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系列博文：
Android 中service 详解
Android service 启动篇之 startService
Android service 启动篇之 bindService
Android service 启动篇之 startForegroundService
基于版本：Android O
0. 前言
通过source code 分析了AMS 中service 的启动过程，bindService 相对复杂一点，主要是多了一些service 和app的绑定关系处理。本文继续结合source code 来剖析。
1. 入口函数
1.1 bindService()
@Override
public boolean bindService(Intent service, ServiceConnection conn,
int flags) {
warnIfCallingFromSystemProcess();
return bindServiceCommon(service, conn, flags, mMainThread.getHandler(),
Process.myUserHandle());
}
/** @hide */
@Override
public boolean bindServiceAsUser(Intent service, ServiceConnection conn, int flags,
UserHandle user) {
return bindServiceCommon(service, conn, flags, mMainThread.getHandler(), user);
}参数：
- service 的intent
- bind 时候的ServiceConnection
- bind service 用到的flag，例如BIND_AUTO_CREATE
- 当前的user
1.2 bindServiceCommon()
private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags, Handler
handler, UserHandle user) {
// Keep this in sync with DevicePolicyManager.bindDeviceAdminServiceAsUser.
IServiceConnection sd;
if (conn == null) {
throw new IllegalArgumentException("connection is null");
}
if (mPackageInfo != null) {
sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(), handler, flags);
} else {
throw new RuntimeException("Not supported in system context");
}
validateServiceIntent(service);
try {
IBinder token = getActivityToken();
if (token == null && (flags&BIND_AUTO_CREATE) == 0 && mPackageInfo != null
&& mPackageInfo.getApplicationInfo().targetSdkVersion
< android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
flags |= BIND_WAIVE_PRIORITY;
}
service.prepareToLeaveProcess(this);
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();
}
}- ServiceConnection 不能为null，必须要创建
- android L 之后的版本不能隐式启动service
- 调用AMS 的bindService()，calling 的thread，calling 的package 都会传入
注意的是bindService 第 5 个参数sd，传入到AMS 不在是client 的ServiceConnection，而是ServiceDispatcher，详细可以看LoadedApk.ServiceDispatcher，每个应用都有这样的dispatcher 会注册到AMS 中，用于AMS 的回调。
static final class ServiceDispatcher {
private final ServiceDispatcher.InnerConnection mIServiceConnection;
private final ServiceConnection mConnection;
private final Context mContext;
private final Handler mActivityThread;
private final ServiceConnectionLeaked mLocation;
private final int mFlags;
private RuntimeException mUnbindLocation;
private boolean mForgotten;
private static class ConnectionInfo {
IBinder binder;
IBinder.DeathRecipient deathMonitor;
}
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);
}
}
}
...
...
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);
}
}
...
...
public void doConnected(ComponentName name, IBinder service, boolean dead) {
ServiceDispatcher.ConnectionInfo old;
ServiceDispatcher.ConnectionInfo info;
...
...
// 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);
}
}
...
...
}最终会调用到应用中定义的ServiceConnection 的onServiceDisconnected() 和 onServiceConnected()， 分析AMS 的时候会继续说明这里用处。
2. bindServiceLocked
通过上面的bindService，最终会调用到ActiveServices 中的bindServiceLocked()
2.1 retrieveServiceLocked()
这个在 Android service 启动篇之 startService 的 3.2 节中已经大概解释了下 ，如果app 已经service 在内部进行运行，那么需要满足下面几个条件：
- service 需要置上flag ServiceInfo.FLAG_EXTERNAL_SERVICE
- service 需要置上flag ServiceInfo.FLAG_ISOLATED_PROCESS
- service 的exported 必须为true
- app 在bind service 的时候置上flag Context.BIND_EXTERNAL_SERVICE
ComponentName name = new ComponentName(
sInfo.applicationInfo.packageName, sInfo.name);
if ((sInfo.flags & ServiceInfo.FLAG_EXTERNAL_SERVICE) != 0) {
if (isBindExternal) {
if (!sInfo.exported) {
throw new SecurityException("BIND_EXTERNAL_SERVICE failed, " + name +
" is not exported");
}
if ((sInfo.flags & ServiceInfo.FLAG_ISOLATED_PROCESS) == 0) {
throw new SecurityException("BIND_EXTERNAL_SERVICE failed, " + name +
" is not an isolatedProcess");
}
// Run the service under the calling package's application.
