Fix handling of multiple DynamicProvider

src/p4p/server/__init__.py

@@ -205,8 +205,9 @@ def __init__(self):
                 def testChannel(self, name): # return True, False, or DynamicProvider.NotYet
                     return name=="blah"
                 def makeChannel(self, name, peer):
-                    assert name=="blah"
-                    return self.pv
+                    if name=="blah":
+                        return self.pv
+                    # return None falls through to next source
             provider = DynamicProvider("arbitrary", DynHandler())
             server = Server(providers=[provider])
     """

src/p4p/test/test_server.py

@@ -8,7 +8,9 @@
 import threading
 
 from ..server import Server, installProvider, removeProvider, DynamicProvider, StaticProvider
+from ..server.thread import SharedPV
 from ..client.thread import Context
+from ..nt import NTScalar
 from .utils import RefTestCase
 
 
@@ -96,6 +98,24 @@ def test_client(self):
         finally:
             removeProvider("foo")
 
+class TestMultipleProviders(RefTestCase):
+    class Single(DynamicProvider):
+        def __init__(self, pv):
+            super(TestMultipleProviders.Single, self).__init__(pv, self)
+            self._name = pv
+            self._pv = SharedPV(nt=NTScalar('s'), initial=pv)
+        def testChannel(self, name):
+            return name==self._name
+        def makeChannel(self, name, peer):
+            if name==self._name:
+                return self._pv
+
+    def test_multiple(self):
+        with Server([self.Single('one'), self.Single('two')], isolate=True) as S:
+            with Context('pva', conf=S.conf(), useenv=False) as C:
+                self.assertEqual('one', C.get('one'))
+                self.assertEqual('two', C.get('two'))
+
 class TestServerConf(RefTestCase):
     def test_bad_iface(self):
         P = StaticProvider('x')

src/pvxs_source.cpp

@@ -111,11 +111,14 @@ struct DynamicSource : public server::Source
             PyErr_Print();
             PyErr_Clear();
 
+        } else if(ret.obj==Py_None) {
+            // This source will not provide.
+
         } else if(auto pv = SharedPV_unwrap(ret.obj)) {
             pv.attach(std::move(op));
 
         } else {
-            PyErr_Format(PyExc_TypeError, "makeChannel(\"%s\") must return SharedPV, not %s",
+            PyErr_Format(PyExc_TypeError, "makeChannel(\"%s\") must return SharedPV or None, not %s",
                          op->name().c_str(),
                          Py_TYPE(ret.obj)->tp_name);
             PyErr_Print();