fix(DISET): reject all connections during throttling to prevent queue growth

The previous throttle mechanism accepted one connection every 0.25s
even while the service was overloaded. When threads were stuck (e.g.
blocked on DB queries or deadlocked), each accepted connection added
to the already-full queue, making recovery impossible.

Now all incoming connections are rejected while wantsThrottle is True,
with a brief sleep to avoid busy-spinning. This prevents the
self-reinforcing stuck state where the queue grows faster than it
can drain.

Author: ryuwd

src/DIRAC/Core/DISET/ServiceReactor.py

@@ -200,7 +200,6 @@ def __acceptIncomingConnection(self, svcName=False):
                                   services at the same time
         """
         sel = self.__getListeningSelector(svcName)
-        throttleExpires = None
         while self.__alive:
             clientTransport = None
             try:
@@ -224,16 +223,13 @@ def __acceptIncomingConnection(self, svcName=False):
                 gLogger.warn(f"Client connected from banned ip {clientIP}")
                 clientTransport.close()
                 continue
-            # Handle throttling
-            if self.__services[svcName].wantsThrottle and throttleExpires is None:
-                throttleExpires = time.time() + THROTTLE_SERVICE_SLEEP_SECONDS
-            if throttleExpires:
-                if time.time() > throttleExpires:
-                    throttleExpires = None
-                else:
-                    gLogger.warn("Rejecting client due to throttling", str(clientTransport.getRemoteAddress()))
-                    clientTransport.close()
-                    continue
+            # Handle throttling: reject all connections while overloaded
+            # to prevent queue growth when threads are stuck
+            if self.__services[svcName].wantsThrottle:
+                gLogger.warn("Rejecting client due to throttling", str(clientTransport.getRemoteAddress()))
+                clientTransport.close()
+                time.sleep(THROTTLE_SERVICE_SLEEP_SECONDS)
+                continue
             # Handle connection
             self.__stats.connectionStablished()
             self.__services[svcName].handleConnection(clientTransport)