ApplicationInfo aInfo = AppGlobals.getPackageManager().getApplicationInfo(
callingPackage, ActivityManagerService.STOCK_PM_FLAGS, userId);
if (aInfo == null) {
throw new SecurityException("BIND_EXTERNAL_SERVICE failed, " +
"could not resolve client package " + callingPackage);
}
sInfo = new ServiceInfo(sInfo);
sInfo.applicationInfo = new ApplicationInfo(sInfo.applicationInfo);
sInfo.applicationInfo.packageName = aInfo.packageName;
sInfo.applicationInfo.uid = aInfo.uid;
name = new ComponentName(aInfo.packageName, name.getClassName());
service.setComponent(name);
} else {
throw new SecurityException("BIND_EXTERNAL_SERVICE required for " +
name);
}
最终获取的ComponentName 的package 为app 的package，name 是service 的name。
2.2 变量AppBindRecord b
AppBindRecord b = s.retrieveAppBindingLocked(service, callerApp);来看下函数retrieveAppBindingLocked()：
public AppBindRecord retrieveAppBindingLocked(Intent intent,
ProcessRecord app) {
Intent.FilterComparison filter = new Intent.FilterComparison(intent);
IntentBindRecord i = bindings.get(filter);
if (i == null) {
i = new IntentBindRecord(this, filter);
bindings.put(filter, i);
}
AppBindRecord a = i.apps.get(app);
if (a != null) {
return a;
}
a = new AppBindRecord(this, i, app);
i.apps.put(app, a);
return a;
}注意，后面在bringUpServiceLocked() 的时候会根据bindings 来确定是否可以bind service。
变量类型为AppBindRecord，如下：
final class AppBindRecord {
final ServiceRecord service; // The running service.
final IntentBindRecord intent; // The intent we are bound to.
final ProcessRecord client; // Who has started/bound the service.
final ArraySet<ConnectionRecord> connections = new ArraySet<>();
// All ConnectionRecord for this client.retrieveServiceLocked查找到ServiceRecord之后，生成Service和Client（callerApp）之间的绑定关系AppBindRecord，AppBindRecord的字段包括service，client，intent，确定了他们之间的绑定关系。
2.3 变量 ConnectionRecord c
ConnectionRecord c = new ConnectionRecord(b, activity,
connection, flags, clientLabel, clientIntent);
其中的connection 是从app 中传进来的，在上面 1.2 节中已经解析过，相当于一个ServiceDispatcher。记住了每一个需要bind 到该service 的所有信息。在bind 信息有更新的时候也会通过这里的conn 进行connected() 调用。
final class ConnectionRecord {
final AppBindRecord binding; // The application/service binding.
final ActivityRecord activity; // If non-null, the owning activity.
final IServiceConnection conn; // The client connection.
final int flags; // Binding options.
final int clientLabel; // String resource labeling this client.
final PendingIntent clientIntent; // How to launch the client.
String stringName; // Caching of toString.
boolean serviceDead; // Well is it?2.4 变量 connections
IBinder binder = connection.asBinder();
ArrayList<ConnectionRecord> clist = s.connections.get(binder);
if (clist == null) {
clist = new ArrayList<ConnectionRecord>();
s.connections.put(binder, clist);
}
clist.add(c);
b.connections.add(c);
if (activity != null) {
if (activity.connections == null) {
activity.connections = new HashSet<ConnectionRecord>();
}
activity.connections.add(c);
}
b.client.connections.add(c);
if ((c.flags&Context.BIND_ABOVE_CLIENT) != 0) {
b.client.hasAboveClient = true;
}
if ((c.flags&Context.BIND_ALLOW_WHITELIST_MANAGEMENT) != 0) {
s.whitelistManager = true;
}
if (s.app != null) {
updateServiceClientActivitiesLocked(s.app, c, true);
}
clist = mServiceConnections.get(binder);
if (clist == null) {
clist = new ArrayList<ConnectionRecord>();
mServiceConnections.put(binder, clist);
}
clist.add(c);AppBindRecord的connections字段则保存了这个client的所有ServiceConnection连接ConnectionRecord，ConnectionRecord和IServiceConnection对象是对应的。ServiceRecord也有个connections列表，但ServiceRecord的connections列表存储的是这个Service相关的所有ConnectionRecord，Service和Client之间是多对多的关系，所以其各自维护了一个connections。
2.5 bringUpServiceLocked()
if ((flags&Context.BIND_AUTO_CREATE) != 0) {
s.lastActivity = SystemClock.uptimeMillis();
if (bringUpServiceLocked(s, service.getFlags(), callerFg, false,
permissionsReviewRequired) != null) {
return 0;
