Caused by java.lang.IllegalStateException Not allowed to start service Intent { cmp=com.x.x.x/.x.x.xService }: app is in background uid UidRecord问题原因分析(二)

应用在适配Android 8.0以上系统时，会发现后台启动不了服务，会报出如下异常，并强退：

Fatal Exception: java.lang.IllegalStateException
Not allowed to start service Intent { act=com.xxx.xxx.xxx pkg=com.xxx.xxx (has extras) }: app is in background uid UidRecord{1cbd9ed u0a1967 CEM idle procs:1 seq(0,0,0)}

问题原因分析

Android 8.0 行为变更

https://developer.android.com/about/versions/oreo/android-8.0-changes.html#back-all

Android 8.0 除了提供诸多新特性和功能外，还对系统和 API 行为做出了各种变更。本文重点介绍您应该了解并在开发应用时加以考虑的一些主要变更。

其中大部分变更会影响所有应用，而不论应用针对的是何种版本的 Android。不过，有几项变更仅影响针对 Android 8.0 的应用。为清楚起见，本页面分为两个部分：针对所有 API 级别的应用和针对 Android 8.0 的应用。

针对所有 API 级别的应用

这些行为变更适用于 在 Android 8.0 平台上运行的 所有应用，无论这些应用是针对哪个 API 级别构建。所有开发者都应查看这些变更，并修改其应用以正确支持这些变更（如果适用）。

后台执行限制

Android 8.0 为提高电池续航时间而引入的变更之一是，当您的应用进入已缓存状态时，如果没有活动的组件，系统将解除应用具有的所有唤醒锁。

此外，为提高设备性能，系统会限制未在前台运行的应用的某些行为。具体而言：

• 现在，在后台运行的应用对后台服务的访问受到限制。
• 应用无法使用其清单注册大部分隐式广播（即，并非专门针对此应用的广播）。

默认情况下，这些限制仅适用于针对 O 的应用。不过，用户可以从 Settings 屏幕为任意应用启用这些限制，即使应用并不是以 O 为目标平台。

Android 8.0 还对特定函数做出了以下变更：

• 如果针对 Android 8.0 的应用尝试在不允许其创建后台服务的情况下使用 startService() 函数，则该函数将引发一个 IllegalStateException。
• 新的 Context.startForegroundService() 函数将启动一个前台服务。现在，即使应用在后台运行，系统也允许其调用 Context.startForegroundService()。不过，应用必须在创建服务后的五秒内调用该服务的 startForeground() 函数。

如需了解详细信息，请参阅后台执行限制。

出错代码定位

在ContextImpl的startServiceCommon函数中爆出异常， 
http://androidxref.com/8.1.0_r33/xref/frameworks/base/core/java/android/app/ContextImpl.java

private ComponentName startServiceCommon(Intent service, boolean requireForeground,
            UserHandle user) {
        try {
            validateServiceIntent(service);
            service.prepareToLeaveProcess(this);
            ComponentName cn = ActivityManager.getService().startService(
                mMainThread.getApplicationThread(), service, service.resolveTypeIfNeeded(
                            getContentResolver()), requireForeground,
                            getOpPackageName(), user.getIdentifier());
            if (cn != null) {
                if (cn.getPackageName().equals("!")) {
                    throw new SecurityException(
                            "Not allowed to start service " + service
                            + " without permission " + cn.getClassName());
                } else if (cn.getPackageName().equals("!!")) {
                    throw new SecurityException(
                            "Unable to start service " + service
                            + ": " + cn.getClassName());
                 //此处就是曝出异常的地方，非法状态，不允许启动服务
                } else if (cn.getPackageName().equals("?")) {
                    throw new IllegalStateException(
                            "Not allowed to start service " + service + ": " + cn.getClassName());
                }
            }
            return cn;
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
    }

startServiceCommon这个函数做的操作是AMS的startService，用于启动服务

AMS的startService

接下去看AMS的startService，稍微注意一下传递的参数，里面有一个前台后台相关的requireForeground，可能跟问题有关系。 
AMS代码位置 

http://androidxref.com/8.1.0_r33/xref/frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

