Android系統中的LocalService
Google将service分成binderservice和localservice。如果service只在本进程使用,则可以将这个service发布为localservice，避免进程间通信。
1 Localservice的定義實現
下面以DeviceStorageMonitorService來解說，該service繼承自SystemService，通過publishLocalService发布为localservice
android/frameworks/base/services/core/java/com/android/server/SystemService.java
public abstract class SystemService {
public static final int PHASE_WAIT_FOR_DEFAULT_DISPLAY = 100; // maybe should be a dependency?
public static final int PHASE_LOCK_SETTINGS_READY = 480;
60 /**
61 * After receiving this boot phase, services can safely call into core system services
62 * such as the PowerManager or PackageManager.
63 */
64 public static final int PHASE_SYSTEM_SERVICES_READY = 500;
66 /**
67 * After receiving this boot phase, services can broadcast Intents.
68 */
69 public static final int PHASE_ACTIVITY_MANAGER_READY = 550;
71 /**
72 * After receiving this boot phase, services can start/bind to third party apps.
73 * Apps will be able to make Binder calls into services at this point.
74 */
75 public static final int PHASE_THIRD_PARTY_APPS_CAN_START = 600;
83 public static final int PHASE_BOOT_COMPLETED = 1000;
85 private final Context mContext;
96 public SystemService(Context context) {
97 mContext = context;
98 }
100 /**
101 * Gets the system context.
102 */
103 public final Context getContext() {
104 return mContext;
105 }
106
107 /**
108 * Get the system UI context. This context is to be used for displaying UI. It is themable,
109 * which means resources can be overridden at runtime. Do not use to retrieve properties that
110 * configure the behavior of the device that is not UX related.
111 */
112 public final Context getUiContext() {
113 // This has already been set up by the time any SystemServices are created.
114 return ActivityThread.currentActivityThread().getSystemUiContext();
115 }
117 /**
118 * Returns true if the system is running in safe mode.
119 * TODO: we should define in which phase this becomes valid
120 */
121 public final boolean isSafeMode() {
122 return getManager().isSafeMode();
123 }
124
125 /**
126 * Called when the dependencies listed in the @Service class-annotation are available
127 * and after the chosen start phase.
128 * When this method returns, the service should be published.
129 */
130 public abstract void onStart();
138 public void onBootPhase(int phase) {}
145 public void onStartUser(int userHandle) {}
161 public void onUnlockUser(int userHandle) {}
169 public void onSwitchUser(int userHandle) {}
181 public void onStopUser(int userHandle) {}
193 public void onCleanupUser(int userHandle) {}
195 /**
196 * Publish the service so it is accessible to other services and apps.
197 */
198 protected final void publishBinderService(String name, IBinder service) {
199 publishBinderService(name, service, false);
200 }
201
202 /**
203 * Publish the service so it is accessible to other services and apps.
204 */
205 protected final void publishBinderService(String name, IBinder service,
206 boolean allowIsolated) {
207 ServiceManager.addService(name, service, allowIsolated);
208 }
209
210 /**
211 * Get a binder service by its name.
212 */
213 protected final IBinder getBinderService(String name) {
214 return ServiceManager.getService(name);
215 }
216
217 /**
218 * Publish the service so it is only accessible to the system process.
219 */
220 protected final <T> void publishLocalService(Class<T> type, T service) {
221 LocalServices.addService(type, service);
222 }
224 /**
225 * Get a local service by interface.
226 */
227 protected final <T> T getLocalService(Class<T> type) {
228 return LocalServices.getService(type);
229 }
230
231 private SystemServiceManager getManager() {
232 return LocalServices.getService(SystemServiceManager.class);
233 }
234 }
在SystemService中和local service 有关的就三个函数,其中外界只能使用getLocalService 和 publishLocalService。getManager 是SystemService 自己使用的 ;通常在onStart()中發佈service。
android/frameworks/base/services/core/java/com/android/server/storage/DeviceStorageMonitorService.java
/**
65 * Service that monitors and maintains free space on storage volumes.
66 *
67 * As the free space on a volume nears the threshold defined by
68 * {@link StorageManager#getStorageLowBytes(File)}, this service will clear out
69 * cached data to keep the disk from entering this low state.
70 */
71 public class DeviceStorageMonitorService extends SystemService {
72 private static final String TAG = "DeviceStorageMonitorService";
......
80 private static final int MSG_CHECK = 1;
......
