【Android】一种提高Android应用进程存活率新方法

SkySeraph Jun. 19st 2016

Email：skyseraph00@163.com

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 一、基础知识

1.Android 进程优先级

1.1 进程优先级等级一般分法：
- Activte process
- Visible Process
- Service process
- Background process
- Empty process

1.2 进程优先级号

 ProcessList.java

 1 // Adjustment used in certain places where we don't know it yet.
 2     // (Generally this is something that is going to be cached, but we
 3     // don't know the exact value in the cached range to assign yet.)
 4     static final int UNKNOWN_ADJ = 16;
 5 
 6     // This is a process only hosting activities that are not visible,
 7     // so it can be killed without any disruption.
 8     static final int CACHED_APP_MAX_ADJ = 15;
 9     static final int CACHED_APP_MIN_ADJ = 9;
10 
11     // The B list of SERVICE_ADJ -- these are the old and decrepit
12     // services that aren't as shiny and interesting as the ones in the A list.
13     static final int SERVICE_B_ADJ = 8;
14 
15     // This is the process of the previous application that the user was in.
16     // This process is kept above other things, because it is very common to
17     // switch back to the previous app.  This is important both for recent
18     // task switch (toggling between the two top recent apps) as well as normal
19     // UI flow such as clicking on a URI in the e-mail app to view in the browser,
20     // and then pressing back to return to e-mail.
21     static final int PREVIOUS_APP_ADJ = 7;
22 
23     // This is a process holding the home application -- we want to try
24     // avoiding killing it, even if it would normally be in the background,
25     // because the user interacts with it so much.
26     static final int HOME_APP_ADJ = 6;
27 
28     // This is a process holding an application service -- killing it will not
29     // have much of an impact as far as the user is concerned.
30     static final int SERVICE_ADJ = 5;
31 
32     // This is a process with a heavy-weight application.  It is in the
33     // background, but we want to try to avoid killing it.  Value set in
34     // system/rootdir/init.rc on startup.
35     static final int HEAVY_WEIGHT_APP_ADJ = 4;
36 
37     // This is a process currently hosting a backup operation.  Killing it
38     // is not entirely fatal but is generally a bad idea.
39     static final int BACKUP_APP_ADJ = 3;
40 
41     // This is a process only hosting components that are perceptible to the
42     // user, and we really want to avoid killing them, but they are not
43     // immediately visible. An example is background music playback.
44     static final int PERCEPTIBLE_APP_ADJ = 2;
45 
46     // This is a process only hosting activities that are visible to the
47     // user, so we'd prefer they don't disappear.
48     static final int VISIBLE_APP_ADJ = 1;
49 
50     // This is the process running the current foreground app.  We'd really
51     // rather not kill it!
52     static final int FOREGROUND_APP_ADJ = 0;
53 
54     // This is a process that the system or a persistent process has bound to,
55     // and indicated it is important.
56     static final int PERSISTENT_SERVICE_ADJ = -11;
57 
58     // This is a system persistent process, such as telephony.  Definitely
59     // don't want to kill it, but doing so is not completely fatal.
60     static final int PERSISTENT_PROC_ADJ = -12;
61 
62     // The system process runs at the default adjustment.
63     static final int SYSTEM_ADJ = -16;
64 
65     // Special code for native processes that are not being managed by the system (so
66     // don't have an oom adj assigned by the system).
67     static final int NATIVE_ADJ = -17;

2. Android Low Memory Killer

　　Android系统内存不足时，系统会杀掉一部分进程以释放空间，谁生谁死的这个生死大权就是由LMK所决定的，这就是Android系统中的Low Memory Killer，其基于Linux的OOM机制,其阈值定义如下面所示的lowmemorykiller文件中，当然也可以通过系统的init.rc实现自定义。

lowmemorykiller.c

 1 static uint32_t lowmem_debug_level = 1;
 2 static int lowmem_adj[6] = {
 3     0,
 4     1,
 5     6,
 6     12,
 7 };
 8 static int lowmem_adj_size = 4;
 9 static int lowmem_minfree[6] = {
10     3 * 512,    /* 6MB */
11     2 * 1024,   /* 8MB */
12     4 * 1024,   /* 16MB */
13     16 * 1024,  /* 64MB */
14 };
15 static int lowmem_minfree_size = 4;

① 在Low Memory Killer中通过进程的oom_adj与占用内存的大小决定要杀死的进程，oom_adj值越小越不容易被杀死。其中，lowmem_minfree是杀进程的时机，谁被杀，则取决于lowmem_adj，具体值得含义参考上面 Android进程优先级 所述.