@Override
public ComponentName startService(IApplicationThread caller, Intent service,
            String resolvedType, boolean requireForeground, String callingPackage, int userId)
           throws TransactionTooLargeException {
        enforceNotIsolatedCaller("startService");
        // Refuse possible leaked file descriptors
       if (service != null && service.hasFileDescriptors() == true) {
            throw new IllegalArgumentException("File descriptors passed in Intent");
       }

        if (callingPackage == null) {
            throw new IllegalArgumentException("callingPackage cannot be null");
       }

        if (DEBUG_SERVICE) Slog.v(TAG_SERVICE,
                "*** startService: " + service + " type=" + resolvedType + " fg=" + requireForeground);
       synchronized(this) {
            final int callingPid = Binder.getCallingPid();
            final int callingUid = Binder.getCallingUid();
            final long origId = Binder.clearCallingIdentity();
            ComponentName res;
            try {
            //调用ActiveServices的startServiceLocked
                res = mServices.startServiceLocked(caller, service,
                        resolvedType, callingPid, callingUid,
                        requireForeground, callingPackage, userId);
            } finally {
                Binder.restoreCallingIdentity(origId);
            }
            return res;
        }
    }

会调用ActiveServices的startServiceLocked

ActiveServices的startServiceLocked

http://androidxref.com/8.1.0_r33/xref/frameworks/base/services/core/java/com/android/server/am/ActiveServices.java

    ComponentName startServiceLocked(IApplicationThread caller, Intent service, String resolvedType,
            int callingPid, int callingUid, boolean fgRequired, String callingPackage, final int userId)
            throws TransactionTooLargeException {
        //...
        // 启动服务之前有2个判断一个是startRequested，一个是fgRequired。
        // startRequested代表的是：是否已经启动过服务，一般出现问题都是启动一个没有运行的服务，
        // 那么这个就是false。
        // fgRequired这个就是启动服务传递的requireForeground，
        if (!r.startRequested && !fgRequired) {
            // 这里面有个关键函数getAppStartModeLocked，判断是否运行启动服务
            // 注意此处传递的最后2个参数：alwaysRestrict和disabledOnly都是false
            final int allowed = mAm.getAppStartModeLocked(r.appInfo.uid, r.packageName,
                    r.appInfo.targetSdkVersion, callingPid, false, false);
            // 如果不允许启动服务则会运行到里面
            if (allowed != ActivityManager.APP_START_MODE_NORMAL) {
                //...
                UidRecord uidRec = mAm.mActiveUids.get(r.appInfo.uid);
                // 此处就是不允许运行服务返回的原因"app is in background"
                // 找到了原因就在这里
                return new ComponentName("?", "app is in background uid " + uidRec);
            }
        }
        //...
    }

这里面由于出现错误，那么startRequested==false而且fgRequired==false，说明这个服务是第一次启动，而且是后台请求启动服务。
至于为什么不允许启动服务，我们还需要查看AMS的getAppStartModeLocked函数。

AMS判断并返回服务启动模式

http://androidxref.com/8.1.0_r33/xref/frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

int getAppStartModeLocked(int uid, String packageName, int packageTargetSdk,
            int callingPid, boolean alwaysRestrict, boolean disabledOnly) {
        UidRecord uidRec = mActiveUids.get(uid);
        if (DEBUG_BACKGROUND_CHECK) Slog.d(TAG, "checkAllowBackground: uid=" + uid + " pkg="
                + packageName + " rec=" + uidRec + " always=" + alwaysRestrict + " idle="
                + (uidRec != null ? uidRec.idle : false));
        if (uidRec == null || alwaysRestrict || uidRec.idle) {
            boolean ephemeral;
            if (uidRec == null) {
                ephemeral = getPackageManagerInternalLocked().isPackageEphemeral(
                        UserHandle.getUserId(uid), packageName);
            } else {
                ephemeral = uidRec.ephemeral;
            }

