C#線程優先級的必要性:如果在應用程序中有多個線程在運行,但一些線程比另一些線程重要,該怎么辦在這種情況下,可以在一個進程中為不同的線程指定不同的優先級。一般情況下,如果有優先級較高的線程在工作,就不會給優先級較低的線程分配任何時間片,其優點是可以保證給接收用戶輸入的線程指定較高的優先級。在大多數的時間內,這個線程什么也不做,而其他線程則執行它們的任務。但是,如果用戶輸入了信息,這個線程就立即獲得比應用程序中其他線程更高的優先級,在短時間內處理用戶輸入事件。
C#線程優先級的規律:高優先級的線程可以完全阻止低優先級的線程執行,因此在改變線程的優先級時要特別小心。線程的優先級可以定義為ThreadPriority枚舉的值,即Highest、AboveNormal、Normal、BelowNormal和 Lowest。
注意,每個進程都有一個基本優先級,這些值與進程的優先級是有關系的。給線程指定較高的優先級,可以確保它在該進程中比其他線程優先執行,但系統上可能還運行着其他進程,它們的線程有更高的優先級。因此Windows給自己的操作系統線程指定高優先級。
在ThreadPlayaround示例中,對Main()方法做如下修改,就可以看出修改線程的優先級的效果:
ThreadStart workerStart = new ThreadStart(StartMethod); Thread workerThread = new Thread(workerStart); workerThread.Name = "Worker"; workerThread.Priority = ThreadPriority.AboveNormal; workerThread.Start();
其中,工作線程的優先級比主線程高,運行結果如下所示:
ThreadPlayaroundWithPriorities
Interval to display results at> 1000000
Starting thread: Main Thread
Main Thread: Current Culture = en-US
Starting thread: Worker
Worker: Current Culture = en-US
Main Thread: count has reached 1000000
Worker: count has reached 1000000
Worker: count has reached 2000000
Worker: count has reached 3000000
Worker: count has reached 4000000
Worker: count has reached 5000000
Worker: count has reached 6000000
Worker: count has reached 7000000
Worker: count has reached 8000000
Worker Thread Finished
Main Thread: count has reached 2000000
Main Thread: count has reached 3000000
Main Thread: count has reached 4000000
Main Thread: count has reached 5000000
Main Thread: count has reached 6000000
Main Thread: count has reached 7000000
Main Thread: count has reached 8000000
Main Thread Finished
這說明,當工作線程的優先級為AboveNormal時,一旦工作線程被啟動,主線程就不再運行。
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