② 在init.rc中定义了init进程（系统进程）的oom_adj为-16，其不可能会被杀死(init的PID是1)，而前台进程是0（这里的前台进程是指用户正在使用的Activity所在的进程），用户按Home键回到桌面时的优先级是6，普通的Service的进程是8.

init.rc

1 # Set init and its forked children's oom_adj.
2     write /proc/1/oom_adj -16

关于Low Memory Killer的具体实现原理可参考Ref-2.

3. 查看某个App的进程

步骤（手机与PC连接）
1. adb shell
2. ps | grep 进程名
3. cat /proc/pid/oom_adj //其中pid是上述grep得到的进程号

 

 4. Android账号和同步机制 

属于Android中较偏冷的知识，具体参考 Ref 3/4/5 

二、现有方法

1. 网络连接保活方法

a. GCM
b. 公共的第三方push通道(信鸽等)
c. 自身跟服务器通过轮询，或者长连接
具体实现请参考 微信架构师杨干荣的"微信Android客户端后台保活经验分享" （Ref-1）.

2. 双service 提高进程优先级

思路：（API level > 18 ）
① 应用启动时启动一个假的Service（FakeService）, startForeground()，传一个空的Notification
② 启动真正的Service（AlwaysLiveService），startForeground()，注意必须相同Notification ID
③ FakeService stopForeground()

效果：通过adb查看,运行在后台的服务其进程号变成了1（优先级仅次于前台进程）

风险：Android系统前台service的一个漏洞，可能在6.0以上系统中修复

实现：核心代码如下

AlwaysLiveService 常驻内存服务

1 @Override
2    public int onStartCommand(Intent intent, int flags, int startId) {
3        startForeground(R.id.notify, new Notification());
4        startService(new Intent(this, FakeService.class));
5        return super.onStartCommand(intent, flags, startId);
6    }

FakeService 临时服务

 1 public class FakeService extends Service {    
 2     @Nullable
 3     @Override
 4     public IBinder onBind(Intent intent) {
 5         return null;
 6     }
 7 
 8     @Override
 9     public int onStartCommand(Intent intent, int flags, int startId) {
10         startForeground(R.id.notify, new Notification());
11         stopSelf();
12         return super.onStartCommand(intent, flags, startId);
13     }
14 
15     @Override
16     public void onDestroy() {
17         stopForeground(true);
18         super.onDestroy();
19     }
20 }

3. 守护进程及时拉起

AlarmReceiver， ConnectReceiver，BootReceiver等

三、新方法(AccountSyncAdapter) 

1. 思路：

利用Android系统提供的账号和同步机制实现

2. 效果：

① 通过adb查看,运行在后台的服务其进程号变成了1（优先级仅次于前台进程），能提高进程优先级，对比如下图

正常情况

采用AccountSyncAdapter方法后

② 进程被系统kill后，可以由syn拉起

3. 风险：

① SyncAdapter时间进度不高，往往会因为手机处于休眠状态，而时间往后调整，同步间隔最低为1分钟
② 用户可以单独停止或者删除，有些手机账号默认是不同步的，需要手动开启 

4. 实现：核心代码如下

① 建立数据同步系统（ContentProvider）

通过一个ContentProvider用来作数据同步，由于并没有实际数据同步，所以此处就直接建立一个空的ContentProvider即可

 1 public class XXAccountProvider extends ContentProvider {
 2     public static final String AUTHORITY = "包名.provider";
 3     public static final String CONTENT_URI_BASE = "content://" + AUTHORITY;
 4     public static final String TABLE_NAME = "data";
 5     public static final Uri CONTENT_URI = Uri.parse(CONTENT_URI_BASE + "/" + TABLE_NAME);
 6 
 7     @Override
 8     public boolean onCreate() {
 9         return true;
10     }
11 
12     @Nullable
13     @Override
14     public Cursor query(Uri uri, String[] projection, String selection,
15                         String[] selectionArgs, String sortOrder) {
16         return null;
17     }
18 
19     @Nullable
20     @Override
21     public String getType(Uri uri) {
22         return new String();
23     }
24 
25     @Nullable
26     @Override
27     public Uri insert(Uri uri, ContentValues values) {
28         return null;
29     }
30 
31     @Override
32     public int delete(Uri uri, String selection, String[] selectionArgs) {
33         return 0;
34     }
35 
36     @Override
37     public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
38         return 0;
39     }
40 }

