mirror of
https://source.quilibrium.com/quilibrium/ceremonyclient.git
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1305 lines
38 KiB
Go
1305 lines
38 KiB
Go
// Copyright 2020 The LevelDB-Go and Pebble Authors. All rights reserved. Use
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// of this source code is governed by a BSD-style license that can be found in
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// the LICENSE file.
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package manifest
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import (
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"bytes"
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"fmt"
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"strings"
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"sync/atomic"
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"unsafe"
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"github.com/cockroachdb/errors"
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"github.com/cockroachdb/pebble/internal/invariants"
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stdcmp "github.com/cockroachdb/pebble/shims/cmp"
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)
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// The Annotator type defined below is used by other packages to lazily
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// compute a value over a B-Tree. Each node of the B-Tree stores one
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// `annotation` per annotator, containing the result of the computation over
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// the node's subtree.
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//
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// An annotation is marked as valid if it's current with the current subtree
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// state. Annotations are marked as invalid whenever a node will be mutated
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// (in mut). Annotators may also return `false` from `Accumulate` to signal
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// that a computation for a file is not stable and may change in the future.
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// Annotations that include these unstable values are also marked as invalid
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// on the node, ensuring that future queries for the annotation will recompute
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// the value.
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// An Annotator defines a computation over a level's FileMetadata. If the
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// computation is stable and uses inputs that are fixed for the lifetime of
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// a FileMetadata, the LevelMetadata's internal data structures are annotated
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// with the intermediary computations. This allows the computation to be
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// computed incrementally as edits are applied to a level.
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type Annotator interface {
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// Zero returns the zero value of an annotation. This value is returned
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// when a LevelMetadata is empty. The dst argument, if non-nil, is an
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// obsolete value previously returned by this Annotator and may be
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// overwritten and reused to avoid a memory allocation.
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Zero(dst interface{}) (v interface{})
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// Accumulate computes the annotation for a single file in a level's
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// metadata. It merges the file's value into dst and returns a bool flag
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// indicating whether or not the value is stable and okay to cache as an
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// annotation. If the file's value may change over the life of the file,
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// the annotator must return false.
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//
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// Implementations may modify dst and return it to avoid an allocation.
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Accumulate(m *FileMetadata, dst interface{}) (v interface{}, cacheOK bool)
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// Merge combines two values src and dst, returning the result.
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// Implementations may modify dst and return it to avoid an allocation.
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Merge(src interface{}, dst interface{}) interface{}
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}
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type btreeCmp func(*FileMetadata, *FileMetadata) int
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func btreeCmpSeqNum(a, b *FileMetadata) int {
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return a.cmpSeqNum(b)
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}
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func btreeCmpSmallestKey(cmp Compare) btreeCmp {
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return func(a, b *FileMetadata) int {
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return a.cmpSmallestKey(b, cmp)
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}
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}
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// btreeCmpSpecificOrder is used in tests to construct a B-Tree with a
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// specific ordering of FileMetadata within the tree. It's typically used to
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// test consistency checking code that needs to construct a malformed B-Tree.
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func btreeCmpSpecificOrder(files []*FileMetadata) btreeCmp {
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m := map[*FileMetadata]int{}
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for i, f := range files {
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m[f] = i
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}
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return func(a, b *FileMetadata) int {
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ai, aok := m[a]
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bi, bok := m[b]
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if !aok || !bok {
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panic("btreeCmpSliceOrder called with unknown files")
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}
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return stdcmp.Compare(ai, bi)
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}
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}
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const (
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degree = 16
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maxItems = 2*degree - 1
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minItems = degree - 1
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)
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type annotation struct {
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annotator Annotator
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// v is an annotation value, the output of either
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// annotator.Value or annotator.Merge.
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v interface{}
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// valid indicates whether future reads of the annotation may use v as-is.
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// If false, v will be zeroed and recalculated.
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valid bool
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}
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type leafNode struct {
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ref atomic.Int32
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count int16
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leaf bool
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// subtreeCount holds the count of files in the entire subtree formed by
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// this node. For leaf nodes, subtreeCount is always equal to count. For
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// non-leaf nodes, it's the sum of count plus all the children's
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// subtreeCounts.
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//
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// NB: We could move this field to the end of the node struct, since leaf =>
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// count=subtreeCount, however the unsafe casting [leafToNode] performs make
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// it risky and cumbersome.
