Running native code on Android #OSDCfr 2012

* cross-compiling 3rd party libraries with the Android Standalone Toolchain,
* using prebuilt libraries,
* using NEON code while still targeting all devices,
* illustrating some Java Native Interface (JNI) tips and tricks

Transcript

1. Running native code on Android OSDC.fr 2012-10-13 Cédric @deltheil C NDK ARM
2. - Why using native code? -
3. 1. Reuse some C code
4. 2. Use 3rd party libraries
5. 3. Create portable components iOS Android ...
6. 4. Use hardware acceleration CPU SIMD algorithm
7. 5. ... because it’s fun :)
8. ...but How? Native Development Kit
9. - Android NDK overview -
10. Downloads http://developer.android.com/tools/sdk/ndk/index.html cross-platform
11. Contents 1. Tools for Linux,OS X,Win to cross-compile native ARM,x86,MIPS binaries.
12. Contents 2. System files and headers for Android native APIs. w/ Java Native Interface (a.k.a JNI) <jni.h>
13. Contents 3. Easy-to-use build system: Android.mk & ndk-build (make wrapper).
14. Contents 4. Documentation and code samples.
15. - Steps to embed C code -
16. 1/3 Wrap C Java JNI C code C Java libmisc.so
17. 1/3 Wrap C /* 1. Wrap your C code with the JNI */ #include <jni.h> jstring Java_com_example_Foo_bar(JNIEnv* env, jobject thiz) { char buffer[512]; /* ... */ return (*env)->NewStringUTF(env, buffer); } namespace class method instance native interface
18. 2/3 Build native lib Java JNI C code C Java libmisc.so
19. # 2. Generate a lib with ndk-build $ ndk-build Compile thumb : misc <= misc.c StaticLibrary : libmisc.a SharedLibrary : libmisc.so Install : libmisc.so => libs/armeabi/libmisc.so ... 2/3 Build native lib
20. 3/3 Java ext Java JNI C code C Java libmisc.so
21. /* 3. Expose the logic via a native extension */ package com.example; public class Foo extends /* ... */ { static { System.loadLibrary("misc"); } public native String bar(); } 3/3 Java ext
22. Basic Java JNI C code C Java libmisc.so
23. Advanced Java JNI libA.a C Java libmisc.so A sources C code libB.a B sources 3rd party libs
24. - Building 3rd party libs -
25. Pro-tip Use the Standalone Toolchain.
26. What? A customized install for a given platform, arch. handy
27. Why? No need to write specific Android.mk makefiles: reuse existing build systems. 0 LOC Makefile autotools
28. How?
29. Makefile [Ex. 1] jsmn JSON C parser
30. [Ex. 1] jsmn 1/3 override Makefile variables
31. [Ex. 1] jsmn 2/3
32. [Ex. 1] jsmn 3/3 choose the proper arch... and that’s it! Full gist @ http://git.io/ndk-jsmn
33. [Ex. 2] msgpack autotools binary C/C+ serialization
34. [Ex. 2] msgpack 1/3
35. [Ex. 2] msgpack 2/3
36. [Ex. 2] msgpack 3/3 Full gist @ http://git.io/ndk-msgpack use the cross-toolchains... and that’s it!
37. - Using a prebuilt library -
38. Overview Android.mk Application.mk ndk-build armeabi/ libfoo.so libs/ single arch
39. Overview Android.mk Application.mk armeabi-v7a/ libfoo.so ndk-build armeabi/ libfoo.so libs/ fat binary
40. - Loading a native library -
41. Basic Pick the right arch vs. target device
42. Medium
43. Custom frontal library native method (frontal lib.) Pick the right arch yourself!
44. Custom: why? [2] Bypass a loadLibrary bug on ICS! [1] Properly target ARMv7 without NEON CPUs when getCpuFeatures() can’t be used at runtime (e.g. 3rd party libs) [2] see http://www.moodstocks.com/2012/03/20/ice-cream-sandwich-why-native-code-support- sucks [1] e.g. «the NVidia Tegra 2 generation SoC has a dual-core ARM Cortex-A9 CPU (lacking ARM's advanced SIMD extension—NEON)» - see http://en.wikipedia.org/wiki/Tegra
45. - Quick JNI hints -
46. C pointer = int field e.g. persist a DB handle and use it throughout the JNI extensions Don’t forget to destruct it (explicitly or at finalize() time)
47. C error codes C error code & string
48. Resources #AltDevBlogADay NDK Part 1 & Part 2 Linux Mag., 07/11 VLC for Android Tokyo Cabinet Java Pkg
49. Thanks! Questions? Comments? cedric@moodstocks.com | @deltheil