然后再Manifest中声明

    <provider
        android:name="**.XXAccountProvider"
        android:authorities="@string/account_auth_provider"
        android:exported="false"
        android:syncable="true"/>

② 建立Sync系统 (SyncAdapter)
通过实现SyncAdapter这个系统服务后, 利用系统的定时器对程序数据ContentProvider进行更新，具体步骤为：
- 创建Sync服务

 1 public class XXSyncService extends Service {
 2     private static final Object sSyncAdapterLock = new Object();
 3     private static XXSyncAdapter sSyncAdapter = null;
 4     @Override
 5     public void onCreate() {
 6         synchronized (sSyncAdapterLock) {
 7             if (sSyncAdapter == null) {
 8                 sSyncAdapter = new XXSyncAdapter(getApplicationContext(), true);
 9             }
10         }
11     }
12 
13     @Override
14     public IBinder onBind(Intent intent) {
15         return sSyncAdapter.getSyncAdapterBinder();
16     }
17 
18     static class XXSyncAdapter extends AbstractThreadedSyncAdapter {
19         public XXSyncAdapter(Context context, boolean autoInitialize) {
20             super(context, autoInitialize);
21         }
22         @Override
23         public void onPerformSync(Account account, Bundle extras, String authority, ContentProviderClient provider, SyncResult syncResult) {
24             getContext().getContentResolver().notifyChange(XXAccountProvider.CONTENT_URI, null, false);
25         }
26     }
27 }

- 声明Sync服务 

 1     <service
 2         android:name="**.XXSyncService"
 3         android:exported="true"
 4         android:process=":core">
 5         
 6             <action
 7                 android:name="android.content.SyncAdapter"/>
 8         
 9         data
10             android:name="android.content.SyncAdapter"
11             android:resource="@xml/sync_adapter"/>
12     

其中sync_adapter为：

1 2               android:accountType="@string/account_auth_type"
3               android:allowParallelSyncs="false"
4               android:contentAuthority="@string/account_auth_provide"
5               android:isAlwaysSyncable="true"
6               android:supportsUploading="false"
7               android:userVisible="true"/>

参数说明：
android:contentAuthority 指定要同步的ContentProvider在其AndroidManifest.xml文件中有个android:authorities属性。
android:accountType 表示进行同步的账号的类型。
android:userVisible 设置是否在“设置”中显示
android:supportsUploading 设置是否必须notifyChange通知才能同步
android:allowParallelSyncs 是否支持多账号同时同步
android:isAlwaysSyncable 设置所有账号的isSyncable为1
android:syncAdapterSettingsAction 指定一个可以设置同步的activity的Action。

- 账户调用Sync服务
首先配置好Account（第三步），然后再通过ContentProvider实现
手动更新

1 public void triggerRefresh() {
2     Bundle b = new Bundle();
3     b.putBoolean(ContentResolver.SYNC_EXTRAS_MANUAL, true);
4     b.putBoolean(ContentResolver.SYNC_EXTRAS_EXPEDITED, true);
5     ContentResolver.requestSync(
6             account,
7             CONTENT_AUTHORITY,
8             b);
9 }

添加账号

1 Account account = AccountService.GetAccount(); 
2 AccountManager accountManager = (AccountManager) context.getSystemService(Context.ACCOUNT_SERVICE);
3 accountManager.addAccountExplicitly(...)

同步周期设置

1 ContentResolver.setIsSyncable(account, CONTENT_AUTHORITY, 1);
2 ContentResolver.setSyncAutomatically(account, CONTENT_AUTHORITY, true);
3 ContentResolver.addPeriodicSync(account, CONTENT_AUTHORITY, new Bundle(), SYNC_FREQUENCY);

③ 建立账号系统 (Account Authenticator)
通过建立Account账号，并关联SyncAdapter服务实现同步
- 创建Account服务

