public final
class Character implements java.io.Serializable, Comparable<Character> {

    // ...

    public static final char MIN_HIGH_SURROGATE = '\uD800';
    public static final char MAX_HIGH_SURROGATE = '\uDBFF';
    public static final char MIN_LOW_SURROGATE  = '\uDC00';
    public static final char MAX_LOW_SURROGATE  = '\uDFFF';

    public static final int MIN_SUPPLEMENTARY_CODE_POINT = 0x010000;

    // ...

    public static int codePointAt(CharSequence seq, int index) {
        char c1 = seq.charAt(index);
        // 码元在 U+D800 到 U+DBFF 之间，并且下一个char的index没到结尾
        if (isHighSurrogate(c1) && ++index < seq.length()) {
            char c2 = seq.charAt(index);
            // 下一个char的码元在 U+DC00 到 U+DFFF 之间
            if (isLowSurrogate(c2)) {
                // 组合起来获得完整字符的码点
                return toCodePoint(c1, c2);
            }
        }
        // 字符码点即是单个char的码元
        return c1;
    }

    // 码元是否在 U+D800 到 U+DBFF 之间
    public static boolean isHighSurrogate(char ch) {
        // Help VM constant-fold; MAX_HIGH_SURROGATE + 1 == MIN_LOW_SURROGATE
        return ch >= MIN_HIGH_SURROGATE && ch < (MAX_HIGH_SURROGATE + 1);
    }

    // 码元是否在 U+DC00 到 U+DFFF 之间
    public static boolean isLowSurrogate(char ch) {
        return ch >= MIN_LOW_SURROGATE && ch < (MAX_LOW_SURROGATE + 1);
    }

    /**
     * 计算规则：
     * 1. 高位上的码元减掉高半区的起始值 0xD800 ，然后左移10位
     * 2. 低位上的码元减掉低半区的起始值 0xDC00
     * 3. 将 1 和 2 的计算结果以及辅助平面的起始值 0x010000 相加，获取到完整的码点值
     */
    public static int toCodePoint(char high, char low) {
        // Optimized form of:
        // return ((high - MIN_HIGH_SURROGATE) << 10)
        //         + (low - MIN_LOW_SURROGATE)
        //         + MIN_SUPPLEMENTARY_CODE_POINT;
        return ((high << 10) + low) + (MIN_SUPPLEMENTARY_CODE_POINT
                                       - (MIN_HIGH_SURROGATE << 10)
                                       - MIN_LOW_SURROGATE);
    }
    
    // ...

}

//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;
}

//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);
    }
}

//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;
}

//frameworks/base/services/core/java/com/android/server/am/ServiceRecord.java
public int makeNextStartId() {
    lastStartId++;
    if (lastStartId < 1) {
        lastStartId = 1;
    }
    return lastStartId;
}

//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);
}

//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);
}

//frameworks/base/core/java/android/app/ActivityThread.java
public final void scheduleStopService(IBinder token) {
    sendMessage(H.STOP_SERVICE, token);
}

//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);
            }
        }
    }
}

//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();
    }
}

//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);
}

//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");
    }
}

//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
    }
}

//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;
    }
}

//frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public boolean unbindService(IServiceConnection connection) {
    synchronized (this) {
        return mServices.unbindServiceLocked(connection);
    }
}

//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;
}

//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);
        }
    }
}

//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;
}

//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;
}

//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;
}

//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
}

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);
    }
}

//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);
            }
        }
    }
}

//frameworks/base/core/java/android/app/ContextImpl.java
final void scheduleFinalCleanup(String who, String what) {
    mMainThread.scheduleContextCleanup(this, who, what);
}

//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);
}

//frameworks/base/core/java/android/app/ContextImpl.java
final void performFinalCleanup(String who, String what) {
    mPackageInfo.removeContextRegistrations(getOuterContext(), who, what);
}

//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);
    }
}

//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);
    }
}

//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);
    }
}

//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);
    }
    ...
}

//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;
}

//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;
    }
}

//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);
}

//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);
    }
}

//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.
                    }
                }
            }
        }
    }
}

//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;
    }
    ...
}

//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);
            }
        }
    }
}

//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);
    }
}

//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 { ... }
}