better handler of Exceptions in async contexts

Author: bfredl

neovim/api/nvim.py

@@ -2,6 +2,8 @@
 import functools
 import os
 
+from traceback import format_exc, format_stack
+
 from msgpack import ExtType
 
 from .buffer import Buffer
@@ -204,9 +206,9 @@ def out_write(self, msg):
         """Print `msg` as a normal message."""
         return self._session.request('vim_out_write', msg)
 
-    def err_write(self, msg):
+    def err_write(self, msg, async=False):
         """Print `msg` as an error message."""
-        return self._session.request('vim_err_write', msg)
+        return self._session.request('vim_err_write', msg, async=async)
 
     def quit(self, quit_command='qa!'):
         """Send a quit command to Nvim.
@@ -226,6 +228,29 @@ def new_highlight_source(self):
         """Return new src_id for use with Buffer.add_highlight."""
         return self.current.buffer.add_highlight("", 0, src_id=0)
 
+    def async_call(self, fn, *args, **kwargs):
+        """Schedule `fn` to be called by the event loop soon.
+
+        This function is thread-safe, and is the only way code not
+        on the main thread could interact with nvim api objects.
+
+        This function can also be called in a synchronous
+        event handler, just before it returns, to defer execution
+        that shouldn't block neovim.
+        """
+        call_point = ''.join(format_stack(None, 5)[:-1])
+
+        def handler():
+            try:
+                fn(*args, **kwargs)
+            except Exception as err:
+                msg = ("error caught while executing async callback:\n"
+                       "{!r}\n{}\n \nthe call was requested at\n{}"
+                       .format(err, format_exc(5), call_point))
+                self.err_write(msg, async=True)
+                raise
+        self._session.threadsafe_call(handler)
+
 
 class Current(object):
 

neovim/msgpack_rpc/session.py

@@ -31,7 +31,11 @@ def __init__(self, async_session):
     def threadsafe_call(self, fn, *args, **kwargs):
         """Wrapper around `AsyncSession.threadsafe_call`."""
         def handler():
-            fn(*args, **kwargs)
+            try:
+                fn(*args, **kwargs)
+            except Exception:
+                warn("error caught while excecuting async callback\n%s\n",
+                     format_exc())
 
         def greenlet_wrapper():
             gr = greenlet.greenlet(handler)
@@ -197,6 +201,7 @@ def handler():
             except Exception:
                 warn("error caught while processing notification '%s %s': %s",
                      name, args, format_exc())
+
             debug('greenlet %s is now dying...', gr)
 
         gr = greenlet.greenlet(handler)

neovim/plugin/host.py

@@ -6,10 +6,11 @@
 import os
 import os.path
 
+from traceback import format_exc
+
 from ..api import DecodeHook
 from ..compat import IS_PYTHON3, find_module
 
-
 __all__ = ('Host')
 
 logger = logging.getLogger(__name__)
@@ -76,7 +77,13 @@ def _on_notification(self, name, args):
             return
 
         debug('calling notification handler for "%s", args: "%s"', name, args)
-        handler(*args)
+        try:
+            handler(*args)
+        except Exception as err:
+            msg = ("error caught in async handler '{} {}':\n{!r}\n{}"
+                   .format(name, args, err, format_exc(5)))
+            self.nvim.err_write(msg, async=True)
+            raise
 
     def _load(self, plugins):
         for path in plugins: