Android

Demo applications and tutorials

Demo applications with code walk-through can be find in this github repo.

Publishing

Release

Release artifacts are published to jcenter:

repositories {
    jcenter()
}

dependencies {
    implementation 'org.pytorch:pytorch_android:1.3.0'
    implementation 'org.pytorch:pytorch_android_torchvision:1.3.0'
}

Nightly

Nightly(snapshots) builds are published every night from master branch to nexus sonatype snapshots repository

To use them repository must be specified explicitly:

repositories {
    maven {
        url "https://oss.sonatype.org/content/repositories/snapshots"
    }
}

dependencies {
    ...
    implementation 'org.pytorch:pytorch_android:1.4.0-SNAPSHOT'
    implementation 'org.pytorch:pytorch_android_torchvision:1.4.0-SNAPSHOT'
    ...
}

The current nightly(snapshots) version is the value of VERSION_NAME in gradle.properties in current folder, at this moment it is 1.4.0-SNAPSHOT.

Building PyTorch Android from Source

In some cases you might want to use a local build of pytorch android, for example you may build custom libtorch binary with another set of operators or to make local changes.

For this you can use ./scripts/build_pytorch_android.sh script.

git clone https://github.com/pytorch/pytorch.git
cd pytorch
sh ./scripts/build_pytorch_android.sh

The workflow contains several steps:

1. Build libtorch for android for all 4 android abis (armeabi-v7a, arm64-v8a, x86, x86_64)

2. Create symbolic links to the results of those builds: android/pytorch_android/src/main/jniLibs/${abi} to the directory with output libraries android/pytorch_android/src/main/cpp/libtorch_include/${abi} to the directory with headers. These directories are used to build libpytorch.so library that will be loaded on android device.

3. And finally run gradle in android/pytorch_android directory with task assembleRelease

Script requires that Android SDK, Android NDK and gradle are installed. They are specified as environment variables:

ANDROID_HOME - path to Android SDK

ANDROID_NDK - path to Android NDK

GRADLE_HOME - path to gradle

After successful build you should see the result as aar file:

$ find pytorch_android/build/ -type f -name *aar
pytorch_android/build/outputs/aar/pytorch_android.aar
pytorch_android_torchvision/build/outputs/aar/pytorch_android.aar
libs/fbjni_local/build/outputs/aar/pytorch_android_fbjni.aar

It can be used directly in android projects, as a gradle dependency:

allprojects {
    repositories {
        flatDir {
            dirs 'libs'
        }
    }
}

android {
    ...
    packagingOptions {
        pickFirst "**/libfbjni.so"
    }
    ...
}

dependencies {
    implementation(name:'pytorch_android', ext:'aar')
    implementation(name:'pytorch_android_torchvision', ext:'aar')
    implementation(name:'pytorch_android_fbjni', ext:'aar')
}

At the moment for the case of using aar files directly we need additional configuration due to packaging specific (libfbjni.so is packaged in both pytorch_android_fbjni.aar and pytorch_android.aar).

packagingOptions {
    pickFirst "**/libfbjni.so"
}

More Details

You can find more details about the PyTorch Android API in the Javadoc.