}
}如果bindService 的时候置上flag Context.BIND_AUTO_CREATE，那么会直接进入bringUpServiceLocked() 进行唤醒。
2.5.1 进入create 流程
在 Android service 启动篇之 startService 的 3.6.1 节中我们对该函数进行的详细的分析，第一次进入唤醒的时候需要通过函数realStartServiceLocked() 进行启动，并且通过函数bumpServiceExecutingLocked(r, execInFg, “create”); 埋下create 流程ANR的炸弹，最后通过scheduleCreateService进入create 流程。
2.5.2 进入bind service 流程
接着会进入bind service 流程：
private final void requestServiceBindingsLocked(ServiceRecord r, boolean execInFg)
throws TransactionTooLargeException {
for (int i=r.bindings.size()-1; i>=0; i--) {
IntentBindRecord ibr = r.bindings.valueAt(i);
if (!requestServiceBindingLocked(r, ibr, execInFg, false)) {
break;
}
}
}这里的bindings 就是上面 2.2 节中创建的。
注意：
其实在start service 的时候也会进入这个流程，但是bindings 为空，所以，最终不会进入bind service 的流程。
详细的函数requestServiceBindingsLocked(r, execInFg); 分析请看下面2.6节。
2.5.3 进入start service 流程
其实在bringUpServiceLocked() 最后会通过函数：
sendServiceArgsLocked(r, execInFg, true);进入start service 的流程，详细可以看 Android service 启动篇之 startService 的 3.6.1.2 节，但是对于bind service 来说，在函数的最开始条件就不满足return 了。详细看Android service 启动篇之 startService 的 3.4 节和3.6.1.1 节。
2.6 requestServiceBindingsLocked()
上一节，我们看到如果service 第一次启动的时候，会进入realStartServiceLocked()。最终会进入该函数，执行bind 的完成流程。
但是，如果service 已经启动，这个时候在bringUpServiceLocked() 中：
if (r.app != null && r.app.thread != null) {
sendServiceArgsLocked(r, execInFg, false);
return null;
}而 sendServiceArgsLocked() 在上面 2.5.3 中知道bind service 是不会执行的。
那最终会跳过 2.5 节的流程继续往下执行：
if (s.app != null && b.intent.received) {
// Service is already running, so we can immediately
// publish the connection.
try {
c.conn.connected(s.name, b.intent.binder, false);
} catch (Exception e) {
Slog.w(TAG, "Failure sending service " + s.shortName
+ " to connection " + c.conn.asBinder()
+ " (in " + c.binding.client.processName + ")", e);
}
// If this is the first app connected back to this binding,
// and the service had previously asked to be told when
// rebound, then do so.
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);
}
第一次bind service 的时候requested 为false，最终会调用到requestServiceBindingLocked()：
private final boolean requestServiceBindingLocked(ServiceRecord r, IntentBindRecord i,
boolean execInFg, boolean rebind) throws TransactionTooLargeException {
if (r.app == null || r.app.thread == null) {
// If service is not currently running, can't yet bind.
return false;
}
if (DEBUG_SERVICE) Slog.d(TAG_SERVICE, "requestBind " + i + ": requested=" + i.requested
+ " rebind=" + rebind);
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) {
// Keep the executeNesting count accurate.
if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Crashed while binding " + r, e);
final boolean inDestroying = mDestroyingServices.contains(r);
serviceDoneExecutingLocked(r, inDestroying, inDestroying);
throw e;
} catch (RemoteException e) {
if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Crashed while binding " + r);
// Keep the executeNesting count accurate.
final boolean inDestroying = mDestroyingServices.contains(r);
serviceDoneExecutingLocked(r, inDestroying, inDestroying);
return false;
}
}
return true;
}通过该函数进行bind 的request 申请，通过函数：
bumpServiceExecutingLocked(r, execInFg, "bind");埋下onBind操作的ANR 炸弹，要求onBind 处理不能超过20s。
并通过：
r.app.thread.scheduleBindService()最终调用handleBindService函数：
private void handleBindService(BindServiceData data) {
Service s = mServices.get(data.token);
...
if (s != null) {
try {
...
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) {
...
}
}
}onBind 接口调用完成后会调用AMS.publishService，最终会调用到ActiveServices.publishServiceLocked 进行onBind 的后期处理，最终会调用serviceDoneExecutingLocked 解除ANR炸弹。
至此，bindService的流程基本完成，总结下：
- 注意两个核心变量AppBindRecord 和ConnectionRecord；
- 如果没有启动service，会顺序进入create、bind、start 流程，并且在每个流程都会埋下ANR炸弹，要求每个流程在20s 内处理完成，在处理结束后ActiveServices 会拆除炸弹；
- 如果已经启动service，会进入onStartCommand流程，同样伴随着ANR炸弹；
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