Lnd: mobile: starting lnd again after stopDaemon results in crash

[hsjoberg]

There are four things that need to be addressed for restart to work properly on mobile builds. Links tp the PR's will be here once they are up.

• [ ] [Fix signal.go channel and state. Currently the state is not cleaned.](https://github.com/lightningnetwork/lnd/pull/4590)
• [x] [Properly call btcwallet.Loader.UnloadWallet on shutdown](https://github.com/lightningnetwork/lnd/pull/4591)
• [ ] [Fix (re-)initialization of falafel listeners](https://github.com/lightninglabs/falafel/pull/8)
• [ ] [Update mobile package to support the new falafel changes](https://github.com/lightningnetwork/lnd/pull/4599)

Old message:

This is on Android, I cannot test if the same thing happens on iOS builds.

Background

Attempting to "restart" lnd by running stopDaemon and then starting lnd again with the normal start entry from the mobile package results in a crash.

E/Go: panic: close of closed channel
    goroutine 270 [running]:
    github.com/lightningnetwork/lnd/signal.mainInterruptHandler()
        /home/coco/go/src/github.com/lightningnetwork/lnd/signal/signal.go:82 +0x26e
    created by github.com/lightningnetwork/lnd/signal.Intercept
        /home/coco/go/src/github.com/lightningnetwork/lnd/signal/signal.go:39 +0xe1
A/libc: Fatal signal 6 (SIGABRT), code -6 (SI_TKILL) in tid 20434 (Thread-5), pid 20335 (example.lndtest)

Lnd logs this:

2020-07-28 17:27:54.027 [INF] LTND: REST API is disabled!
2020-07-28 17:27:54.028 [INF] LTND: Listening on the p2p interface is disabled!
2020-07-28 17:27:54.028 [INF] LTND: Version: 0.10.99-beta commit=clock/v1.0.0-246-g22cd1203fe96a1417b428a009f4e28d31f921d85, build=development, logging=default
2020-07-28 17:27:54.028 [INF] LTND: Active chain: Bitcoin (network=testnet)
2020-07-28 17:27:54.028 [INF] LTND: Opening the main database, this might take a few minutes...
2020-07-28 17:27:54.031 [INF] CHDB: Checking for schema update: latest_version=17, db_version=17
2020-07-28 17:27:54.032 [INF] LTND: Database now open (time_to_open=3.3948ms)!

This is on master at the time of writing (22cd1203fe96a1417b428a009f4e28d31f921d85), but the bug has existed since the beginning of mobile builds.

Your environment

• current lnd master (22cd1203fe96a1417b428a009f4e28d31f921d85), but any version would suffice
• Android build (compiled .aar file under Linux)

Steps to reproduce

I have a repository up here where you can see the issue in action: https://github.com/hsjoberg/lndmobile-speed-tests
Monitor via logcat.

To test: Click on writeConfig, then startLnd, then InitWallet.
After lnd has opened the wallet, click on stopDaemon. Tying to run startLnd again will result in a crash.

My guess is that some subserver or something isn't properly stopped.
I would be happy to help on this issue, this is really important for me. Although I don't know what's wrong.

Expected behaviour

Running start after stopDaemon should start the lnd again.

Actual behaviour

Lnd crashes (which makes the main android app crash as well).

[halseth]

Thanks for raising it, it is something we have been aware of from the beginning. Definitely something that would be nice to fix, I think a prerequisite would be #3982

[weaklysubjective]

Confirming similar behavior on iOS. Attached image shows GRPC debug log. As noted in issue #4500 , this too results in "leaking" promise.

[weaklysubjective]

Confirming behavior on iOS with a different log

2020-08-05 18:35:42.945 [INF] LTND: Version: 0.10.99-beta commit=clock/v1.0.0-217-g77549f1fb8f046fc565d42151a4ae3900391170e-dirty, build=development, logging=default
2020-08-05 18:35:42.945 [INF] LTND: Active chain: Bitcoin (network=testnet)
2020-08-05 18:35:42.945 [INF] LTND: Opening the main database, this might take a few minutes...
2020-08-05 18:35:42.947 [INF] LTND: Gracefully shutting down.
panic: close of closed channel

goroutine 38660 [running]:
github.com/lightningnetwork/lnd/signal.mainInterruptHandler()
go/src/github.com/lightningnetwork/lnd/signal/signal.go:82 +0x224
created by github.com/lightningnetwork/lnd/signal.Intercept
go/src/github.com/lightningnetwork/lnd/signal/signal.go:39 +0xcc

[hsjoberg]

I've now opened pull requests covering everything that is needed to fix restarting lnd.