close and reset Python subprocess state on clear

Move popen2 reset logic to a new helper function, and call it using a
persistent onCleanup object.

Fixes #1015.

inst/private/python_ipc_popen2.m

@@ -34,7 +34,7 @@
 
 function [A, info] = python_ipc_popen2(what, cmd, varargin)
 
-  persistent fin fout pid
+  persistent cleanup fin fout pid
 
   py_startup_timeout = 30;  % seconds
 
@@ -43,24 +43,11 @@
   info = [];
 
   if (strcmp(what, 'reset'))
-    if (~isempty(pid))
-      if (verbose)
-        disp ('Closing the Python communications link.')
-      end
-    end
-    if (~isempty(fin))
-      % produces a single newline char: not sure why
-      t = fclose(fin); fin = [];
-      waitpid(pid);
-      pid = [];
-      A = (t == 0);
-    else
-      A = true;
-    end
-    if (~isempty(fout))
-      t = fclose(fout); fout = [];
-      A = A && (t == 0);
-    end
+    cleanup = [];
+    fin = [];
+    fout = [];
+    pid = [];
+    A = true;
     return
   end
 
@@ -87,6 +74,8 @@
       error('popen2() failed');
     end
 
+    cleanup = onCleanup (@() python_ipc_popen2_reset (fin, fout, pid));
+
     headers = python_header();
     fputs (fin, headers);
     fprintf (fin, '\n\n');

inst/private/python_ipc_popen2_reset.m

@@ -0,0 +1,51 @@
+%% Copyright (C) 2020 Mike Miller
+%%
+%% This file is part of OctSymPy.
+%%
+%% OctSymPy is free software; you can redistribute it and/or modify
+%% it under the terms of the GNU General Public License as published
+%% by the Free Software Foundation; either version 3 of the License,
+%% or (at your option) any later version.
+%%
+%% This software is distributed in the hope that it will be useful,
+%% but WITHOUT ANY WARRANTY; without even the implied warranty
+%% of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
+%% the GNU General Public License for more details.
+%%
+%% You should have received a copy of the GNU General Public
+%% License along with this software; see the file COPYING.
+%% If not, see <http://www.gnu.org/licenses/>.
+
+%% -*- texinfo -*-
+%% @deftypefun {@var{A} =} python_ipc_popen2_reset (@var{fin}, @var{fout}, @var{pid})
+%% Private helper function for Python IPC.
+%%
+%% @var{A} is the resulting object, which might be an error code.
+%% @end deftypefun
+
+function A = python_ipc_popen2_reset (fin, fout, pid)
+
+  verbose = ~ sympref ('quiet');
+
+  if (~ isempty (pid))
+    if (verbose)
+      disp ('Closing the Python communications link.')
+    end
+  end
+
+  if (~ isempty (fin))
+    % produces a single newline char: not sure why
+    t = fclose (fin); fin = [];
+    waitpid (pid);
+    pid = [];
+    A = (t == 0);
+  else
+    A = true;
+  end
+
+  if (~ isempty (fout))
+    t = fclose (fout); fout = [];
+    A = A && (t == 0);
+  end
+
+end