Unity協程(Coroutine)原理深入剖析
阿新 • • 發佈:2018-12-26
本文只是從Unity的角度去分析理解協程的內部執行原理,而不是從C#底層的語法實現來介紹(後續有需要再進行介紹),一共分為三部分:
執行緒(Thread)和協程(Coroutine)
Unity中協程的執行原理
IEnumerator & Coroutine
執行緒(Thread)和協程(Coroutine)
使用協程的作用一共有兩點:1)延時(等待)一段時間執行程式碼;2)等某個操作完成之後再執行後面的程式碼。總結起來就是一句話:控制程式碼在特定的時機執行。 很多初學者,都會下意識地覺得協程是非同步執行的,都會覺得協程是C# 執行緒的替代品,是Unity不使用執行緒的解決方案。 所以首先,請你牢記:協程不是執行緒,也不是非同步執行的。協程和 MonoBehaviour 的 Update函式一樣也是在MainThread中執行的。使用協程你不用考慮同步和鎖的問題。
Unity中協程的執行原理
UnityGems.com給出了協程的定義: A coroutine is a function that is executed partially and, presuming suitable conditions are met, will be resumed at some point in the future until its work is done. 即協程是一個分部執行,遇到條件(yield return 語句)會掛起,直到條件滿足才會被喚醒繼續執行後面的程式碼。 Unity在每一幀(Frame)都會去處理物件上的協程。Unity主要是在Update後去處理協程(檢查協程的條件是否滿足),但也有寫特例: 從上圖的剖析就明白,協程跟Update()其實一樣的,都是Unity每幀對會去處理的函式(如果有的話)。如果MonoBehaviour 是處於啟用(active)狀態的而且yield的條件滿足,就會協程方法的後面程式碼。還可以發現:如果在一個物件的前期呼叫協程,協程會立即執行到第一個 yield return 語句處,如果是 yield return null ,就會在同一幀再次被喚醒。如果沒有考慮這個細節就會出現一些奇怪的問題『1』。 『1』注 圖和結論都是從UnityGems.com 上得來的,經過下面的驗證發現與實際不符,D.S.Qiu用的是Unity 4.3.4f1 進行測試的。 經過測試驗證,協程至少是每幀的LateUpdate()後去執行。
下面使用 yield return new WaitForSeconds(1f); 在Start,Update 和 LateUpdate 中分別進行測試:
using UnityEngine;
using System.Collections;
public class TestCoroutine : MonoBehaviour {
private bool isStartCall = false; //Makesure Update() and LateUpdate() Log only once
private bool isUpdateCall = false;
private bool isLateUpdateCall = false;
// Use this for initialization
void Start () {
if (!isStartCall)
{
Debug.Log("Start Call Begin");
StartCoroutine(StartCoutine());
Debug.Log("Start Call End");
isStartCall = true;
}
}
IEnumerator StartCoutine()
{
Debug.Log("This is Start Coroutine Call Before");
yield return null;
Debug.Log("This is Start Coroutine Call After");
}
// Update is called once per frame
void Update () {
if (!isUpdateCall)
{
Debug.Log("Update Call Begin");
StartCoroutine(UpdateCoutine());
Debug.Log("Update Call End");
isUpdateCall = true;
}
}
IEnumerator UpdateCoutine()
{
Debug.Log("This is Update Coroutine Call Before");
yield return null;
Debug.Log("This is Update Coroutine Call After");
}
void LateUpdate()
{
if (!isLateUpdateCall)
{
Debug.Log("LateUpdate Call Begin");
StartCoroutine(LateCoutine());
Debug.Log("LateUpdate Call End");
isLateUpdateCall = true;
}
}
IEnumerator LateCoutine()
{
Debug.Log("This is Late Coroutine Call Before");
yield return null;
Debug.Log("This is Late Coroutine Call After");
}
}
得到日誌輸入結果如下:
然後將yield return new WaitForSeconds(1f);改為 yield return null; 發現日誌輸入結果和上面是一樣的,沒有出現上面說的情況.
