public static void TrimCopies()
{
bool tookFlag = false;
try
{
try { }
finally
{
tookFlag = Interlocked.CompareExchange(ref _trimFlag, 1, 0) == 0;
}
if (!tookFlag) return;
var old = _oldestRead;
SimpleHashSet toTrim = null;
while (old != _current && Interlocked.CompareExchange(ref old.ReaderCount, int.MinValue, 0) == 0)
{
// we do not want to move "old" to an element which still has not finished writing, since
// we must maintain the invariant that says _oldestRead.Changes have already been trimmed.
if (old.Later.Changes == null)
break;
// likewise, thanks to that same invariant, we first move forward, then take Changes...
old = old.Later;
if (toTrim == null)
toTrim = new SimpleHashSet();
toTrim.UnionWith(old.Changes);
}
if (toTrim == null)
return;
old.Changes = null;
_oldestRead = old;
var version = old.Stamp;
toTrim.TrimCopies(version);
}
finally
{
if (tookFlag)
Interlocked.Exchange(ref _trimFlag, 0);
}
}
