Improve handling of closed debug processes

Currently the debug processes can be closed but the user may not be
notified. This can lead to them submitting commands that don't do
anything with no feedback.

These changes to `mdb/mdb_client.py` and `mdb/mdb_shell.py` provide a
warning when all debug processes `client.dbg_procs` are closed.

This may also paves the way for handling debug session restarts (pending
a re-write of the mdb launcher).

mdb/mdb_client.py

@@ -32,17 +32,19 @@ def __init__(self, prog_opts: Prog_opts) -> None:
     def close_procs(self) -> None:
         """Close all open processes."""
 
-        with Progress(
-            TextColumn("[progress.description]{task.description}"),
-            BarColumn(),
-            MofNCompleteColumn(),
-        ) as progress:
-            connect_progress = progress.add_task(
-                "Closing processes...", total=self.ranks
-            )
-            for proc in self.dbg_procs:
-                proc.close()
-                progress.advance(connect_progress)
+        if self.dbg_procs:
+            with Progress(
+                TextColumn("[progress.description]{task.description}"),
+                BarColumn(),
+                MofNCompleteColumn(),
+            ) as progress:
+                connect_progress = progress.add_task(
+                    "Closing processes...", total=self.ranks
+                )
+                for proc in self.dbg_procs:
+                    proc.close()
+                    progress.advance(connect_progress)
+            self.dbg_procs = []
         return
 
     def clear_stdout(self) -> None:

mdb/mdb_shell.py

@@ -17,6 +17,7 @@
 
 import matplotlib.pyplot as plt
 import numpy as np
+import pexpect  # type: ignore
 
 from .utils import (
     parse_ranks,
@@ -26,7 +27,7 @@
 )
 
 if TYPE_CHECKING:
-    from pexpect import spawn  # type: ignore
+    from pexpect import spawn
 
     from .mdb_attach import Prog_opts
     from .mdb_client import Client
@@ -237,7 +238,12 @@ def send_command(command: str, rank: int) -> None:
             select = parse_ranks(commands[0])
             command = " ".join(commands[1:])
 
-        self.client.pool.starmap(send_command, zip(itertools.repeat(command), select))
+        try:
+            self.client.pool.starmap(
+                send_command, zip(itertools.repeat(command), select)
+            )
+        except pexpect.EOF:
+            self.client.close_procs()
 
         return
 
@@ -384,8 +390,16 @@ def status_to_color(rank: int, at_breakpoint: bool) -> str:
 
         return
 
+    def precmd(self, line: str) -> str:
+        """Override Cmd.precmd() to only run the command if debug processes are open."""
+        if self.client.dbg_procs or line in ["quit", "EOF"]:
+            return line
+        else:
+            print("warning: no debug processes running. Please relaunch the debugger")
+            return "NULL"
+
     def preloop(self) -> None:
-        """Override cmd preloop method to load mdb history."""
+        """Override Cmd.preloop() to load mdb history."""
 
         readline.parse_and_bind('"\\e[A": history-search-backward')
         readline.parse_and_bind('"\\e[B": history-search-forward')
@@ -396,7 +410,7 @@ def preloop(self) -> None:
         return
 
     def postloop(self) -> None:
-        """Override cmd postloop method to save mdb history and close gdb processes."""
+        """Override Cmd.postloop() to save mdb history and close gdb processes."""
 
         readline.set_history_length(self.hist_filesize)
         readline.write_history_file(self.hist_file)
@@ -429,8 +443,13 @@ def send_interrupt(rank: int) -> None:
     def default(self, line: str) -> bool:  # type: ignore[override]
         """Method called on an input line when the command prefix is not recognized."""
         if line == "EOF":
+            # Cmd converts CTRL+D to "EOF"
             self.onecmd("quit")
             return True
+        elif line == "NULL":
+            # do nothing
+            # useful to have a fake command for precmd()
+            return False
         else:
             print(
                 f"unrecognized command [{line}]. Type help to find out list of possible commands."