            if (ephemeral) {
                // We are hard-core about ephemeral apps not running in the background.
                return ActivityManager.APP_START_MODE_DISABLED;
            } else {
                if (disabledOnly) {
                    // The caller is only interested in whether app starts are completely
                    // disabled for the given package (that is, it is an instant app).  So
                    // we don't need to go further, which is all just seeing if we should
                    // apply a "delayed" mode for a regular app.
                    return ActivityManager.APP_START_MODE_NORMAL;
                }
　　　　　　　　　 // 此处alwaysRestrict==false，于是调用的是appServicesRestrictedInBackgroundLocked
                final int startMode = (alwaysRestrict)
                        ? appRestrictedInBackgroundLocked(uid, packageName, packageTargetSdk)
                        : appServicesRestrictedInBackgroundLocked(uid, packageName,
                                packageTargetSdk);
                if (DEBUG_BACKGROUND_CHECK) Slog.d(TAG, "checkAllowBackground: uid=" + uid
                        + " pkg=" + packageName + " startMode=" + startMode
                        + " onwhitelist=" + isOnDeviceIdleWhitelistLocked(uid));
                if (startMode == ActivityManager.APP_START_MODE_DELAYED) {
                    // This is an old app that has been forced into a "compatible as possible"
                    // mode of background check.  To increase compatibility, we will allow other
                    // foreground apps to cause its services to start.
                    if (callingPid >= 0) {
                        ProcessRecord proc;
                        synchronized (mPidsSelfLocked) {
                            proc = mPidsSelfLocked.get(callingPid);
                        }
                        if (proc != null &&
                                !ActivityManager.isProcStateBackground(proc.curProcState)) {
                            // Whoever is instigating this is in the foreground, so we will allow it
                            // to go through.
                            return ActivityManager.APP_START_MODE_NORMAL;
                        }
                    }
                }
                return startMode;
            }
        }
        return ActivityManager.APP_START_MODE_NORMAL;
    }

根据alwaysRestrict的值会调用appRestrictedInBackgroundLocked或者appServicesRestrictedInBackgroundLocked；
其中appRestrictedInBackgroundLocked是直接根据应用sdk进行判断，
appServicesRestrictedInBackgroundLocked会进行条件过滤，直接运行部分应用启动服务，其它的进行应用sdk的判断。

接下来看appServicesRestrictedInBackgroundLocked进行条件过滤,允许部分启动服务

int appServicesRestrictedInBackgroundLocked(int uid, String packageName, int packageTargetSdk) {
        // Persistent app?
        // 如果是常驻内存的，可以直接启动服务

        if (mPackageManagerInt.isPackagePersistent(packageName)) {
            if (DEBUG_BACKGROUND_CHECK) {
                Slog.i(TAG, "App " + uid + "/" + packageName
                        + " is persistent; not restricted in background");
            }
            return ActivityManager.APP_START_MODE_NORMAL;
        }

        // Non-persistent but background whitelisted?
　　　　 // 如果是非常驻内存的话，但是在白名单列表里面的uid也是允许的 
　　 　　// 目前这个白名单里面就只有一个：蓝牙BLUETOOTH_UID = 1002

        if (uidOnBackgroundWhitelist(uid)) {
            if (DEBUG_BACKGROUND_CHECK) {
                Slog.i(TAG, "App " + uid + "/" + packageName
                        + " on background whitelist; not restricted in background");
            }
            return ActivityManager.APP_START_MODE_NORMAL;
        }

        // Is this app on the battery whitelist?
        // 如果是在电源相关的白名单里面，也是允许启动服务的

        if (isOnDeviceIdleWhitelistLocked(uid)) {
            if (DEBUG_BACKGROUND_CHECK) {
                Slog.i(TAG, "App " + uid + "/" + packageName
                        + " on idle whitelist; not restricted in background");
            }
            return ActivityManager.APP_START_MODE_NORMAL;
        }

        // None of the service-policy criteria apply, so we apply the common criteria
        return appRestrictedInBackgroundLocked(uid, packageName, packageTargetSdk);
    }

分别对于： 
1. 是否常驻内存应用，常驻内存允许启动服务 
2.如果是蓝牙也是允许启动服务 
3.是在电源相关的DeviceIdle白名单里面，允许启动服务的 
4.如果都不是则执行默认策略appRestrictedInBackgroundLocked

