How to prevent from C++ to recompile all files in Android NDK?

Question

Hello,

I'm using the Android Studio with NDK and JNI in a project with a large amount of C++ files. When I make changes in a single C++ file it won't apply in the code unless I rebuild the whole project and refresh the entire C++ files so they have to recompile. The compilation process takes more than 3 minutes for every small change, make it 20 times a day and you have lost an hour.

According to today, after I make a change to a file I go to

Build >> Refresh Linked C++ Projects,

and then run the project, resulting in a full, redundant compilation of all files.

I'm looking for way for the compiler to refresh only the changed file, and as a result shorten the build process.

NOTE: This problem only occurs in windows, when I run Android Studio on a Mac, the compiler recompiles only the relevant files.

This is my CMakeLists.txt file:

cmake_minimum_required(VERSION 3.4.1)

FILE(GLOB CPP_SRC
     "src/main/cpp/*.c"
     "src/main/cpp/*.h"
     "src/main/cpp/*.cpp"
     "src/main/cpp/*.hpp"
 )


add_library(MyLib

             SHARED
             ${CPP_SRC} )

find_library(
              log-lib
              log )

target_link_libraries(
                       MyLib

                       ${log-lib} )

target_link_libraries(MyLib
                      android
                      log
                      EGL
                      GLESv2)

And my gradle.build file:

apply plugin: 'com.android.library'

android {
    signingConfigs {
        config {
            keyAlias '*****'
            keyPassword '*****'
            storeFile file(*****)
            storePassword '*****'
        }
    }
    compileSdkVersion 27
    buildToolsVersion '27.0.3'
    defaultConfig {

    minSdkVersion 16
    targetSdkVersion 27
    versionCode 1

    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

    externalNativeBuild {
        cmake {

            arguments "-DANDROID_ARM_NEON=TRUE", "-DANDROID_TOOLCHAIN=clang", "-DANDROID_STL=c++_shared", "-DCMAKE_BUILD_TYPE=Release", "-DANDROID_CPP_FEATURES=rtti exceptions"
            cppFlags "-D__STDC_FORMAT_MACROS", '-Ofast', '-fsigned-char', "-std=c++14", "-frtti", "-fexceptions", "-mtune=arm7", "-mfpu=vfpv3-d16", "-mfloat-abi=softfp", "-Wall",
                    "-DCOMPILE_EUROPE_ID_AND_FACE_OCR_MANAGER",
                    "-DCOMPILE_FRENCH_PASSPORT_SIGNATURE",
                    "-DCOMPILE_FRENCH_ID_BACK_OCR",
                    "-DCOMPILE_FRENCH_PASSPORT_SIGNATURE_MANAGER",
                    "-DCOMPILE_PASSPORT_AND_FACE_OCR_MANAGER",
                    "-DCOMPILE_MRZ_OCR",
                    "-DCOMPILE_FRENCH_ID_BACK_OCR_MANAGER"
        }

        ndk {
            abiFilters 'x86', 'armeabi-v7a'
        }
    }

    splits {
        abi {
            enable true
            reset()
            include 'x86', 'armeabi-v7a'
            universalApk true
        }
    }
}
    buildTypes {
       release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 
           'proguard-rules.pro'
            signingConfig signingConfigs.config
    }
}
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }

    libraryVariants.all { variant -> variant.outputs.all { output -> 
    outputFileName = "${"libScanovateImaging"}.aar" }
        }
    }

    allprojects {
            repositories {
            jcenter()
            maven {
                url "https://maven.google.com"
            }
        }    
    }
    dependencies {
        implementation 'com.google.android.gms:play-services-vision:15.0.0'
        implementation 'com.android.support:recyclerview-v7:27.1.1'
        implementation fileTree(dir: 'libs', include: ['*.jar'])
        implementation 'com.android.support.constraint:constraint-layout:1.1.0-beta6'
        implementation 'com.android.support:appcompat-v7:27.1.1'
        implementation 'com.android.support:design:27.1.1'

}

Thanks in advance!

Answer 1

Introduction

I think this has been a problem for a long time (judging by the complaints) in Android Studio (more specifically the NDK build system). Now, in the latest version, it is finally ready and working (hopefully).

Note: gradlew builds are significantly faster than using the Android Studio IDE, and can be built using a batch file script (.bat).

CMake possible problems(P = problem, C = cause, S = solution)

(P1) Android Studio rebuilds everything every time if multiple ABIs are supported See this SO Q/A.
(C1) Build variants all had the same output directory for the .o files.
(S1) You need to split out the build directory into release/debug and into the different ABIs.

My Setup (ndkBuild)

Android Studio 3.1, NDK release 10, gradle version 4.4 (plugin 3.1.0)

I have 2 libraies to build (libhello_world.so with 1 c++ file, and libjni_photoeditor.so with 24 c++ files).

