Android ndk: Entering the native world
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Transcript of Android ndk: Entering the native world
Intel Developers Relations Division
android ndk: Entering the native worldEduardo CarraraDeveloper Evangelist – Intel
@DuCarrara+EduardoCarraraDeAraujo
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Agenda
The Android NDK
Are you using and is not aware?
Be careful with the Binary Interface
Starting with Android Studio + gradle-experimental
Questions?
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Android ndkThe Native Development Kit
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“The Android NDK is a set of tools that allows the
implementation of parts of your app using native code
languages like C and C++."
- NDK Android Developers Portal
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and maybe you are doing that already...
... let’s a few interesting NDK usages.
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Usages of NDKWhat can we do with it?
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Game Engines
Others+…
*Other names and brands may be claimed as the property of others.
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Computer Vision
• Linear and Non-Linear image filtering.
• Images Geometric Transformations.
• Moviments Prediction in Videos.
• Background segmentation on Videos.
• Object Tracking.
• ...
Outras: Cardboard-SDK, Vuforia, Layar, LibCCV, Wikitude ...
OpenCV.org
*Other names and brands may be claimed as the property of others.
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Cross Platform Development
*Other names and brands may be claimed as the property of others.
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Other Usages and Libraries
Realm
Swift
Libpng
Intel TBB
Intel IPP
Libcairo and libpixman
Libsonic
Busybox
Speex
FFMpeg
OpenSSL
Lua
...
*Other names and brands may be claimed as the property of others.
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So many interesting usages!
Can we use NDK for
everything?!
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Understanding the ndk
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Source: Using the NDK Performantly (Big Android BBQ 2015)
15
Architecture Overview
App Code
Framework Classes
Runtime
System Libraries
Linux Kernel
JNI
Your Libraries
Stable ABI
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In practice...
Microchip Icon – Icon Finder.
App00100111000011100111
x86
ARM
MIPS
Your code is:
• Closer to HW
• Platform Dependent
You must be careful about it!
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You APK X-Ray with NDK usage
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3 Golden Rules for NDK Adoption
1
2
3 Legacy Code that must be re-used and/or to expensive to port to Java*.
Specific performance problems.
Features and Experiences that demand performance.
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3 (Main) Barriers for NDK Adoption
1
2
3 Perfomance gains are not assured.
Complexity of Implementation and Maintenance.
Platform Dependency and Compatibility.
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We can, but we should not use NDK for everything.
So...
Still interested?
Take the “red pill” and we will show you how far this
can go...
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using the ndk
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Fundamentals: Java Native Interface (JNI)
Defines how Java and native code will interop.
Java C / C++
• Load lib with:
• System.loadLibrary()
• Definition of Native Methods:
• Reserved word native
• Include the JNI Header:• #include <jni.h>
• Use specific JNI data types:• jstring, jint, jboolean, etc.
• Special Variables:• JNIEnv*, JavaVM*
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JNI: Mapping Java Methods To C / C++
In C/C++ the function must:
Use and return Java JNI primitives and Objects:
Follows the naming standards:
Or register functions manually:
jint xxx(JNIEnv* env, jobject instance, ...) { ... }
Java_com_example_hellojni_HelloWorldJni_method
JNIEnv->RegisterNatives();
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JNI: Example
Java
C / C++
public class HelloWorldJNI {
static {
System.loadLibrary("hello-jni");
}
public native String getHelloWorldStringFromJNI();
}
#include <jni.h>
jstring
Java_com_example_hellojni_HelloWorldJNI_getHelloWorldStringFromJNI(JNIEnv *env, jobject instance) {
return (*env)->NewStringUTF(env, "Hello World!");
}
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Old but Gold
Building NDK Apps classic style.J
NI
Co
de
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := hello-jni
LOCAL_SRC_FILES := hello-jni.c
include $(BUILD_SHARED_LIBRARY)
APP_ABI := all
jni/Android.mk jni/Application.mk
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Old but Gold
ndk_build script
Building NDK Apps classic style.
