一种提高Android应用进程存活率新方法

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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

// Adjustment used in certain places where we don't know it yet.
// (Generally this is something that is going to be cached, but we
// don't know the exact value in the cached range to assign yet.)
static final int UNKNOWN_ADJ = 16;

// This is a process only hosting activities that are not visible,
// so it can be killed without any disruption.
static final int CACHED_APP_MAX_ADJ = 15;
static final int CACHED_APP_MIN_ADJ = 9;

// The B list of SERVICE_ADJ -- these are the old and decrepit
// services that aren't as shiny and interesting as the ones in the A list.
static final int SERVICE_B_ADJ = 8;

// This is the process of the previous application that the user was in.
// This process is kept above other things, because it is very common to
// switch back to the previous app.  This is important both for recent
// task switch (toggling between the two top recent apps) as well as normal
// UI flow such as clicking on a URI in the e-mail app to view in the browser,
// and then pressing back to return to e-mail.
static final int PREVIOUS_APP_ADJ = 7;

// This is a process holding the home application -- we want to try
// avoiding killing it, even if it would normally be in the background,
// because the user interacts with it so much.
static final int HOME_APP_ADJ = 6;

// This is a process holding an application service -- killing it will not
// have much of an impact as far as the user is concerned.
static final int SERVICE_ADJ = 5;

// This is a process with a heavy-weight application.  It is in the
// background, but we want to try to avoid killing it.  Value set in
// system/rootdir/init.rc on startup.
static final int HEAVY_WEIGHT_APP_ADJ = 4;

// This is a process currently hosting a backup operation.  Killing it
// is not entirely fatal but is generally a bad idea.
static final int BACKUP_APP_ADJ = 3;

// This is a process only hosting components that are perceptible to the
// user, and we really want to avoid killing them, but they are not
// immediately visible. An example is background music playback.
static final int PERCEPTIBLE_APP_ADJ = 2;

// This is a process only hosting activities that are visible to the
// user, so we'd prefer they don't disappear.
static final int VISIBLE_APP_ADJ = 1;

// This is the process running the current foreground app.  We'd really
// rather not kill it!
static final int FOREGROUND_APP_ADJ = 0;

// This is a process that the system or a persistent process has bound to,
// and indicated it is important.
static final int PERSISTENT_SERVICE_ADJ = -11;

// This is a system persistent process, such as telephony.  Definitely
// don't want to kill it, but doing so is not completely fatal.
static final int PERSISTENT_PROC_ADJ = -12;

// The system process runs at the default adjustment.
static final int SYSTEM_ADJ = -16;

// Special code for native processes that are not being managed by the system (so
// don't have an oom adj assigned by the system).
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

static uint32_t lowmem_debug_level = 1;
static int lowmem_adj[6] = {
0,
1,
6,
12,
};
static int lowmem_adj_size = 4;
static int lowmem_minfree[6] = {
3 * 512,    /* 6MB */
2 * 1024,   /* 8MB */
4 * 1024,   /* 16MB */
16 * 1024,  /* 64MB */
};
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

# Set init and its forked children's oom_adj.
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 ）

- 应用启动时启动一个假的Service（FakeService）, startForeground()，传一个空的Notification

- 启动真正的Service（AlwaysLiveService），startForeground()，注意必须相同Notification ID

- 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

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

FakeService 临时服务

public class FakeService extends Service {
@Nullable
@Override
public IBinder onBind(Intent intent) {
return null;
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
startForeground(R.id.notify, new Notification());
stopSelf();
return super.onStartCommand(intent, flags, startId);
}

@Override
public void onDestroy() {
stopForeground(true);
super.onDestroy();
}
}

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：

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





进程被系统kill后，可以由syn拉起

3. 风险：

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

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

public class XXAccountProvider extends ContentProvider {
public static final String AUTHORITY = "包名.provider";
public static final String CONTENT_URI_BASE = "content://" + AUTHORITY;
public static final String TABLE_NAME = "data";
public static final Uri CONTENT_URI = Uri.parse(CONTENT_URI_BASE + "/" + TABLE_NAME);

@Override
public boolean onCreate() {
return true;
}

@Nullable
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
return null;
}

@Nullable
@Override
public String getType(Uri uri) {
return new String();
}

@Nullable
@Override
public Uri insert(Uri uri, ContentValues values) {
return null;
}

@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
return 0;
}

@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
return 0;
}
}

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

public class XXSyncService extends Service {
private static final Object sSyncAdapterLock = new Object();
private static XXSyncAdapter sSyncAdapter = null;
@Override
public void onCreate() {
synchronized (sSyncAdapterLock) {
if (sSyncAdapter == null) {
sSyncAdapter = new XXSyncAdapter(getApplicationContext(), true);
}
}
}

@Override
public IBinder onBind(Intent intent) {
return sSyncAdapter.getSyncAdapterBinder();
}

static class XXSyncAdapter extends AbstractThreadedSyncAdapter {
public XXSyncAdapter(Context context, boolean autoInitialize) {
super(context, autoInitialize);
}
@Override
public void onPerformSync(Account account, Bundle extras, String authority, ContentProviderClient provider, SyncResult syncResult) {
getContext().getContentResolver().notifyChange(XXAccountProvider.CONTENT_URI, null, false);
}
}
}

