/// <summary>
/// Removes all the elements.
/// </summary>
public void Clear()
{
_entriesOld = null;
_entriesNew = new FixedSizeHashBucket <TKey, TValue>(INT_DefaultCapacity, _keyComparer);
Thread.VolatileWrite(ref _status, (int)BucketStatus.Free);
Thread.VolatileWrite(ref _count, 0);
_revision++;
}
private bool ContainsKeyExtracted(TKey key, FixedSizeHashBucket <TKey, TValue> entries)
{
for (int attempts = 0; attempts < _maxProbing; attempts++)
{
if (entries.ContainsKey(key, attempts) != -1)
{
return(true);
}
}
return(false);
}
private bool TryGetExtracted(int index, FixedSizeHashBucket <TKey, TValue> entries, out TKey key, out TValue value)
{
value = default(TValue);
key = default(TKey);
if (entries != null)
{
if (entries.TryGet(index, out key, out value))
{
return(true);
}
}
return(false);
}
private bool RemoveExtracted(TKey key, FixedSizeHashBucket <TKey, TValue> entries)
{
if (entries != null)
{
for (int attempts = 0; attempts < _maxProbing; attempts++)
{
if (entries.Remove(key, attempts) != -1)
{
return(true);
}
}
}
return(false);
}
/// <summary>
/// Initializes a new instance of the <see cref="HashBucket{TValue}" /> class.
/// </summary>
/// <param name="capacity">The initial capacity.</param>
/// <param name="comparer">The key comparer.</param>
/// <param name="maxProbing">The maximum number of steps in linear probing.</param>
/// <exception cref="System.ArgumentOutOfRangeException">maxProbing;maxProbing must be greater or equal to 1 and less than capacity.</exception>
public HashBucket(int capacity, IEqualityComparer <TKey> comparer, int maxProbing)
{
if (maxProbing < 1 || maxProbing >= capacity)
{
throw new ArgumentOutOfRangeException("maxProbing", "maxProbing must be greater or equal to 1 and less than capacity.");
}
else
{
_keyComparer = comparer ?? EqualityComparer <TKey> .Default;
_entriesOld = null;
_entriesNew = new FixedSizeHashBucket <TKey, TValue>(capacity, _keyComparer);
_maxProbing = maxProbing;
}
}
private bool TryGetValueExtracted(TKey key, FixedSizeHashBucket <TKey, TValue> entries, out TValue value)
{
value = default(TValue);
if (entries != null)
{
for (int attempts = 0; attempts < _maxProbing; attempts++)
{
if (entries.TryGetValue(key, attempts, out value) != -1)
{
return(true);
}
}
}
return(false);
}
private int TryAddExtracted(TKey key, TValue value, FixedSizeHashBucket <TKey, TValue> entries, out KeyValuePair <TKey, TValue> previous)
{
previous = default(KeyValuePair <TKey, TValue>);
if (entries != null)
{
for (int attempts = 0; attempts < _maxProbing; attempts++)
{
int index = entries.TryAdd(key, value, attempts, out previous);
if (index != -1)
{
return(index);
}
}
}
return(-1);
}
private int SetExtracted(TKey key, TValue value, FixedSizeHashBucket <TKey, TValue> entries, out bool isNew)
{
isNew = false;
if (entries != null)
{
for (int attempts = 0; attempts < _maxProbing; attempts++)
{
int index = entries.Set(key, value, attempts, out isNew);
if (index != -1)
{
return(index);
}
}
}
return(-1);
}
private int AddExtracted(TKey key, TValue value, FixedSizeHashBucket <TKey, TValue> entries, out bool isCollision)
{
isCollision = true;
if (entries != null)
{
for (int attempts = 0; attempts < _maxProbing; attempts++)
{
int index = entries.Add(key, value, attempts, out isCollision);
if (index != -1 || !isCollision)
{
return(index);
}
}
}
return(-1);
}
private void CooperativeGrow()
{
int status;
do
{
status = Thread.VolatileRead(ref _status);
int oldStatus;
switch (status)
{
case (int)BucketStatus.GrowRequested:
// This area is only accessed by one thread, if that thread is aborted, we are doomed.
// This class is not abort safe
// If a thread is being aborted here it's pending operation will be lost and there is risk of a livelock
var priority = Thread.CurrentThread.Priority;
oldStatus = Interlocked.CompareExchange(ref _status, (int)BucketStatus.Waiting, (int)BucketStatus.GrowRequested);
if (oldStatus == (int)BucketStatus.GrowRequested)
{
try
{
// The progress of other threads depend of this one, we should not allow a priority inversion.
Thread.CurrentThread.Priority = ThreadPriority.Highest;
//_copyPosition is set to -1. _copyPosition is incremented before it is used, so the first time it is used it will be 0.
Thread.VolatileWrite(ref _copyPosition, -1);
//The new capacity is twice the old capacity, the capacity must be a power of two.
var newCapacity = _entriesNew.Capacity * 2;
_entriesOld = Interlocked.Exchange(ref _entriesNew, new FixedSizeHashBucket <TKey, TValue>(newCapacity, _keyComparer));
oldStatus = Interlocked.CompareExchange(ref _status, (int)BucketStatus.Copy, (int)BucketStatus.Waiting);
}
finally
{
Thread.CurrentThread.Priority = priority;
_revision++;
}
}
break;
case (int)BucketStatus.Waiting:
// This is the whole reason why this datastructure is not wait free.
// Testing shows that it is uncommon that a thread enters here.
// _status is 2 only for a short period.
// Still, it happens, so this is needed for correctness.
// Going completely wait-free adds complexity with deminished value.
Thread.SpinWait(INT_SpinWaitHint);
if (Thread.VolatileRead(ref _status) == 2)
{
Thread.Sleep(0);
}
break;
case (int)BucketStatus.Copy:
// It is time to cooperate to copy the old storage to the new one
var old = _entriesOld;
if (old != null)
{
// This class is not abort safe
// If a thread is being aborted here it will causing lost items.
_revision++;
Interlocked.Increment(ref _copyingThreads);
TKey key;
TValue value;
int index = Interlocked.Increment(ref _copyPosition);
for (; index < old.Capacity; index = Interlocked.Increment(ref _copyPosition))
{
if (old.TryGet(index, out key, out value))
{
// We have read an item, so let's try to add it to the new storage
bool dummy;
if (SetExtracted(key, value, _entriesNew, out dummy) == -1)
{
GC.KeepAlive(dummy);
}
}
}
Interlocked.CompareExchange(ref _status, (int)BucketStatus.CopyCleanup, (int)BucketStatus.Copy);
_revision++;
Interlocked.Decrement(ref _copyingThreads);
}
break;
case (int)BucketStatus.CopyCleanup:
// Our copy is finished, we don't need the old storage anymore
oldStatus = Interlocked.CompareExchange(ref _status, (int)BucketStatus.Waiting, (int)BucketStatus.CopyCleanup);
if (oldStatus == (int)BucketStatus.CopyCleanup)
{
_revision++;
Interlocked.Exchange(ref _entriesOld, null);
Interlocked.CompareExchange(ref _status, (int)BucketStatus.Free, (int)BucketStatus.Waiting);
}
break;
default:
break;
}
}while (status != (int)BucketStatus.Free);
}
