Add decorator for handing child-process side of pipe

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:
-            self.handle_response(newdata) #TODO: make this a customizable callback
+        if resp is not None:
+            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