声明Sync服务

<service
android:name="**.XXSyncService"
android:exported="true"
android:process=":core">
<intent-filter>
<action
android:name="android.content.SyncAdapter"/>
</intent-filter>
<meta-data
android:name="android.content.SyncAdapter"
android:resource="@xml/sync_adapter"/>
</service>

其中sync_adapter为：

<sync-adapter xmlns:android="http://schemas.android.com/apk/res/android"
android:accountType="@string/account_auth_type"
android:allowParallelSyncs="false"
android:contentAuthority="@string/account_auth_provide"
android:isAlwaysSyncable="true"
android:supportsUploading="false"
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

public void triggerRefresh() {
Bundle b = new Bundle();
b.putBoolean(ContentResolver.SYNC_EXTRAS_MANUAL, true);
b.putBoolean(ContentResolver.SYNC_EXTRAS_EXPEDITED, true);
ContentResolver.requestSync(
account,
CONTENT_AUTHORITY,
b);
}

添加账号

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

同步周期设置

ContentResolver.setIsSyncable(account, CONTENT_AUTHORITY, 1);
ContentResolver.setSyncAutomatically(account, CONTENT_AUTHORITY, true);
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

public class XXAuthService extends Service {
private XXAuthenticator mAuthenticator;

@Override
public void onCreate() {
mAuthenticator = new XXAuthenticator(this);
}

private XXAuthenticator getAuthenticator() {
if (mAuthenticator == null)
mAuthenticator = new XXAuthenticator(this);
return mAuthenticator;
}

@Override
public IBinder onBind(Intent intent) {
return getAuthenticator().getIBinder();
}

class XXAuthenticator extends AbstractAccountAuthenticator {
private final Context context;
private AccountManager accountManager;
public XXAuthenticator(Context context) {
super(context);
this.context = context;
accountManager = AccountManager.get(context);
}

@Override
public Bundle addAccount(AccountAuthenticatorResponse response, String accountType, String authTokenType, String[] requiredFeatures, Bundle options)
throws NetworkErrorException {
// 添加账号 示例代码
final Bundle bundle = new Bundle();
final Intent intent = new Intent(context, AuthActivity.class);
intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE, response);
bundle.putParcelable(AccountManager.KEY_INTENT, intent);
return bundle;
}

@Override
public Bundle getAuthToken(AccountAuthenticatorResponse response, Account account, String authTokenType, Bundle options)
throws NetworkErrorException {
// 认证 示例代码
String authToken = accountManager.peekAuthToken(account, getString(R.string.account_token_type));
//if not, might be expired, register again
if (TextUtils.isEmpty(authToken)) {
final String password = accountManager.getPassword(account);
if (password != null) {
//get new token
authToken = account.name + password;
}
}
//without password, need to sign again
final Bundle bundle = new Bundle();
if (!TextUtils.isEmpty(authToken)) {
bundle.putString(AccountManager.KEY_ACCOUNT_NAME, account.name);
bundle.putString(AccountManager.KEY_ACCOUNT_TYPE, account.type);
bundle.putString(AccountManager.KEY_AUTHTOKEN, authToken);
return bundle;
}

//no account data at all, need to do a sign
final Intent intent = new Intent(context, AuthActivity.class);
intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE, response);
intent.putExtra(AuthActivity.ARG_ACCOUNT_NAME, account.name);
bundle.putParcelable(AccountManager.KEY_INTENT, intent);
return bundle;
}

@Override
public String getAuthTokenLabel(String authTokenType) {
//            throw new UnsupportedOperationException();
return null;
}

@Override
public Bundle editProperties(AccountAuthenticatorResponse response, String accountType) {
return null;
}

@Override
public Bundle confirmCredentials(AccountAuthenticatorResponse response, Account account, Bundle options)
throws NetworkErrorException {
return null;
}

@Override
public Bundle updateCredentials(AccountAuthenticatorResponse response, Account account, String authTokenType, Bundle options)
throws NetworkErrorException {
return null;
}

@Override
public Bundle hasFeatures(AccountAuthenticatorResponse response, Account account, String[] features)
throws NetworkErrorException {
return null;
}
}
}

声明Account服务

<service
android:name="**.XXAuthService"
android:exported="true"
android:process=":core">
<intent-filter>
<action
android:name="android.accounts.AccountAuthenticator"/>
</intent-filter>
<meta-data
android:name="android.accounts.AccountAuthenticator"
android:resource="@xml/authenticator"/>
</service>

其中authenticator为：

<?xml version="1.0" encoding="utf-8"?>
<account-authenticator xmlns:android="http://schemas.android.com/apk/res/android"
android:accountType="@string/account_auth_type"
android:icon="@drawable/icon"
android:smallIcon="@drawable/icon"
android:label="@string/app_name"
/>

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

微信Android客户端后台保活经验分享

Android Low Memory Killer原理

stackOverflow 上介绍的双Service方法

Write your own Android Sync Adapter

Write your own Android Authenticator

Android developer

android.accounts

AccountManager

AbstractAccountAuthenticator

AccountAuthenticatorActivity

Creating a Sync Adapter



By SkySeraph-2016