开篇
本篇以android-11.0.0_r25作为基础解析
在上一篇文章 Android源码分析 - Service启动流程 中，我们分析了一个Service是怎么启动的，这次我们再来看看一个Service是如何被停止的，什么情况下Service会被重建以及它的重建过程
流程图
由于Service的停止与重建在实际情况下会收到各种条件影响产生不同的情况，所以这里的流程图我也只画最简路径，以供大家参考
主动停止
首先，我们来看主动停止的情况，主动停止也分三种：
-
Service自己调用stopSelf或stopSelfResult方法停止 -
使用
startService启动的Service，使用stopService方法停止 -
使用
bindService启动的Service，使用unbindService方法解除绑定，当没有任何Client和Service绑定时，Service就会自行停止
Service.stopSelf 或 Service.stopSelfResult
stopSelf和stopSelfResult方法唯一的区别是一个没返回值，一个会返回是否成功
java
//frameworks/base/core/java/android/app/Service.java
public final void stopSelf() {
stopSelf(-1);
}
public final void stopSelf(int startId) {
if (mActivityManager == null) {
return;
}
try {
mActivityManager.stopServiceToken(
new ComponentName(this, mClassName), mToken, startId);
} catch (RemoteException ex) {
}
}
public final boolean stopSelfResult(int startId) {
if (mActivityManager == null) {
return false;
}
try {
return mActivityManager.stopServiceToken(
new ComponentName(this, mClassName), mToken, startId);
} catch (RemoteException ex) {
}
return false;
}这个方法也是直接调用了AMS.stopServiceToken方法
java
//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public boolean stopServiceToken(ComponentName className, IBinder token,
int startId) {
synchronized(this) {
return mServices.stopServiceTokenLocked(className, token, startId);
}
}然后AMS转手调用了ActiveServices.stopServiceTokenLocked方法
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
boolean stopServiceTokenLocked(ComponentName className, IBinder token,
int startId) {
//通过className查找相应的ServiceRecord
//在Service启动过程中调用的retrieveServiceLocked方法会查找Service，创建ServiceRecord
//并将其添加到Map中，findServiceLocked方法只需要从这个Map中去获取即可
ServiceRecord r = findServiceLocked(className, token, UserHandle.getCallingUserId());
if (r != null) {
if (startId >= 0) {
// Asked to only stop if done with all work. Note that
// to avoid leaks, we will take this as dropping all
// start items up to and including this one.
//查找startId所对应的已分发的启动项
ServiceRecord.StartItem si = r.findDeliveredStart(startId, false, false);
//从已分发启动请求列表中移除
if (si != null) {
while (r.deliveredStarts.size() > 0) {
ServiceRecord.StartItem cur = r.deliveredStarts.remove(0);
cur.removeUriPermissionsLocked();
if (cur == si) {
break;
}
}
}
//如果传入的启动ID不是Service最后一次启动的ID，则不能停止服务
//ps：每次启动Service，startId都会递增，初始值为1
if (r.getLastStartId() != startId) {
return false;
}
}
... //记录
//重置启动状态（重要，后文中会分析）
r.startRequested = false;
r.callStart = false;
final long origId = Binder.clearCallingIdentity();
//接着停止Service
bringDownServiceIfNeededLocked(r, false, false);
Binder.restoreCallingIdentity(origId);
return true;
}
return false;
}startId机制
这里要说一下Service的startId机制，每次启动Service时，ActiveServices.startServiceLocked方法会向ServiceRecord.pendingStarts列表中添加一个启动项ServiceRecord.StartItem，构建这个启动项需要提供一个startId，而这个startId是由ServiceRecord.makeNextStartId生成的
java
//frameworks/base/services/core/java/com/android/server/am/ServiceRecord.java
public int makeNextStartId() {
lastStartId++;
if (lastStartId < 1) {
lastStartId = 1;
}
return lastStartId;
}由于lastStartId的初始值为 0 ，所以第一次调用这个方法，得到的startId就是 1 ，即startId是从 1 开始递增的，由于当Service被停止后，ServiceRecord会从之前的缓存Map中移除，所以下一次再启动Service时会重新创建ServiceRecord，startId会被重置
当我们调用stopSelf停止服务时，如果传入了大于等于 0 的startId，此时便会判断这个startId是不是最后一次启动所对应的startId，如果不是的话，则不能停止这个Service
这个startId设计的意义是什么呢？我们从IntentService的设计中可以管中窥豹：
IntentService是一个运行在另一个线程的，每次处理完任务都会自动停止的Service，但如果你调用多次startService会发现，IntentService.onDestroy方法只会调用一次，这是为什么呢？因为IntentService每次停止，调用stopSelf方法都是带上这次启动的startId的，这样如果一次性有多个启动请求，前面的任务执行完，停止时发现，此次启动请求的startId不是最后一个startId，这样就不会停止掉自身，直到最后一个任务处理完成，避免了Service的多次停止启动消耗系统资源
接着，在这个方法的最后，调用bringDownServiceIfNeededLocked方法继续停止服务
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
private final void bringDownServiceIfNeededLocked(ServiceRecord r, boolean knowConn,
boolean hasConn) {
//检查此服务是否还被需要
//在用stopSelf停止服务的这种情况下
//检查的就是是否有auto-create的连接（flag为BIND_AUTO_CREATE）
//如有则不能停止服务
if (isServiceNeededLocked(r, knowConn, hasConn)) {
return;
}
// Are we in the process of launching?
//不要停止正在启动中的Service
if (mPendingServices.contains(r)) {
return;
}
//继续停止服务
bringDownServiceLocked(r);
}这个方法主要就做了一些能否停止服务的检查，主要的停止操作都在下一个bringDownServiceLocked方法中
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
private final void bringDownServiceLocked(ServiceRecord r) {
... //处理Client与Serivce的连接，进行断开连接以及解除绑定操作
// Check to see if the service had been started as foreground, but being
// brought down before actually showing a notification. That is not allowed.
//如果此Service是以前台服务的形式启动，并且当前还尚未成为前台服务
if (r.fgRequired) {
r.fgRequired = false;
r.fgWaiting = false;
... //记录
//将前台服务的超时回调取消
mAm.mHandler.removeMessages(
ActivityManagerService.SERVICE_FOREGROUND_TIMEOUT_MSG, r);
//这种情况直接令App崩溃，杀死应用
if (r.app != null) {
Message msg = mAm.mHandler.obtainMessage(
ActivityManagerService.SERVICE_FOREGROUND_CRASH_MSG);
msg.obj = r.app;
msg.getData().putCharSequence(
ActivityManagerService.SERVICE_RECORD_KEY, r.toString());
mAm.mHandler.sendMessage(msg);
}
}
//记录销毁时间
r.destroyTime = SystemClock.uptimeMillis();
//从缓存中移除ServiceRecord
final ServiceMap smap = getServiceMapLocked(r.userId);
ServiceRecord found = smap.mServicesByInstanceName.remove(r.instanceName);
// Note when this method is called by bringUpServiceLocked(), the service is not found
// in mServicesByInstanceName and found will be null.
if (found != null && found != r) {
// This is not actually the service we think is running... this should not happen,
// but if it does, fail hard.
//如果找到的服务不是我们目前停止的服务，应该是一个不可能的情况
//碰到这种情况，将ServiceRecord重新放回去并抛出异常
smap.mServicesByInstanceName.put(r.instanceName, found);
throw new IllegalStateException("Bringing down " + r + " but actually running "
+ found);
}
//清除ServiceRecord
smap.mServicesByIntent.remove(r.intent);
r.totalRestartCount = 0;
//取消之前的Service重启任务（如果有）
unscheduleServiceRestartLocked(r, 0, true);
// Also make sure it is not on the pending list.
//从待启动Service列表中移除
for (int i=mPendingServices.size()-1; i>=0; i--) {
if (mPendingServices.get(i) == r) {
mPendingServices.remove(i);
}
}
//关闭前台服务通知
cancelForegroundNotificationLocked(r);
//对于已经成为前台服务的Service
if (r.isForeground) {
//修改应用的活动前台计数，如果计数小于等于0，将其从mActiveForegroundApps列表中移除
decActiveForegroundAppLocked(smap, r);
... //更新统计信息
}
//各种清理操作
r.isForeground = false;
r.foregroundId = 0;
r.foregroundNoti = null;
r.mAllowWhileInUsePermissionInFgs = false;
// Clear start entries.