再看appServicesRestrictedInBackgroundLocked进行条件过滤,允许部分启动服务

 int appRestrictedInBackgroundLocked(int uid, String packageName, int packageTargetSdk) {
        // Apps that target O+ are always subject to background check
        // 如果apk的sdk版本大于AndroidO的话，那么默认是不允许启动服务的

        if (packageTargetSdk >= Build.VERSION_CODES.O) {
            if (DEBUG_BACKGROUND_CHECK) {
                Slog.i(TAG, "App " + uid + "/" + packageName + " targets O+, restricted");
            }
            return ActivityManager.APP_START_MODE_DELAYED_RIGID;
        }
        // ...and legacy apps get an AppOp check
       // 如果是之前版本的apk，会查看AppOps是否允许后台运行权限， 
       // 由于我们sdk版本肯定会升级的，这个就暂时不考虑了

        int appop = mAppOpsService.noteOperation(AppOpsManager.OP_RUN_IN_BACKGROUND,
                uid, packageName);
        if (DEBUG_BACKGROUND_CHECK) {
            Slog.i(TAG, "Legacy app " + uid + "/" + packageName + " bg appop " + appop);
        }
        switch (appop) {
            case AppOpsManager.MODE_ALLOWED:
                return ActivityManager.APP_START_MODE_NORMAL;
            case AppOpsManager.MODE_IGNORED:
                return ActivityManager.APP_START_MODE_DELAYED;
            default:
                return ActivityManager.APP_START_MODE_DELAYED_RIGID;
        }
    }

如果apk的sdk版本大于AndroidO的话，那么默认是不允许启动服务的，那么要适配Android O/GO以后的版本，此处是绕不过去的坎，建议尽早处理。

网上所传的notification隐藏是否可以？

有的需求是启动服务，但是又不想有通知，这和Google定的规则有冲突呀，有没有什么办法呢？网上2年前的方案是启动两个Service，一个Service干活，另外一个Service把通知隐藏掉。

Android O Google应该考虑到这个漏洞了：

private void cancelForegroundNotificationLocked(ServiceRecord r) {
        if (r.foregroundId != 0) {
            // First check to see if this app has any other active foreground services
            // with the same notification ID.  If so, we shouldn't actually cancel it,
            // because that would wipe away the notification that still needs to be shown
            // due the other service.
            ServiceMap sm = getServiceMapLocked(r.userId);
            if (sm != null) {
                for (int i = sm.mServicesByName.size()-1; i >= 0; i--) {
                    ServiceRecord other = sm.mServicesByName.valueAt(i);
                    if (other != r && other.foregroundId == r.foregroundId
                            && other.packageName.equals(r.packageName)) {
                        // Found one!  Abort the cancel.
                        return;
                    }
                }
            }
            r.cancelNotification();
        }
    }

如果前台服务的通知还有被占用，那就别想用其他服务把它干掉了

 框架规避方案

修改方案（仅供参考）：ActiveServices.java如下加一个packageName的crash的规避，anr同理，发出消息的地方可以修改为不发出timeout消息，也可以在startForeground的时候就移除。(如果Service耗时小于5s，Service在stop流程的时候会将anr消息移除，可不修改)

        // Check to see if the service had been started as foreground, but being
        // brought down before actually showing a notification.  That is not allowed.
        if (r.fgRequired) {
            Slog.w(TAG_SERVICE, "Bringing down service while still waiting for start foreground: "
                    + r);
            r.fgRequired = false;
            r.fgWaiting = false;
            mAm.mHandler.removeMessages(
                    ActivityManagerService.SERVICE_FOREGROUND_TIMEOUT_MSG, r);
            if (r.app != null && !"packageName".equals(r.packageName)) {
                Message msg = mAm.mHandler.obtainMessage(
                        ActivityManagerService.SERVICE_FOREGROUND_CRASH_MSG);
                msg.obj = r.app;
                mAm.mHandler.sendMessage(msg);
            }
        }

