private static bool IsRWEntryEmpty(ReaderWriterCount rwc)
{
if (rwc.ThreadId == -1)
{
return(true);
}
if (rwc.ReaderCount == 0 && rwc.Rc == null)
{
return(true);
}
if (rwc.ReaderCount == 0 && rwc.Rc.WriterCount == 0 && rwc.Rc.UpgradeCount == 0)
{
return(true);
}
return(false);
}
/// <summary>
/// This routine retrieves/sets the per-thread counts needed to enforce the
/// various rules related to acquiring the lock. It's a simple hash table,
/// where the first entry is pre-allocated for optimizing the common case.
/// After the first element has been allocated, duplicates are kept of in
/// linked-list. The entries are never freed, and the max size of the
/// table would be bounded by the max number of threads that held the lock
/// simultaneously.
///
/// DontAllocate is set to true if the caller just wants to get an existing
/// entry for this thread, but doesn't want to add one if an existing one
/// could not be found.
/// </summary>
private ReaderWriterCount GetThreadRWCount(int id, bool dontAllocate)
{
int hash = id & HashTableSize;
ReaderWriterCount firstfound = null;
#if DEBUG
Debug.Assert(MyLockHeld);
#endif
if (null == _rwc[hash])
{
if (dontAllocate)
{
return(null);
}
_rwc[hash] = new ReaderWriterCount(_isReentrant);
}
if (_rwc[hash].ThreadId == id)
{
return(_rwc[hash]);
}
if (IsRWEntryEmpty(_rwc[hash]) && !dontAllocate)
{
//No more entries in chain, so no more searching required.
if (_rwc[hash].Next == null)
{
_rwc[hash].ThreadId = id;
return(_rwc[hash]);
}
firstfound = _rwc[hash];
}
//SlowPath
var temp = _rwc[hash].Next;
while (temp != null)
{
if (temp.ThreadId == id)
{
return(temp);
}
if (firstfound == null)
{
if (IsRWEntryEmpty(temp))
{
firstfound = temp;
}
}
temp = temp.Next;
}
if (dontAllocate)
{
return(null);
}
if (firstfound == null)
{
temp = new ReaderWriterCount(_isReentrant)
{
ThreadId = id,
Next = _rwc[hash].Next
};
_rwc[hash].Next = temp;
return(temp);
}
firstfound.ThreadId = id;
return(firstfound);
}
private static bool IsRwHashEntryChanged(ReaderWriterCount lrwc, int id)
{
return(lrwc.ThreadId != id);
}