r.clearDeliveredStartsLocked();
r.pendingStarts.clear();
smap.mDelayedStartList.remove(r);
if (r.app != null) {
synchronized (r.stats.getBatteryStats()) {
r.stats.stopLaunchedLocked();
}
//从ProcessRecord中移除Service记录
r.app.stopService(r);
//更新服务进程绑定的应用uids
r.app.updateBoundClientUids();
//允许绑定Service的应用程序管理白名单
if (r.whitelistManager) {
updateWhitelistManagerLocked(r.app);
}
if (r.app.thread != null) {
//更新进程前台服务信息
updateServiceForegroundLocked(r.app, false);
try {
//记录Service执行操作并设置超时回调
//前台服务超时时间为20s，后台服务超时时间为200s
bumpServiceExecutingLocked(r, false, "destroy");
//添加到销毁中Service列表中
mDestroyingServices.add(r);
//标记正在销毁中
r.destroying = true;
//更新进程优先级
mAm.updateOomAdjLocked(r.app, true,
OomAdjuster.OOM_ADJ_REASON_UNBIND_SERVICE);
//回到App进程，调度执行Service的stop操作
r.app.thread.scheduleStopService(r);
} catch (Exception e) {
serviceProcessGoneLocked(r);
}
}
}
//清除连接
if (r.bindings.size() > 0) {
r.bindings.clear();
}
//对于主动停止的Service，不需要重启
if (r.restarter instanceof ServiceRestarter) {
((ServiceRestarter)r.restarter).setService(null);
}
... //记录
//将此Service从正在后台启动服务列表和延迟启动服务列表中移除
//如果正在后台启动服务列表中存在此服务的话，将之前设置为延迟启动的服务调度出来后台启动
smap.ensureNotStartingBackgroundLocked(r);
}这个方法主要做了以下几件事：
- 处理
Client与Serivce的连接，进行断开连接以及解除绑定操作（具体等到后面分析unbindService时再说） - 对于以前台服务形式启动，并且当前还尚未成为前台服务的
Service，直接杀死App - 各种重置，清理操作
- 关闭前台服务通知
- 将
Service添加到销毁中服务列表，并调度执行停止操作，最终回调Service.onDestroy - 将
ServiceRestarter内的ServiceRecord变量设为null，避免其后续重启
我们重点看第5步，在这个方法中调用了ActivityThread$ApplicationThread.scheduleStopService去调度执行停止服务操作
java
//frameworks/base/core/java/android/app/ActivityThread.java
public final void scheduleStopService(IBinder token) {
sendMessage(H.STOP_SERVICE, token);
}同样的，也是通过Handler发送Message处理服务停止，这里最终调用的是ActivityThread.handleStopService方法
java
//frameworks/base/core/java/android/app/ActivityThread.java
private void handleStopService(IBinder token) {
//从Service列表中取出并移除此服务
Service s = mServices.remove(token);
if (s != null) {
try {
//调用Service.onDestroy
s.onDestroy();
//解绑以及清理（解除对ServiceRecord的Binder远程对象的引用）
s.detachAndCleanUp();
//执行清理操作，具体来说就是断开其他客户端与Service的连接以及解除绑定
Context context = s.getBaseContext();
if (context instanceof ContextImpl) {
final String who = s.getClassName();
((ContextImpl) context).scheduleFinalCleanup(who, "Service");
}
//确保其他异步任务执行完成
QueuedWork.waitToFinish();
try {
//Service相关任务执行完成
//这一步中会把之前的超时定时器取消
ActivityManager.getService().serviceDoneExecuting(
token, SERVICE_DONE_EXECUTING_STOP, 0, 0);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
} catch (Exception e) {
if (!mInstrumentation.onException(s, e)) {
throw new RuntimeException(
"Unable to stop service " + s
+ ": " + e.toString(), e);
}
}
}
}可以看到，这里首先从mServices列表中取出并移除此服务，然后触发Service.onDestroy回调，之后还需要调用ContextImpl.scheduleFinalCleanup方法执行一些清理工作，这一部分的分析我们留到后面unbindService章节里再讲，这样，整个Service的停止流程就到此结束了
stopService
接下来我们来看一下调用方调用stopService停止服务的情况
java
//frameworks/base/core/java/android/app/ContextImpl.java
public boolean stopService(Intent service) {
warnIfCallingFromSystemProcess();
return stopServiceCommon(service, mUser);
}
private boolean stopServiceCommon(Intent service, UserHandle user) {
try {
//验证Intent有效性
validateServiceIntent(service);
//跨进程处理
service.prepareToLeaveProcess(this);
//调用AMS.stopService
int res = ActivityManager.getService().stopService(
mMainThread.getApplicationThread(), service,
service.resolveTypeIfNeeded(getContentResolver()), user.getIdentifier());
if (res < 0) {
throw new SecurityException(
"Not allowed to stop service " + service);
}
return res != 0;
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}这里基本上是直接调用AMS.stopService进入系统进程处理服务停止
java
//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public int stopService(IApplicationThread caller, Intent service,
String resolvedType, int userId) {
enforceNotIsolatedCaller("stopService");
// Refuse possible leaked file descriptors
if (service != null && service.hasFileDescriptors() == true) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
synchronized(this) {
//转交给ActiveServices处理
return mServices.stopServiceLocked(caller, service, resolvedType, userId);
}
}
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
int stopServiceLocked(IApplicationThread caller, Intent service,
String resolvedType, int userId) {
final ProcessRecord callerApp = mAm.getRecordForAppLocked(caller);
if (caller != null && callerApp == null) {
throw new SecurityException(
"Unable to find app for caller " + caller
+ " (pid=" + Binder.getCallingPid()
+ ") when stopping service " + service);
}
// If this service is active, make sure it is stopped.
//查找相应的Service，其中入参createIfNeeded为false，所以如果从缓存中找不到ServiceRecord的话则会直接返回null
ServiceLookupResult r = retrieveServiceLocked(service, null, resolvedType, null,
Binder.getCallingPid(), Binder.getCallingUid(), userId, false, false, false, false);
if (r != null) {
if (r.record != null) {
final long origId = Binder.clearCallingIdentity();
try {
//接着处理停止服务
stopServiceLocked(r.record);
} finally {
Binder.restoreCallingIdentity(origId);
}
return 1;
}
return -1;
}
return 0;
}
private void stopServiceLocked(ServiceRecord service) {
if (service.delayed) {
// If service isn't actually running, but is being held in the
// delayed list, then we need to keep it started but note that it
// should be stopped once no longer delayed.
service.delayedStop = true;
return;
}
... //统计信息记录
//重置启动状态（重要，后文中会分析）
service.startRequested = false;
service.callStart = false;
//和上文一样，停止Service
bringDownServiceIfNeededLocked(service, false, false);
}可以看到，这里和上文中分析的以stopSelf方式停止服务一样，先重置启动状态，然后调用bringDownServiceIfNeededLocked停止服务
unbindService
接下来的是通过bindService方法，并且flag为BIND_AUTO_CREATE启动的Service，我们需要通过unbindService方法解除绑定，当最终没有任何flag为BIND_AUTO_CREATE的客户端与Service绑定，这个Service就会被停止
java
//frameworks/base/core/java/android/app/ContextImpl.java
public void unbindService(ServiceConnection conn) {
if (conn == null) {
throw new IllegalArgumentException("connection is null");
}
if (mPackageInfo != null) {
//将ServiceDispatcher的状态设置为forgotten，之后便不再会回调ServiceConnection任何方法
IServiceConnection sd = mPackageInfo.forgetServiceDispatcher(
getOuterContext(), conn);
try {
//调用AMS.unbindService方法
ActivityManager.getService().unbindService(sd);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
} else {
throw new RuntimeException("Not supported in system context");
}
}这个方法中首先调用了LoadedApk.forgetServiceDispatcher方法
java
//frameworks/base/core/java/android/app/LoadedApk.java
public final IServiceConnection forgetServiceDispatcher(Context context,
ServiceConnection c) {
synchronized (mServices) {
ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher> map
= mServices.get(context);
LoadedApk.ServiceDispatcher sd = null;
if (map != null) {
sd = map.get(c);
if (sd != null) {
//移除ServiceDispatcher
map.remove(c);
//清理连接并标记遗忘
sd.doForget();
if (map.size() == 0) {
mServices.remove(context);
}
... //debug
return sd.getIServiceConnection();
}
}
... //debug
... //异常
}
}将ServiceDispatcher从缓存中移除并调用LoadedApk$ServiceDispatcher.doForget方法
java
//frameworks/base/core/java/android/app/LoadedApk.java
void doForget() {
synchronized(this) {
for (int i=0; i<mActiveConnections.size(); i++) {
ServiceDispatcher.ConnectionInfo ci = mActiveConnections.valueAt(i);
ci.binder.unlinkToDeath(ci.deathMonitor, 0);
}
mActiveConnections.clear();
mForgotten = true;
}
}这里将所有连接的binder死亡回调移除，然后清除所有连接，再将mForgotten标记设为true
接着我们会走到AMS.unbindService方法中
java
//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public boolean unbindService(IServiceConnection connection) {
synchronized (this) {
return mServices.unbindServiceLocked(connection);
}
}同样的，将工作转交给ActiveServices
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
boolean unbindServiceLocked(IServiceConnection connection) {
IBinder binder = connection.asBinder();
ArrayList<ConnectionRecord> clist = mServiceConnections.get(binder);
//找不到连接记录，直接返回
if (clist == null) {
return false;
}
final long origId = Binder.clearCallingIdentity();
try {
//遍历连接
while (clist.size() > 0) {
ConnectionRecord r = clist.get(0);
//移除连接
removeConnectionLocked(r, null, null);
//removeConnectionLocked方法会将此ConnectionRecord从连接列表中移除
//如果此ConnectionRecord仍然存在的话，是一个严重的错误，这里再移除一次
if (clist.size() > 0 && clist.get(0) == r) {
// In case it didn't get removed above, do it now.
