bot: Fix sequential message processing with proper consumer pool

Replace the flawed cnsr_thrd_size threshold with cnsr_active, which
tracks the number of consumers currently executing a task. A new
consumer thread is now spawned the moment the queue is non-empty and
all existing consumers are busy, enabling true parallel execution of
slow and fast commands. The pool is capped at os.cpu_count() threads.

- bot.py: replace cnsr_thrd_size with cnsr_active + cnsr_lock + cnsr_max
- consumer.py: increment/decrement cnsr_active around stm.run(), remove
  itself from cnsr_thrd under the lock, mark thread as daemon

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nemubot/bot.py

@@ -143,11 +143,16 @@ class Bot(threading.Thread):
             return res
         self.treater.hm.add_hook(nemubot.hooks.Command(_help_msg, "help"), "in", "Command")
 
+        import os
         from queue import Queue
-        # Messages to be treated
+        # Messages to be treated — shared across all server connections.
+        # cnsr_active tracks consumers currently inside stm.run() (not idle),
+        # which lets us spawn a new thread the moment all existing ones are busy.
         self.cnsr_queue  = Queue()
         self.cnsr_thrd   = list()
-        self.cnsr_thrd_size = -1
+        self.cnsr_lock   = threading.Lock()
+        self.cnsr_active = 0                      # consumers currently executing a task
+        self.cnsr_max    = os.cpu_count() or 4    # upper bound on concurrent consumer threads
 
 
     def __del__(self):
@@ -234,11 +239,12 @@ class Bot(threading.Thread):
                     sync_queue.task_done()
 
 
-            # Launch new consumer threads if necessary
+            # Spawn a new consumer whenever the queue has work and every
-            while self.cnsr_queue.qsize() > self.cnsr_thrd_size:
+            # existing consumer is already busy executing a task.
-                # Next launch if two more items in queue
+            with self.cnsr_lock:
-                self.cnsr_thrd_size += 2
+                while (not self.cnsr_queue.empty()
-
+                       and self.cnsr_active >= len(self.cnsr_thrd)
+                       and len(self.cnsr_thrd) < self.cnsr_max):
                     c = Consumer(self)
                     self.cnsr_thrd.append(c)
                     c.start()
@@ -518,7 +524,8 @@ class Bot(threading.Thread):
             srv.close()
 
         logger.info("Stop consumers")
-        k = self.cnsr_thrd
+        with self.cnsr_lock:
+            k = list(self.cnsr_thrd)
         for cnsr in k:
             cnsr.stop = True
 

nemubot/consumer.py

@@ -105,18 +105,25 @@ class Consumer(threading.Thread):
     def __init__(self, context):
         self.context = context
         self.stop = False
-        super().__init__(name="Nemubot consumer")
+        super().__init__(name="Nemubot consumer", daemon=True)
 
 
     def run(self):
         try:
             while not self.stop:
+                try:
                     stm = self.context.cnsr_queue.get(True, 1)
-                stm.run(self.context)
-                self.context.cnsr_queue.task_done()
-
                 except queue.Empty:
-            pass
+                    break
+
+                with self.context.cnsr_lock:
+                    self.context.cnsr_active += 1
+                try:
+                    stm.run(self.context)
                 finally:
-            self.context.cnsr_thrd_size -= 2
+                    self.context.cnsr_queue.task_done()
+                    with self.context.cnsr_lock:
+                        self.context.cnsr_active -= 1
+        finally:
+            with self.context.cnsr_lock:
                 self.context.cnsr_thrd.remove(self)