修改原理：

编译一个service.jar，打印报错堆栈

01-01 07:02:17.669   918  1334 W ActivityManager: Bringing down service while still waiting for start foreground: ServiceRecord{2d44a2d u0 packageName/.servicename}
01-01 07:02:17.669   918  1334 W ActivityManager: java.lang.Throwable
01-01 07:02:17.669   918  1334 W ActivityManager:     at com.android.server.am.ActiveServices.bringDownServiceLocked(ActiveServices.java:2612)
01-01 07:02:17.669   918  1334 W ActivityManager:     at com.android.server.am.ActiveServices.bringDownServiceIfNeededLocked(ActiveServices.java:2559)
01-01 07:02:17.669   918  1334 W ActivityManager:     at com.android.server.am.ActiveServices.stopServiceTokenLocked(ActiveServices.java:792)
01-01 07:02:17.669   918  1334 W ActivityManager:     at com.android.server.am.ActivityManagerService.stopServiceToken(ActivityManagerService.java:18789)
01-01 07:02:17.669   918  1334 W ActivityManager:     at android.app.IActivityManager$Stub.onTransact(IActivityManager.java:759)
01-01 07:02:17.669   918  1334 W ActivityManager:     at com.android.server.am.ActivityManagerService.onTransact(ActivityManagerService.java:3080)
01-01 07:02:17.669   918  1334 W ActivityManager:     at android.os.Binder.execTransact(Binder.java:697)

找到对应抛出Context.startForegroundService() did not then call Service.startForeground()的逻辑代码：

ActiveServices.java bringDownServiceLocked

      // Check to see if the service had been started as foreground, but being
        // brought down before actually showing a notification.  That is not allowed.
        if (r.fgRequired) {
            Slog.w(TAG_SERVICE, "Bringing down service while still waiting for start foreground: "
                    + r);
            r.fgRequired = false;
            r.fgWaiting = false;
            mAm.mHandler.removeMessages(
                    ActivityManagerService.SERVICE_FOREGROUND_TIMEOUT_MSG, r);
            if (r.app != null) {
                Message msg = mAm.mHandler.obtainMessage(
                        ActivityManagerService.SERVICE_FOREGROUND_CRASH_MSG);
                msg.obj = r.app;
                mAm.mHandler.sendMessage(msg);
            }
        }

走到这里面继而会由ams发出一个service_foreground_crash_msg的消息，导致crash。

至于为嘛会走到这里呢，都是id = 0 的过，既没有走前台服务的流程也没有将r.fgRequired设为false,anr的msg也没有移除掉。

private void setServiceForegroundInnerLocked(ServiceRecord r, int id,
            Notification notification, int flags) {
        if (id != 0) {
            if (notification == null) {
                throw new IllegalArgumentException("null notification");
            }
            // Instant apps need permission to create foreground services.
            ...
            if (r.fgRequired) {
                if (DEBUG_SERVICE || DEBUG_BACKGROUND_CHECK) {
                    Slog.i(TAG, "Service called startForeground() as required: " + r);
                }
                r.fgRequired = false;
                r.fgWaiting = false;
                mAm.mHandler.removeMessages(
                        ActivityManagerService.SERVICE_FOREGROUND_TIMEOUT_MSG, r);
            }
            if (r.foregroundId != id) {
                cancelForegroundNotificationLocked(r);
                r.foregroundId = id;
            }
            notification.flags |= Notification.FLAG_FOREGROUND_SERVICE;
            r.foregroundNoti = notification;
            if (!r.isForeground) {
                final ServiceMap smap = getServiceMapLocked(r.userId);
                if (smap != null) {
                    ActiveForegroundApp active = smap.mActiveForegroundApps.get(r.packageName);
                    if (active == null) {
                        active = new ActiveForegroundApp();
                        active.mPackageName = r.packageName;
                        active.mUid = r.appInfo.uid;
                        active.mShownWhileScreenOn = mScreenOn;
                        if (r.app != null) {
                            active.mAppOnTop = active.mShownWhileTop =
                                    r.app.uidRecord.curProcState
                                            <= ActivityManager.PROCESS_STATE_TOP;
                        }
                        active.mStartTime = active.mStartVisibleTime
                                = SystemClock.elapsedRealtime();
                        smap.mActiveForegroundApps.put(r.packageName, active);
                        requestUpdateActiveForegroundAppsLocked(smap, 0);
                    }
                    active.mNumActive++;
                }
                r.isForeground = true;
            }
            r.postNotification();
            if (r.app != null) {
                updateServiceForegroundLocked(r.app, true);
            }
            getServiceMapLocked(r.userId).ensureNotStartingBackgroundLocked(r);
            mAm.notifyPackageUse(r.serviceInfo.packageName,
                                 PackageManager.NOTIFY_PACKAGE_USE_FOREGROUND_SERVICE);
        } else {
            if (r.isForeground) {
                final ServiceMap smap = getServiceMapLocked(r.userId);
                if (smap != null) {
                    decActiveForegroundAppLocked(smap, r);
                }
                r.isForeground = false;
                if (r.app != null) {
                    mAm.updateLruProcessLocked(r.app, false, null);
                    updateServiceForegroundLocked(r.app, true);
                }
            }
            if ((flags & Service.STOP_FOREGROUND_REMOVE) != 0) {
                cancelForegroundNotificationLocked(r);
                r.foregroundId = 0;
                r.foregroundNoti = null;
            } else if (r.appInfo.targetSdkVersion >= Build.VERSION_CODES.LOLLIPOP) {
                r.stripForegroundServiceFlagFromNotification();
                if ((flags & Service.STOP_FOREGROUND_DETACH) != 0) {
                    r.foregroundId = 0;
                    r.foregroundNoti = null;
                }
            }
        }
    }

