debounce()

Debounce a function to only be called after wait milliseconds of inactivity.

Implementation

The debounced function will be called with the last provided arguments after wait milliseconds have passed since the last call. This is useful for preventing excessive calls to a function that is expensive or has side effects. The debounced function is thread-safe and will not raise exceptions if the original function raises an exception. Args: func: The function to debounce wait: The delay in milliseconds Returns: A debounced function

Example

                            def api_call():
    return "Called!"
debounced = debounce(api_call, 100)
# Function will execute after 100ms of inactivity
                        

Expected output: Function that executes 200ms after the last call

Source Code

                        def debounce(func: Callable, wait: int) -> Callable:
    wait_seconds = wait / 1000.0
    timer = None
    lock = threading.RLock()  # Reentrant lock for safety
    max_pending_timers = 10   # Prevent DoS
    pending_count = [0]
    
    def debounced(*args, **kwargs):
        nonlocal timer
        
        # DoS protection
        if pending_count[0] > max_pending_timers:
            return  # Silently drop excessive calls
        
        with lock:  # Atomic check-and-set
            if timer is not None:
                timer.cancel()
                pending_count[0] = max(0, pending_count[0] - 1)
            
            def safe_call():
                try:
                    with lock:
                        pending_count[0] = max(0, pending_count[0] - 1)
                    func(*args, **kwargs)
                except Exception:
                    # Prevent exceptions from breaking debounce state
                    with lock:
                        pending_count[0] = max(0, pending_count[0] - 1)
            
            timer = threading.Timer(wait_seconds, safe_call)
            timer.daemon = True
            pending_count[0] += 1
            timer.start()
    
    return debounced
                    