Next, let's test the Android application with the ARM JNI library.
The JNI library can be found at ch05/test2/jni. The processor architecture that can be supported is defined in Application.mk as follows:
# Build both ARMv5TE and ARMv7-A and x86 machine code.
# armeabi armeabi-v7a
APP_ABI := armeabi armeabi-v7a
APP_PLATFORM := android-23
We can see that we build the JNI library for armeabi and armeabi-v7a. Let's build the JNI library using NDK first:
$ cd ch05/test2/jni
$ ./build.sh
[armeabi] Install : libHelloJNI.so => libs/armeabi/libHelloJNI.so
[armeabi-v7a] Install: libHelloJNI.so => libs/armeabi-v7a/libHelloJNI.so
After we build the JNI library, we can import the Android source code to Eclipse or Android Studio to build the application itself. We won't explain the details of importing and building Android applications. You can read books on how to develop an Android application and how to develop a JNI library to find out more. What we want to investigate here is the test result. After we have the APK file, we can install it in the emulator and run it. At the same time, we can catch the debug log using logcat. Here is the log from my environment:
...
10-02 00:44:57.871: I/ActivityManager(1527): START u0 {act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=fr.myrddin.hellojni/.HelloJNIActivity (has extras)} from uid 10008 on display 0
10-02 00:44:57.900: I/ActivityManager(1527): Start proc 2652:fr.myrddin.hellojni/u0a53 for activity fr.myrddin.hellojni/.HelloJNIActivity
10-02 00:44:57.902: I/art(2652): Late-enabling JIT
10-02 00:44:57.903: D/houdini(2652): [2652] Initialize library(version: 6.1.1a_x.48413 RELEASE)... successfully.
10-02 00:44:57.907: W/art(2652): Unexpected CPU variant for X86 using defaults: x86
10-02 00:44:57.907: I/art(2652): JIT created with code_cache_capacity=2MB compile_threshold=1000
10-02 00:44:58.546: W/art(1527): Long monitor contention event with owner method=int com.android.server.wm.WindowManagerService.relayoutWindow(com.android.server.wm.Session, android.view.IWindow, int, android.view.WindowManager$LayoutParams, int, int, int, int, android.graphics.Rect, android.graphics.Rect, android.graphics.Rect, android.graphics.Rect, android.graphics.Rect, android.graphics.Rect, android.content.res.Configuration, android.view.Surface) from WindowManagerService.java:3104 waiters=0 for 632ms
10-02 00:44:58.580: W/dex2oat(2667): Unexpected CPU variant for X86 using defaults: x86
10-02 00:44:58.581: W/dex2oat(2667): Mismatch between dex2oat instruction set features (ISA: X86 Feature string: smp,-ssse3,-sse4.1,-sse4.2,-avx,-avx2) and those of dex2oat executable (ISA: X86 Feature string: smp,ssse3,-sse4.1,-sse4.2,-avx,-avx2) for the command line:
10-02 00:44:58.581: W/dex2oat(2667): /system/bin/dex2oat --runtime-arg -classpath --runtime-arg --compiler-filter=interpret-only --instruction-set=x86 --instruction-set-features=smp,ssse3,-sse4.1,-sse4.2,-avx,-avx2 --runtime-arg -Xrelocate --boot-image=/system/framework/boot.art --runtime-arg -Xms64m --runtime-arg -Xmx512m --compiler-filter=verify-at-runtime --instruction-set-variant=x86 --instruction-set-features=default --dex-file=/data/app/fr.myrddin.hellojni-1/base.apk --oat-file=/data/dalvik-cache/x86/data@[email protected]@[email protected]
10-02 00:44:58.581: E/dex2oat(2667): Failed to create oat file: /data/dalvik-cache/x86/data@[email protected]@[email protected]: Permission denied
10-02 00:44:58.581: I/dex2oat(2667): dex2oat took 774.330us (threads: 2)
10-02 00:44:58.582: W/art(2652): Failed execv(/system/bin/dex2oat --runtime-arg -classpath --runtime-arg --compiler-filter=interpret-only --instruction-set=x86 --instruction-set-features=smp,ssse3,-sse4.1,-sse4.2,-avx,-avx2 --runtime-arg -Xrelocate --boot-image=/system/framework/boot.art --runtime-arg -Xms64m --runtime-arg -Xmx512m --compiler-filter=verify-at-runtime --instruction-set-variant=x86 --instruction-set-features=default --dex-file=/data/app/fr.myrddin.hellojni-1/base.apk --oat-file=/data/dalvik-cache/x86/data@[email protected]@[email protected]) because non-0 exit status
10-02 00:44:58.603: D/houdini(2652): [2652] Added shared library /data/app/fr.myrddin.hellojni-1/lib/arm/libHelloJNI.so for ClassLoader by Native Bridge.
10-02 00:44:58.603: E/JNI(2652): Number : 4
...
10-02 00:44:59.906: I/ActivityManager(1527): Displayed fr.myrddin.hellojni/.HelloJNIActivity: +2s9ms
...
We can see from the preceding log message that Houdini is initialized successfully and that the libHelloJNI.so JNI library is loaded by Native Bridge.