 1 public class XXAuthService extends Service {
 2     private XXAuthenticator mAuthenticator;
 3 
 4     @Override
 5     public void onCreate() {
 6         mAuthenticator = new XXAuthenticator(this);
 7     }
 8 
 9     private XXAuthenticator getAuthenticator() {
10         if (mAuthenticator == null)
11             mAuthenticator = new XXAuthenticator(this);
12         return mAuthenticator;
13     }
14 
15     @Override
16     public IBinder onBind(Intent intent) {
17         return getAuthenticator().getIBinder();
18     }
19 
20     class XXAuthenticator extends AbstractAccountAuthenticator {
21         private final Context context;
22         private AccountManager accountManager;
23         public XXAuthenticator(Context context) {
24             super(context);
25             this.context = context;
26             accountManager = AccountManager.get(context);
27         }
28 
29         @Override
30         public Bundle addAccount(AccountAuthenticatorResponse response, String accountType, String authTokenType, String[] requiredFeatures, Bundle options)
31                 throws NetworkErrorException {
32             // 添加账号 示例代码
33             final Bundle bundle = new Bundle();
34             final Intent intent = new Intent(context, AuthActivity.class);
35             intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE, response);
36             bundle.putParcelable(AccountManager.KEY_INTENT, intent);
37             return bundle;
38         }
39 
40         @Override
41         public Bundle getAuthToken(AccountAuthenticatorResponse response, Account account, String authTokenType, Bundle options)
42                 throws NetworkErrorException {
43             // 认证 示例代码
44             String authToken = accountManager.peekAuthToken(account, getString(R.string.account_token_type));
45             //if not, might be expired, register again
46             if (TextUtils.isEmpty(authToken)) {
47                 final String password = accountManager.getPassword(account);
48                 if (password != null) {
49                     //get new token
50                     authToken = account.name + password;
51                 }
52             }
53             //without password, need to sign again
54             final Bundle bundle = new Bundle();
55             if (!TextUtils.isEmpty(authToken)) {
56                 bundle.putString(AccountManager.KEY_ACCOUNT_NAME, account.name);
57                 bundle.putString(AccountManager.KEY_ACCOUNT_TYPE, account.type);
58                 bundle.putString(AccountManager.KEY_AUTHTOKEN, authToken);
59                 return bundle;
60             }
61 
62             //no account data at all, need to do a sign
63             final Intent intent = new Intent(context, AuthActivity.class);
64             intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE, response);
65             intent.putExtra(AuthActivity.ARG_ACCOUNT_NAME, account.name);
66             bundle.putParcelable(AccountManager.KEY_INTENT, intent);
67             return bundle;
68         }
69 
70         @Override
71         public String getAuthTokenLabel(String authTokenType) {
72 //            throw new UnsupportedOperationException();
73             return null;
74         }
75 
76         @Override
77         public Bundle editProperties(AccountAuthenticatorResponse response, String accountType) {
78             return null;
79         }
80 
81         @Override
82         public Bundle confirmCredentials(AccountAuthenticatorResponse response, Account account, Bundle options)
83                 throws NetworkErrorException {
84             return null;
85         }
86 
87         @Override
88         public Bundle updateCredentials(AccountAuthenticatorResponse response, Account account, String authTokenType, Bundle options)
89                 throws NetworkErrorException {
90             return null;
91         }
92 
93         @Override
94         public Bundle hasFeatures(AccountAuthenticatorResponse response, Account account, String[] features)
95                 throws NetworkErrorException {
96             return null;
97         }
98     }
99 }

- 声明Account服务

 1 <service
 2     android:name="**.XXAuthService"
 3     android:exported="true"
 4     android:process=":core">
 5     
 6         <action
 7             android:name="android.accounts.AccountAuthenticator"/>
 8     
 9     data
10         android:name="android.accounts.AccountAuthenticator"
11         android:resource="@xml/authenticator"/>
12 

其中authenticator为：

1 <?xml version="1.0" encoding="utf-8"?>
2 3     android:accountType="@string/account_auth_type"
4     android:icon="@drawable/icon"
5     android:smallIcon="@drawable/icon"
6     android:label="@string/app_name"
7 />

- 使用Account服务
同SyncAdapter，通过AccountManager使用

　　- 申请Token主要是通过 [AccountManager.getAuthToken]系列方法

　　- 添加账号则通过 [AccountManager.addAccount]

　　- 查看是否存在账号通过 [AccountManager.getAccountsByType] 

Refs

1. [微信Android客户端后台保活经验分享]

2. [Android Low Memory Killer原理]

3. [stackOverflow 上介绍的双Service方法]

4. [Write your own Android Sync Adapter]

5. [Write your own Android Authenticator]

6. Android developer
- [android.accounts]
- [AccountManager]
- [AbstractAccountAuthenticator]
- [AccountAuthenticatorActivity]
- [Creating a Sync Adapter]

 

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