From 634fe767a9d620c8b83daa4bef436659a8511288 Mon Sep 17 00:00:00 2001
From: Ivo Hanak <hanak@ipp.cas.cz>
Date: Tue, 17 Oct 2023 17:09:57 +0200
Subject: [PATCH] Prevented unsubscribing events from a cleared channel

---
 .gitignore                  |  1 +
 epics/ca.py                 | 14 ++++++++++----
 epics/pv.py                 |  5 +++++
 tests/test_ca_clearcache.py | 22 ++++++++++++++++++----
 4 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/.gitignore b/.gitignore
index cec08d3f..c8185830 100644
--- a/.gitignore
+++ b/.gitignore
@@ -12,5 +12,6 @@ dist
 NonGit
 venv
 .vscode
+.coverage
 pyepics.egg-info
 epics.egg-info
diff --git a/epics/ca.py b/epics/ca.py
index 7c458879..64bff9cb 100755
--- a/epics/ca.py
+++ b/epics/ca.py
@@ -494,6 +494,16 @@ def clear_cache():
     multiprocessing (and is done internally by CAProcess),
     but can be useful to fully reset a Channel Access session.
     """
+    # Clear the cache of PVs used by epics.caget()-like functions
+    # by disconnecting PVs so that all subscriptions are released
+    # prior clearing channels.
+    from . import pv
+    pv_cache = pv._PVcache_
+    pv._PVcache_ = {}
+    for pv in pv_cache.values():
+        pv.disconnect()
+    pv_cache.clear()
+
     # Unregister callbacks (if any)
     for chid, entry in list(_chid_cache.items()):
         try:
@@ -505,10 +515,6 @@ def clear_cache():
     _cache.clear()
     _chid_cache.clear()
 
-    # Clear the cache of PVs used by epics.caget()-like functions
-    from . import pv
-    pv._PVcache_ = {}
-
     # The old context is copied directly from the old process
     # in systems with proper fork() implementations
     detach_context()
diff --git a/epics/pv.py b/epics/pv.py
index 129ab5b9..cbc1a3c2 100755
--- a/epics/pv.py
+++ b/epics/pv.py
@@ -1120,6 +1120,11 @@ def disconnect(self, deepclean=True):
         it from _PVcache_, so that subsequent connection to this PV will almost
         always make a completely new connection.
 
+        However, this method keeps the EPICS channel ID alive
+        so that it can be re-used later. This may block some resources.
+        Use `ca.clear_channel()` to clear the channel ID if needed
+        only after disconnecting the PV.
+
         Arguments
         -----------
         deepclean, bool  removal all cache connection and access-rights callbacks [True]
diff --git a/tests/test_ca_clearcache.py b/tests/test_ca_clearcache.py
index 02ee0f67..3e38b2a1 100644
--- a/tests/test_ca_clearcache.py
+++ b/tests/test_ca_clearcache.py
@@ -1,9 +1,8 @@
 import epics
-from epics import ca
+import epics.ca
+import epics.pv
 
-import os
 import time
-import sys
 import subprocess
 import pvnames
 enabledpv = pvnames.clear_cache_enabled
@@ -24,7 +23,22 @@ def run():
         assert value is not None, \
             "PV {} is offline".format(beaconpv)
     time.sleep(0.2)
-    ca.clear_cache()
+    epics.ca.clear_cache()
+
+
+def test_use_monitor():
+    # This test verifies that clear_cache clears subscriptions created by
+    # use_monitor=True prior clearing channels.
+    # Otherwise, EPICS will crash on an attempt to clear subscription
+    # on a cleared channel.
+    assert epics.caget(enabledpv, use_monitor=True) is not None, \
+        "PV {} is offline".format(enabledpv)
+
+    pv = epics.pv.get_pv(enabledpv)
+
+    epics.ca.clear_cache()
+
+    pv.disconnect()
 
 
 def test_subscribe():