Slog.wtf(TAG, "Connection " + r + " not removed for binder " + binder);
clist.remove(0);
}
if (r.binding.service.app != null) {
if (r.binding.service.app.whitelistManager) {
updateWhitelistManagerLocked(r.binding.service.app);
}
// This could have made the service less important.
if ((r.flags&Context.BIND_TREAT_LIKE_ACTIVITY) != 0) {
r.binding.service.app.treatLikeActivity = true;
mAm.updateLruProcessLocked(r.binding.service.app,
r.binding.service.app.hasClientActivities()
|| r.binding.service.app.treatLikeActivity, null);
}
}
}
//更新顶层应用进程优先级
mAm.updateOomAdjLocked(OomAdjuster.OOM_ADJ_REASON_UNBIND_SERVICE);
} finally {
Binder.restoreCallingIdentity(origId);
}
return true;
}没看到什么特别重要的逻辑，看来重点应该在removeConnectionLocked这个方法中了
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
void removeConnectionLocked(ConnectionRecord c, ProcessRecord skipApp,
ActivityServiceConnectionsHolder skipAct) {
IBinder binder = c.conn.asBinder();
AppBindRecord b = c.binding;
ServiceRecord s = b.service;
//这里的clist是ServiceRecord中的列表，和上一个方法中的clist不是一个对象
ArrayList<ConnectionRecord> clist = s.getConnections().get(binder);
//移除各种连接
if (clist != null) {
clist.remove(c);
if (clist.size() == 0) {
s.removeConnection(binder);
}
}
b.connections.remove(c);
c.stopAssociation();
if (c.activity != null && c.activity != skipAct) {
c.activity.removeConnection(c);
}
if (b.client != skipApp) {
b.client.connections.remove(c);
... //各种flag的处理
//更新是否有与Service建立连接的Activity
if (s.app != null) {
updateServiceClientActivitiesLocked(s.app, c, true);
}
}
//将连接从mServiceConnections列表中移除
//这个clist才是和上一个方法是同一个对象
clist = mServiceConnections.get(binder);
if (clist != null) {
clist.remove(c);
if (clist.size() == 0) {
mServiceConnections.remove(binder);
}
}
mAm.stopAssociationLocked(b.client.uid, b.client.processName, s.appInfo.uid,
s.appInfo.longVersionCode, s.instanceName, s.processName);
//如果调用方App没有其他连接和Service绑定
//则将整个AppBindRecord移除
if (b.connections.size() == 0) {
b.intent.apps.remove(b.client);
}
if (!c.serviceDead) {
//如果服务端进程存活并且没有其他连接绑定了，同时服务还处在绑定关系中（尚未回调过Service.onUnbind）
if (s.app != null && s.app.thread != null && b.intent.apps.size() == 0
&& b.intent.hasBound) {
try {
bumpServiceExecutingLocked(s, false, "unbind");
if (b.client != s.app && (c.flags&Context.BIND_WAIVE_PRIORITY) == 0
&& s.app.setProcState <= ActivityManager.PROCESS_STATE_HEAVY_WEIGHT) {
// If this service's process is not already in the cached list,
// then update it in the LRU list here because this may be causing
// it to go down there and we want it to start out near the top.
mAm.updateLruProcessLocked(s.app, false, null);
}
mAm.updateOomAdjLocked(s.app, true,
OomAdjuster.OOM_ADJ_REASON_UNBIND_SERVICE);
//标记为未绑定
b.intent.hasBound = false;
// Assume the client doesn't want to know about a rebind;
// we will deal with that later if it asks for one.
b.intent.doRebind = false;
//回到App进程，调度执行Service的unbind操作
s.app.thread.scheduleUnbindService(s, b.intent.intent.getIntent());
} catch (Exception e) {
serviceProcessGoneLocked(s);
}
}
// If unbound while waiting to start and there is no connection left in this service,
// remove the pending service
if (s.getConnections().isEmpty()) {
mPendingServices.remove(s);
}
if ((c.flags&Context.BIND_AUTO_CREATE) != 0) {
//是否有其他含有BIND_AUTO_CREATE标记的连接
boolean hasAutoCreate = s.hasAutoCreateConnections();
... //记录
bringDownServiceIfNeededLocked(s, true, hasAutoCreate);
}
}
}这个方法主要做了以下几件事：
-
执行各种移除操作
-
如果目标服务在此次解绑后不再有任何其他连接与其绑定，则调度执行
Service的unbind操作 -
如果此次断开的连接的
flag中包含BIND_AUTO_CREATE，则调用bringDownServiceIfNeededLocked尝试停止服务
2、3两点都很重要，我们首先看第2点，什么情况下会在这里调度执行Service的unbind操作，前面描述的其实不是很准确，准确的来说应该是目标服务在同一个IntentBindRecord下，此次解绑后不再有任何其他连接与其绑定。那么什么叫同一个IntentBindRecord呢？这和我们启动服务传入的Intent有关，IntentBindRecord的第一次创建是在我们调用bindService后，走到ActiveServices.bindServiceLocked方法中，其中有一段代码调用了ServiceRecord.retrieveAppBindingLocked方法产生的
java
//frameworks/base/services/core/java/com/android/server/am/ServiceRecord.java
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;
}在这个方法中，它将我们传入的Intent包装成了Intent.FilterComparison对象，然后尝试用它作为key从ArrayMap``bindings中取获取IntentBindRecord，如果获取不到则会创建一个新的，那么是否是同一个IntentBindRecord的判断标准就是包装后的Intent.FilterComparison对象的HashCode是否相等，我们来看一下它的HashCode是怎样计算的：
java
//frameworks/base/core/java/android/content/Intent.java
public static final class FilterComparison {
private final Intent mIntent;
private final int mHashCode;
public FilterComparison(Intent intent) {
mIntent = intent;
mHashCode = intent.filterHashCode();
}
...
@Override
public int hashCode() {
return mHashCode;
}
}
public int filterHashCode() {
int code = 0;
if (mAction != null) {
code += mAction.hashCode();
}
if (mData != null) {
code += mData.hashCode();
}
if (mType != null) {
code += mType.hashCode();
}
if (mIdentifier != null) {
code += mIdentifier.hashCode();
}
if (mPackage != null) {
code += mPackage.hashCode();
}
if (mComponent != null) {
code += mComponent.hashCode();
}
if (mCategories != null) {
code += mCategories.hashCode();
}
return code;
}可以看到，只有以上参数全部相等，才会被视为同一个Intent，而我们通常使用Intent只会设置它的mComponent，所以在一般情况下Service的onBind和onUnbind也只会触发一次（在Service没有被销毁的情况下）
接着我们来看第3点，如果此次断开的连接的flag中包含BIND_AUTO_CREATE，首先会去查询是否有其他含有BIND_AUTO_CREATE标记的连接，然后以此作为参数调用bringDownServiceIfNeededLocked尝试停止服务
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
private final void bringDownServiceIfNeededLocked(ServiceRecord r, boolean knowConn,
boolean hasConn) {
//检查此服务是否还被需要
if (isServiceNeededLocked(r, knowConn, hasConn)) {
return;
}
// Are we in the process of launching?
//不要停止正在启动中的Service
if (mPendingServices.contains(r)) {
return;
}
//继续停止服务
bringDownServiceLocked(r);
}
private final boolean isServiceNeededLocked(ServiceRecord r, boolean knowConn,
boolean hasConn) {
// Are we still explicitly being asked to run?
//Service之前是否通过startService启动过并且未stop
if (r.startRequested) {
return true;
}
// Is someone still bound to us keeping us running?
//这里我们传入的是true
//因为我们之前已经做了检查，知道了是否还有其他auto-create的连接
if (!knowConn) {
hasConn = r.hasAutoCreateConnections();
}
//如果还有其他auto-create的连接
//则此服务还被需要
if (hasConn) {
return true;
}
return false;
}可以看到，经过上述检查，如果发现此Service确实可以被停止了，则会调用bringDownServiceLocked方法停止服务
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
private final void bringDownServiceLocked(ServiceRecord r) {
//断开所有连接
ArrayMap<IBinder, ArrayList<ConnectionRecord>> connections = r.getConnections();
for (int conni = connections.size() - 1; conni >= 0; conni--) {
ArrayList<ConnectionRecord> c = connections.valueAt(conni);
for (int i=0; i<c.size(); i++) {
ConnectionRecord cr = c.get(i);
// There is still a connection to the service that is
// being brought down. Mark it as dead.
//将服务标记为死亡
cr.serviceDead = true;
cr.stopAssociation();
//回调ServiceConnection各种方法
//通知client服务断开连接以及死亡
cr.conn.connected(r.name, null, true);
}
}
// Tell the service that it has been unbound.
//通知Service解除绑定
if (r.app != null && r.app.thread != null) {
boolean needOomAdj = false;
//遍历所有连接，解除绑定
for (int i = r.bindings.size() - 1; i >= 0; i--) {
IntentBindRecord ibr = r.bindings.valueAt(i);
//如果还处在绑定关系中（尚未回调过Service.onUnbind）
if (ibr.hasBound) {
try {
//记录Service执行操作并设置超时回调
//前台服务超时时间为20s，后台服务超时时间为200s
bumpServiceExecutingLocked(r, false, "bring down unbind");
needOomAdj = true;
//标记为未绑定
ibr.hasBound = false;
ibr.requested = false;
//回到App进程，调度执行Service的unbind操作
r.app.thread.scheduleUnbindService(r,
ibr.intent.getIntent());
} catch (Exception e) {
needOomAdj = false;
serviceProcessGoneLocked(r);
break;
}
}
}
//更新服务端进程优先级
if (needOomAdj) {
mAm.updateOomAdjLocked(r.app, true,
OomAdjuster.OOM_ADJ_REASON_UNBIND_SERVICE);
}
}
... //和上文相同
}这个方法我们在前面分析stopSelf的时候说过了，这次我们只看和绑定服务有关的部分
首先断开所有连接，回调ServiceConnection各种方法，通知客户端服务断开连接以及死亡，这里需要注意的是，我们本次执行unbindService操作的连接已经在上一步中从ServiceRecord.connections列表中移除，所以并不会回调它的ServiceConnection的任何方法，这也是很多人对unbindService方法的误解（包括我自己），bindService方法在成功绑定服务后会回调ServiceConnection.onServiceConnected方法，但unbindService方法在成功解绑服务后并不会回调ServiceConnection.onServiceDisconnected以及任何其它方法，这些方法只会在Service被以其他方式停止（比如后面会分析的混合启动的服务如何停止）或者Service意外停止（比如服务端应用崩溃或被杀死）的情况才会被调用
所以这里处理的是断开其他的连接，我们假设一个场景，使用同一个Intent和两个不同的ServiceConnection，一个使用BIND_AUTO_CREATE标记，一个使用其他标记，先绑定BIND_AUTO_CREATE标记的Service，然后再绑定其他标记的Service，接着我们对BIND_AUTO_CREATE标记的Serivce调用unbindService解绑，此时就会走到这个方法中，ServiceRecord.connections列表中会存在那个使用其他标记的连接，然后其内部成员变量conn的connected方法，这个conn是一个IServiceConnection类型，实际上的实现类为LoadedApk$ServiceDispatcher$InnerConnection，最终会调用到LoadedApk$ServiceDispatcher.doConnected方法
java
public void doConnected(ComponentName name, IBinder service, boolean dead) {
ServiceDispatcher.ConnectionInfo old;
ServiceDispatcher.ConnectionInfo info;
synchronized (this) {
//被标记为遗忘则不处理任何事情
//调用unbindService就会将这个标志设为true
if (mForgotten) {
// We unbound before receiving the connection; ignore
// any connection received.
return;
}
old = mActiveConnections.get(name);
//如果旧的连接信息中的IBinder对象和本次调用传入的IBinder对象是同一个对象
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.
