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      1 /*
      2  * Copyright (C) 2016 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package android.net.util;
     18 
     19 import android.net.INetd;
     20 import android.os.RemoteException;
     21 import android.os.ServiceManager;
     22 import android.os.ServiceSpecificException;
     23 import android.os.SystemClock;
     24 import android.util.Log;
     25 
     26 
     27 /**
     28  * @hide
     29  */
     30 public class NetdService {
     31     private static final String TAG = NetdService.class.getSimpleName();
     32     private static final String NETD_SERVICE_NAME = "netd";
     33     private static final long BASE_TIMEOUT_MS = 100;
     34     private static final long MAX_TIMEOUT_MS = 1000;
     35 
     36 
     37     /**
     38      * Return an INetd instance, or null if not available.
     39      *
     40      * It is the caller's responsibility to check for a null return value
     41      * and to handle RemoteException errors from invocations on the returned
     42      * interface if, for example, netd dies and is restarted.
     43      *
     44      * Returned instances of INetd should not be cached.
     45      *
     46      * @return an INetd instance or null.
     47      */
     48     public static INetd getInstance() {
     49         // NOTE: ServiceManager does no caching for the netd service,
     50         // because netd is not one of the defined common services.
     51         final INetd netdInstance = INetd.Stub.asInterface(
     52                 ServiceManager.getService(NETD_SERVICE_NAME));
     53         if (netdInstance == null) {
     54             Log.w(TAG, "WARNING: returning null INetd instance.");
     55         }
     56         return netdInstance;
     57     }
     58 
     59     /**
     60      * Blocks for a specified time until an INetd instance is available.
     61      *
     62      * It is the caller's responsibility to handle RemoteException errors
     63      * from invocations on the returned interface if, for example, netd
     64      * dies after this interface was returned.
     65      *
     66      * Returned instances of INetd should not be cached.
     67      *
     68      * Special values of maxTimeoutMs include: 0, meaning try to obtain an
     69      * INetd instance only once, and -1 (or any value less than 0), meaning
     70      * try to obtain an INetd instance indefinitely.
     71      *
     72      * @param maxTimeoutMs the maximum time to spend getting an INetd instance
     73      * @return an INetd instance or null if no instance is available
     74      * within |maxTimeoutMs| milliseconds.
     75      */
     76     public static INetd get(long maxTimeoutMs) {
     77         if (maxTimeoutMs == 0) return getInstance();
     78 
     79         final long stop = (maxTimeoutMs > 0)
     80                 ? SystemClock.elapsedRealtime() + maxTimeoutMs
     81                 : Long.MAX_VALUE;
     82 
     83         long timeoutMs = 0;
     84         while (true) {
     85             final INetd netdInstance = getInstance();
     86             if (netdInstance != null) {
     87                 return netdInstance;
     88             }
     89 
     90             final long remaining = stop - SystemClock.elapsedRealtime();
     91             if (remaining <= 0) break;
     92 
     93             // No netdInstance was received; sleep and retry.
     94             timeoutMs = Math.min(timeoutMs + BASE_TIMEOUT_MS, MAX_TIMEOUT_MS);
     95             timeoutMs = Math.min(timeoutMs, remaining);
     96             try {
     97                 Thread.sleep(timeoutMs);
     98             } catch (InterruptedException e) {}
     99         }
    100         return null;
    101     }
    102 
    103     /**
    104      * Blocks until an INetd instance is available.
    105      *
    106      * It is the caller's responsibility to handle RemoteException errors
    107      * from invocations on the returned interface if, for example, netd
    108      * dies after this interface was returned.
    109      *
    110      * Returned instances of INetd should not be cached.
    111      *
    112      * @return an INetd instance.
    113      */
    114     public static INetd get() {
    115         return get(-1);
    116     }
    117 
    118     public static interface NetdCommand {
    119         void run(INetd netd) throws RemoteException;
    120     }
    121 
    122     /**
    123      * Blocks until an INetd instance is availabe, and retries until either
    124      * the command succeeds or a runtime exception is thrown.
    125      */
    126     public static void run(NetdCommand cmd) {
    127         while (true) {
    128             try {
    129                 cmd.run(get());
    130                 return;
    131             } catch (RemoteException re) {
    132                 Log.e(TAG, "error communicating with netd: " + re);
    133             }
    134         }
    135     }
    136 }
    137