问题
Recently I answered this question, where was described whole installation process of .apk file to android phone. The one thing it was about using Dalvik VM. And now I'm wondered is installation process is exactly same using ART? What are the differences?
I mean the work of PackageManager, path, convertion to dex format etc.
Googling didn't give much info, only about performance power, managing memory and something similar.
I would be very thankful if someone with knowledge could share this information.
回答1:
Android apps come in the .apk file format, with Java classes converted into DEX bytecode. The DEX bytecode format is independent of device architecture and needs to be translated to native machine code to run on the device. This is the same for both the ART and the Dalvik runtimes.
The most significant change from Dalvik to ART is that Dalvik is based on Just-in-Time (JIT) compilation, while ART is based on Ahead-of-Time (AOT) compilation.
With the Dalvik JIT compiler, each time when the app is run, it dynamically translates a part of the Dalvik bytecode into machine code. As the execution progresses, more bytecode is compiled and cached. On the other hand, ART is equipped with an Ahead-of-Time compiler. During the app’s installation phase, it statically translates the DEX bytecode into machine code and stores in the device’s storage. This is a one-time event which happens when the app is installed on the device.
Performance
The most important benefit of ART runtime over Dalvik runtime is that the app runs faster on ART. Because DEX bytecode has been translated into machine code during installation, no extra time is needed to compile it during the runtime. The app starts faster as well when launched with ART for the same reason.
Because Dalvik requires extra memory for JIT code cache, an app occupies a smaller memory footprint when it runs on ART.
Battery Life
With Dalvik runtime, the JIT compilation is CPU bound. Because of AOT compilation, ART frees the CPU from translating DEX bytecode to machine code during the app’s execution, thus reducing energy consumption. Using ART leads to a longer battery life, which is the time interval when a battery recharging is needed.
Installation Time
Because the AOT compiler translates DEX bytecode into machine code during the app installation, an app takes longer to install on a device with ART runtime. Considering the benefits of faster execution and shorter launch time we discussed in the previous section, this extra time which happens only once during the app’s installation is well worth it.
Storage Footprint
With ART runtime, the AOT compiler translates the app’s DEX bytecode into machine code and stores it in the device’s storage. The pre-compiled binary occupies more space than the DEX bytecode. Thus results in a larger storage footprint comparing with Dalvik runtime.
Summary
To this point we have introduced the new ART runtime for Android. We also discussed its benefits and compromises, centralizing in its Ahead-of-Time compilation and performance improvement. Currently released for preview and still under active development and optimization, at this point of time we cannot provide a quantitative conclusion on how much performance gained by switching to ART Runtime. One thing for sure is ART will replace Dalvik as the Android runtime on the x86 based devices.
Source.
回答2:
In dvm architecture, at each time when the application launches the entire application byte code converted into dex and then execute the dex files. So when at each Time of launch same thing going to done, so to overcome this problem ART comes into picture. In ART while at the time of application installation only converts byte to Dex and then at every launch execute that same dex files, here no need to require conversion at each launch., so less time take to launch an app in ART compare to dvm.
来源：https://stackoverflow.com/questions/30442481/installation-process-of-apk-within-art-difference-from-dalvik-vm-installation