如何實現簡單的多線程函數

Question

我需要實現從多線程調用的簡單函數。該功能的邏輯很簡單 - 想想賽馬 - 只有第一匹馬才能獲得金牌，一旦我們贏得比賽結束的贏家。

class ConditionalOrderGroup 
{ 
    private volatile bool _locked = false; 
    private List<ConditionalOrder> _ConditionalOrderList = null;   

public bool LockGroup(ConditionalOrder initiator) 
{ 
    // this is finishline - we need to let only the first one proceed 
    if (_locked) 
     return false; 
    else 
    { 
     _locked = true; 
    } 

    // this is what winner gets 
    foreach (ConditionalOrder order in _ConditionalOrderList) 
    { 

     \\ cancel other orders 
    } 

    return true; 
} 
} 

我不開心

if (_locked) 
    return false; 
else 
{ 
    _locked = true; 
} 

如果兩個命令可以通過如果檢查，並繼續其他。如何重寫此代碼 而不使用鎖聲明？

UPDATE 我的意思是我的目標是不使用任何阻塞方法，如鎖定語句。

Answer 1

你需要一個獨立的，私人的對象，並使用built-in locking：

private object padLock = new object(); // 1-to-1 with _ConditionalOrderList 

if (Monitor.TryEnter(padLock)) 
{ 
    try 
    { 
     // cancel other orders 

     return true; 
    } 
    finally 
    { 
     Monitor.Exit(padLock); 
    } 
} 
else 
{ 
    return false; 
} 

Answer 2

使用Interlocked類來改變一個線程安全的方式變量的值。

Answer 3

擴展在談到互鎖什麼decyclone，這正是你會怎麼做：

const int LOCKED = 1; 
const int UNLOCKED = 0; 

volatile int lockState = UNLOCKED; 

public bool Foo() 
{ 
    try 
    { 
     //locking 
     //compare exchange returns the value that was in lockState before the compareExchange operation, so from that you can determine if you grabbed the lock or not 
     //if it was locked before, then you know the lock is not yours 
     if (Interlocked.CompareExchange(ref lockState, UNLOCKED, LOCKED) == LOCKED) 
      return false; 

     //lock is yours, do whatever stuff you like here, including throw exceptions 
    } 
    finally 
    { 
     //unlocking 
     //because this is in finally this lock will be released even if something goes wrong with your code 
     Interlocked.Exchange(ref lockstate, UNLOCKED); 
    } 
}