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This article mainly introduces "how to achieve garbage collection in Android". In daily operation, I believe many people have doubts about how to achieve garbage collection in Android. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful for you to answer the doubts about "how to achieve garbage collection in Android"! Next, please follow the editor to study!

First of all, all classes will vainly inherit the refbase class, because it implements all the function needed to achieve Android garbage collection, so virtually all objects are declared with the ability to automatically release themselves, that is to say, the smart pointer is actually our object itself, which maintains a count of its own strong and weak references, and releases itself once the strong reference count is 0.

First of all, let's see that sp,sp is actually not an acronym for smart pointer, but strong pointer, which actually contains a pointer to an object. We can simply look at one of the constructors of sp:

Template

< typename T>

Sp

< T>

:: sp (T* other): m_ptr (other) {if (other) other- > incStrong (this);}

For example, let's declare an object:

Sp

< CameraHardwareInterface>

Hardware (new CameraHal ())

In fact, the sp pointer does nothing to itself, just a pointer assignment that contains a pointer to the object, but the object adds a strong reference count to the object itself, and the implementation of this incStrong is in the refbase class. The new new comes out a CameraHal object and gives its value to sp

< CameraHardwareInterface>

Its strong reference count changes from 0 to 1. So every time you assign an object to a sp pointer, the strong reference count of the object is incremented by 1. Let's take a look at the destructor of sp:

Template

< typename T>

Sp

< T>

:: ~ sp () {if (m_ptr) mroomptra > decStrong (this);}

In fact, every time you delete a sp object, the strong reference count of the object pointed to by the sp pointer is reduced by one, and when the strong reference technology of the object is 0, the object is automatically released.

Let's take a look at wp,wp, which is the abbreviation of weak pointer. The principle of weak reference pointer is to apply Android garbage collection to reduce the memory consumption of fat objects. Let's first look at a constructor of wp:

Wp

< T>

:: wp (T* other): m_ptr (other) {if (other) m_refs = other- > createWeak (this);}

Like sp, it actually just assigns a value to the pointer, and the object itself adds a count of weak references to itself, while wp also contains a m_ref pointer, which is mainly used to upgrade wp to sp:

Template

< typename T>

Sp

< T>

Wp

< T>

:: promote () const {return sp

< T>

(m_ptr, m_refs);} template

< typename T>

Sp

< T>

:: sp (T* p, weakref_type* refs): m_ptr ((p & & refs- > attemptIncStrong (this))? P: 0) {}

In fact, what we can do with the wp pointer * * is to upgrade the wp pointer to a sp pointer, and then determine whether the upgrade is successful. If it succeeds, the object still exists, and if it fails, the object has been released. What I see now is that wp pointers are used a lot in singletons, making sure that there is only one mhardware object, such as:

Wp

< CameraHardwareInterface>

CameraHardwareStub::singleton; sp

< CameraHardwareInterface>

CameraHal::createInstance () {LOG_FUNCTION_NAME if (singleton! = 0) {sp

< CameraHardwareInterface>

Hardware = singleton.promote (); if (hardware! = 0) {return hardware;}} sp

< CameraHardwareInterface>

Hardware (new CameraHal ()); / strong reference plus 1 singleton = hardware;// weak reference plus 1 return hardware;// assignment constructor, strong reference plus 1} / / hardware is deleted, strong reference minus 1, the study on "how to achieve garbage collection in Android" is over, hoping to solve everyone's doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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