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subtreeCount int
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items [maxItems]*FileMetadata
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// annot contains one annotation per annotator, merged over the entire
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// node's files (and all descendants for non-leaf nodes).
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annot []annotation
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}
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type node struct {
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leafNode
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children [maxItems + 1]*node
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}
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//go:nocheckptr casts a ptr to a smaller struct to a ptr to a larger struct.
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func leafToNode(ln *leafNode) *node {
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return (*node)(unsafe.Pointer(ln))
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}
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func newLeafNode() *node {
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n := leafToNode(new(leafNode))
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n.leaf = true
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n.ref.Store(1)
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return n
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}
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func newNode() *node {
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n := new(node)
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n.ref.Store(1)
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return n
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}
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// mut creates and returns a mutable node reference. If the node is not shared
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// with any other trees then it can be modified in place. Otherwise, it must be
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// cloned to ensure unique ownership. In this way, we enforce a copy-on-write
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// policy which transparently incorporates the idea of local mutations, like
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// Clojure's transients or Haskell's ST monad, where nodes are only copied
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// during the first time that they are modified between Clone operations.
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//
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// When a node is cloned, the provided pointer will be redirected to the new
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// mutable node.
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func mut(n **node) *node {
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if (*n).ref.Load() == 1 {
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// Exclusive ownership. Can mutate in place.
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// Whenever a node will be mutated, reset its annotations to be marked
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// as uncached. This ensures any future calls to (*node).annotation
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// will recompute annotations on the modified subtree.
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for i := range (*n).annot {
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(*n).annot[i].valid = false
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}
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return *n
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}
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// If we do not have unique ownership over the node then we
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// clone it to gain unique ownership. After doing so, we can
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// release our reference to the old node. We pass recursive
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// as true because even though we just observed the node's
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// reference count to be greater than 1, we might be racing
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// with another call to decRef on this node.
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c := (*n).clone()
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(*n).decRef(true /* contentsToo */, nil)
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*n = c
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// NB: We don't need to clear annotations, because (*node).clone does not
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// copy them.
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return *n
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}
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// incRef acquires a reference to the node.
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func (n *node) incRef() {
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n.ref.Add(1)
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}
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// decRef releases a reference to the node. If requested, the method will unref
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// its items and recurse into child nodes and decrease their refcounts as well.
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// Some internal codepaths that manually copy the node's items or children to
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// new nodes pass contentsToo=false to preserve existing reference counts during
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// operations that should yield a net-zero change to descendant refcounts.
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// When a node is released, its contained files are dereferenced.
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func (n *node) decRef(contentsToo bool, obsolete *[]*FileBacking) {
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if n.ref.Add(-1) > 0 {
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// Other references remain. Can't free.
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return
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}
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// Dereference the node's metadata and release child references if
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// requested. Some internal callers may not want to propagate the deref
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// because they're manually copying the filemetadata and children to other
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// nodes, and they want to preserve the existing reference count.
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if contentsToo {
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for _, f := range n.items[:n.count] {
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if f.Unref() == 0 {
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// There are two sources of node dereferences: tree mutations
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// and Version dereferences. Files should only be made obsolete
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// during Version dereferences, during which `obsolete` will be
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// non-nil.
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if obsolete == nil {
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panic(fmt.Sprintf("file metadata %s dereferenced to zero during tree mutation", f.FileNum))
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}
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// Reference counting is performed on the FileBacking. In the case
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// of a virtual sstable, this reference counting is performed on
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// a FileBacking which is shared by every single virtual sstable
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// with the same backing sstable. If the reference count hits 0,
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// then we know that the FileBacking won't be required by any
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// sstable in Pebble, and that the backing sstable can be deleted.
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*obsolete = append(*obsolete, f.FileBacking)
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}
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}
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if !n.leaf {
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for i := int16(0); i <= n.count; i++ {
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n.children[i].decRef(true /* contentsToo */, obsolete)
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}
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}
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}
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}
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// clone creates a clone of the receiver with a single reference count.
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func (n *node) clone() *node {
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var c *node
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if n.leaf {
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c = newLeafNode()
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} else {
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c = newNode()
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}
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// NB: copy field-by-field without touching n.ref to avoid
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// triggering the race detector and looking like a data race.