//建立一个新的连接信息
info = new ConnectionInfo();
info.binder = service;
info.deathMonitor = new DeathMonitor(name, service);
try {
//注册Binder死亡通知
service.linkToDeath(info.deathMonitor, 0);
//保存本次连接信息
mActiveConnections.put(name, info);
} catch (RemoteException e) {
// This service was dead before we got it... just
// don't do anything with it.
//服务已死亡，移除连接信息
mActiveConnections.remove(name);
return;
}
} else {
// The named service is being disconnected... clean up.
mActiveConnections.remove(name);
}
//移除Binder死亡通知
if (old != null) {
old.binder.unlinkToDeath(old.deathMonitor, 0);
}
}
// If there was an old service, it is now disconnected.
//回调ServiceConnection.onServiceDisconnected
//通知client之前的连接已被断开
if (old != null) {
mConnection.onServiceDisconnected(name);
}
//如果Service死亡需要回调ServiceConnection.onBindingDied通知client服务死亡
if (dead) {
mConnection.onBindingDied(name);
}
// If there is a new viable service, it is now connected.
if (service != null) {
//回调ServiceConnection.onServiceConnected方法
//告知client已建立连接
mConnection.onServiceConnected(name, service);
} else {
// The binding machinery worked, but the remote returned null from onBind().
//当Service.onBind方法返回null，或者Service停止时
//回调ServiceConnection.onNullBinding方法
mConnection.onNullBinding(name);
}
}这个方法其实我们在上一篇文章中已经说过了，不过在上一篇文章中我们关注的是Service绑定的部分，而这次我们关注的是解绑的部分
首先映入眼帘的就是对mForgotten变量的判断，它在客户端调用unbindService就会被设为true，然后便会直接返回，不再处理后续事项。当然，实际上执行完unbindService方法后，客户端与Service的连接会被移除，理论上应该也不会再走到这个方法里才对（这里我也感觉有点疑惑）
根据这段代码，我们能看出来Service停止后，对客户端的回调是什么：
-
当
Service.onBind方法的返回不为null时，此时会依次回调ServiceConnection.onServiceDisconnected、ServiceConnection.onBindingDied和ServiceConnection.onNullBinding方法 -
当
Service.onBind方法的返回为null时，此时会依次回调ServiceConnection.onBindingDied和ServiceConnection.onNullBinding方法
大家也可以自己写写Demo来检验一下我说的是否正确
这一步处理完后，接下来要做的便是处理Service那边的解绑，遍历IntentBindRecord列表，调用ActivityThread$ApplicationThread.scheduleUnbindService去调度执行服务解绑操作，这里通过Handler最终调用的是ActivityThread.handleUnbindService方法
java
//frameworks/base/core/java/android/app/ActivityThread.java
private void handleUnbindService(BindServiceData data) {
Service s = mServices.get(data.token);
if (s != null) {
try {
data.intent.setExtrasClassLoader(s.getClassLoader());
data.intent.prepareToEnterProcess();
//回调Service.onUnbind方法，如果返回值为true
//当再次建立连接时，服务会回调Service.onRebind方法
boolean doRebind = s.onUnbind(data.intent);
try {
if (doRebind) {
ActivityManager.getService().unbindFinished(
data.token, data.intent, doRebind);
} else {
ActivityManager.getService().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
}
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
} catch (Exception e) {
if (!mInstrumentation.onException(s, e)) {
throw new RuntimeException(
"Unable to unbind to service " + s
+ " with " + data.intent + ": " + e.toString(), e);
}
}
}
}可以看到，这里回调了Service.onUnbind方法，它的返回值表示当Service后面再与其他客户端建立连接时，是否需要回调Service.onRebind方法，但是这有一个前提，那就是Service中途没有被停止，具体原因以及rebind流程我们稍后再分析
到了这一步，解绑就完成了，接下来和之前在stopSelf章节里分析的后续流程就一样了，最终调用ActivityThread.handleStopService方法停止服务，还记得我们之前分析在这个方法中触发完Service.onDestroy回调，之后还需要调用ContextImpl.scheduleFinalCleanup方法吗？现在我们就来看看这个方法又做了什么事情
java
//frameworks/base/core/java/android/app/ContextImpl.java
final void scheduleFinalCleanup(String who, String what) {
mMainThread.scheduleContextCleanup(this, who, what);
}这里的mMainThread就是应用的ActivityThread
java
//frameworks/base/core/java/android/app/ActivityThread.java
final void scheduleContextCleanup(ContextImpl context, String who,
String what) {
ContextCleanupInfo cci = new ContextCleanupInfo();
cci.context = context;
cci.who = who;
cci.what = what;
sendMessage(H.CLEAN_UP_CONTEXT, cci);
}还是老样子通过Handler发消息，最终调用的是ContextImpl.performFinalCleanup方法
java
//frameworks/base/core/java/android/app/ContextImpl.java
final void performFinalCleanup(String who, String what) {
mPackageInfo.removeContextRegistrations(getOuterContext(), who, what);
}然后调用LoadedApk.removeContextRegistrations方法执行清理操作
java
//frameworks/base/core/java/android/app/LoadedApk.java
public void removeContextRegistrations(Context context,
String who, String what) {
... //清理广播接收器
synchronized (mServices) {
ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher> smap =
mServices.remove(context);
if (smap != null) {
for (int i = 0; i < smap.size(); i++) {
LoadedApk.ServiceDispatcher sd = smap.valueAt(i);
... //报告ServiceConnection泄露
try {
ActivityManager.getService().unbindService(
sd.getIServiceConnection());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
sd.doForget();
}
}
mUnboundServices.remove(context);
}
}可能看到这里，有很多小伙伴会有疑问，为什么之前已经清理过了，这里还要再进行清理、这里为什么会有ServiceConnection泄露、这里为什么还要再次unbindService？那我们需要注意了，这里被调用的对象到底是谁？其实是Service的Context，假设我们在Serivce里调用bindService又绑定了一个其他Service，那这个Service被销毁后，它和另一个Service的连接怎么办？是不是就产生了泄露？为了防止这种情况，所以我们需要在Service销毁时调用一下这个方法解除它与其他Service的绑定
而且这个方法不仅会在这里被调用到哦，在我们之前分析过的 Android源码分析 - Activity销毁流程 中，也存在它的身影，当Activity被销毁，走到handleDestroyActivity方法时，会调用到我们ContextImpl.scheduleFinalCleanup方法，进行广播接收器的清理以及服务的解绑
至此，Service的主动停止流程我们都分析完了，还有一些细枝末节的事情可以说一说
rebind流程
之前我们说过，rebind的前提是Service中途没有被停止，为什么呢？带着疑问，我们来看之前没有分析的，当Service.onUnbind方法返回值为true时，会调用的AMS.unbindFinished方法
java
//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public void unbindFinished(IBinder token, Intent intent, boolean doRebind) {
// Refuse possible leaked file descriptors
if (intent != null && intent.hasFileDescriptors() == true) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
synchronized(this) {
mServices.unbindFinishedLocked((ServiceRecord)token, intent, doRebind);
}
}还是转交给ActiveServices去实现
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
void unbindFinishedLocked(ServiceRecord r, Intent intent, boolean doRebind) {
final long origId = Binder.clearCallingIdentity();
try {
if (r != null) {
Intent.FilterComparison filter
= new Intent.FilterComparison(intent);
IntentBindRecord b = r.bindings.get(filter);
boolean inDestroying = mDestroyingServices.contains(r);
if (b != null) {
//服务unbind的前提就是IntentBindRecord.apps.size == 0
if (b.apps.size() > 0 && !inDestroying) {
...
} else {
// Note to tell the service the next time there is
// a new client.
//将doRebind标记置为true，下一次再次建立连接时
//服务会回调Service.onRebind方法
b.doRebind = true;
}
}
serviceDoneExecutingLocked(r, inDestroying, false);
}
} finally {
Binder.restoreCallingIdentity(origId);
}
}根据我们之前的分析，我们知道，回调Service.onUnbind的前提就是这个Service没有任何连接与其绑定了，即IntentBindRecord.apps.size == 0，在这个case下，这个方法会将IntentBindRecord的doRebind变量置为true
此时让我们再回顾一下上一篇文章 Android源码分析 - Service启动流程 中分析的bindService流程，在ActiveServices.bindServiceLocked方法中有这么一段代码
java
//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 instanceName, String callingPackage, final int userId)
throws TransactionTooLargeException {
...
if (s.app != null && b.intent.received) {
// Service is already running, so we can immediately
// publish the connection.
