In game development, "waiting" and "pausing" operations occur frequently. For example, waiting for an animation to finish, waiting for a network response, or resuming a process after a certain amount of time. To efficiently handle these operations without blocking the main loop (frame processing), asynchronous processing and coroutines are essential concepts.
In Godot Engine's GDScript, the await keyword was introduced to handle asynchronous processing in a simple yet powerful way. This article provides a comprehensive explanation of await, from its basic usage to the coroutine mechanisms behind it, and migration strategies from Godot 3's yield system, targeting beginners to intermediate developers.
Why Asynchronous Processing and await Matter
Games need to run smoothly at all times. If any processing (such as loading large files or performing complex calculations) occupies the main thread for an extended period, the game will freeze, severely degrading user experience. This is called blocking.
Asynchronous processing is a technique to prevent blocking. It pauses execution, allows other processes (like game rendering and input handling) to continue while waiting, and resumes the original process once the wait is complete.
In Godot Engine, await is primarily used for two purposes:
- Signal Waiting: Pause processing until a specific signal is emitted from a node.
- Coroutine Implementation: Implement coroutines (cooperative multitasking) that pause execution within a function and resume after specific conditions are met.
This allows you to write complex sequence processing (e.g., dialogue events, cutscenes, staged enemy spawning) in readable, top-to-bottom code without falling into callback hell.
Basic Usage of await
GDScript's await keyword waits for the completion of a specific awaitable object. The most common awaitable objects are signals and timers.
1. Waiting for Signals
Node signals are the most common wait targets for asynchronous processing. You use them when waiting for animations to finish, buttons to be pressed, etc.
# Player.gd
func play_attack_animation():
$AnimationPlayer.play("attack")
# Execution pauses here until the "animation_finished" signal is emitted
await $AnimationPlayer.animation_finished
print("Attack animation finished. Moving to next action.")
# Processing resumes after the wait
In this example, the function play_attack_animation pauses execution at the await line until the $AnimationPlayer.animation_finished signal is emitted. When the signal fires, the function automatically resumes.
2. Time-based Waiting with Timers
When you want to wait for a specific duration in-game, use the SceneTree's create_timer method in combination with await.
# World.gd
func start_game_sequence():
print("Game start!")
# Wait for 3 seconds
await get_tree().create_timer(3.0).timeout
print("3 seconds have passed. Spawning enemies.")
# Enemy spawning logic follows after the wait
get_tree().create_timer(3.0) returns a SceneTreeTimer object. By awaiting its timeout signal, you can pause execution for the specified number of seconds.
The Relationship Between await and Coroutines
A function containing await is automatically treated as a coroutine. A coroutine is a function that can suspend its execution and resume later. In GDScript, functions containing await are executed asynchronously.
Characteristics of Coroutines:
| Feature | Description |
|---|---|
| Cooperative | Process switching is explicitly controlled by the programmer using the await keyword. |
| Pause and Resume | Execution pauses at await points and automatically resumes when the awaited target completes. |
| Stack Preservation | Even when paused, the execution context (stack), including local variables, is preserved. |
This allows you to write complex asynchronous logic in a natural flow, as if it were synchronous code.
Migrating from Godot 3's yield to await
In Godot Engine 4.0 and later, the approach to asynchronous processing has significantly changed from Godot 3. The yield keyword used in Godot 3 was deprecated and replaced with the more modern await keyword.
Basic Migration Patterns
While yield could be used not only for waiting on signals but also as a generator function returning values, await is specifically designed for waiting on signals or function completion.
Godot 3.x (yield) | Godot 4.x (await) | Notes |
|---|---|---|
yield(object, "signal_name") | await object.signal_name | Signal waiting is the simplest migration pattern. |
yield(get_tree().create_timer(time), "timeout") | await get_tree().create_timer(time).timeout | Timer waiting is also written as signal waiting. |
yield(func_call(), "completed") | await func_call() | When waiting for asynchronous function completion. |
Practical Migration Example: Timer Processing
Let's look at a commonly used timer processing example from Godot 3.x.
# Godot 3.x (yield)
func wait_and_do_something():
# Wait for 2 seconds
yield(get_tree().create_timer(2.0), "timeout")
print("2 seconds have passed!")
Converted to Godot 4.x's await, it becomes:
# Godot 4.x (await)
func wait_and_do_something():
# Wait for 2 seconds
await get_tree().create_timer(2.0).timeout
print("2 seconds have passed!")
The code becomes more intuitive, making it immediately clear which signal is being awaited.
Practical Example: Controlling Dialogue Events
Using await, you can write complex in-game event sequences very concisely. Here's an example combining dialogue events with camera movement.
# EventController.gd
extends Node
@export var dialogue_manager: Node2D
@export var camera_controller: Node2D
# Write complex event sequences synchronously
func start_cutscene():
print("--- Cutscene Start ---")
# 1. Move camera to Character A and wait for movement to complete
print("Moving camera to Character A...")
await camera_controller.move_to_target($CharacterA.global_position)
# 2. Display Character A's dialogue and wait for player button press
print("Starting dialogue A...")
await dialogue_manager.start_dialogue("CharacterA", "Hey, long time no see.")
# 3. Move camera to Character B and wait for movement to complete
print("Moving camera to Character B...")
await camera_controller.move_to_target($CharacterB.global_position)
# 4. Display Character B's dialogue and wait for player button press
print("Starting dialogue B...")
await dialogue_manager.start_dialogue("CharacterB", "Indeed. What a surprise to meet you here.")
# 5. Wait for 2 seconds
print("Enjoying the atmosphere for 2 seconds...")
await get_tree().create_timer(2.0).timeout
print("--- Cutscene End ---")
# Asynchronous function that would be implemented in camera_controller node
# func move_to_target(target_pos: Vector2):
# # Execute camera movement animation
# # Await animation finished signal
# await $CameraAnimationPlayer.animation_finished
# return # Wait for completion
By using await, each step of the event is guaranteed to execute sequentially from top to bottom, dramatically improving code readability and maintainability.
Summary: Accelerate Game Development by Mastering Asynchronous Processing
Godot Engine's await keyword is a powerful tool for handling asynchronous processing and coroutines in GDScript.
| Concept | Keyword | Role |
|---|---|---|
| Asynchronous Processing | await | Enables waiting and resuming of processes without blocking the main thread. |
| Coroutines | Functions containing await | Functions that can suspend execution and resume later. Allows concise sequence writing. |
When migrating from Godot 3 to Godot 4, replacing yield with await is mandatory, but await enables more intuitive and modern asynchronous processing. Actively utilize await for waiting on signals and timers to create smooth, rich game experiences that don't keep players waiting.