private void Hit(WindowCache.Ref r)
{
// We don't need to be 100% accurate here. Its sufficient that at least
// one thread performs the increment. Any other concurrent access at
// exactly the same time can simply use the same clock value.
//
// Consequently we attempt the set, but we don't try to recover should
// it fail. This is why we don't use getAndIncrement() here.
//
long c = clock.Get();
clock.CompareAndSet(c, c + 1);
r.lastAccess = c;
}
/// <summary>Lookup a cached object, creating and loading it if it doesn't exist.</summary>
/// <remarks>Lookup a cached object, creating and loading it if it doesn't exist.</remarks>
/// <param name="pack">the pack that "contains" the cached object.</param>
/// <param name="position">offset within <code>pack</code> of the object.</param>
/// <returns>the object reference.</returns>
/// <exception cref="System.IO.IOException">
/// the object reference was not in the cache and could not be
/// obtained by
/// <see cref="Load(PackFile, long)">Load(PackFile, long)</see>
/// .
/// </exception>
private ByteWindow GetOrLoad(PackFile pack, long position)
{
int slot = Slot(pack, position);
WindowCache.Entry e1 = table.Get(slot);
ByteWindow v = Scan(e1, pack, position);
if (v != null)
{
return(v);
}
lock (LockCache(pack, position))
{
WindowCache.Entry e2 = table.Get(slot);
if (e2 != e1)
{
v = Scan(e2, pack, position);
if (v != null)
{
return(v);
}
}
v = Load(pack, position);
WindowCache.Ref @ref = CreateRef(pack, position, v);
Hit(@ref);
for (; ;)
{
WindowCache.Entry n = new WindowCache.Entry(Clean(e2), @ref);
if (table.CompareAndSet(slot, e2, n))
{
break;
}
e2 = table.Get(slot);
}
}
if (evictLock.TryLock())
{
try
{
Gc();
Evict();
}
finally
{
evictLock.Unlock();
}
}
return(v);
}
private ByteWindow Scan(WindowCache.Entry n, PackFile pack, long position)
{
for (; n != null; n = n.next)
{
WindowCache.Ref r = n.@ref;
if (r.pack == pack && r.position == position)
{
ByteWindow v = r.Get();
if (v != null)
{
Hit(r);
return(v);
}
n.Kill();
break;
}
}
return(null);
}
internal Entry(WindowCache.Entry n, WindowCache.Ref r)
{
next = n;
@ref = r;
}
private void Clear(WindowCache.Ref @ref)
{
openBytes.AddAndGet([email protected]);
Close(@ref.pack);
}
private WindowCache.Ref CreateRef(PackFile p, long o, ByteWindow v)
{
WindowCache.Ref @ref = new WindowCache.Ref(p, o, v, queue);
openBytes.AddAndGet(@ref.size);
return(@ref);
}