//如果服务之前就已经在运行，即Service.onBind方法已经被执行，返回的IBinder对象也已经被保存
//调用LoadedApk$ServiceDispatcher$InnerConnection.connected方法
//回调ServiceConnection.onServiceConnected方法
c.conn.connected(s.name, b.intent.binder, false);
// 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.
//当服务解绑，调用到Service.onUnbind方法时返回true，此时doRebind变量就会被赋值为true
//此时，当再次建立连接时，服务会回调Service.onRebind方法
if (b.intent.apps.size() == 1 && b.intent.doRebind) {
requestServiceBindingLocked(s, b.intent, callerFg, true);
}
} else if (!b.intent.requested) {
//如果服务是因这次绑定而创建的
//请求执行Service.onBind方法，获取返回的IBinder对象
//发布Service，回调ServiceConnection.onServiceConnected方法
requestServiceBindingLocked(s, b.intent, callerFg, false);
}
...
}如果Service被停止了，那么它相应的ServiceRecord会从缓存mServicesByInstanceName和mServicesByIntent中移除，那么等到重新启动Service时会新建出一个ServiceRecord，此时里面的变量全部被初始化，b.intent.received == false，b.intent.requested == false，b.intent.doRebind == false，在这种情况下，调用requestServiceBindingLocked方法的最后一个入参rebind为false，就会直接回调Service.onBind方法，而不会回调Service.onRebind方法
如果Service没有被停止，且之前有被绑定过，那么b.intent.received == true，代表IBinder对象已获取到，此时如果之前的Service.onUnbind回调返回值为true，那么这里的b.intent.doRebind也为true，再加上如果这是Service断开所有连接后建立的第一次连接，即b.intent.apps.size() == 1，那么此时调用的requestServiceBindingLocked方法的最后一个入参rebind为true，就会直接回调Service.onRebind方法，而不会回调Service.onBind方法
混合启动的Service该如何停止
单一启动方式的Service的停止很简单，那么混合启动的Service该如何停止呢？
何为混合启动？指的是通过startService方式启动Service并且以BIND_AUTO_CREATE标志调用bindService方法绑定Service，两者不分先后
在上面的分析中，我们注意到，不管用哪种方式停止服务，最后都会走到bringDownServiceIfNeededLocked方法中，在这个方法里又会调用isServiceNeededLocked判断是否Service是否被需要，那被需要的条件是什么呢？Service.startRequested为true，并且没有标志为BIND_AUTO_CREATE的连接绑定，那么，只要不符合这两个条件，服务自然就可以被停止了
没有标志为BIND_AUTO_CREATE的连接绑定这个简单，只需要把标记为BIND_AUTO_CREATE的连接全部解绑了就好，那么怎么让Service.startRequested为false呢？我们回顾一下之前对stopSelf和stopService的分析，在他们调用bringDownServiceIfNeededLocked方法之前，都会先将Service.startRequested设置为false，所以答案就很明显了：只要unbindService掉所有BIND_AUTO_CREATE的标志的连接，然后stopService就能停止掉混合启动的服务，当然你也可以先stopService，再unbindService掉所有BIND_AUTO_CREATE的标志的连接
小测验
经过以上一系列的分析，我给大家出几个小问题：
-
先通过
startService启动服务，然后再用BIND_AUTO_CREATE标志bindService（连接1），此时，Service的生命周期是怎样的？ServiceConnection会回调哪些方法？ -
在上一题的基础上，再使用一个非
BIND_AUTO_CREATE标志bindService（连接2），此时，Service的生命周期是怎样的？ServiceConnection会回调哪些方法？ -
此时，使用
unbindService解绑连接1，会发生什么？ServiceConnection会回调哪些方法？ -
此时，使用
unbindService解绑连接2，会发生什么？ServiceConnection会回调哪些方法？ -
接着，再使用连接1
bindService，会发生什么？ServiceConnection会回调哪些方法？ -
然后，调用
stopService停止服务，服务真的会被停止吗？Service的生命周期是怎样的？连接1的ServiceConnection会回调哪些方法？ -
紧接着，再使用连接2
bindService，会发生什么？连接2的ServiceConnection会回调哪些方法？ -
最后，调用
unbindService解绑连接1，会发生什么？Service的生命周期是怎样的？ServiceConnection会回调哪些方法？
请大家思考片刻，可以去回顾之前的Service启动分析以及停止流程分析，如果以上问题能全部回答正确，证明你对Service已经有了一个很深刻的理解，接下来揭晓答案：
-
生命周期：
onCreate->onStartCommand->onBind，如果onBind的返回值不为null，ServiceConnection会回调onServiceConnected方法，如果onBind的返回值为null，ServiceConnection会回调onNullBinding方法 -
生命周期不会发生变化，如果
onBind的返回值不为null，ServiceConnection会回调onServiceConnected方法，如果onBind的返回值为null，ServiceConnection会回调onNullBinding方法 -
生命周期不会发生变化，
ServiceConnection不会回调任何方法 -
生命周期：
onUnbind，ServiceConnection不会回调任何方法 -
如果之前
onUnbind的返回值为true，则生命周期为：onRebind，否则生命周期不会发生变化，如果之前onBind的返回值不为null，ServiceConnection会回调onServiceConnected方法，如果之前onBind的返回值为null，ServiceConnection会回调onNullBinding方法 -
不会真的被停止，生命周期不会发生变化，
ServiceConnection不会回调任何方法 -
生命周期不会发生变化，如果之前
onBind的返回值不为null，ServiceConnection会回调onServiceConnected方法，如果之前onBind的返回值为null，ServiceConnection会回调onNullBinding方法 -
服务会被停止，生命周期：
onUnbind->onDestroy，连接1的ServiceConnection不会回调任何方法，如果之前onBind的返回值不为null，连接2的ServiceConnection会回调onServiceDisconnected、onBindingDied以及onNullBinding方法，如果之前onBind的返回值为null，连接2的ServiceConnection会回调onBindingDied以及onNullBinding方法
被动停止
Service除了主动停止，还会因为各种情况导致被动停止
用户手动从最近任务移除Task
注：由于各家系统对进程或任务调度策略不同，所以这里的Task移除逻辑和Service停止逻辑可能会有些许不同，我们还是以原生Android为准分析
不管用户是从最近任务划走了一个Task，还是点击了全部清除，最终都会走到ActivityStackSupervisor.removeTaskById方法
java
//frameworks/base/services/core/java/com/android/server/wm/ActivityStackSupervisor.java
boolean removeTaskById(int taskId, boolean killProcess, boolean removeFromRecents,
String reason) {
//通过id查询Task
final Task task =
mRootWindowContainer.anyTaskForId(taskId, MATCH_TASK_IN_STACKS_OR_RECENT_TASKS);
if (task != null) {
removeTask(task, killProcess, removeFromRecents, reason);
return true;
}
return false;
}这里的入参，killProcess为true，如果是移除单一Task，那么removeFromRecents为true，如果是清除全部Task，那么removeFromRecents为false
先通过id，使用RootWindowContainer查询相应的Task，然后再调用removeTask方法继续移除Task
java
//frameworks/base/services/core/java/com/android/server/wm/ActivityStackSupervisor.java
void removeTask(Task task, boolean killProcess, boolean removeFromRecents, String reason) {
//如果Task正在清理中则直接返回
if (task.mInRemoveTask) {
// Prevent recursion.
return;
}
//标记Task正在清理中
task.mInRemoveTask = true;
try {
//销毁此Task下所有Activity
task.performClearTask(reason);
//清理Task
cleanUpRemovedTaskLocked(task, killProcess, removeFromRecents);
//关闭屏幕固定
mService.getLockTaskController().clearLockedTask(task);
//通知任务栈发生变化
mService.getTaskChangeNotificationController().notifyTaskStackChanged();
//启动任务持久化程序，将任何挂起的任务写入磁盘
if (task.isPersistable) {
mService.notifyTaskPersisterLocked(null, true);
}
} finally {
//取消标记
task.mInRemoveTask = false;
}
}这个方法最重要的有两个部分，一个是销毁此Task下所有Activity，对于我们本次而言不需要关注，另一个是调用cleanUpRemovedTaskLocked继续清理Task
java
//frameworks/base/services/core/java/com/android/server/wm/ActivityStackSupervisor.java
void cleanUpRemovedTaskLocked(Task task, boolean killProcess, boolean removeFromRecents) {
//从最近任务列表中移除
//对于清除全部Task而言，之前在RecentTasks中已经进行过移除操作了
//所以传入的removeFromRecents为false
if (removeFromRecents) {
mRecentTasks.remove(task);
}
ComponentName component = task.getBaseIntent().getComponent();
if (component == null) {
return;
}
// Find any running services associated with this app and stop if needed.