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c.count = n.count
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c.items = n.items
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c.subtreeCount = n.subtreeCount
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// Increase the refcount of each contained item.
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for _, f := range n.items[:n.count] {
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f.Ref()
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}
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if !c.leaf {
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// Copy children and increase each refcount.
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c.children = n.children
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for i := int16(0); i <= c.count; i++ {
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c.children[i].incRef()
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}
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}
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return c
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}
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// insertAt inserts the provided file and node at the provided index. This
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// function is for use only as a helper function for internal B-Tree code.
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// Clients should not invoke it directly.
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func (n *node) insertAt(index int, item *FileMetadata, nd *node) {
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if index < int(n.count) {
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copy(n.items[index+1:n.count+1], n.items[index:n.count])
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if !n.leaf {
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copy(n.children[index+2:n.count+2], n.children[index+1:n.count+1])
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}
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}
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n.items[index] = item
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if !n.leaf {
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n.children[index+1] = nd
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}
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n.count++
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}
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// pushBack inserts the provided file and node at the tail of the node's items.
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// This function is for use only as a helper function for internal B-Tree code.
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// Clients should not invoke it directly.
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func (n *node) pushBack(item *FileMetadata, nd *node) {
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n.items[n.count] = item
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if !n.leaf {
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n.children[n.count+1] = nd
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}
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n.count++
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}
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// pushFront inserts the provided file and node at the head of the
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// node's items. This function is for use only as a helper function for internal B-Tree
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// code. Clients should not invoke it directly.
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func (n *node) pushFront(item *FileMetadata, nd *node) {
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if !n.leaf {
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copy(n.children[1:n.count+2], n.children[:n.count+1])
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n.children[0] = nd
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}
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copy(n.items[1:n.count+1], n.items[:n.count])
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n.items[0] = item
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n.count++
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}
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// removeAt removes a value at a given index, pulling all subsequent values
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// back. This function is for use only as a helper function for internal B-Tree
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// code. Clients should not invoke it directly.
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func (n *node) removeAt(index int) (*FileMetadata, *node) {
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var child *node
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if !n.leaf {
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child = n.children[index+1]
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copy(n.children[index+1:n.count], n.children[index+2:n.count+1])
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n.children[n.count] = nil
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}
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n.count--
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out := n.items[index]
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copy(n.items[index:n.count], n.items[index+1:n.count+1])
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n.items[n.count] = nil
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return out, child
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}
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// popBack removes and returns the last element in the list. This function is
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// for use only as a helper function for internal B-Tree code. Clients should
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// not invoke it directly.
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func (n *node) popBack() (*FileMetadata, *node) {
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n.count--
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out := n.items[n.count]
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n.items[n.count] = nil
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if n.leaf {
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return out, nil
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}
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child := n.children[n.count+1]
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n.children[n.count+1] = nil
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return out, child
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}
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// popFront removes and returns the first element in the list. This function is
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// for use only as a helper function for internal B-Tree code. Clients should
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// not invoke it directly.
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func (n *node) popFront() (*FileMetadata, *node) {
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n.count--
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var child *node
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if !n.leaf {
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child = n.children[0]
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copy(n.children[:n.count+1], n.children[1:n.count+2])
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n.children[n.count+1] = nil
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}
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out := n.items[0]
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copy(n.items[:n.count], n.items[1:n.count+1])
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n.items[n.count] = nil
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return out, child
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}
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// find returns the index where the given item should be inserted into this
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// list. 'found' is true if the item already exists in the list at the given
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// index.
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//
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// This function is for use only as a helper function for internal B-Tree code.
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// Clients should not invoke it directly.
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func (n *node) find(cmp btreeCmp, item *FileMetadata) (index int, found bool) {
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// Logic copied from sort.Search. Inlining this gave
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// an 11% speedup on BenchmarkBTreeDeleteInsert.
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i, j := 0, int(n.count)
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for i < j {
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h := int(uint(i+j) >> 1) // avoid overflow when computing h
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// i ≤ h < j
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v := cmp(item, n.items[h])
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if v == 0 {
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return h, true
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} else if v > 0 {
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i = h + 1
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} else {
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j = h
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}
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}
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return i, false
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}
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// split splits the given node at the given index. The current node shrinks,
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// and this function returns the item that existed at that index and a new
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// node containing all items/children after it.
