Add decorator for handing child-process side of pipe

__init__.py

@@ -34,6 +34,8 @@ def register():
             return new_module
 
         blender_common = reload_mod('blender_common')
+        subprocess_adapter = reload_mod('subprocess_adapter')
+        bpackage = reload_mod('bpackage')
 
     else:
         from . import blender_common

blender_common.py

@@ -5,7 +5,7 @@ import logging
 import bpy
 from bpy.props import CollectionProperty
 from bpy.types import PropertyGroup, Panel, UIList, AddonPreferences, Operator
-from .subprocess_adapter import subprocess_operator
+from .subprocess_adapter import subprocess_operator, subprocess_function
 from . import bpackage as bpkg
 
 class RepositoryProperty(PropertyGroup):
@@ -42,27 +42,30 @@ class PackagePreferences(AddonPreferences):
 
 @subprocess_operator
 class PACKAGE_OT_refresh(Operator):
+    """
+    Operator which checks for updates to known package lists
+    """
     bl_idname = "package.refresh"
-    bl_label = "Update package list(s)"
+    bl_label = "Refresh package list(s)"
 
     log = logging.getLogger(__name__)
 
     def invoke(self, context, event):
         prefs = context.user_preferences.addons[__package__].preferences
+
         if 'repositories' not in prefs:
             return {'FINISHED'}
+
         # HACK: just do the active repo for now
         repo = bpkg.Repository(prefs['repositories'][prefs.active_repository].to_dict())
-        self.proc_args = []
-        self.proc_kwargs = {'target': repo.refresh}
 
-    def execute(self, context, event):
+        self.proc_kwargs = {'target': subprocess_function(repo.refresh, pipe=self.pipe)}
-        pass
         
     def modal(self, context, event):
         # try:
         self.poll_subprocess()
         # except:
+        return {'RUNNING_MODAL'}
 
     def handle_response(self, resp):
         self.report({'INFO'}, "Request returned %s" % resp)

subprocess_adapter.py

@@ -2,6 +2,8 @@ import logging
 from multiprocessing import Process, Pipe
 from bpy.types import Operator
 
+log = logging.getLogger(__name__)
+
 def subprocess_operator(cls: Operator, polling_interval=.01) -> Operator:
     """
     Class decorator which wraps Operator methods with setup code for running a subprocess.
@@ -34,9 +36,10 @@ def subprocess_operator(cls: Operator, polling_interval=.01) -> Operator:
 
     def decorate_invoke(orig_invoke):
         def invoke(self, context, event):
+            self.pipe = Pipe()
+
             orig_invoke(self, context, event)
 
-            self.pipe = Pipe()
             self.proc = Process(
                     *getattr(self, 'proc_args', []),
                     **getattr(self, 'proc_kwargs', [])
@@ -57,15 +60,19 @@ def subprocess_operator(cls: Operator, polling_interval=.01) -> Operator:
         self.log.debug("polling")
         try:
             if self.pipe[0].poll():
-                newdata = self.pipe[0].recv()
+                resp = self.pipe[0].recv()
+                assert(isinstance(resp, SubprocessMessage))
             else:
-                newdata = None
+                resp = None
         except EOFError:
             self.log.debug("done polling")
             return {'FINISHED'}
 
-        if newdata is not None:
+        if resp is not None:
-            self.handle_response(newdata) #TODO: make this a customizable callback
+            if resp.exception is not None:
+                raise resp.exception
+            elif resp.data is not None:
+                self.handle_response(resp.data) #TODO: make this a customizable callback
             # this should allow chaining of multiple subprocess in a single operator
 
         return {'PASS_THROUGH'}
@@ -75,3 +82,28 @@ def subprocess_operator(cls: Operator, polling_interval=.01) -> Operator:
     setattr(cls, 'poll_subprocess', poll_subprocess)
 
     return cls
+
+def subprocess_function(func, *args, pipe, **kwargs):
+    """
+    Wrapper which feeds the return val of `func` into the latter end of a pipe
+    """
+    def wrapper(*args, **kwargs):
+        # we have to explicitly close the end of the pipe we are NOT using,
+        # otherwise no exception will be generated when the other process closes its end.
+        pipe[0].close()
+
+        try:
+            return_val = func(*args, **kwargs)
+            pipe[1].send(SubprocessMessage(data=return_val))
+        except Exception as err:
+            log.debug("Caught exception from subprocess: %s", err)
+            pipe[1].send(SubprocessMessage(exception=err))
+        finally:
+            pipe[1].close()
+
+    return wrapper
+
+class SubprocessMessage:
+    def __init__(self, exception=None, data=None):
+        self.exception = exception
+        self.data = data