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CSharp_刘锦丰_无24 #22

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67 changes: 67 additions & 0 deletions hw1/hw1/Program.cs
Original file line number Diff line number Diff line change
Expand Up @@ -70,7 +70,74 @@ public class LongProgressByTime: ILongProgressByTime
// 只允许修改LongProgressByTime类中的代码
// 要求实现ILongProgressByTime中的要求
// 可利用Environment.TickCount64获取当前时间(单位ms)
private long startTime;
private long needTime;
private long elapsedTime;

public bool Start(long needTime)
{
lock (this) // 为了线程安全性,在访问共享变量时使用锁来同步线程
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@shangfengh shangfengh Sep 26, 2023

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使用lock(this)需谨慎,因为将this作为lock,会使得其完全被占用,不能被其他线程占用。
http://blog.chinaunix.net/uid-7448695-id-2626484
这里有一个简易的理解,为什么对实例采用锁容易死锁

{
if (startTime == 0 && elapsedTime == 0) // 进度尚未开始或已经完成
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elapsedTime没有及时更新!
elapsedTime也不应当作为字段,而应当随用随算

{
this.needTime = needTime;
startTime = Environment.TickCount64;
return true;
}
else
{
return false;
}
}
}

public bool TrySet0()
{
lock (this)
{
if (startTime != 0 && elapsedTime == 0) // 进度正在进行中且尚未完成
{
startTime = 0;
return true;
}
else
{
return false;
}
}
}

public void Set0()
{
lock (this)
{
startTime = 0;
}
}

public (long ElapsedTime, long NeedTime) GetProgress()
{
lock (this)
{
if (startTime != 0)
{
elapsedTime = Environment.TickCount64 - startTime;
if (elapsedTime >= needTime) // 进度已完成
{
startTime = 0;
return (elapsedTime, needTime);
}
else // 进度正在进行中
{
return (elapsedTime, needTime);
}
}
else // 进度尚未开始或已经完成
{
return (0, 0);
}
}
}
//挑战:利用原子操作
//long.MaxValue非常久
}
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