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//
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// split is called when we want to perform a transformation like the one
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// depicted in the following diagram.
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//
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// Before:
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// +-----------+
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// n *node | x y z |
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// +--/-/-\-\--+
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//
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// After:
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// +-----------+
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// | y | n's parent
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// +----/-\----+
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// / \
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// v v
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// +-----------+ +-----------+
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// n *node | x | | z | next *node
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// +-----------+ +-----------+
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//
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// split does not perform the complete transformation; the caller is responsible
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// for updating the parent appropriately. split splits `n` into two nodes, `n`
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// and `next`, returning `next` and the file that separates them. In the diagram
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// above, `n.split` removes y and z from `n`, returning y in the first return
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// value and `next` in the second return value. The caller is responsible for
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// updating n's parent to now contain `y` as the separator between nodes `n` and
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// `next`.
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//
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// This function is for use only as a helper function for internal B-Tree code.
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// Clients should not invoke it directly.
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func (n *node) split(i int) (*FileMetadata, *node) {
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out := n.items[i]
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var next *node
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if n.leaf {
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next = newLeafNode()
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} else {
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next = newNode()
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}
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next.count = n.count - int16(i+1)
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copy(next.items[:], n.items[i+1:n.count])
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for j := int16(i); j < n.count; j++ {
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n.items[j] = nil
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}
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if !n.leaf {
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copy(next.children[:], n.children[i+1:n.count+1])
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descendantsMoved := 0
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for j := int16(i + 1); j <= n.count; j++ {
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descendantsMoved += n.children[j].subtreeCount
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n.children[j] = nil
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}
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n.subtreeCount -= descendantsMoved
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next.subtreeCount += descendantsMoved
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}
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n.count = int16(i)
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// NB: We subtract one more than `next.count` from n's subtreeCount because
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// the item at index `i` was removed from `n.items`. We'll return the item
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// at index `i`, and the caller is responsible for updating the subtree
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// count of whichever node adopts it.
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n.subtreeCount -= int(next.count) + 1
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next.subtreeCount += int(next.count)
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return out, next
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}
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// Insert inserts a item into the subtree rooted at this node, making sure no
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// nodes in the subtree exceed maxItems items.
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func (n *node) Insert(cmp btreeCmp, item *FileMetadata) error {
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i, found := n.find(cmp, item)
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if found {
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// cmp provides a total ordering of the files within a level.
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// If we're inserting a metadata that's equal to an existing item
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// in the tree, we're inserting a file into a level twice.
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return errors.Errorf("files %s and %s collided on sort keys",
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errors.Safe(item.FileNum), errors.Safe(n.items[i].FileNum))
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}
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if n.leaf {
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n.insertAt(i, item, nil)
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n.subtreeCount++
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return nil
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}
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if n.children[i].count >= maxItems {
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splitLa, splitNode := mut(&n.children[i]).split(maxItems / 2)
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n.insertAt(i, splitLa, splitNode)
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switch cmp := cmp(item, n.items[i]); {
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case cmp < 0:
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// no change, we want first split node
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case cmp > 0:
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i++ // we want second split node
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default:
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// cmp provides a total ordering of the files within a level.
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// If we're inserting a metadata that's equal to an existing item
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// in the tree, we're inserting a file into a level twice.
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return errors.Errorf("files %s and %s collided on sort keys",
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errors.Safe(item.FileNum), errors.Safe(n.items[i].FileNum))
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}
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}
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err := mut(&n.children[i]).Insert(cmp, item)
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if err == nil {
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n.subtreeCount++
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}
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return err
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}
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|
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// removeMax removes and returns the maximum item from the subtree rooted at
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// this node. This function is for use only as a helper function for internal
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// B-Tree code. Clients should not invoke it directly.
