cache

type Cache interface {
	// SetCapacity sets cache tree capacity.
	SetCapacity(capacity int)

	// Capacity returns cache tree capacity.
	Capacity() int

	// Used returns used cache tree capacity.
	Used() int

	// Size returns entire alive cache objects size.
	Size() int

	// NumObjects returns number of alive objects.
	NumObjects() int

	// GetNamespace gets cache namespace with the given id.
	// GetNamespace is never return nil.
	GetNamespace(id uint64) Namespace

	// PurgeNamespace purges cache namespace with the given id from this cache tree.
	// Also read Namespace.Purge.
	PurgeNamespace(id uint64, fin PurgeFin)

	// ZapNamespace detaches cache namespace with the given id from this cache tree.
	// Also read Namespace.Zap.
	ZapNamespace(id uint64)

	// Purge purges all cache namespace from this cache tree.
	// This is behave the same as calling Namespace.Purge method on all cache namespace.
	Purge(fin PurgeFin)

	// Zap detaches all cache namespace from this cache tree.
	// This is behave the same as calling Namespace.Zap method on all cache namespace.
	Zap()
}

type DelFin func(exist, pending bool)

type Handle interface {
	// Release releases this cache handle. This method can be safely called mutiple
	// times.
	Release()

	// Value returns value of this cache handle.
	// Value will returns nil after this cache handle have be released.
	Value() interface{}
}

type Namespace interface {
	// Get gets cache object with the given key.
	// If cache object is not found and setf is not nil, Get will atomically creates
	// the cache object by calling setf. Otherwise Get will returns nil.
	//
	// The returned cache handle should be released after use by calling Release
	// method.
	Get(key uint64, setf SetFunc) Handle

	// Delete removes cache object with the given key from cache tree.
	// A deleted cache object will be released as soon as all of its handles have
	// been released.
	// Delete only happen once, subsequent delete will consider cache object doesn't
	// exist, even if the cache object ins't released yet.
	//
	// If not nil, fin will be called if the cache object doesn't exist or when
	// finally be released.
	//
	// Delete returns true if such cache object exist and never been deleted.
	Delete(key uint64, fin DelFin) bool

	// Purge removes all cache objects within this namespace from cache tree.
	// This is the same as doing delete on all cache objects.
	//
	// If not nil, fin will be called on all cache objects when its finally be
	// released.
	Purge(fin PurgeFin)

	// Zap detaches namespace from cache tree and release all its cache objects.
	// A zapped namespace can never be filled again.
	// Calling Get on zapped namespace will always return nil.
	Zap()
}

type PurgeFin func(ns, key uint64)

type SetFunc func() (charge int, value interface{})