prevent concurrent bot instances

.gitignore

@@ -13,5 +13,6 @@ schedule_client.py
 config.py
 .env
 .venv
+.bot.lock
 /schedule_requests.json*
 /navigator_requests.json*

main.py

@@ -1,28 +1,131 @@
-if __name__ == '__main__':
-    import os, sys, event, bot
-    from multiprocessing import Process
-    sys.path.append(os.path.dirname(os.path.abspath(__file__)))
+from __future__ import annotations
 
+import os
+import signal
+import sys
+from multiprocessing import Process, get_context
+from pathlib import Path
+from collections.abc import Callable
+from typing import BinaryIO
+
+
+LOCK_PATH = Path(__file__).resolve().with_name(".bot.lock")
+SHUTDOWN_TIMEOUT = 10.0
+
+
+def acquire_instance_lock() -> BinaryIO:
+    """Hold a process lock for this checkout until the last worker exits."""
+    lock_file = LOCK_PATH.open("a+b")
+    try:
+        if os.name == "nt":
+            import msvcrt
+
+            lock_file.seek(0)
+            if lock_file.read(1) == b"":
+                lock_file.write(b"\0")
+                lock_file.flush()
+            lock_file.seek(0)
+            msvcrt.locking(lock_file.fileno(), msvcrt.LK_NBLCK, 1)
+        else:
+            import fcntl
+
+            fcntl.flock(lock_file.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
+    except (BlockingIOError, OSError):
+        lock_file.close()
+        raise RuntimeError(f"another bot instance already holds {LOCK_PATH}") from None
+
+    lock_file.seek(0)
+    lock_file.truncate()
+    lock_file.write(f"{os.getpid()}\n".encode())
+    lock_file.flush()
+    return lock_file
+
+
+def stop_processes(processes: list[Process]) -> None:
+    started = [process for process in processes if process.pid is not None]
+    for process in started:
+        if process.is_alive():
+            process.terminate()
+    for process in started:
+        process.join(SHUTDOWN_TIMEOUT)
+    for process in started:
+        if process.is_alive():
+            process.kill()
+            process.join()
+
+
+def run_worker(target: Callable[[], None], lock_fd: int) -> None:
+    # Keep an explicit duplicate alive in the worker. A Linux flock belongs to
+    # the shared open-file description, so it remains held if the parent dies.
+    with os.fdopen(os.dup(lock_fd), "rb"):
+        target()
+
+
+def run() -> int:
+    # Import only after taking the lock so a rejected duplicate has no bot/event
+    # side effects. Linux workers explicitly retain the lock descriptor: if the
+    # supervisor dies unexpectedly, an orphan cannot poll alongside a replacement.
+    instance_lock = acquire_instance_lock()
+    import bot
+    import event
     import models.logger
-    # Reuse the interpreter that launched this process.  Calling ``uv`` from
-    # a child shell breaks when uv was installed outside PATH (and also makes
-    # ``uv run main.py`` recurse through a second environment).
-    CMD = 'python3.13.exe' if sys.platform == 'win32' else f'"{sys.executable}"'
-    PROCESSES = [
-        Process(target=bot.run if sys.platform == 'win32' else os.system, args=() if sys.platform == 'win32' else (f'{CMD} -c "import bot; bot.run()"',)),
-        # Process(target=bot.run),
-        Process(target=event.run),
+
+    context = get_context("spawn" if sys.platform == "win32" else "fork")
+    if sys.platform == "win32":
+        processes = [
+            context.Process(target=bot.run, name="bot"),
+            context.Process(target=event.run, name="events"),
+        ]
+    else:
+        processes = [
+            context.Process(
+                target=run_worker,
+                args=(bot.run, instance_lock.fileno()),
+                name="bot",
+            ),
+            context.Process(
+                target=run_worker,
+                args=(event.run, instance_lock.fileno()),
+                name="events",
+            ),
         ]
 
-    os.system('cls' if sys.platform == 'win32' else 'clear')
-    models.logger.log('Main', 'Startup...')
+    def request_shutdown(_signum, _frame) -> None:
+        raise KeyboardInterrupt
+
+    signal.signal(signal.SIGINT, request_shutdown)
+    signal.signal(signal.SIGTERM, request_shutdown)
+
+    os.system("cls" if sys.platform == "win32" else "clear")
+    models.logger.log("Main", "Startup...")
     try:
-        [process.start() for process in PROCESSES]
-        [process.join() for process in PROCESSES]
+        for process in processes:
+            process.start()
 
+        while all(process.is_alive() for process in processes):
+            for process in processes:
+                process.join(timeout=0.5)
+
+        stopped = next(process for process in processes if not process.is_alive())
+        models.logger.error(
+            "Main",
+            f"{stopped.name} process exited unexpectedly with code {stopped.exitcode}",
+        )
+        return 1
     except KeyboardInterrupt:
-        [process.terminate() for process in PROCESSES]
-        [process.join() for process in PROCESSES]
+        models.logger.error("Main", "Stopping...")
+        return 0
+    except Exception as error:
+        models.logger.error("Main", f"{error}")
+        return 1
+    finally:
+        stop_processes(processes)
+        instance_lock.close()
 
-    except Exception as e:
-        models.logger.error('Main', f'{e}')
+
+if __name__ == "__main__":
+    try:
+        raise SystemExit(run())
+    except RuntimeError as error:
+        print(f"Bot startup refused: {error}", file=sys.stderr)
+        raise SystemExit(1)