/// <summary>
/// Assigns a hash code to the object in a thread-safe way.
/// </summary>
private static unsafe int AssignHashCode(int *pHeader)
{
int newHash = RuntimeHelpers.GetNewHashCode() & MASK_HASHCODE_INDEX;
int bitAndValue;
// Never use the zero hash code. SyncTable treats the zero value as "not assigned".
if (newHash == 0)
{
newHash = 1;
}
while (true)
{
int oldBits = Volatile.Read(ref *pHeader);
bitAndValue = oldBits & (BIT_SBLK_IS_HASHCODE | MASK_HASHCODE_INDEX);
if (bitAndValue != 0)
{
// The header already stores some value
break;
}
// The header stores nothing. Try to store the hash code.
int newBits = oldBits | BIT_SBLK_IS_HASHCODE | newHash;
if (Interlocked.CompareExchange(ref *pHeader, newBits, oldBits) == oldBits)
{
return(newHash);
}
// Another thread modified the header; try again
}
if ((bitAndValue & BIT_SBLK_IS_HASHCODE) == 0)
{
// Set the hash code in SyncTable. This call will resolve the potential race.
return(SyncTable.SetHashCode(bitAndValue, newHash));
}
// Another thread set the hash code, use it
Debug.Assert((bitAndValue & ~BIT_SBLK_IS_HASHCODE) != 0);
return(bitAndValue & ~BIT_SBLK_IS_HASHCODE);
}