//清理和此Task有关联的服务
final Message msg = PooledLambda.obtainMessage(ActivityManagerInternal::cleanUpServices,
mService.mAmInternal, task.mUserId, component, new Intent(task.getBaseIntent()));
mService.mH.sendMessage(msg);
//如果不需要杀死进程，到这里就为止了
if (!killProcess) {
return;
}
// Determine if the process(es) for this task should be killed.
final String pkg = component.getPackageName();
ArrayList<Object> procsToKill = new ArrayList<>();
ArrayMap<String, SparseArray<WindowProcessController>> pmap =
mService.mProcessNames.getMap();
//遍历App进程，确定要杀死的进程
for (int i = 0; i < pmap.size(); i++) {
SparseArray<WindowProcessController> uids = pmap.valueAt(i);
for (int j = 0; j < uids.size(); j++) {
WindowProcessController proc = uids.valueAt(j);
//不要杀死其他用户下的进程
if (proc.mUserId != task.mUserId) {
// Don't kill process for a different user.
continue;
}
//不要杀死首页进程
//HomeProcess指的是含有分类为android.intent.category.HOME的进程
//也就是能成为首页Launcher的进程
if (proc == mService.mHomeProcess) {
// Don't kill the home process along with tasks from the same package.
continue;
}
//不要杀死和这个Task无关的进程
if (!proc.mPkgList.contains(pkg)) {
// Don't kill process that is not associated with this task.
continue;
}
//如果这个进程有Activity在不同的Task里，并且这个Task也在最近任务里
//或者有Activity还没有被停止，则不要杀死进程
if (!proc.shouldKillProcessForRemovedTask(task)) {
// Don't kill process(es) that has an activity in a different task that is also
// in recents, or has an activity not stopped.
return;
}
//有前台服务的话不要杀死进程
if (proc.hasForegroundServices()) {
// Don't kill process(es) with foreground service.
return;
}
// Add process to kill list.
procsToKill.add(proc);
}
}
// Kill the running processes. Post on handle since we don't want to hold the service lock
// while calling into AM.
//杀死进程
final Message m = PooledLambda.obtainMessage(
ActivityManagerInternal::killProcessesForRemovedTask, mService.mAmInternal,
procsToKill);
mService.mH.sendMessage(m);
}这个方法主要做两件事，一是清理和此Task有关联的服务，二是杀死应该杀死的进程
清理服务这一步用到了池化技术，这里大家不用管，就当做调用了mService.mAmInternal.cleanUpServices即可，这里的mService.mAmInternal是AMS里的一个内部类LocalService
java
//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public void cleanUpServices(int userId, ComponentName component, Intent baseIntent) {
synchronized(ActivityManagerService.this) {
mServices.cleanUpServices(userId, component, baseIntent);
}
}同样，关于Service的工作都转交给ActiveServices
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
void cleanUpServices(int userId, ComponentName component, Intent baseIntent) {
ArrayList<ServiceRecord> services = new ArrayList<>();
//获得此用户下所有的活动Service
ArrayMap<ComponentName, ServiceRecord> alls = getServicesLocked(userId);
//筛选出此Task下的所有活动Service
for (int i = alls.size() - 1; i >= 0; i--) {
ServiceRecord sr = alls.valueAt(i);
if (sr.packageName.equals(component.getPackageName())) {
services.add(sr);
}
}
// Take care of any running services associated with the app.
for (int i = services.size() - 1; i >= 0; i--) {
ServiceRecord sr = services.get(i);
if (sr.startRequested) {
if ((sr.serviceInfo.flags&ServiceInfo.FLAG_STOP_WITH_TASK) != 0) {
//如果在manifest里设置了stopWithTask，那么会直接停止Service
stopServiceLocked(sr);
} else {
//如果没有设置stopWithTask的话，则会回调Service.onTaskRemoved方法
sr.pendingStarts.add(new ServiceRecord.StartItem(sr, true,
sr.getLastStartId(), baseIntent, null, 0));
if (sr.app != null && sr.app.thread != null) {
// We always run in the foreground, since this is called as
// part of the "remove task" UI operation.
try {
sendServiceArgsLocked(sr, true, false);
} catch (TransactionTooLargeException e) {
// Ignore, keep going.
}
}
}
}
}
}首先要获取到所有需要清理的Service记录，然后再对它们进行处理
对于在manifest文件里设置了stopWithTask标识的Service，直接调用stopServiceLocked方法停止服务，而对于没有这个标识的Service，则是增加一个启动项，接着调用sendServiceArgsLocked处理这个启动项
我们观察这个启动项的构建，第二个参数为true，我们可以去这个类的构造方法那里看到，第二个参数的名字为_taskRemoved，意思很明显了，然后根据我们在上一篇文章 Android源码分析 - Service启动流程 中分析的sendServiceArgsLocked方法可以知道，它最终会走到ActivityThread.handleServiceArgs方法中
java
//frameworks/base/core/java/android/app/ActivityThread.java
private void handleServiceArgs(ServiceArgsData data) {
...
int res;
if (!data.taskRemoved) {
//正常情况调用
res = s.onStartCommand(data.args, data.flags, data.startId);
} else {
//用户关闭Task栈时调用
s.onTaskRemoved(data.args);
res = Service.START_TASK_REMOVED_COMPLETE;
}
...
}可以发现，当taskRemoved变量为true时，会回调Service.onTaskRemoved方法
我们接着回到cleanUpRemovedTaskLocked方法中，当它清理完服务后，便会尝试杀死进程，这里面其他的判断条件我们都不用管，我们只需要关心其中的一段，有前台服务的话不要杀死进程
以上是我根据AOSP源码分析得出的结果，在模拟器上也验证通过，但在我的小米MIX4上表现却完全不是这样，大家开发时还是要以实际为准
内存不足
当内存不足时，系统会通过OOM Killer或Low Memory Killer等手段杀死各种进程，如果被杀死的进程里有Service正在运行，那自然也会被停止
重建
当Service所在进程被杀死后，根据Service.onStartCommand的返回值，系统会决定是否重建，怎么重建。我们先把其可能的返回值以及产生的结果先列出来：
START_STICKY_COMPATIBILITY：targetSdkVersion< 5 (Android 2.0) 的App默认会返回这个，Service被杀后会被重建，但onStartCommand方法不会被执行START_STICKY：targetSdkVersion>= 5 (Android 2.0) 的App默认会返回这个，Service被杀后会被重建，onStartCommand方法也会被执行，但此时onStartCommand方法的第一个参数Intent为nullSTART_NOT_STICKY：Service被杀后不会被重建START_REDELIVER_INTENT：Service被杀后会被重建，onStartCommand方法也会被执行，此时onStartCommand方法的第一个参数Intent为Service被杀死前最后一次调用onStartCommand方法时传递的Intent
对于其返回值我们需要先了解一下是怎么处理的，这需要回顾一下上一篇文章分析的handleServiceArgs方法了
java
//frameworks/base/core/java/android/app/ActivityThread.java
private void handleServiceArgs(ServiceArgsData data) {
Service s = mServices.get(data.token);
if (s != null) {
try {
...
int res;
if (!data.taskRemoved) {
//正常情况调用
res = s.onStartCommand(data.args, data.flags, data.startId);
} else {
//用户关闭Task栈时调用
s.onTaskRemoved(data.args);
res = Service.START_TASK_REMOVED_COMPLETE;
}
//确保其他异步任务执行完成
QueuedWork.waitToFinish();
try {
//Service相关任务执行完成
//这一步会根据onStartCommand的返回值，调整Service死亡重建策略
//同时会把之前的启动超时定时器取消
ActivityManager.getService().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_START, data.startId, res);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
} catch (Exception e) {
if (!mInstrumentation.onException(s, e)) {
throw new RuntimeException(
"Unable to start service " + s
+ " with " + data.args + ": " + e.toString(), e);
}
}
}
}可以看到，这里从Service.onStartCommand得到返回值后以其作为参数调用了AMS.serviceDoneExecuting方法
java
//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public void serviceDoneExecuting(IBinder token, int type, int startId, int res) {
synchronized(this) {
...
mServices.serviceDoneExecutingLocked((ServiceRecord)token, type, startId, res);
}
}转交给了ActiveServices.serviceDoneExecutingLocked方法
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
void serviceDoneExecutingLocked(ServiceRecord r, int type, int startId, int res) {
boolean inDestroying = mDestroyingServices.contains(r);
if (r != null) {
if (type == ActivityThread.SERVICE_DONE_EXECUTING_START) {
// This is a call from a service start... take care of
// book-keeping.
r.callStart = true;
switch (res) {
case Service.START_STICKY_COMPATIBILITY:
case Service.START_STICKY: {
// We are done with the associated start arguments.
r.findDeliveredStart(startId, false, true);
// Don't stop if killed.
r.stopIfKilled = false;
break;
}
case Service.START_NOT_STICKY: {
// We are done with the associated start arguments.
r.findDeliveredStart(startId, false, true);
if (r.getLastStartId() == startId) {
// There is no more work, and this service
// doesn't want to hang around if killed.
r.stopIfKilled = true;
}
break;
}
case Service.START_REDELIVER_INTENT: {
// We'll keep this item until they explicitly
// call stop for it, but keep track of the fact
// that it was delivered.
ServiceRecord.StartItem si = r.findDeliveredStart(startId, false, false);
if (si != null) {
si.deliveryCount = 0;
si.doneExecutingCount++;
// Don't stop if killed.
r.stopIfKilled = true;
}
break;
}
case Service.START_TASK_REMOVED_COMPLETE: {
// Special processing for onTaskRemoved(). Don't
// impact normal onStartCommand() processing.
r.findDeliveredStart(startId, true, true);
break;
}
default:
throw new IllegalArgumentException(
"Unknown service start result: " + res);
}
if (res == Service.START_STICKY_COMPATIBILITY) {
r.callStart = false;
}
} else if (type == ActivityThread.SERVICE_DONE_EXECUTING_STOP) {
...
}
...