MonoBehaviour 沒有針對特定的協程提供Stop方法,其實不然,可以通過MonoBehaviour enabled = false 或者 gameObject.active = false 就可以停止協程的執行『2』。
經過驗證,『2』的結論也是錯誤的,正確的結論是,MonoBehaviour.enabled = false 協程會照常執行,但 gameObject.SetActive(false) 後協程卻全部停止,即使在Inspector把 gameObject 啟用還是沒有繼續執行:
using UnityEngine;
using System.Collections;
public class TestCoroutine : MonoBehaviour {
private bool isStartCall = false; //Makesure Update() and LateUpdate() Log only once
private bool isUpdateCall = false;
private bool isLateUpdateCall = false;
// Use this for initialization
void Start () {
if (!isStartCall)
{
Debug.Log("Start Call Begin");
StartCoroutine(StartCoutine());
Debug.Log("Start Call End");
isStartCall = true;
}
}
IEnumerator StartCoutine()
{
Debug.Log("This is Start Coroutine Call Before");
yield return new WaitForSeconds(1f);
Debug.Log("This is Start Coroutine Call After");
}
// Update is called once per frame
void Update () {
if (!isUpdateCall)
{
Debug.Log("Update Call Begin");
StartCoroutine(UpdateCoutine());
Debug.Log("Update Call End");
isUpdateCall = true;
this.enabled = false;
//this.gameObject.SetActive(false);
}
}
IEnumerator UpdateCoutine()
{
Debug.Log("This is Update Coroutine Call Before");
yield return new WaitForSeconds(1f);
Debug.Log("This is Update Coroutine Call After");
yield return new WaitForSeconds(1f);
Debug.Log("This is Update Coroutine Call Second");
}
void LateUpdate()
{
if (!isLateUpdateCall)
{
Debug.Log("LateUpdate Call Begin");
StartCoroutine(LateCoutine());
Debug.Log("LateUpdate Call End");
isLateUpdateCall = true;
}
}
IEnumerator LateCoutine()
{
Debug.Log("This is Late Coroutine Call Before");
yield return null;
Debug.Log("This is Late Coroutine Call After");
}
}
先在Update中呼叫 this.enabled = false; 得到的結果:
然後把 this.enabled = false; 註釋掉,換成 this.gameObject.SetActive(false); 得到的結果如下:
整理得到 :通過設定MonoBehaviour指令碼的enabled對協程是沒有影響的,但如果 gameObject.SetActive(false) 則已經啟動的協程則完全停止了,即使在Inspector把gameObject 啟用還是沒有繼續執行。也就說協程雖然是在MonoBehvaviour啟動的(StartCoroutine)但是協程函式的地位完全是跟MonoBehaviour是一個層次的,不受MonoBehaviour的狀態影響,但跟MonoBehaviour指令碼一樣受gameObject 控制,也應該是和MonoBehaviour指令碼一樣每幀“輪詢” yield 的條件是否滿足。
yield 後面可以有的表示式:
a) null - the coroutine executes the next time that it is eligible
b) WaitForEndOfFrame - the coroutine executes on the frame, after all of the rendering and GUI is complete
c) WaitForFixedUpdate - causes this coroutine to execute at the next physics step, after all physics is calculated
d) WaitForSeconds - causes the coroutine not to execute for a given game time period
e) WWW - waits for a web request to complete (resumes as if WaitForSeconds or null)
f) Another coroutine - in which case the new coroutine will run to completion before the yielder is resumed
值得注意的是 WaitForSeconds()受Time.timeScale影響,當Time.timeScale = 0f 時,yield return new WaitForSecond(x) 將不會滿足。
IEnumerator & Coroutine
協程其實就是一個IEnumerator(迭代器),IEnumerator 介面有兩個方法 Current 和 MoveNext() ,前面介紹的TaskManager就是利用者兩個方法對協程進行了管理,這裡在介紹一個協程的交叉呼叫類 Hijack:
using System;
using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using System.Collections;
using UnityEngine.UI;
[RequireComponent(typeof(Text))]
public class HiJack : MonoBehaviour {
//This will hold the counting up coroutine
IEnumerator _countUp;
//This will hold the counting down coroutine
IEnumerator _countDown;
//This is the coroutine we are currently
//hijacking
IEnumerator _current;
//A value that will be updated by the coroutine
//that is currently running
int value = 0;
void Start()
{
//Create our count up coroutine
_countUp = CountUp();
//Create our count down coroutine
_countDown = CountDown();
//Start our own coroutine for the hijack
StartCoroutine(DoHijack());
}
void Update()
{
//Show the current value on the screen
GetComponent<Text> ().text = value.ToString ();
}
void OnGUI()
{
//Switch between the different functions
if(GUILayout.Button("Switch functions"))
{
if(_current == _countUp)
_current = _countDown;
else
_current = _countUp;
}
}
IEnumerator DoHijack()
{
while(true)
{
//Check if we have a current coroutine and MoveNext on it if we do
if(_current != null && _current.MoveNext())
{
//Return whatever the coroutine yielded, so we will yield the
//same thing
yield return _current.Current;
}
else
//Otherwise wait for the next frame
yield return null;
}
}
IEnumerator CountUp()
{
//We have a local increment so the routines
//get independently faster depending on how
//long they have been active
float increment = 0;
while(true)
{
//Exit if the Q button is pressed
if(Input.GetKey(KeyCode.Q))
break;
increment+=Time.deltaTime;
value += Mathf.RoundToInt(increment);
yield return null;
}
}
IEnumerator CountDown()
{
float increment = 0f;
while(true)
{
if(Input.GetKey(KeyCode.Q))
break;
increment+=Time.deltaTime;
value -= Mathf.RoundToInt(increment);
//This coroutine returns a yield instruction
yield return new WaitForSeconds(0.1f);
}
}
}
上面的程式碼實現是兩個協程交替呼叫,對有這種需求來說實在太精妙了。