnection是一个AIDL接口， 具体实现为ServiceDispatcher.InnerConnection,其中ServiceDispatcher是LoadedApk的内部类 frameworks/base/core/java/android/app/LoadedApk.java
static final class ServiceDispatcher {
...
private static class InnerConnection extends IServiceConnection.Stub {
final WeakReference<LoadedApk.ServiceDispatcher> mDispatcher;
InnerConnection(LoadedApk.ServiceDispatcher sd) {
mDispatcher = new WeakReference<LoadedApk.ServiceDispatcher>(sd);
}
public void connected(ComponentName name, IBinder service, boolean dead)
throws RemoteException {
LoadedApk.ServiceDispatcher sd = mDispatcher.get();
if (sd != null) {
sd.connected(name, service, dead);
}
}
}
}
然后看下ServiceDispatcher的connected方法
frameworks/base/core/java/android/app/LoadedApk.java#ServiceDispatcher
public void connected(ComponentName name, IBinder service, boolean dead) {
if (mActivityThread != null) {
mActivityThread.post(new RunConnection(name, service, 0, dead));
} else {
doConnected(name, service, dead);
}
}
这个方法向ActivityThread post了一个Runnable
private final class RunConnection implements Runnable {
RunConnection(ComponentName name, IBinder service, int command, boolean dead) {
mName = name;
mService = service;
mCommand = command;
mDead = dead;
}
public void run() {
if (mCommand == 0) {
doConnected(mName, mService, mDead);
} else if (mCommand == 1) {
doDeath(mName, mService);
}
}
final ComponentName mName;
final IBinder mService;
final int mCommand;
final boolean mDead;
}
Runnable里面是连接和关闭连接的代码。
public void doConnected(ComponentName name, IBinder service, boolean dead) {
ServiceDispatcher.ConnectionInfo old;
ServiceDispatcher.ConnectionInfo info;
synchronized (this) {
if (mForgotten) {
// We unbound before receiving the connection; ignore
// any connection received.
return;
}
old = mActiveConnections.get(name);
if (old != null && old.binder == service) {
// Huh, already have this one. Oh well!
return;
}
if (service != null) {
// A new service is being connected... set it all up.
info = new ConnectionInfo();
info.binder = service;
info.deathMonitor = new DeathMonitor(name, service);
try {
service.linkToDeath(info.deathMonitor, 0);
mActiveConnections.put(name, info);
} catch (RemoteException e) {
// This service was dead before we got it... just
// don't do anything with it.
mActiveConnections.remove(name);
return;
}
} else {
// The named service is being disconnected... clean up.
mActiveConnections.remove(name);
}
if (old != null) {
old.binder.unlinkToDeath(old.deathMonitor, 0);
}
}
// If there was an old service, it is now disconnected.
if (old != null) {
mConnection.onServiceDisconnected(name);
}
if (dead) {
mConnection.onBindingDied(name);
}
// If there is a new service, it is now connected.
if (service != null) {
mConnection.onServiceConnected(name, service);
}
}
当绑定成功时会回调mConnection.onServiceConnected(name, service)方法
总结
Service 的启动
- Context通知AMS
- AMS通知ActivityThread
- ActivityThread启动Service
ContextImpl到AMS的调用过程
AMS通知ActivityThread
ActivityThread启动Service
Service 的绑定
绑定过程比较复杂，单纯时序图不好描叙，加了个流程图
- Context通知AMS
- AMS通知ActivityThread
- 若设置BIND_AUTO_CREATE，则直接启动服务，否则继续绑定
- ActivityThread绑定Service
- 若是首次绑定，调用AMS的publishService方法，连接Service，并回调onBind，否则直接调用AMS的serviceDoneExecutingLocked方法并回调onReBind
ContextImpl到AMS的调用过程
AMS通知ActivityThread
ActivityThread绑定Service
参考文献
[1]刘望舒.Android进阶解密[M]:电子工业出版社,2018-10
