preserve connection order in blinker

docs/plugins.rst

@@ -94,9 +94,12 @@ which you map the signals to your plugin logic. Let's take a simple example::
     your ``register`` callable or they will be garbage-collected before the
     signal is emitted.
 
-If multiple plugins connect to the same signal, there is no way to guarantee or
-control in which order the plugins will be executed. This is a limitation
-inherited from Blinker_, the dependency Pelican uses to implement signals.
+If multiple plugins connect to the same signal, plugins will be executed in the
+order they are connected. With ``PLUGINS`` setting, order will be as defined in
+the setting. If you rely on auto-discovered namespace plugins, no ``PLUGINS``
+setting, they will be connected in the same order they are discovered (same
+order as ``pelican-plugins`` output). If you want to specify the order
+explicitly, disable auto-discovery by defining ``PLUGINS`` in the desired order.
 
 Namespace plugin structure
 --------------------------
@@ -341,4 +344,3 @@ custom article, using the ``article_generator_pretaxonomy`` signal::
 
 .. _Pip: https://pip.pypa.io/
 .. _pelican-plugins bug #314: https://github.com/getpelican/pelican-plugins/issues/314
-.. _Blinker: https://pythonhosted.org/blinker/

pelican/plugins/signals.py

@@ -1,4 +1,8 @@
-from blinker import signal
+from blinker import signal, Signal
+from ordered_set import OrderedSet
+
+# Signals will call functions in the order of connection, i.e. plugin order
+Signal.set_class = OrderedSet
 
 # Run-level signals:
 

pelican/tests/test_plugins.py

@@ -8,6 +8,7 @@
     load_plugins,
     plugin_enabled,
 )
+from pelican.plugins.signals import signal
 from pelican.tests.support import unittest
 
 
@@ -263,3 +264,23 @@ def get_plugin_names(plugins):
             self.assertTrue(plugin_enabled("pelican.plugins.ns_plugin", plugins))
             self.assertTrue(plugin_enabled("normal_plugin", plugins))
             self.assertFalse(plugin_enabled("unknown", plugins))
+
+    def test_blinker_is_ordered(self):
+        """ensure that call order is connetion order"""
+        dummy_signal = signal("dummpy_signal")
+
+        functions = []
+        expected = []
+        for i in range(50):
+            # function appends value of i to a list
+            def func(input, i=i):
+                input.append(i)
+
+            functions.append(func)
+            # we expect functions to be run in the connection order
+            dummy_signal.connect(func)
+            expected.append(i)
+
+        input = []
+        dummy_signal.send(input)
+        self.assertEqual(input, expected)

pyproject.toml

@@ -29,10 +29,11 @@ classifiers = [
 ]
 requires-python = ">=3.8.1,<4.0"
 dependencies = [
-    "blinker>=1.6.3",
+    "blinker>=1.7.0",
     "docutils>=0.20.1",
     "feedgenerator>=2.1.0",
     "jinja2>=3.1.2",
+    "ordered-set>=4.1.0",
     "pygments>=2.16.1",
     "python-dateutil>=2.8.2",
     "rich>=13.6.0",