提高Android应用进程存活率的小技巧
来源:长沙北大青鸟|发布时间:2017-03-27|浏览量:
Android 进程优先级
1 进程优先级等级一般分法
Activte process
Visible Process
Service process
Background process
Empty process
2 Service技巧
onStartCommand返回START_STICKY
onDestroy中startself
Service后台变前置,setForground(true)
android:persistent = “true”
3 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;
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.
查看某个App的进程
步骤(手机与PC连接)
adb shell
ps | grep 进程名
cat /proc/pid/oom_adj //其中pid是上述grep得到的进程号
Linux AM命令
am命令:在Android系统中通过adb shell 启动某个Activity、Service、拨打电话、启动浏览器等操作Android的命令.其源码在Am.java中,在shell环境下执行am命令实际是启动一个线程执行Am.java中的主函数(main方法),am命令后跟的参数都会当做运行时参数传递到主函数中,主要实现在Am.java的run方法中。
拨打电话
命令:am start -a android.intent.action.CALL -d tel:电话号码
示例:am start -a android.intent.action.CALL -d tel:10086
打开一个网页
命令:am start -a android.intent.action.VIEW -d 网址
示例:am start -a android.intent.action.VIEW -d //www.skyseraph.com
启动一个服务
命令:am startservice <服务名称>
示例:am startservice -n com.android.music/ com.android.music.MediaPlaybackService
NotificationListenerService
“A service that receives calls from the system when new notifications are posted or removed, or their ranking changed.” From Google
用来监听到通知的发送以及移除和排名位置变化,如果我们注册了这个服务,当系统任何一条通知到来或者被移除掉,我们都能通过这个service来监听到,甚至可以做一些管理工作。
Android账号和同步机制
属于Android中较偏冷的知识
Android多进程
实现:android:process
好处:一个独立的进程可以充分利用自己的RAM预算,使其主进程拥有更多的空间处理资源。此外,操作系统对待运行在不同组件中的进程是不一样的。这意味着,当系统运行在低可用内存的条件时,并不是所有的进程都会被杀死
大坑:每一个进程将有自己的Dalvik VM实例,意味着你不能通过这些实例共享数据,至少不是传统意义上的。例如,静态字段在每个进程都有自己的值,而不是你倾向于相信的只有一个值。
现有方法
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).
双service(通知栏) 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();
}
}
Service及时拉起
AlarmReceiver, ConnectReceiver,BootReceiver等
Service设置(见上面基础部分)
通过监听系统广播,如开机,锁屏,亮屏等重新启动服务
通过alarm定时器,启动服务
守护进程/进程互拉
在分析360手机助手app时,发现其拥有N多个进程,一个进程kill后会被其它未kill的进程拉起,这也是一种思路吧,虽然有点流氓~
守护进程一般有这样两种方式:
多个java进程守护互拉
底层C守护进程拉起App上层/java进程
Linux Am命令开启后台进程
一种底层实现让进程不被杀死的方法,在Android4.4以上可能有兼容性问题,具体参考Ref-7
NotificationListenerService通知
一种需要用户允许特定权限的系统拉起方式,4.3以上系统
前台浮窗
有朋友提出一种应用退出后启动一个不可交互的浮窗,个人觉得这种方法是无效的,读者有兴趣可以一试
新方法(AccountSync)
思路
利用Android系统提供的账号和同步机制实现
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
正常情况
采用AccountSyncAdapter方法后
进程被系统kill后,可以由syn拉起
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
实现 (核心代码)
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="//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
Account account = AccountService.GetAccount();
AccountManager accountManager = (AccountManager) context.getSystemService(Context.ACCOUNT_SERVICE);
accountManager.addAccountExplicitly(...)
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:
<account-authenticator xmlns:android="//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
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