使用多个线程
线程
线程允许同时执行代码.它允许从主线程卸载工作.
Godot支持线程,并提供了许多方便使用的功能.
注解
如果使用其他语言(C#、C++),它们支持的线程类可能会更容易使用.
创建线程
创建一个线程非常简单,只需使用以下代码:
GDScript
var thread
# The thread will start here.
func _ready():
thread = Thread.new()
# Third argument is optional userdata, it can be any variable.
thread.start(self, "_thread_function", "Wafflecopter")
# Run here and exit.
# The argument is the userdata passed from start().
# If no argument was passed, this one still needs to
# be here and it will be null.
func _thread_function(userdata):
# Print the userdata ("Wafflecopter")
print("I'm a thread! Userdata is: ", userdata)
# Thread must be disposed (or "joined"), for portability.
func _exit_tree():
thread.wait_to_finish()
然后,你的函数将在一个单独的线程中运行,直到它返回.即使函数已经返回,线程也必须收集它,所以调用 Thread.wait_to_finish() ,它将等待线程完成(如果还没有完成),然后妥善处理它.
Mutexes
并不总是支持从多个线程访问对象或数据(如果你这样做,会导致意外行为或崩溃).请阅读 线程安全的API 文档,了解哪些引擎API支持多线程访问.
在处理自己的数据或调用自己的函数时,通常情况下,尽量避免从不同的线程直接访问相同的数据.你可能会遇到同步问题,因为数据被修改后,CPU核之间并不总是更新.当从不同线程访问一个数据时,一定要使用 Mutex .
当调用 Mutex.lock() 时,一个线程确保所有其他线程如果试图 锁 同一个mutex,就会被阻塞(进入暂停状态).当通过调用 Mutex.unlock() 来解锁该mutex时,其他线程将被允许继续锁定(但每次只能锁定一个).
下面是一个使用 Mutex 的例子:
GDScript
var counter = 0
var mutex
var thread
# The thread will start here.
func _ready():
mutex = Mutex.new()
thread = Thread.new()
thread.start(self, "_thread_function")
# Increase value, protect it with Mutex.
mutex.lock()
counter += 1
mutex.unlock()
# Increment the value from the thread, too.
func _thread_function(userdata):
mutex.lock()
counter += 1
mutex.unlock()
# Thread must be disposed (or "joined"), for portability.
func _exit_tree():
thread.wait_to_finish()
print("Counter is: ", counter) # Should be 2.
Semaphores
有时你希望你的线程能 “按需 “工作.换句话说,告诉它什么时候工作,让它在不工作的时候暂停.为此,可以使用 Semaphores .线程中使用函数 Semaphore.wait() 来暂停它的工作,直到有数据到达.
而主线程则使用 Semaphore.post() 来表示数据已经准备好被处理:
GDScript
var counter = 0
var mutex
var semaphore
var thread
var exit_thread = false
# The thread will start here.
func _ready():
mutex = Mutex.new()
semaphore = Semaphore.new()
exit_thread = false
thread = Thread.new()
thread.start(self, "_thread_function")
func _thread_function(userdata):
while true:
semaphore.wait() # Wait until posted.
mutex.lock()
var should_exit = exit_thread # Protect with Mutex.
mutex.unlock()
if should_exit:
break
mutex.lock()
counter += 1 # Increment counter, protect with Mutex.
mutex.unlock()
func increment_counter():
semaphore.post() # Make the thread process.
func get_counter():
mutex.lock()
# Copy counter, protect with Mutex.
var counter_value = counter
mutex.unlock()
return counter_value
# Thread must be disposed (or "joined"), for portability.
func _exit_tree():
# Set exit condition to true.
mutex.lock()
exit_thread = true # Protect with Mutex.
mutex.unlock()
# Unblock by posting.
semaphore.post()
# Wait until it exits.
thread.wait_to_finish()
# Print the counter.
print("Counter is: ", counter)