/**
158 * Handler that checks the amount of disk space on the device and sends a
159 * notification if the device runs low on disk space
160 */
161 private final Handler mHandler = new Handler(IoThread.get().getLooper()) {
162 @Override
163 public void handleMessage(Message msg) {
164 switch (msg.what) {
165 case MSG_CHECK:
166 check();
167 return;
168 }
169 }
170 };
public DeviceStorageMonitorService(Context context) {
258 super(context);
259 }
//實現onStart()
@Override
271 public void onStart() {
272 final Context context = getContext();
273 mNotifManager = context.getSystemService(NotificationManager.class);
274
275 mCacheFileDeletedObserver = new CacheFileDeletedObserver();
276 mCacheFileDeletedObserver.startWatching();
277
278 // Ensure that the notification channel is set up
279 PackageManager packageManager = context.getPackageManager();
280 boolean isTv = packageManager.hasSystemFeature(PackageManager.FEATURE_LEANBACK);
281
282 if (isTv) {
283 mNotifManager.createNotificationChannel(new NotificationChannel(
284 TV_NOTIFICATION_CHANNEL_ID,
285 context.getString(
286 com.android.internal.R.string.device_storage_monitor_notification_channel),
287 NotificationManager.IMPORTANCE_HIGH));
288 }
289 //發佈 binderservice
290 publishBinderService(SERVICE, mRemoteService);
//發佈localservice
291 publishLocalService(DeviceStorageMonitorInternal.class, mLocalService);
292
293 // Kick off pass to examine storage state
294 mHandler.removeMessages(MSG_CHECK);
295 mHandler.obtainMessage(MSG_CHECK).sendToTarget();
296 }
private final DeviceStorageMonitorInternal mLocalService = new DeviceStorageMonitorInternal() {
299 @Override
300 public void checkMemory() {
301 // Kick off pass to examine storage state
302 mHandler.removeMessages(MSG_CHECK);
303 mHandler.obtainMessage(MSG_CHECK).sendToTarget();
304 }
305
306 @Override
307 public boolean isMemoryLow() {
308 return Environment.getDataDirectory().getUsableSpace() < getMemoryLowThreshold();
309 }
310
311 @Override
312 public long getMemoryLowThreshold() {
313 return getContext().getSystemService(StorageManager.class)
314 .getStorageLowBytes(Environment.getDataDirectory());
315 }
316 };
317
318 private final Binder mRemoteService = new Binder() {
319 @Override
320 protected void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
321 if (!DumpUtils.checkDumpPermission(getContext(), TAG, pw)) return;
322 dumpImpl(fd, pw, args);
323 }
324
325 @Override
326 public void onShellCommand(FileDescriptor in, FileDescriptor out,
327 FileDescriptor err, String[] args, ShellCallback callback,
328 ResultReceiver resultReceiver) {
329 (new Shell()).exec(this, in, out, err, args, callback, resultReceiver);
330 }
331 };
332
DeviceStorageMonitorInternal.java接口的定義：
android/frameworks/base/services/core/java/com/android/server/storage/DeviceStorageMonitorInternal.java
17 package com.android.server.storage;
18
19 public interface DeviceStorageMonitorInternal {
20 boolean isMemoryLow();
21 long getMemoryLowThreshold();
22 void checkMemory();
23 }
2 Localservice的使用
我們看下PackageManagerService中對DeviceStorageMonitorService發佈的localservice的使用
通過final class LocalServices獲取getService(DeviceStorageMonitorInternal.class)獲取localservice的實例dsm，然後調用其方法 dsm.checkMemory()
frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java
20257 @Override
20258 public void clearApplicationUserData(final String packageName,
20259 final IPackageDataObserver observer, final int userId) {
// Queue up an async operation since the package deletion may take a little while.
20276 mHandler.post(new Runnable() {
20277 public void run() {
20278 mHandler.removeCallbacks(this);
20279 final boolean succeeded;
20280 try (PackageFreezer freezer = freezePackage(packageName,
20281 "clearApplicationUserData")) {
20282 synchronized (mInstallLock) {
20283 succeeded = clearApplicationUserDataLIF(packageName, userId);
20284 }
20285 clearExternalStorageDataSync(packageName, userId, true);
20286 synchronized (mPackages) {
20287 mInstantAppRegistry.deleteInstantApplicationMetadataLPw(
20288 packageName, userId);
20289 }
20290 }
20291 if (succeeded) {
20292 // invoke DeviceStorageMonitor's update method to clear any notifications
20293 DeviceStorageMonitorInternal dsm = LocalServices
20294 .getService(DeviceStorageMonitorInternal.class);
20295 if (dsm != null) {
20296 dsm.checkMemory();
20297 }
20298 }
20299 if(observer != null) {
20300 try {
20301 observer.onRemoveCompleted(packageName, succeeded);
20302 } catch (RemoteException e) {
20303 Log.i(TAG, "Observer no longer exists.");
20304 }
20305 } //end if observer
20306 } //end run
20307 });
發佈localservice實際是調用LocalServices.addService(), 放入一個靜態數組中sLocalServiceObjects ，而getService 也是以class type爲key从sLocalServiceObjects 数组中拿到是实现的class
android/frameworks/base/core/java/com/android/server/LocalServices.java
public final class LocalServices {
33 private LocalServices() {}
34
35 private static final ArrayMap<Class<?>, Object> sLocalServiceObjects =
36 new ArrayMap<Class<?>, Object>();
37
38 /**
39 * Returns a local service instance that implements the specified interface.
40 *
41 * @param type The type of service.
42 * @return The service object.
43 */
44 @SuppressWarnings("unchecked")
45 public static <T> T getService(Class<T> type) {
46 synchronized (sLocalServiceObjects) {
47 return (T) sLocalServiceObjects.get(type);
48 }
49 }
50
51 /**
52 * Adds a service instance of the specified interface to the global registry of local services.
53 */
54 public static <T> void addService(Class<T> type, T service) {
55 synchronized (sLocalServiceObjects) {
56 if (sLocalServiceObjects.containsKey(type)) {
57 throw new IllegalStateException("Overriding service registration");
58 }
59 sLocalServiceObjects.put(type, service);
60 }
61 }
62
......