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Old but Gold
Building NDK Apps (almost) classic style.
• Add libs to jniLibs directory.
• Create java – jni interfaces.
• For libs pre-builts that is all.
• To build from source is a bit more complicated but is possible as well..
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Limitations
• Debug is not possible on AS. It is necessary to use ndk-gdb and/or Eclipse.
• Current support of gradle plugin was deprecated (ouch).
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... So where do we go?
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Android studio + ndk + gradle-experimental
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Important Warnings
• The experimental version of android gradle plugin will be used.
• Integration with Android Studio was improved but it stills unstable and has some bugs.
• On Windows there are issues with the Editor and/or build that prevent its usage. (Issues 195483 and 204552).
• Documentation is virtually inexistent or incomplete.
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AS Integration
NDK Installation
and Configuration
are now integrated
to Android Studio.
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AS Integration
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AS Integration
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gradle-experimental
Configuration
distributionUrl=https\://services
.gradle.org/distributions/gradle-
2.10-all.zip
./build.gradle ./gradle/gradle-wrapper/gradle-wrapper.properties
dependencies {
classpath
'com.android.tools.build:gradle-
experimental:0.7.0'
}
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gradle-experimental
Configuration: Combining Versions
Android Studio 1.5 2.0 2.1
gradle 2.8 2.10 2.10
gradle plugin 1.5.0 2.0.0 2.1.0
gradle-experimental plugin 0.4.0 0.6.0 0.7.0
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gradle-experimental
Configuration: build.gradle DSL
changes.
Always Check:
- NDK Samples
- gradle-experimental docs
apply plugin: 'com.android.model.application'
model {
}
android {
compileSdkVersion = 23
buildToolsVersion = "23.0.3"
defaultConfig.with {
applicationId = "com.example.hellojni"
minSdkVersion.apiLevel = 4
targetSdkVersion.apiLevel = 23
}
}
android.ndk {
moduleName = "hello-jni"
}
android.buildTypes {
release {
minifyEnabled = false
proguardFiles.add(file('proguard-rules.txt'))
}
}
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gradle-experimental
Configuration: multiple apks.
apply plugin: 'com.android.model.application'
model {
}
android.productFlavors {
}
// … standard gradle stuff
// … other gradle stuff
create ("armv7") {
}
create (“x86") {
}
ndk.abiFilters.add("armeabi-v7a")
ndk.abiFilters.add(“x86")
versionCode = calculateVersionCodeFor(
"armeabi-v7a")
versionCode = calculateVersionCodeFor(
“x86")
create (“fat")
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gradle-experimental
Configuration: multiple apks.
apply plugin: 'com.android.model.application'
model {
}
def actualVersionCode = 13;
// … gradle stuff
// … other gradle stuff
def baseVersionCode = 1000000;
def versionCodeABIPrefixes = [
'armeabi':1, 'armeabi-v7a':2, 'arm64-v8a':3,
'mips': 5,'mips64': 6,
'x86': 8, 'x86_64': 9];
def calculateVersionCodeFor = { String abi ->
return versionCodeABIPrefixes.get(abi, 0) *
baseVersionCode + actualVersionCode
}
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gradle-experimental
• It is also possible:
• Configure pre-built libs;
• Add build flags (general and by flavor);
• The current documentation generally do not follow the releases, then:
• Keep an eye to NDK Samples for references!
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Final Thoughts
When using NDK, direct or inderectly,add support to as many platform architectures as possibles.
Use NDK wisely: test, create benchmarks and assure that it is the right solution to your problem.
Follow and test the gradle-experimental plugin for the NDK!
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Questions?
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References
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References
• NDK Development on Intel
• Intel Tools
• Android* NDK Official Documentation
• Android* NDK Gradle Experimental Documentation
• Android* NDK Google* Samples
• Gradle Stable NDK Support - Xavier Hallade
• New Android Studio NDK Support - Xavier Hallade
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thanks
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