BindService启动的Service为何在Activity销毁时自动解绑（Service销毁时也是一样处理）

骑猪看日落 2022-04-10 06:47 482阅读 0赞

以bindService启动服务后，直接退出Activity，日志会输出：

ActivityThread: Activity com.example.administrator.layoutmanager.MainActivity has leaked ServiceConnection com.example.administrator.layoutmanager.MainActivity1@52816718thatwasoriginallyboundhereandroid.app.ServiceConnectionLeaked:Activitycom.example.administrator.layoutmanager.MainActivityhasleakedServiceConnectioncom.example.administrator.layoutmanager.MainActivity

1@52816718 that was originally bound here

紧接着就是我们服务的解绑与销毁

MyService: call onUnbind…  
call onDestroy…

既然我们没去主动解绑，系统会帮我们解绑，那么它一定缓存了服务的connection。

所以我们先看下bindService的流程，看看在哪里保存了我们的Service信息，直接到ContextImpl中找bindService方法

@Override
        public boolean bindService(Intent service, ServiceConnection conn,
                int flags) {
            warnIfCallingFromSystemProcess();
            return bindServiceCommon(service, conn, flags, mMainThread.getHandler(),
                    Process.myUserHandle());
        }

bindServiceCommon方法：

private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags, Handler
                handler, UserHandle user) {
            // Keep this in sync with DevicePolicyManager.bindDeviceAdminServiceAsUser.
            IServiceConnection sd;
            if (conn == null) {
                throw new IllegalArgumentException("connection is null");
            }
            if (mPackageInfo != null) {
                sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(), handler, flags);
            } else {
                throw new RuntimeException("Not supported in system context");
            }
            validateServiceIntent(service);
            try {
                IBinder token = getActivityToken();
                if (token == null && (flags&BIND_AUTO_CREATE) == 0 && mPackageInfo != null
                        && mPackageInfo.getApplicationInfo().targetSdkVersion
                        < android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
                    flags |= BIND_WAIVE_PRIORITY;
                }
                service.prepareToLeaveProcess(this);
                int res = ActivityManager.getService().bindService(
                    mMainThread.getApplicationThread(), getActivityToken(), service,
                    service.resolveTypeIfNeeded(getContentResolver()),
                    sd, flags, getOpPackageName(), user.getIdentifier());
                if (res < 0) {
                    throw new SecurityException(
                            "Not allowed to bind to service " + service);
                }
                return res != 0;
            } catch (RemoteException e) {
                throw e.rethrowFromSystemServer();
            }
        }

代码很少，也不难理解，我们只管 看看 ServiceConnection 在哪里用到了 便知道 在哪里保存了。只有一行代码将其传了进去：

IServiceConnection sd;
       sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(), handler, flags);

我们继续点进去 发现点不进去，来看看这个mPackageInfo：

final @NonNull LoadedApk mPackageInfo;

这个类最上面还有两个异常：  
一个是IntentReceiver没有反注册，一个是ServiceConnection没有解绑。一切都答案都在这个类里了。

final class IntentReceiverLeaked extends AndroidRuntimeException {
        public IntentReceiverLeaked(String msg) {
            super(msg);
        }
    }
    
    final class ServiceConnectionLeaked extends AndroidRuntimeException {
        public ServiceConnectionLeaked(String msg) {
            super(msg);
        }
    }

LoadedApk类开头有一句注释：

/**
     * Local state maintained about a currently loaded .apk.
     * @hide
     */

当前加载的apk的本地状态维护  
来看看里面有些什么，emmm 应有尽有…

static final String TAG = "LoadedApk";
        static final boolean DEBUG = false;
    
        private final ActivityThread mActivityThread;
        final String mPackageName;
        private ApplicationInfo mApplicationInfo;
        private String mAppDir;
        private String mResDir;
        private String[] mOverlayDirs;
        private String[] mSharedLibraries;
        private String mDataDir;
        private String mLibDir;
        private File mDataDirFile;
        private File mDeviceProtectedDataDirFile;
        private File mCredentialProtectedDataDirFile;
        private final ClassLoader mBaseClassLoader;
        private final boolean mSecurityViolation;
        private final boolean mIncludeCode;
        private final boolean mRegisterPackage;
        private final DisplayAdjustments mDisplayAdjustments = new DisplayAdjustments();
        /** WARNING: This may change. Don't hold external references to it. */
        Resources mResources;
        private ClassLoader mClassLoader;
        private Application mApplication;
    
        private String[] mSplitNames;
        private String[] mSplitAppDirs;
        private String[] mSplitResDirs;
    
        private final ArrayMap<Context, ArrayMap<BroadcastReceiver, ReceiverDispatcher>> mReceivers
            = new ArrayMap<>();
        private final ArrayMap<Context, ArrayMap<BroadcastReceiver, LoadedApk.ReceiverDispatcher>> mUnregisteredReceivers
            = new ArrayMap<>();
        private final ArrayMap<Context, ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher>> mServices
            = new ArrayMap<>();
        private final ArrayMap<Context, ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher>> mUnboundServices
            = new ArrayMap<>();