} else { ... }
}我们就只看对Service.onStartCommand的返回值进行处理的部分
首先，不管返回值是什么，都会调用ServiceRecord.findDeliveredStart方法，只不过入参不同
java
//frameworks/base/services/core/java/com/android/server/am/ServiceRecord.java
public StartItem findDeliveredStart(int id, boolean taskRemoved, boolean remove) {
final int N = deliveredStarts.size();
for (int i=0; i<N; i++) {
StartItem si = deliveredStarts.get(i);
if (si.id == id && si.taskRemoved == taskRemoved) {
if (remove) deliveredStarts.remove(i);
return si;
}
}
return null;
}前两个参数，不管返回值是什么，传进来的都是一样的，而第三个参数remove就不同了，当返回值为START_REDELIVER_INTENT的时候，它为false，其他情况都为true，意味着要删除这个已分发的启动项，START_REDELIVER_INTENT由于需要保留最后一次调用onStartCommand时的Intent，所以它不应该被删除
接着我们回到serviceDoneExecutingLocked方法，可以发现，START_STICKY和START_STICKY_COMPATIBILITY情况下的ServiceRecord.stopIfKilled被置为了false，其他则被置为了true，这和我们之前对结果的描述不同啊？不是说好了返回START_REDELIVER_INTENT也会重启吗？这是因为START_REDELIVER_INTENT比较特殊，它的重启不需要看stopIfKilled这个标志位，这个等到我们后面分析到怎么判断是否应该停止服务时就知道了
以上的内容我们先记下来，会在后面的重启流程中发挥作用
然后我们来看进程死亡后会发生什么，我们曾在之前的文章 Android源码分析 - Activity启动流程（中） 中提到过，当App启动时，AMS会为其注册一个App进程死亡回调AppDeathRecipient，当App进程死亡后便会回调其binderDied方法
java
//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
private final class AppDeathRecipient implements IBinder.DeathRecipient {
final ProcessRecord mApp;
final int mPid;
final IApplicationThread mAppThread;
AppDeathRecipient(ProcessRecord app, int pid,
IApplicationThread thread) {
mApp = app;
mPid = pid;
mAppThread = thread;
}
@Override
public void binderDied() {
synchronized(ActivityManagerService.this) {
appDiedLocked(mApp, mPid, mAppThread, true, null);
}
}
}接着便会调用appDiedLocked方法处理进程死亡
java
//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
final void appDiedLocked(ProcessRecord app, int pid, IApplicationThread thread,
boolean fromBinderDied, String reason) {
// First check if this ProcessRecord is actually active for the pid.
//检查pid所属ProcessRecord是否与传入ProcessRecord相符
synchronized (mPidsSelfLocked) {
ProcessRecord curProc = mPidsSelfLocked.get(pid);
if (curProc != app) {
return;
}
}
... //记录电池统计信息
//如果App进程尚未死亡的话，杀死进程
if (!app.killed) {
if (!fromBinderDied) {
killProcessQuiet(pid);
mProcessList.noteAppKill(app, ApplicationExitInfo.REASON_OTHER,
ApplicationExitInfo.SUBREASON_UNKNOWN, reason);
}
ProcessList.killProcessGroup(app.uid, pid);
app.killed = true;
}
// Clean up already done if the process has been re-started.
if (app.pid == pid && app.thread != null &&
app.thread.asBinder() == thread.asBinder()) {
//一般情况下非自动化测试，先置为true
boolean doLowMem = app.getActiveInstrumentation() == null;
boolean doOomAdj = doLowMem;
if (!app.killedByAm) { //不通过AMS杀死的进程，一般就是被 Low Memory Killer (LMK) 杀死的
... //报告信息
//被LMK杀死，说明系统内存不足
mAllowLowerMemLevel = true;
} else { //通过AMS杀死的进程
// Note that we always want to do oom adj to update our state with the
// new number of procs.
mAllowLowerMemLevel = false;
//正常情况下非内存不足
doLowMem = false;
}
... //事件记录
//继续处理App进程死亡
handleAppDiedLocked(app, false, true);
//调整进程优先级
if (doOomAdj) {
updateOomAdjLocked(OomAdjuster.OOM_ADJ_REASON_PROCESS_END);
}
//当因为内存不足而杀死App进程时
//调用App层各处的的onLowMemory方法，释放内存
if (doLowMem) {
doLowMemReportIfNeededLocked(app);
}
} else if (app.pid != pid) { //新进程已启动
// A new process has already been started.
... //报告记录信息
}
...
}这里的其他代码我们都不用关心，直接看handleAppDiedLocked方法继续处理App进程死亡
java
//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
final void handleAppDiedLocked(ProcessRecord app,
boolean restarting, boolean allowRestart) {
...
//清理进程的主要方法
boolean kept = cleanUpApplicationRecordLocked(app, restarting, allowRestart, -1,
false /*replacingPid*/);
...
}
final boolean cleanUpApplicationRecordLocked(ProcessRecord app,
boolean restarting, boolean allowRestart, int index, boolean replacingPid) {
...
mServices.killServicesLocked(app, allowRestart);
...
}可以看到，这里调用了ActiveServices.killServicesLocked方法停止还在运行中的服务
java
final void killServicesLocked(ProcessRecord app, boolean allowRestart) {
// Clean up any connections this application has to other services.
//清理所有连接
for (int i = app.connections.size() - 1; i >= 0; i--) {
ConnectionRecord r = app.connections.valueAt(i);
removeConnectionLocked(r, app, null);
}
updateServiceConnectionActivitiesLocked(app);
app.connections.clear();
app.whitelistManager = false;
// Clear app state from services.
//遍历所有正在运行中的服务
for (int i = app.numberOfRunningServices() - 1; i >= 0; i--) {
ServiceRecord sr = app.getRunningServiceAt(i);
synchronized (sr.stats.getBatteryStats()) {
sr.stats.stopLaunchedLocked();
}
if (sr.app != app && sr.app != null && !sr.app.isPersistent()) {
//记录服务已停止
sr.app.stopService(sr);
//更新绑定的客户端uids
sr.app.updateBoundClientUids();
}
sr.setProcess(null);
sr.isolatedProc = null;
sr.executeNesting = 0;
sr.forceClearTracker();
if (mDestroyingServices.remove(sr)) {
if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "killServices remove destroying " + sr);
}
final int numClients = sr.bindings.size();
for (int bindingi=numClients-1; bindingi>=0; bindingi--) {
IntentBindRecord b = sr.bindings.valueAt(bindingi);
//释放对服务Binder的引用
b.binder = null;
//重置
b.requested = b.received = b.hasBound = false;
// If this binding is coming from a cached process and is asking to keep
// the service created, then we'll kill the cached process as well -- we
// don't want to be thrashing around restarting processes that are only
// there to be cached.
... //遍历客户端进程（实际上没做任何事）
}
}
ServiceMap smap = getServiceMapLocked(app.userId);
// Now do remaining service cleanup.
for (int i = app.numberOfRunningServices() - 1; i >= 0; i--) {
ServiceRecord sr = app.getRunningServiceAt(i);
// Unless the process is persistent, this process record is going away,
// so make sure the service is cleaned out of it.
//非持久化进程
if (!app.isPersistent()) {
//记录服务已停止
app.stopService(sr);
//更新绑定的客户端uids
app.updateBoundClientUids();
}
// Sanity check: if the service listed for the app is not one
// we actually are maintaining, just let it drop.
//一致性检查
final ServiceRecord curRec = smap.mServicesByInstanceName.get(sr.instanceName);
if (curRec != sr) {
if (curRec != null) {
Slog.wtf(TAG, "Service " + sr + " in process " + app
+ " not same as in map: " + curRec);
}
continue;
}
// Any services running in the application may need to be placed
// back in the pending list.
//允许重启，但Service崩溃的次数超出重试上限（默认为16），并且它不是系统应用
if (allowRestart && sr.crashCount >= mAm.mConstants.BOUND_SERVICE_MAX_CRASH_RETRY
&& (sr.serviceInfo.applicationInfo.flags
&ApplicationInfo.FLAG_PERSISTENT) == 0) {
... //记录
//停止服务
bringDownServiceLocked(sr);
} else if (!allowRestart
|| !mAm.mUserController.isUserRunning(sr.userId, 0)) {
//不允许重启或者服务进程所在用户不在运行，停止服务
bringDownServiceLocked(sr);
} else {
//尝试调度重启服务
final boolean scheduled = scheduleServiceRestartLocked(sr, true /* allowCancel */);
// Should the service remain running? Note that in the
// extreme case of so many attempts to deliver a command
// that it failed we also will stop it here.
if (!scheduled) { //未调度重启
//停止服务
bringDownServiceLocked(sr);
} else if (sr.canStopIfKilled(false /* isStartCanceled */)) {
// Update to stopped state because the explicit start is gone. The service is
// scheduled to restart for other reason (e.g. connections) so we don't bring
// down it.
//将服务的启动状态更新为停止
sr.startRequested = false;
... //记录
}
}
}
//不允许重启的话
if (!allowRestart) {
//停止所有服务
app.stopAllServices();
//清理绑定的客户端uids
app.clearBoundClientUids();
// Make sure there are no more restarting services for this process.
//确保这个进程不再会重启服务，清理所有待重启待启动的服务
for (int i=mRestartingServices.size()-1; i>=0; i--) {
ServiceRecord r = mRestartingServices.get(i);
if (r.processName.equals(app.processName) &&
r.serviceInfo.applicationInfo.uid == app.info.uid) {
mRestartingServices.remove(i);
clearRestartingIfNeededLocked(r);
}
}
for (int i=mPendingServices.size()-1; i>=0; i--) {
ServiceRecord r = mPendingServices.get(i);
if (r.processName.equals(app.processName) &&
r.serviceInfo.applicationInfo.uid == app.info.uid) {
mPendingServices.remove(i);
}
}
}
// Make sure we have no more records on the stopping list.
