Long callback refactor

dash/_callback_context.py

@@ -1,16 +1,22 @@
 import functools
 import warnings
 import json
+import contextvars
+
 import flask
 
 from . import exceptions
 from ._utils import AttributeDict
 
 
+context_value = contextvars.ContextVar("callback_context")
+context_value.set({})
+
+
 def has_context(func):
     @functools.wraps(func)
     def assert_context(*args, **kwargs):
-        if not flask.has_request_context():
+        if not context_value.get():
             raise exceptions.MissingCallbackContextException(
                 f"dash.callback_context.{getattr(func, '__name__')} is only available from a callback!"
             )
@@ -19,6 +25,10 @@ def assert_context(*args, **kwargs):
     return assert_context
 
 
+def _get_context_value():
+    return context_value.get()
+
+
 class FalsyList(list):
     def __bool__(self):
         # for Python 3
@@ -37,12 +47,12 @@ class CallbackContext:
     @property
     @has_context
     def inputs(self):
-        return getattr(flask.g, "input_values", {})
+        return getattr(_get_context_value(), "input_values", {})
 
     @property
     @has_context
     def states(self):
-        return getattr(flask.g, "state_values", {})
+        return getattr(_get_context_value(), "state_values", {})
 
     @property
     @has_context
@@ -64,7 +74,7 @@ def triggered(self):
         # value - to avoid breaking existing apps, add a dummy item but
         # make the list still look falsy. So `if ctx.triggered` will make it
         # look empty, but you can still do `triggered[0]["prop_id"].split(".")`
-        return getattr(flask.g, "triggered_inputs", []) or falsy_triggered
+        return getattr(_get_context_value(), "triggered_inputs", []) or falsy_triggered
 
     @property
     @has_context
@@ -90,7 +100,7 @@ def triggered_prop_ids(self):
         `if "btn-1.n_clicks" in ctx.triggered_prop_ids:
             do_something()`
         """
-        triggered = getattr(flask.g, "triggered_inputs", [])
+        triggered = getattr(_get_context_value(), "triggered_inputs", [])
         ids = AttributeDict({})
         for item in triggered:
             component_id, _, _ = item["prop_id"].rpartition(".")
@@ -146,12 +156,12 @@ def display(btn1, btn2):
                return "No clicks yet"
 
         """
-        return getattr(flask.g, "args_grouping", [])
+        return getattr(_get_context_value(), "args_grouping", [])
 
     @property
     @has_context
     def outputs_grouping(self):
-        return getattr(flask.g, "outputs_grouping", [])
+        return getattr(_get_context_value(), "outputs_grouping", [])
 
     @property
     @has_context
@@ -162,7 +172,7 @@ def outputs_list(self):
                 DeprecationWarning,
             )
 
-        return getattr(flask.g, "outputs_list", [])
+        return getattr(_get_context_value(), "outputs_list", [])
 
     @property
     @has_context
@@ -173,7 +183,7 @@ def inputs_list(self):
                 DeprecationWarning,
             )
 
-        return getattr(flask.g, "inputs_list", [])
+        return getattr(_get_context_value(), "inputs_list", [])
 
     @property
     @has_context
@@ -183,12 +193,12 @@ def states_list(self):
                 "states_list is deprecated, use args_grouping instead",
                 DeprecationWarning,
             )
-        return getattr(flask.g, "states_list", [])
+        return getattr(_get_context_value(), "states_list", [])
 
     @property
     @has_context
     def response(self):
-        return getattr(flask.g, "dash_response")
+        return getattr(_get_context_value(), "dash_response")
 
     @staticmethod
     @has_context
@@ -221,7 +231,7 @@ def using_args_grouping(self):
         Return True if this callback is using dictionary or nested groupings for
         Input/State dependencies, or if Input and State dependencies are interleaved
         """
-        return getattr(flask.g, "using_args_grouping", [])
+        return getattr(_get_context_value(), "using_args_grouping", [])
 
     @property
     @has_context
@@ -230,7 +240,12 @@ def using_outputs_grouping(self):
         Return True if this callback is using dictionary or nested groupings for
         Output dependencies.
         """
-        return getattr(flask.g, "using_outputs_grouping", [])
+        return getattr(_get_context_value(), "using_outputs_grouping", [])
+
+    @property
+    @has_context
+    def timing_information(self):
+        return getattr(flask.g, "timing_information", {})
 
 
 callback_context = CallbackContext()

dash/_utils.py

@@ -217,3 +217,9 @@ def gen_salt(chars):
     return "".join(
         secrets.choice(string.ascii_letters + string.digits) for _ in range(chars)
     )
+
+
+def coerce_to_list(obj):
+    if not isinstance(obj, (list, tuple)):
+        return [obj]
+    return obj

dash/_validate.py

@@ -7,7 +7,7 @@
 from ._grouping import grouping_len, map_grouping
 from .development.base_component import Component
 from . import exceptions
-from ._utils import patch_collections_abc, stringify_id, to_json
+from ._utils import patch_collections_abc, stringify_id, to_json, coerce_to_list
 
 
 def validate_callback(outputs, inputs, state, extra_args, types):
@@ -479,3 +479,35 @@ def validate_module_name(module):
             "The first attribute of dash.register_page() must be a string or '__name__'"
         )
     return module
+
+
+def validate_long_callbacks(callback_map):
+    # Validate that long callback side output & inputs are not circular
+    # If circular, triggering a long callback would result in a fatal server/computer crash.
+    all_outputs = set()
+    input_indexed = {}
+    for callback in callback_map.values():
+        out = coerce_to_list(callback["output"])
+        all_outputs.update(out)
+        for o in out:
+            input_indexed.setdefault(o, set())
+            input_indexed[o].update(coerce_to_list(callback["raw_inputs"]))
+
+    for callback in (x for x in callback_map.values() if x.get("long")):
+        long_info = callback["long"]
+        progress = long_info.get("progress", [])
+        running = long_info.get("running", [])
+
+        long_inputs = coerce_to_list(callback["raw_inputs"])
+        outputs = set([x[0] for x in running] + progress)
+        circular = [
+            x
+            for x in set(k for k, v in input_indexed.items() if v.intersection(outputs))
+            if x in long_inputs
+        ]
+
+        if circular:
+            raise exceptions.LongCallbackError(
+                f"Long callback circular error!\n{circular} is used as input for a long callback"
+                f" but also used as output from an input that is updated with progress or running argument."
+            )