Repository: dls-controls/aioca

Issue:
Provide mechanism to access Channels
It would be useful to be able to interrogate the currently active Channels in `aioca`, to enable things like counting the number of open/closed connections.

This will need some new public getter functions, and probably a small amount of re-naming of various files and objects to make them public.

Comments:

Patch:
diff --git a/.github/workflows/code.yml b/.github/workflows/code.yml
index b26b076..95e0c7c 100644
--- a/.github/workflows/code.yml
+++ b/.github/workflows/code.yml
@@ -42,7 +42,7 @@ jobs:
 
       - name: Install Python Dependencies
         run: |
-          pip install pipenv build
+          pip install pipenv==2022.4.8 build
           pipenv install --dev --${{ matrix.pipenv }} --python $(python -c 'import sys; print(sys.executable)') && pipenv graph
 
       - name: Create Sdist and Wheel
diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 9522c2b..8245674 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -9,7 +9,9 @@ and this project adheres to `Semantic Versioning <https://semver.org/spec/v2.0.0
 Unreleased_
 -----------
 
-Nothing yet
+Added: 
+
+- `Add methods to allow inspecting Channels <../../pull/38>`_
 
 1.6_ - 2023-04-06
 -----------------
diff --git a/aioca/__init__.py b/aioca/__init__.py
index 11d056e..90ba0a4 100644
--- a/aioca/__init__.py
+++ b/aioca/__init__.py
@@ -24,12 +24,14 @@ from epicscorelibs.ca.dbr import (
 from ._catools import (
     CAInfo,
     CANothing,
+    ChannelInfo,
     Subscription,
     caget,
     cainfo,
     camonitor,
     caput,
     connect,
+    get_channel_infos,
     purge_channel_caches,
     run,
 )
@@ -45,6 +47,8 @@ __all__ = [
     "cainfo",  # Returns ca_info describing PV connection
     "CAInfo",  # Ca info object
     "CANothing",  # No value
+    "ChannelInfo",  # Information about a particular channel
+    "get_channel_infos",  # Return information about all channels
     "purge_channel_caches",  # Get rid of old channels
     "run",  # Run one aioca coroutine and clean up
     # The version of aioca
diff --git a/aioca/_catools.py b/aioca/_catools.py
index 6b99166..dfb96a8 100644
--- a/aioca/_catools.py
+++ b/aioca/_catools.py
@@ -54,6 +54,9 @@ class ValueEvent(Generic[T]):
         self._event.set()
         self.value = value
 
+    def is_set(self) -> bool:
+        return self._event.is_set()
+
     def clear(self):
         self._event.clear()
         self.value = RuntimeError("No value set")
@@ -252,6 +255,14 @@ class Channel(object):
         """Removes the given subscription from the list of receivers."""
         self.__subscriptions.remove(subscription)
 
+    def count_subscriptions(self) -> int:
+        """Return the number of currently active subscriptions for this Channel"""
+        return len(self.__subscriptions)
+
+    def connected(self) -> bool:
+        """Return whether this Channel is currently connected to a PV"""
+        return self.__connect_event.is_set()
+
     async def wait(self):
         """Waits for the channel to become connected if not already connected."""
         await self.__connect_event.wait()
@@ -278,6 +289,9 @@ class ChannelCache(object):
             self.__channels[name] = channel
             return channel
 
+    def get_channels(self) -> List[Channel]:
+        return list(self.__channels.values())
+
     def purge(self):
         """Purges all the channels in the cache: closes them right now.  Will
         cause other channel access to fail, so only to be done on shutdown."""
@@ -1081,6 +1095,32 @@ def get_channel(pv: str) -> Channel:
     return channel
 
 
+class ChannelInfo:
+    """Information about a particular Channel
+
+    Attributes:
+        name: Process Variable name the Channel is targeting
+        connected: True if the Channel is currently connected
+        subscriber_count: Number of clients subscribed to this Channel"""
+
+    name: str
+    connected: bool
+    subscriber_count: int
+
+    def __init__(self, name, connected, subscriber_count):
+        self.name = name
+        self.connected = connected
+        self.subscriber_count = subscriber_count
+
+
+def get_channel_infos() -> List[ChannelInfo]:
+    """Return information about all Channels"""
+    return [
+        ChannelInfo(channel.name, channel.connected(), channel.count_subscriptions())
+        for channel in _Context.get_channel_cache().get_channels()
+    ]
+
+
 # Another delicacy arising from relying on asynchronous CA event dispatching is
 # that we need to manually flush IO events such as caget commands.  To ensure
 # that large blocks of channel access activity really are aggregated we used to
diff --git a/docs/api.rst b/docs/api.rst
index 2a58dc4..ec0888a 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -141,6 +141,11 @@ event loop. A convenience function is provided to do this:
 
 .. autofunction:: run
 
+.. autoclass:: ChannelInfo()
+    :members:
+
+.. autofunction:: get_channel_infos
+
 ..  _Values:
 
 Working with Values


Test patch:
diff --git a/tests/test_aioca.py b/tests/test_aioca.py
index bd1c28b..56ef8aa 100644
--- a/tests/test_aioca.py
+++ b/tests/test_aioca.py
@@ -24,6 +24,7 @@ from aioca import (
     camonitor,
     caput,
     connect,
+    get_channel_infos,
     purge_channel_caches,
     run,
 )
@@ -610,3 +611,35 @@ def test_import_in_a_different_thread(ioc: subprocess.Popen) -> None:
         ]
     )
     assert output.strip() == b"42"
+
+
+@pytest.mark.asyncio
+async def test_channel_connected(ioc: subprocess.Popen) -> None:
+    values: List[AugmentedValue] = []
+    m = camonitor(LONGOUT, values.append, notify_disconnect=True)
+
+    # Wait for connection
+    await poll_length(values)
+
+    channels = get_channel_infos()
+    assert len(channels) == 1
+
+    channel = channels[0]
+    # Initially the PV is connected and has one monitor
+    assert channel.name == LONGOUT
+    assert channel.connected
+    assert channel.subscriber_count == 1
+
+    ioc.communicate("exit")
+    await asyncio.sleep(0.1)
+
+    # After IOC exits the channel is disconnected but still has one monitor
+    channel = get_channel_infos()[0]
+    assert not channel.connected
+    assert channel.subscriber_count == 1
+
+    m.close()
+
+    # Once the monitor is closed the subscription disappears
+    channel = get_channel_infos()[0]
+    assert channel.subscriber_count == 0