//清理所有停止中的服务
int i = mDestroyingServices.size();
while (i > 0) {
i--;
ServiceRecord sr = mDestroyingServices.get(i);
if (sr.app == app) {
sr.forceClearTracker();
mDestroyingServices.remove(i);
}
}
//清理所有执行中的服务
//这里的执行中指的是有事务正在运行，比如说正在停止过程中，不是指运行中
app.executingServices.clear();
}这里做了各种清理工作，客户端进程的清理呀，服务端进程的清理，然后就是Service重启的核心，scheduleServiceRestartLocked方法
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
private final boolean scheduleServiceRestartLocked(ServiceRecord r, boolean allowCancel) {
//系统正在关机，直接返回
if (mAm.mAtmInternal.isShuttingDown()) {
return false;
}
//一致性检查
ServiceMap smap = getServiceMapLocked(r.userId);
if (smap.mServicesByInstanceName.get(r.instanceName) != r) {
ServiceRecord cur = smap.mServicesByInstanceName.get(r.instanceName);
Slog.wtf(TAG, "Attempting to schedule restart of " + r
+ " when found in map: " + cur);
return false;
}
final long now = SystemClock.uptimeMillis();
final String reason;
if ((r.serviceInfo.applicationInfo.flags
&ApplicationInfo.FLAG_PERSISTENT) == 0) { //对于非系统应用
//服务至少要过多长时间才能重启，默认1000ms
long minDuration = mAm.mConstants.SERVICE_RESTART_DURATION;
//服务被杀死重启后需要运行多长时间，默认60s
long resetTime = mAm.mConstants.SERVICE_RESET_RUN_DURATION;
boolean canceled = false;
// Any delivered but not yet finished starts should be put back
// on the pending list.
//对应着返回值为START_REDELIVER_INTENT的情况
final int N = r.deliveredStarts.size();
if (N > 0) {
for (int i=N-1; i>=0; i--) {
ServiceRecord.StartItem si = r.deliveredStarts.get(i);
si.removeUriPermissionsLocked();
if (si.intent == null) {
// We'll generate this again if needed.
} else if (!allowCancel || (si.deliveryCount < ServiceRecord.MAX_DELIVERY_COUNT
&& si.doneExecutingCount < ServiceRecord.MAX_DONE_EXECUTING_COUNT)) {
//如果该启动项的失败次数小于最大容忍次数
//MAX_DELIVERY_COUNT默认为3
//MAX_DONE_EXECUTING_COUNT默认为6
r.pendingStarts.add(0, si);
//这种情况下延时是现在距离启动时间的两倍
long dur = SystemClock.uptimeMillis() - si.deliveredTime;
dur *= 2;
if (minDuration < dur) minDuration = dur;
if (resetTime < dur) resetTime = dur;
} else {
//如果该启动项的失败次数大于等于最大容忍次数
canceled = true;
}
}
r.deliveredStarts.clear();
}
if (allowCancel) {
//判断是否应该停止（只考虑非绑定启动的情况）
final boolean shouldStop = r.canStopIfKilled(canceled);
if (shouldStop && !r.hasAutoCreateConnections()) {
// Nothing to restart.
//如果应该停止，直接返回
return false;
}
reason = (r.startRequested && !shouldStop) ? "start-requested" : "connection";
} else {
reason = "always";
}
r.totalRestartCount++;
if (r.restartDelay == 0) { //第一次重启的情况
r.restartCount++;
r.restartDelay = minDuration;
} else if (r.crashCount > 1) { //Service所在进程在Service运行过程中发生崩溃导致重启的话
//重启延时为 30min * (崩溃次数 - 1)
r.restartDelay = mAm.mConstants.BOUND_SERVICE_CRASH_RESTART_DURATION
* (r.crashCount - 1);
} else { //非第一次重启的情况
// If it has been a "reasonably long time" since the service
// was started, then reset our restart duration back to
// the beginning, so we don't infinitely increase the duration
// on a service that just occasionally gets killed (which is
// a normal case, due to process being killed to reclaim memory).
if (now > (r.restartTime+resetTime)) {
//如果服务重启后运行达到了一定时间，则重启延时为
r.restartCount = 1;
r.restartDelay = minDuration;
} else {
//如果服务重启后运行没有达到一定时间（短时间内又要重启）
//则增长重启延时，默认因子为4
r.restartDelay *= mAm.mConstants.SERVICE_RESTART_DURATION_FACTOR;
if (r.restartDelay < minDuration) {
r.restartDelay = minDuration;
}
}
}
//确定重启时间
r.nextRestartTime = now + r.restartDelay;
// Make sure that we don't end up restarting a bunch of services
// all at the same time.
//确保不会在同一时间启动大量服务
boolean repeat;
do {
repeat = false;
final long restartTimeBetween = mAm.mConstants.SERVICE_MIN_RESTART_TIME_BETWEEN;
for (int i=mRestartingServices.size()-1; i>=0; i--) {
ServiceRecord r2 = mRestartingServices.get(i);
if (r2 != r && r.nextRestartTime >= (r2.nextRestartTime-restartTimeBetween)
&& r.nextRestartTime < (r2.nextRestartTime+restartTimeBetween)) {
r.nextRestartTime = r2.nextRestartTime + restartTimeBetween;
r.restartDelay = r.nextRestartTime - now;
repeat = true;
break;
}
}
} while (repeat);
} else { //对于系统进程，立马重启
// Persistent processes are immediately restarted, so there is no
// reason to hold of on restarting their services.
r.totalRestartCount++;
r.restartCount = 0;
r.restartDelay = 0;
r.nextRestartTime = now;
reason = "persistent";
}
//添加到重启列表中
if (!mRestartingServices.contains(r)) {
r.createdFromFg = false;
mRestartingServices.add(r);
r.makeRestarting(mAm.mProcessStats.getMemFactorLocked(), now);
}
//取消前台服务通知
cancelForegroundNotificationLocked(r);
//通过Handler调度重启
mAm.mHandler.removeCallbacks(r.restarter);
mAm.mHandler.postAtTime(r.restarter, r.nextRestartTime);
r.nextRestartTime = SystemClock.uptimeMillis() + r.restartDelay;
... //事件记录
return true;
}这个方法主要做了几件事情，一是判断服务需不需要重启，二是计算服务的下次重启时间，最后通过Handler执行延时重启
还记得我们前面说的当返回值为START_REDELIVER_INTENT时，不会从ServiceRecord.deliveredStarts中删除启动项吗？这里就体现出了这一点，遍历整个deliveredStarts列表，从中找出符合重启条件的启动项，将其加入到pendingStarts列表中，需要注意的是，在这种情况下，重启延时为现在距离启动时间的两倍，所以一般情况下START_REDELIVER_INTENT比START_STICKY重启的要更慢
接下来便要判断服务需不需要重启，这里调用了ServiceRecord.canStopIfKilled方法
java
//frameworks/base/services/core/java/com/android/server/am/ServiceRecord.java
boolean canStopIfKilled(boolean isStartCanceled) {
return startRequested && (stopIfKilled || isStartCanceled) && pendingStarts.isEmpty();
}之前说过，如果返回值为START_STICKY或START_STICKY_COMPATIBILITY，那这里的stopIfKilled就为false，所以整体会返回false，而对于返回值START_REDELIVER_INTENT而言，之前已经进行过操作，将启动项添加到pendingStarts列表中了，所以只要这里为false，整体就为false，stopIfKilled的值就不重要了
最后就是通过Handler执行延时重启了，这里Handler传入的Runnable是ServiceRecord.restarter，它是在服务启动，调用retrieveServiceLocked方法时被创建的
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
private class ServiceRestarter implements Runnable {
private ServiceRecord mService;
void setService(ServiceRecord service) {
mService = service;
}
public void run() {
synchronized(mAm) {
performServiceRestartLocked(mService);
}
}
}可以看到，在一定的延时后，会调用到performServiceRestartLocked方法重启服务
java
//frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
final void performServiceRestartLocked(ServiceRecord r) {
if (!mRestartingServices.contains(r)) {
return;
}
if (!isServiceNeededLocked(r, false, false)) {
// Paranoia: is this service actually needed? In theory a service that is not
// needed should never remain on the restart list. In practice... well, there
// have been bugs where this happens, and bad things happen because the process
// ends up just being cached, so quickly killed, then restarted again and again.
// Let's not let that happen.
Slog.wtf(TAG, "Restarting service that is not needed: " + r);
return;
}
try {
//参考上一篇文章，Service启动流程
bringUpServiceLocked(r, r.intent.getIntent().getFlags(), r.createdFromFg, true, false);
} catch (TransactionTooLargeException e) {
// Ignore, it's been logged and nothing upstack cares.
}
}最终调用了bringUpServiceLocked方法启动服务，这一部分可以看上一篇文章 Android源码分析 - Service启动流程 中的分析，还记得上一篇文章中分析的realStartServiceLocked方法中，有一个逻辑是：如果Service已经启动，并且没有启动项，则构建一个假的启动参数供onStartCommand使用 吗？之前看到这个逻辑的时候我还有些疑惑为什么需要这样，现在就豁然开朗了，原来这是为Service重启做的逻辑，而对于返回值START_REDELIVER_INTENT而言，pendingStarts列表本身就不为空，直接正常执行启动任务就可以了
总结
至此，整个Service篇章就到此结束了，通过这次的写作，我自身也是受益匪浅，了解到了很多我以前不知道的知识，也纠正了一些我以前错误的认知，如果也能帮到正在看文章的你们，那就再好不过了