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func (n *node) removeMax() *FileMetadata {
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if n.leaf {
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n.count--
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n.subtreeCount--
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out := n.items[n.count]
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n.items[n.count] = nil
|
|
return out
|
|
}
|
|
child := mut(&n.children[n.count])
|
|
if child.count <= minItems {
|
|
n.rebalanceOrMerge(int(n.count))
|
|
return n.removeMax()
|
|
}
|
|
n.subtreeCount--
|
|
return child.removeMax()
|
|
}
|
|
|
|
// Remove removes a item from the subtree rooted at this node. Returns
|
|
// the item that was removed or nil if no matching item was found.
|
|
func (n *node) Remove(cmp btreeCmp, item *FileMetadata) (out *FileMetadata) {
|
|
i, found := n.find(cmp, item)
|
|
if n.leaf {
|
|
if found {
|
|
out, _ = n.removeAt(i)
|
|
n.subtreeCount--
|
|
return out
|
|
}
|
|
return nil
|
|
}
|
|
if n.children[i].count <= minItems {
|
|
// Child not large enough to remove from.
|
|
n.rebalanceOrMerge(i)
|
|
return n.Remove(cmp, item)
|
|
}
|
|
child := mut(&n.children[i])
|
|
if found {
|
|
// Replace the item being removed with the max item in our left child.
|
|
out = n.items[i]
|
|
n.items[i] = child.removeMax()
|
|
n.subtreeCount--
|
|
return out
|
|
}
|
|
// File is not in this node and child is large enough to remove from.
|
|
out = child.Remove(cmp, item)
|
|
if out != nil {
|
|
n.subtreeCount--
|
|
}
|
|
return out
|
|
}
|
|
|
|
// rebalanceOrMerge grows child 'i' to ensure it has sufficient room to remove a
|
|
// item from it while keeping it at or above minItems. This function is for use
|
|
// only as a helper function for internal B-Tree code. Clients should not invoke
|
|
// it directly.
|
|
func (n *node) rebalanceOrMerge(i int) {
|
|
switch {
|
|
case i > 0 && n.children[i-1].count > minItems:
|
|
// Rebalance from left sibling.
|
|
//
|
|
// +-----------+
|
|
// | y |
|
|
// +----/-\----+
|
|
// / \
|
|
// v v
|
|
// +-----------+ +-----------+
|
|
// | x | | |
|
|
// +----------\+ +-----------+
|
|
// \
|
|
// v
|
|
// a
|
|
//
|
|
// After:
|
|
//
|
|
// +-----------+
|
|
// | x |
|
|
// +----/-\----+
|
|
// / \
|
|
// v v
|
|
// +-----------+ +-----------+
|
|
// | | | y |
|
|
// +-----------+ +/----------+
|
|
// /
|
|
// v
|
|
// a
|
|
//
|
|
left := mut(&n.children[i-1])
|
|
child := mut(&n.children[i])
|
|
xLa, grandChild := left.popBack()
|
|
yLa := n.items[i-1]
|
|
child.pushFront(yLa, grandChild)
|
|
n.items[i-1] = xLa
|
|
child.subtreeCount++
|
|
left.subtreeCount--
|
|
if grandChild != nil {
|
|
child.subtreeCount += grandChild.subtreeCount
|
|
left.subtreeCount -= grandChild.subtreeCount
|
|
}
|
|
|
|
case i < int(n.count) && n.children[i+1].count > minItems:
|
|
// Rebalance from right sibling.
|
|
//
|
|
// +-----------+
|
|
// | y |
|
|
// +----/-\----+
|
|
// / \
|
|
// v v
|
|
// +-----------+ +-----------+
|
|
// | | | x |
|
|
// +-----------+ +/----------+
|
|
// /
|
|
// v
|
|
// a
|
|
//
|
|
// After:
|
|
//
|
|
// +-----------+
|
|
// | x |
|
|
// +----/-\----+
|
|
// / \
|
|
// v v
|
|
// +-----------+ +-----------+
|
|
// | y | | |
|
|
// +----------\+ +-----------+
|
|
// \
|
|
// v
|
|
// a
|
|
//
|
|
right := mut(&n.children[i+1])
|
|
child := mut(&n.children[i])
|
|
xLa, grandChild := right.popFront()
|
|
yLa := n.items[i]
|
|
child.pushBack(yLa, grandChild)
|
|
child.subtreeCount++
|
|
right.subtreeCount--
|
|
if grandChild != nil {
|
|
child.subtreeCount += grandChild.subtreeCount
|
|
right.subtreeCount -= grandChild.subtreeCount
|
|
}
|
|
n.items[i] = xLa
|
|
|
|
default:
|
|
// Merge with either the left or right sibling.