anr的时限为嘛是5s呢？

    void scheduleServiceForegroundTransitionTimeoutLocked(ServiceRecord r) {
        if (r.app.executingServices.size() == 0 || r.app.thread == null) {
            return;
        }
        Message msg = mAm.mHandler.obtainMessage(
                ActivityManagerService.SERVICE_FOREGROUND_TIMEOUT_MSG);
        msg.obj = r;
        r.fgWaiting = true;
        mAm.mHandler.sendMessageDelayed(msg, SERVICE_START_FOREGROUND_TIMEOUT);
    }
    // How long the startForegroundService() grace period is to get around to
    // calling startForeground() before we ANR + stop it.
    static final int SERVICE_START_FOREGROUND_TIMEOUT = 5*1000;

这种timeout流程就很熟悉了。

修改方案

有上面可知，问题原因主要是后台启动了服务，在这部分Android O/GO做了限制，
根据章节2.4的过滤条件可以提供如下修改方案：
1) 提升应用优先级到常驻内存级别 (不建议应用采纳这种方式，会导致手机出现很多性能问题)
=> 在AndroidManifest.xml添加android:persistent=”true”
并且签上系统签名
2) 类似与蓝牙BLUETOOTH_UID一样放在白名单里面(需要拥有源码修改权限，而且修改了源码，不利于apk的版本兼容，不建议采纳)
3) 添加在电源相关的DeviceIdle白名单(不建议添加，可能导致功耗增加)

按照上面的都说是不建议采取，是否没有办法了呢？

我们继续往源头找找看看是否有办法：
在ContextImpl的startServiceCommon、ActiveServices的startServiceLocked有一个参数requireForeground/fgRequired，是否前台请求，如果requireForeground/fgRequired为false才会进行后台请求判断，如果是true的话，是可以直接绕过去的

回到ActiveServices的startServiceLocked=>

  ComponentName startServiceLocked(IApplicationThread caller, Intent service, String resolvedType,
            int callingPid, int callingUid, boolean fgRequired, String callingPackage, final int userId)
            throws TransactionTooLargeException {
        //...
        // fgRequired是true可以直接绕过
        if (!r.startRequested && !fgRequired) {
            //..
        }
        //...
    }

那么方案4，我们可以采取如下方式
4) 通过Context(activity、service的this都是包含context的，故不用担心调用方式)，将之前的startService，修改成ContextImpl的startForegroundService或者startForegroundServiceAsUser方法，启动一个前台服务。
//frameworks/base/core/java/android/app/ContextImpl.java

    @Override
    public ComponentName startForegroundService(Intent service) {
        warnIfCallingFromSystemProcess();
        return startServiceCommon(service, true, mUser);
    }

    @Override
    public ComponentName startForegroundServiceAsUser(Intent service, UserHandle user) {
        return startServiceCommon(service, true, user);
    }

ps：注意上面的方法是启动前台服务，你的服务需要是前台的，这个怎么做呢，下面提供2种方法：
1) 在service中调用startForeground (最常见方法)
2) 设置service为前台，可以使用AMS的setProcessImportant设置优先级别 (优点是：不会在通知栏中出现通知图标。缺点是：需要相应的权限)

解决办法

https://www.cnblogs.com/mingfeng002/p/9647720.html