[英]Thread safe limited size queue
I'm trying to write a subj queue, but I get deadlocks and other multithreading problems. 我正在尝试写一个subj队列,但遇到死锁和其他多线程问题。 I want to use Interlocked.CompareExchange
to avoid lock
usage. 我想使用Interlocked.CompareExchange
避免使用lock
。 But this code doesn't work as expected: it just wipe entire Queue. 但是此代码无法按预期工作:只会擦除整个Queue。 What am I doing wrong here? 我在这里做错了什么?
public class FixedSizedQueue<T> : IEnumerable<T>
{
readonly ConcurrentQueue<T> _queue = new ConcurrentQueue<T>();
public int Limit { get; set; }
public FixedSizedQueue(int limit)
{
Limit = limit;
}
public void Enqueue(T obj)
{
_queue.Enqueue(obj);
if (_queue.Count <= Limit)
return;
int count = _queue.Count;
if (_queue.Count != Interlocked.CompareExchange(ref count, count, _queue.Count))
{
T overflow;
while (_queue.TryDequeue(out overflow))
{
}
}
}
public T[] ToArray()
{
return _queue.ToArray();
}
public IEnumerator<T> GetEnumerator()
{
return _queue.GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
Maybe I just need another thread that will just cut the queue... 也许我只需要另一个线程即可削减队列...
Interlocked.CompareExchange
is meaningless on stack variable count
, as it is accessed from single thread. Interlocked.CompareExchange
对堆栈变量count
没有意义,因为它是从单线程访问的。 As I guess, you tried to use this method on _queue.Count
, but it failed to be compiled because .Count
is a property, not a simple variable. 我猜想,您尝试在_queue.Count
上使用此方法,但由于.Count
是属性而不是简单变量,因此无法编译。 So you need to define counter in your class. 因此,你需要在你的类定义计数器。
public class FixedSizedQueue<T> : IEnumerable<T>
{
readonly ConcurrentQueue<T> _queue = new ConcurrentQueue<T>();
int CountShadow = 0; // Counter for check constraints.
public int Limit { get; set; }
public FixedSizedQueue(int limit)
{
Limit = limit;
}
public void Enqueue(T obj)
{
/* Update shadow counter first for check constraints. */
int count = CountShadow;
while(true)
{
if(count => Limit) return; // Adding element would violate constraint
int countOld = Interlocked.CompareExchange(ref CountShadow, count, count + 1);
if(countOld == count) break; //Successful update
count = countOld;
}
_queue.Enqueue(obj); // This will update real counter.
}
...
}
Also, you need to set your own setter for Limit
property, which would maintain invariant CountShadow <= Limit
. 另外,您需要为Limit
属性设置自己的设置器,该设置器将保持CountShadow <= Limit
不变。 Or just forbid user to set that property after object's construction. 或者只是禁止用户在对象构造后设置该属性。
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