Dafny language server does not clean up z3 child processes

[mitchellholt]

Dafny version

4.4.0

Code to produce this issue

class BoundedQueue<T(0)>
{
    ghost var Elements : seq<T>
    ghost var Repr : set<object>
    ghost const max : nat
    var arr : array<T>
    var wr : nat
    var rd : nat

    ghost predicate Valid()
        reads this, Repr
        ensures Valid() ==> this in Repr && |Elements| <= max
    {
        this in Repr
        && arr in Repr
        && max > 0
        && |Elements| <= max
        && |Elements| % max == wr - rd % max
        && (|Elements| > 0 ==> (forall k :: 0 <= k < (wr - rd) % max ==>
            Elements[k] == arr[(wr - k) % max]))
    }

    constructor(max : nat)
        requires max > 0
        ensures Valid() && fresh(Repr)
        ensures wr == rd == 0 && Elements == [] && this.max == max
    {
        this.max := max;
        arr := new T[max];
        wr := 0;
        rd := 0;
        Repr := {this, arr};
        Elements := [];
    }
}

Command to run and resulting output

For whatever reason, dafny takes a long time to verify this code via z3 (my code is probably pretty terrible). I haven't actually waited around for long enough before to see if z3 terminates. When I run dafny verify and send an interrupt signal, dafny will clean up the z3 child process:

$ dafny verify oops.dfy
^C
$ ps -ef | grep z3
mitchell  294922  236630  0 09:07 pts/2    00:00:00 grep --color=auto z3

However, when I open the file in my editor, wait for the language server to start sending some alerts, and then close my editor, there is still an instance of z3 running:

$ nvim oops.dfy
$ ps -ef | grep z3
mitchell  299126    1444 99 09:15 ?        00:00:17 /home/mitchell/Documents/CSSE3100/dafny/Binaries/z3/bin/z3-4.12.1 -smt2 -in
mitchell  299268  236630  0 09:15 pts/2    00:00:00 grep --color=auto z3

The only other instance of neovim running on my machine was inside a separate tmux session, and it was not running anything dafny-related. I concluded that the language server probably just isn't cleaning up the child z3 process, whereas verify does.

What happened?

I expected that the dafny server would clean up its child processes (although maybe this is a neovim thing?)

What type of operating system are you experiencing the problem on?

Linux

[keyboardDrummer]

I can confirm this issue does not occur when using VSCode. dafny server has code to kill z3 processes when it exits, but I'm not sure if this only runs when you shutdown the language server through its shutdown and exit APIs, or also when you send a sigterm. Do you know how neovim kills its LSP servers? Maybe you could do a little experiment with killing the LSP server yourself to see if it then cleans up the Z3 processes. If you can confirm there's a Dafny LSP server issue that would help prioritize this.

[mitchellholt]

I'm not sure how neovim kills LSP servers. I tried killing the server with SIGTERM, but this doesn't clean up all of the instances of z3 or dotnet:

$ ps -ef | grep dafny
mitchell  534157  505209  0 08:44 pts/3    00:00:00 grep --color=auto dafny
--- Open oops.dfy in neovim in a different tmux pane ---
$ ps -ef | grep dafny
mitchell  537144  537140  0 08:48 ?        00:00:00 bash /home/mitchell/bin/dafny server
mitchell  537152  537144 44 08:48 ?        00:00:03 /usr/bin/dotnet /home/mitchell/Documents/CSSE3100/dafny/Scripts/../Binaries/Dafny.dll server
mitchell  537238  537152 79 08:48 ?        00:00:03 /home/mitchell/Documents/CSSE3100/dafny/Binaries/z3/bin/z3-4.12.1 -smt2 -in
mitchell  537239  537152  0 08:49 ?        00:00:00 /home/mitchell/Documents/CSSE3100/dafny/Binaries/z3/bin/z3-4.12.1 -smt2 -in
mitchell  537288  536871  0 08:49 pts/4    00:00:00 grep --color=auto dafny
$ kill -SIGTERM 537144
$ ps -ef | grep dafny
mitchell  537152    1444  7 08:48 ?        00:00:03 /usr/bin/dotnet /home/mitchell/Documents/CSSE3100/dafny/Scripts/../Binaries/Dafny.dll server
mitchell  537238  537152 97 08:48 ?        00:00:43 /home/mitchell/Documents/CSSE3100/dafny/Binaries/z3/bin/z3-4.12.1 -smt2 -in
mitchell  537239  537152  0 08:49 ?        00:00:00 /home/mitchell/Documents/CSSE3100/dafny/Binaries/z3/bin/z3-4.12.1 -smt2 -in
mitchell  537663  536871  0 08:49 pts/4    00:00:00 grep --color=auto dafny

I hope this helps, let me know if there is anything else I can do or if I have misunderstood you.

[keyboardDrummer]

but this doesn't clean up all of the instances of z3 or dotnet

When I have a dafny server process and I kill it with SIGTERM, I see that it and the Z3 processes under it terminate. I'm not sure what you mean by the dotnet instances are not cleaned up. Isn't that the process you're terminating? What process is being terminated by your SIGTERM then?