Im instant messaging development application keeping alive process anti kill

stay Android 4.4 And later systems , Whether the application can be resident in memory , It has always been a headache , Especially mobile terminal IM、 Message push applications , In order to ensure “ Full time online ” The concept of , It's been a lot of effort . although APP Resident memory is more important for users ” nausea ”, But in places like IM And message push ,APP The resident memory is especially important .

therefore , With a skeptical eye , Retrieve the original code for testing , Incidentally, the mainstream sports in the market are analyzed APP Method of keeping alive （ WeChat 、 hand Q Forget it , The children of the rich , Not representative ）, At the same time, it is also applicable to the system and the memory APP The management rules of .

 

Andriod Apply the core idea of keeping alive to sum up

about Android6.0 And above APP Keep alive , I think it is mainly through these two aspects , namely ：

    Reduce omm_adj value , Try to ensure that the process is not killed by the system （ What this article will discuss ）;

    After the process is killed , Reactivate the process in other ways （ We will discuss in the next article ）.

But it needs to be understood that , Facing the deep customization of various mobile phone manufacturers and Google's increasingly strict resource management mechanism , The combination of these two ways is not permanent , It can only exist relatively , Different models have different results .

Due to space limitation , This article mainly analyzes how to reduce oom_adj To reduce the value of APP The chance of being killed , as well as oom_adj How value is achieved ？

Next , We need to understand Android The rules by which the system reclaims processes in memory ：

There are five main states for a process to be active while it is in memory ： Foreground process 、 See the process 、 Service process 、 Background processes 、 Empty process , The process priority of these States is from high to low ,oom_adj Value from low to high ( stay ProcessList Definition ). then Android According to the current system resources and processes oom_adj Value to reclaim the corresponding process , Foreground processes are generally not recycled , Empty processes are the easiest to recycle , This kind of management rule is " According to legend " Of Low Memory Killer.

notes ： priority 1 Represents the highest level , Of ordinary processes oom_adj>=0, System processes oom_adj<0, The system will match a certain segment according to the corresponding memory threshold oom_adj Value of the process . in addition ,oom_adj The value also increases as the physical memory is consumed , System processes will never be killed by the system .

Next, I will first analyze the mainstream in the market APP Anti killing method , Provide reference for my next plan , Please read on

APP The first stage of the process anti kill scheme ： Open the front desk Service,“ Force you to ascend ”

take Service Set it as the front desk , The goal is to improve the process Service Of oom_adj value , To reduce the probability of being recycled by the system . The principle of the scheme is , By using startForeground() Method will be current Service Put it on the front desk to improve Service The priority of the . It should be noted that , Yes API Greater than 18 for startForeground() Method needs to pop up a visible notification , If you feel uncomfortable , Can open another Service Remove the notification bar , Its oom_adj The value has not changed .

Explain , There are also two techniques used here ：

    One is in onStartCommand Return in method START_STICKY, Its function is when Service The process is kill after , The system will try to recreate this Service, And will keep Service Is in the start state , But do not keep the passed Intent object ,onStartCommand Methods must be called again ;

    Second, in onDestory Method , in other words , as long as Service When it was destroyed, it came to onDestory Here we will restart it .

Explain ：

From what we know , One Service There is no independent process , It usually runs as a thread in the application process where it is located , And the application process name is consistent with the package name . If you want the specified components and applications to run in the specified process , It needs to pass android:process Property to create a process for it , therefore android:process=":daemon_service" Is to make DaemonService Run under the name “com.jiangdg.keepappalive:daemon_service” In progress ;android:enabled The function of attributes is Android Whether the system instantiates components in the application ;android:exported Property is used for the current component (Service) Whether it can be started by components in applications other than itself . Instant messaging development

 

test result ：

Next , Let's observe KeepAppAlive Process oom_adj Value change .

First ,adb see KeepAppAlive Process number of the process ：

E:\Android\StudioProject\KeepAppAlive>adb shell

[email protected]:/ $ su

[email protected]:/ # ps | grep jiangdg

APP The second stage of the process anti kill scheme ： Monitor lock screen broadcast ,“ manufacture ‘1 Pixels ’ tragedy ”

Explain ：

Java There are four levels of references to objects in ： Strong citation 、 Soft citation 、 Weak reference 、 Virtual reference . here , We use weak references WeakReference To prevent memory leaks , To explain the problem , Let's take an example ： There are two classes class A and class B, Instantiate these two classes respectively to get a,b, among a As an instance B The construction parameter passed in when , The code is as follows ：

A a = newA();

B b = newB(a);