I am using externalNativeBuild -> ndkBuild to build my native code (you could use CMake also, I have not tested that).

app level build.gradle:

apply plugin: 'com.android.application'
        android {
            compileSdkVersion 25

            defaultConfig {
                applicationId "xxxxxxxxxxxxxxxxxxxxx"
                minSdkVersion 16
                targetSdkVersion 16
                versionCode 1
                versionName "1.0"
                ndk {
                         abiFilters 'armeabi-v7a' //,'x86'
                }//ndk
            }//defaultConfig

            buildTypes {
                release {
                    minifyEnabled true
                    proguardFiles.add(file('proguard-android-optimize.txt'))
                    proguardFiles.add(file('proguard-rules.pro'))
                }//release
                debug {
                    minifyEnabled false
                    jniDebuggable true
                    renderscriptDebuggable true
                }//debug
            }//buildTypes

            externalNativeBuild {
                // Encapsulates your CMake build configurations.
//              cmake {
//                // Provides a relative path to your CMake build script.
//                path "src/main/cpp/CMakeLists.txt"
//              }
                ndkBuild {
                //****this is the working build****
                    path 'src/main/cpp/Android.mk'
                }//ndkBuild
            }//externalNativeBuild
        }//android

        dependencies {
        }//dependencies

Application.mk:

APP_ABI := armeabi-v7a
APP_PLATFORM := android-19
APP_STL := stlport_static

Android.mk:

#================================================
LOCAL_PATH := $(call my-dir) #only call it ONCE !
#================================================
include $(CLEAR_VARS)
LOCAL_MODULE      := hello_world
LOCAL_MULTILIB := 32
LOCAL_SRC_FILES :=  hello_world.cpp
include $(BUILD_SHARED_LIBRARY)
#================================================
include $(CLEAR_VARS)
LOCAL_MODULE      := libjni_photoeditor
LOCAL_MODULE_TAGS := optional
LOCAL_SHARED_LIBRARIES := libm liblog libjnigraphics
LOCAL_LDLIBS := -lm -llog -ljnigraphics -lbcc
LOCAL_LDLIBS := -lm -llog -ljnigraphics
LOCAL_SRC_FILES := _jni.cpp utils.cpp quantize.cpp #etc.. 24 files
LOCAL_CFLAGS := -Werror \
    -I$(OUT)/../../../../frameworks/compile/libbcc/include
LOCAL_LDFLAGS := -L$(OUT)/system/lib
include $(BUILD_SHARED_LIBRARY)

Test 1. Android Studio Build -> Build APK(s) build

(A) Modify one of my projects 24 C++ files (quantize.cpp) and rebuild.

(B) Build -> Build APK(s)

(C) Only the C:\Android\PhotoRend1\app\build\intermediates\ndkBuild\debug\obj\local\armeabi-v7a\objs-debug\jni_photoeditor\quantize.o timestamp changed (and the library).

Test 2. gradlew terminal window (command line) build

From the project root I use gradlew in a terminal window to assemble my apk.

(1) Every thing is up-to-date build:

C:\Android\PhotoRend1>gradlew assembleDebug

Starting a Gradle Daemon, 1 busy and 1 incompatible and 1 stopped Daemons could not be reused, use --status for details
> Configure project :app
> Task :app:externalNativeBuildDebug
Build hello_world armeabi-v7a
make.exe: `C:/Android/PhotoRend1/app/build/intermediates/ndkBuild/debug/obj/local/armeabi-v7a/libhello_world.so' is up to date.
Build jni_photoeditor armeabi-v7a
make.exe: `C:/Android/PhotoRend1/app/build/intermediates/ndkBuild/debug/obj/local/armeabi-v7a/libjni_photoeditor.so' is up to date.
BUILD SUCCESSFUL in 3m 46s

(2) Modify one of my projects 24 C++ files (quantize.cpp) and re-assemble.

(3) One file changes is up-to-date build:

C:\Android\PhotoRend1>gradlew assembleDebug

> Configure project :app
> Task :app:externalNativeBuildDebug
Build hello_world armeabi-v7a
make.exe: `C:/Android/PhotoRend1/app/build/intermediates/ndkBuild/debug/obj/local/armeabi-v7a/libhello_world.so' is up to date.
Build jni_photoeditor armeabi-v7a
[armeabi-v7a] Compile++ thumb: jni_photoeditor <= quantize.cpp
[armeabi-v7a] SharedLibrary  : libjni_photoeditor.so
BUILD SUCCESSFUL in 59s

(4) As you can see it did an incremental build.

Structure (with abiFilters 'x86', 'armeabi-v7a'):

C:\Android\PhotoRend1\app\build\intermediates\ndkBuild
|
V
└───debug
    └───obj
        └───local
            ├───armeabi-v7a
            │   └───objs-debug
            │       ├───hello_world
            │       └───jni_photoeditor
            └───x86
                └───objs-debug
                    ├───hello_world
                    └───jni_photoeditor

Some links: Manual NDK updates