Android support

[krisskross]

As I try to phase users over from lmdbjni to lmdbjava it might be worth considering having support for Android also. The current lmdbjni release for android are built manually using the Android NDK through the ARM toolchain.

Since there are also other platforms such as MIPS we might choose not want to have an automated build procedure, but instead let users build releases at their own convince?

Thoughts?

[benalexau]

There are several pieces to get this working:

1. Ensuring JNR works at all with Android
2. Building the LMDB native library for Android
3. Resolving any LmdbJava-specific interop issues (eg buffers, unsafe, reflection etc)
4. Continuous integration of the resulting LmdbJava Android integration

On the first item, I'm unclear if JNR works with Android:

• JNR-FFI doesn't support for Andoird jnr/jnr-ffi#37
• Support for android jnr/jffi#17
• jffi doesn't support for Android at all. jnr/jffi#44

On the second item, a quick look at the NDK Samples suggests compiling the native library on Travis should work. As such we could compile and deploy an additional LmdbJava Native target.

Item three is stalled pending resolution of items one and two.

Item four looks achievable on Travis given Android is officially supported.

So the main question is clearly surrounding JNR. Maybe we (or an interested community member?) could start with a "hello world" test of JNR calling any Android library, preferably migrating that to a public GitHub project and verifying via Travis. At least this would offer useful details for the earlier-mentioned JNR tickets (ie a proof of concept or specific issues to work through for the JNR project team).

[octalide]

I would love to see this come to fruition.

[mtunnel]

Is there any chance in the status of this ticket? Can LmdbJava be run android now?

[EternalDeiwos]

lmdbjava/native#5 should add the necessary native libraries for armv7, armv8 and x86 which should cross off item two on this list.

I'll admit when I opened the issue at lmdbjava/native#4 I hadn't considered that there might be more blocking the use of lmdb on Android.

A quick look at recent issues/PRs on jnr/jnr-ffi had me find these:

• Throws NullPointerException when running on Android Emulator jnr/jnr-ffi#173 / Platform: fix arch NPE and add arm cpus #173 jnr/jnr-ffi#182
• Could not load the native lib from jffi-native when launching in Android system jnr/jffi#57 / Update ARM32 binary with hardfp version. jnr/jffi#58 / Platform.determineCPU to recognize armv7l as 32bit jnr/jffi#59
• . so file failed to load interface jnr/jnr-ffi#114

The first two seem to have been resolved (and fairly recently at that, the changes haven't made it into a release yet) -- would it be wishful thinking to hope that JNR-FFI could "just work" after these changes?

[benalexau]

@EternalDeiwos would you be happy to try the "hello world" test I mentioned above on Android? I do not have any Android developer toolchain or experience to move this forward myself. If you run into issue with "hello world" it's perhaps best to take it up with the JNR project so they have something specific to address.

Assuming Android theoretically works with JNR, from an LmdbJava perspective the only obvious thing we'd need to do is add some code to Library to auto-detect Android and try to find the correct system library. It may be a good opportunity to improve the library location logic as discussed in lmdbjava/native#3.

[EternalDeiwos]

I've set up a project with the example code and I'm running into the exact error they describe in the above issues. I've asked about a release containing those fixes so we'll wait and see whether that solves the problem.

[tomholub]

@EternalDeiwos do you know who is responsible for new releases? Who to ping? I would sure like to see if you can get a hello world sample working after my fixes 🙏

[EternalDeiwos]

@tomholub I see jnr-ffi and jffi both had releases containing your latest fixes on this topic approximately 24 days ago. It also seems that @benalexau published lmdbjava 0.7.0 28 days ago which seems to have just missed those releases.

I can fire up my test setup of lmdbjava again and give it a try with the new jffi version. I'll let you know as soon as I can.

[EternalDeiwos]

@tomholub @benalexau compiles and runs quite happily as far as I can see -- the only caveat is that due to some of the Java features in use it'll only let me build with minSdkVersion = 26 (Android O), so backward compatibility might be a bit of a problem for some. Haven't tried anything serious yet -- just getting it to compile really. Will try a bit more when I get a chance.

[EternalDeiwos]

@tomholub I've been doing some testing with the jnr-ffi library and it still isn't working. I'll mention you in the relevant issues there.

[mikemee]

@EternalDeiwos Curious if you abandoned this, or if you're still waiting on jnr-ffi issues to be resolved? I'm looking for LMDB on Android as well.

[EternalDeiwos]

@mikemee I'm still bumping this occasionally. See jnr/jnr-ffi#173 for the latest.