Fix #1008: Re-attaching continuously creates 'accept_worker' threads in debugpy

Don't recreate the server socket needlessly.

Author: Pavel Minaev

setup.cfg

@@ -1,5 +1,5 @@
 [metadata]
-license_file = LICENSE
+license_files = LICENSE
 
 [versioneer]
 VCS = git
@@ -10,4 +10,4 @@ tag_prefix = v
 parentdir_prefix = debugpy-
 
 [aliases]
-test=pytest
+test = pytest

src/debugpy/adapter/clients.py

@@ -470,12 +470,16 @@ def attach_request(self, request):
             )
 
         if listen != ():
+            if servers.is_serving():
+                raise request.isnt_valid('Multiple concurrent "listen" sessions are not supported')
             host = listen("host", "127.0.0.1")
             port = listen("port", int)
             adapter.access_token = None
             host, port = servers.serve(host, port)
         else:
-            host, port = servers.serve()
+            if not servers.is_serving():
+                servers.serve()
+            host, port = servers.listener.getsockname()
 
         # There are four distinct possibilities here.
         #

src/debugpy/adapter/servers.py

@@ -19,6 +19,9 @@
 access_token = None
 """Access token used to authenticate with the servers."""
 
+listener = None
+"""Listener socket that accepts server connections."""
+
 _lock = threading.RLock()
 
 _connections = []
@@ -433,9 +436,16 @@ def serve(host="127.0.0.1", port=0):
     return listener.getsockname()
 
 
+def is_serving():
+    return listener is not None
+
+
 def stop_serving():
+    global listener
     try:
-        listener.close()
+        if listener is not None:
+            listener.close()
+            listener = None
     except Exception:
         log.swallow_exception(level="warning")
 

src/debugpy/common/log.py

@@ -339,6 +339,7 @@ def report_paths(get_paths, label=None):
 
     report_paths("os.__file__")
     report_paths("threading.__file__")
+    report_paths("debugpy.__file__")
 
     result = "".join(result).rstrip("\n")
     info("{0}", result)
@@ -376,3 +377,8 @@ def _vars(*names):  # pragma: no cover
 def _stack():  # pragma: no cover
     stack = "\n".join(traceback.format_stack())
     warning("$STACK:\n\n{0}", stack)
+
+
+def _threads():  # pragma: no cover
+    output = "\n".join([str(t) for t in threading.enumerate()])
+    warning("$THREADS:\n\n{0}", output)