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POSIXSpec.md

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Cardano.Launcher.POSIX

Goal

By default, the Haskell runtime and the process library we use to spawn new processes in the launcher don't catch SIGTERM signals on a unix system. This means that if we kill the launcher process, the sub-processes it has spawned will endure.

What follows are steps which explains how to test that SIGINT and SIGTERM signals are correctly handled on a unix system.

Steps

SIGINT

  • Start the launcher using stack exec -- cardano-wallet-launcher

  • In another terminal, run ps -ef | grep cardano, there should be three processes running (the launcher, the wallet and the underlying chain producer)

    $ ps -ef | grep cardano
10983  4904  0 09:42 pts/1 00:00:00 /home/user/Documents/IOHK/cardano-wallet/.stack-work/install/x86_64-linux/lts-13.8/8.6.3/bin/cardano-wallet-launcher
11003 10983 75 09:42 pts/1 00:03:30 cardano-http-bridge start --port 8080
11071 10983 58 09:42 pts/1 00:02:41 cardano-wallet-server --wallet-server-port 8090 --http-bridge-port 8080 --network mainnet

  • Send a SIGINT signal using by pressing CTRL-C in the first terminal

  • Run ps -ef | grep cardano, there's no more process running: the launcher, the wallet and the chain producer have all stopped.

SIGQUIT

  • Start the launcher using stack exec -- cardano-wallet-launcher

  • In another terminal, run ps -ef | grep cardano, there should be three processes running (the launcher, the wallet and the underlying chain producer)

    $ ps -ef | grep cardano
10983  4904  0 09:42 pts/1 00:00:00 /home/user/Documents/IOHK/cardano-wallet/.stack-work/install/x86_64-linux/lts-13.8/8.6.3/bin/cardano-wallet-launcher
11003 10983 75 09:42 pts/1 00:03:30 cardano-http-bridge start --port 8080
11071 10983 58 09:42 pts/1 00:02:41 cardano-wallet-server --wallet-server-port 8090 --http-bridge-port 8080 --network mainnet

  • Send a SIGQUIT signal using by pressing CTRL-\ in the first terminal

  • Run ps -ef | grep cardano, there's no more process running: the launcher, the wallet and the chain producer have all stopped.

SIGTERM

  • Start the launcher in background using stack exec -- cardano-wallet-launcher &
  • Run ps -ef | grep cardano and lookup the pid of the launcher process (and control that there are indeed three processes running: the launcher, the wallet and the chain producer) 
    $ ps -ef | grep cardano
10983  4904  0 09:42 pts/1 00:00:00 /home/user/Documents/IOHK/cardano-wallet/.stack-work/install/x86_64-linux/lts-13.8/8.6.3/bin/cardano-wallet-launcher
11003 10983 75 09:42 pts/1 00:03:30 cardano-http-bridge start --port 8080
11071 10983 58 09:42 pts/1 00:02:41 cardano-wallet-server --wallet-server-port 8090 --http-bridge-port 8080 --network mainnet
  • Send a SIGTERM signal to this pid using kill <pid>
  • Run ps -ef | grep cardano, there's no more process running: the launcher, the wallet and the chain producer have all stopped.

SIGKILL

Disclaimer

The semantic of SIGKILL doesn't allow us to do any clean-up after receiving it (we can't shove a signal handler for a SIGKILL!). So, if one kills the launcher, one doesn't kill the sub-processes the launcher has started. This should be handled at the OS level, or via different mechanism (like, having a shared socket between the launcher and its children).

As a consequence, sending a SIGKILL to the launcher will NOT terminates the sub-processes started by the launcher. This is, for now, a known limitation.

  • Start the launcher in background using stack exec -- cardano-wallet-launcher &
  • Run ps -ef | grep cardano and lookup the pid of the launcher process (and control that there are indeed three processes running: the launcher, the wallet and the chain producer) 
    $ ps -ef | grep cardano
10983  4904  0 09:42 pts/1 00:00:00 /home/user/Documents/IOHK/cardano-wallet/.stack-work/install/x86_64-linux/lts-13.8/8.6.3/bin/cardano-wallet-launcher
11003 10983 75 09:42 pts/1 00:03:30 cardano-http-bridge start --port 8080
11071 10983 58 09:42 pts/1 00:02:41 cardano-wallet-server --wallet-server-port 8090 --http-bridge-port 8080 --network mainnet
  • Send a SIGKILL signal to this pid using kill -9 <pid>
  • Run ps -ef | grep cardano, and control that the launcher isn't running anymore. The wallet server and the underlying chain producer should however still be up-and-running.