From these two lines of code ,a It's the object A References to ,b It's the object B References to , object B At the same time, it depends on the object A, object A And the object B A strong reference is formed between . When a=null when ,a Not pointing to object A, Usually , object A When it is not referenced by other objects, it will be GC Recycling , But because of B It also depends on objects A, object A It won't be GC Recycling , This causes memory leaks ( Unless b=null, object A And the object B Will be GC Recycle at the same time ). If you use weak references , object A Will only be WeakReference Depend on , When a=null when ,GC Will recycle it , This avoids memory leaks .

stay UI Interface architecture , Every Activity All contain a Window object , stay Android in Window Objects are usually made of PhoneWindow To achieve ,PhoneWindow Will a DecorView Set to the root of the entire application window View, It acts as the top-level view of the window interface , It encapsulates many methods of general operation windows ... Okay , Not far , Now that we know Window The object is in a Activity Position in , Here we go through getWindow How to get SinglePixelActivity Of Window object , Then set relevant properties for it , For example, the size of the form 、 Location 、 Coordinates, etc , To achieve the desired "1 Pixels " Interface effect .

Explain ：

1）android:launchMode attribute ： Is used to specify the activity Start mode of , There are four kinds in total , namely ：

- standar Pattern , Each start activity Will create its instance , And add it to the top of the task stack ;

- singleTop Pattern , Each start activity If at the top of the stack activity No need to create , For the rest of the cases, create this activity Example ;

- singleTask Pattern , If it's activated activity Instances of exist on the stack , You don't need to create , Just put this activity Add to the top of the stack , And put the activity The above activity All instances pop;

- singleInstance Pattern ： Will create the activity The instance is placed on a separate stack , The stack can only store this instance , And exists as a shared instance .

2）android:configChanges attribute ： Used to capture changes in phone status , That is, when the mobile phone is in ( Such as switching between horizontal and vertical screens 、 The screen size ) The current active state will be saved and restarted when changing Activity, because SinglePixelActivity Shouldering the special mission of keeping alive , Use here android:configChanges attribute ： prevent Activity restart , It just calls onConfigurationChanged(Configuration newConfig) To notify the change of mobile phone status ;

3）android:excludeFromRecents attribute ： Used to control the SinglePixelActivity Do not show in the recent task list ;

4）android:finishOnTaskLaunch attribute ： Used to mark when the user starts the application again (TASK) Whether to close the existing Activity Example ,false Means not to close ;

5）android:theme attribute ： Is used to specify the Activity Show theme , Here we customize the theme SingleActivityStyle.

Monitor lock screen broadcast , The screen lock will SportActivity Put it on the front desk ( so ) ：

Monitor lock screen broadcast , Turn on when locking the screen SinglePixelActivity(1 Pixels )：

APP The third stage of process anti kill scheme ： Loop through a silent audio ," Create a Vajra body that is not bad "

For Samsung C9、Note4 And Huawei 4X Come on , Combined with the front desk Service And levitation interface (1 Pixels ) How to keep alive , When the user does not take the initiative to clean up or kill , test APP The effect of keeping alive is very good .

however , For huawei Mate8 Come on , The effect is still not satisfactory , Especially when using one click to clean up memory , test APP It's almost impossible to survive . then ," splash " But miraculously survived , You can't get rid of it with one click , Just when I can't think about it " The elder sister " when , One " nausea " The interface of appears in front of me . fuck ！ See the red box below ," splash " Actually playing a silent music loop in the background , No wonder the vitality is so strong , But power consumption is also a lever .

ok , Not so much , This is just a study from the perspective of technology , After all, users are still very sensitive to power consumption , It's still a convergence point if you have to , Don't be so " Coquettish ", User experience is important , If you're not careful " Diarrhea " After you .

test result ：

Here it is cmd Window use "ps | grep jiangdg" command , If the process exists in memory , Then print the process information ; If it doesn't exist , There is no information .

The test conditions of each model are as follows ：

1） Huawei Mate8(Android 7.0)： Will test APP In the background , The front desk Service In the black screen state 1 Be killed in minutes ,"1 Pixels " suspension Activity Test in black screen 2 Hours still live , The effect is OK . however , When the user cleans up recent apps with one click , Will be killed , When turned on in the background Serive When playing a silent audio loop , One click cleanup is still alive , Live in black screen mode in the background 12 hours ;

2） samsung C9(Android 6.0)： Open the front desk Service and 1 Pixels ,KeepAppAlive Live in black background mode 9 Over hours , It seems that the native system is softer ; Start the background playing audio service , The user can clean up the recent application with one click and keep it alive ;

3） Huawei 4X(Android 6.0)： The effect is the same C9;

4） samsung Note4(Android 5.0)： The effect is the same C9.

notes ：Mate8 Loop through a silent audio , When the user clicks one button to clean up the recent application ,KeepAppAlive Won't be killed , But if the user only chooses to clean KeepAppAlive when , Will also be killed , This is related to " splash " The effect of keeping alive is consistent .