我们接着 bindService的流程走，看看

mPackageInfo.getServiceDispatcher(conn, getOuterContext(), handler, flags);

里面发生了什么

public final IServiceConnection getServiceDispatcher(ServiceConnection c,
                Context context, Handler handler, int flags) {
            synchronized (mServices) {
                LoadedApk.ServiceDispatcher sd = null;
                ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher> map = mServices.get(context);
                if (map != null) {
                    if (DEBUG) Slog.d(TAG, "Returning existing dispatcher " + sd + " for conn " + c);
                    sd = map.get(c);
                }
                if (sd == null) {
                    sd = new ServiceDispatcher(c, context, handler, flags);
                    if (DEBUG) Slog.d(TAG, "Creating new dispatcher " + sd + " for conn " + c);
                    if (map == null) {
                        map = new ArrayMap<>();
                        mServices.put(context, map);
                    }
                    map.put(c, sd);
                } else {
                    sd.validate(context, handler);
                }
                return sd.getIServiceConnection();
            }
        }

代码中很清楚的的交代了， map.put(c, sd); 将ServiceConnection 存到了mServices当中。

然后看Activity在销毁时的处理，这里我就直接说代码位置，大家可以实际 去研究下Activity相关流程。  
ActivityThread 的 handleDestroyActivity 中有一段代码：

if (c instanceof ContextImpl) {
                    ((ContextImpl) c).scheduleFinalCleanup(
                            r.activity.getClass().getName(), "Activity");
                }
    //接下来
      final void scheduleFinalCleanup(String who, String what) {
            mMainThread.scheduleContextCleanup(this, who, what);
        }

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);
        }
    
    //这个消息
          case CLEAN_UP_CONTEXT:
                        ContextCleanupInfo cci = (ContextCleanupInfo)msg.obj;
                        cci.context.performFinalCleanup(cci.who, cci.what);
                        break;
     //最后  来到
      final void performFinalCleanup(String who, String what) {
            //Log.i(TAG, "Cleanup up context: " + this);
            mPackageInfo.removeContextRegistrations(getOuterContext(), who, what);
        }

mPackageInfo熟悉吗？绕了一圈 又来到了 LoadApk。我们来看removeContextRegistrations

public void removeContextRegistrations(Context context,
                String who, String what) {
            final boolean reportRegistrationLeaks = StrictMode.vmRegistrationLeaksEnabled();
            synchronized (mReceivers) {
                ArrayMap<BroadcastReceiver, LoadedApk.ReceiverDispatcher> rmap =
                        mReceivers.remove(context);
                if (rmap != null) {
                    for (int i = 0; i < rmap.size(); i++) {
                        LoadedApk.ReceiverDispatcher rd = rmap.valueAt(i);
                        IntentReceiverLeaked leak = new IntentReceiverLeaked(
                                what + " " + who + " has leaked IntentReceiver "
                                + rd.getIntentReceiver() + " that was " +
                                "originally registered here. Are you missing a " +
                                "call to unregisterReceiver()?");
                        leak.setStackTrace(rd.getLocation().getStackTrace());
                        Slog.e(ActivityThread.TAG, leak.getMessage(), leak);
                        if (reportRegistrationLeaks) {
                            StrictMode.onIntentReceiverLeaked(leak);
                        }
                        try {
                            ActivityManager.getService().unregisterReceiver(
                                    rd.getIIntentReceiver());
                        } catch (RemoteException e) {
                            throw e.rethrowFromSystemServer();
                        }
                    }
                }
                mUnregisteredReceivers.remove(context);
            }
    
            synchronized (mServices) {
                //Slog.i(TAG, "Receiver registrations: " + mReceivers);
                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);
                        ServiceConnectionLeaked leak = new ServiceConnectionLeaked(
                                what + " " + who + " has leaked ServiceConnection "
                                + sd.getServiceConnection() + " that was originally bound here");
                        leak.setStackTrace(sd.getLocation().getStackTrace());
                        Slog.e(ActivityThread.TAG, leak.getMessage(), leak);
                        if (reportRegistrationLeaks) {
                            StrictMode.onServiceConnectionLeaked(leak);
                        }
                        try {
                            ActivityManager.getService().unbindService(
                                    sd.getIServiceConnection());
                        } catch (RemoteException e) {
                            throw e.rethrowFromSystemServer();
                        }
                        sd.doForget();
                    }
                }
                mUnboundServices.remove(context);
                //Slog.i(TAG, "Service registrations: " + mServices);
            }
        }

很明显 这里去 帮我们解绑 我们没有解绑的Receiver和Service，并输出异常。

到这里就基本结束了，现在来组织下语言：  
\- 为什么bindService可以跟Activity生命周期联动？  
答： 因为bindService时LoadApk将ServiceConnection用map保存了起来，当Activity被destroy时会执行removeContextRegistrations来清除 该context的相关注册。所以Activity退出时服务也被解绑。

其余变量的用处可以自行参阅源码。  
\---------------------  
作者：风卷云飞会天黑  
来源：CSDN  
原文：https://blog.csdn.net/castledrv/article/details/80311502