|
|
//
|
|
// +-----------+
|
|
// | u y v |
|
|
// +----/-\----+
|
|
// / \
|
|
// v v
|
|
// +-----------+ +-----------+
|
|
// | x | | z |
|
|
// +-----------+ +-----------+
|
|
//
|
|
// After:
|
|
//
|
|
// +-----------+
|
|
// | u v |
|
|
// +-----|-----+
|
|
// |
|
|
// v
|
|
// +-----------+
|
|
// | x y z |
|
|
// +-----------+
|
|
//
|
|
if i >= int(n.count) {
|
|
i = int(n.count - 1)
|
|
}
|
|
child := mut(&n.children[i])
|
|
// Make mergeChild mutable, bumping the refcounts on its children if necessary.
|
|
_ = mut(&n.children[i+1])
|
|
mergeLa, mergeChild := n.removeAt(i)
|
|
child.items[child.count] = mergeLa
|
|
copy(child.items[child.count+1:], mergeChild.items[:mergeChild.count])
|
|
if !child.leaf {
|
|
copy(child.children[child.count+1:], mergeChild.children[:mergeChild.count+1])
|
|
}
|
|
child.count += mergeChild.count + 1
|
|
child.subtreeCount += mergeChild.subtreeCount + 1
|
|
|
|
mergeChild.decRef(false /* contentsToo */, nil)
|
|
}
|
|
}
|
|
|
|
// InvalidateAnnotation removes any existing cached annotations for the provided
|
|
// annotator from this node's subtree.
|
|
func (n *node) InvalidateAnnotation(a Annotator) {
|
|
// Find this annotator's annotation on this node.
|
|
var annot *annotation
|
|
for i := range n.annot {
|
|
if n.annot[i].annotator == a {
|
|
annot = &n.annot[i]
|
|
}
|
|
}
|
|
|
|
if annot != nil && annot.valid {
|
|
annot.valid = false
|
|
annot.v = a.Zero(annot.v)
|
|
}
|
|
if !n.leaf {
|
|
for i := int16(0); i <= n.count; i++ {
|
|
n.children[i].InvalidateAnnotation(a)
|
|
}
|
|
}
|
|
}
|
|
|
|
// Annotation retrieves, computing if not already computed, the provided
|
|
// annotator's annotation of this node. The second return value indicates
|
|
// whether the future reads of this annotation may use the first return value
|
|
// as-is. If false, the annotation is not stable and may change on a subsequent
|
|
// computation.
|
|
func (n *node) Annotation(a Annotator) (interface{}, bool) {
|
|
// Find this annotator's annotation on this node.
|
|
var annot *annotation
|
|
for i := range n.annot {
|
|
if n.annot[i].annotator == a {
|
|
annot = &n.annot[i]
|
|
}
|
|
}
|
|
|
|
// If it exists and is marked as valid, we can return it without
|
|
// recomputing anything.
|
|
if annot != nil && annot.valid {
|
|
return annot.v, true
|
|
}
|
|
|
|
if annot == nil {
|
|
// This is n's first time being annotated by a.
|
|
// Create a new zeroed annotation.
|
|
n.annot = append(n.annot, annotation{
|
|
annotator: a,
|
|
v: a.Zero(nil),
|
|
})
|
|
annot = &n.annot[len(n.annot)-1]
|
|
} else {
|
|
// There's an existing annotation that must be recomputed.
|
|
// Zero its value.
|
|
annot.v = a.Zero(annot.v)
|
|
}
|
|
|
|
annot.valid = true
|
|
for i := int16(0); i <= n.count; i++ {
|
|
if !n.leaf {
|
|
v, ok := n.children[i].Annotation(a)
|
|
annot.v = a.Merge(v, annot.v)
|
|
annot.valid = annot.valid && ok
|
|
}
|
|
if i < n.count {
|
|
v, ok := a.Accumulate(n.items[i], annot.v)
|
|
annot.v = v
|
|
annot.valid = annot.valid && ok
|
|
}
|
|
}
|
|
return annot.v, annot.valid
|
|
}
|
|
|
|
func (n *node) verifyInvariants() {
|
|
recomputedSubtreeCount := int(n.count)
|
|
if !n.leaf {
|
|
for i := int16(0); i <= n.count; i++ {
|
|
n.children[i].verifyInvariants()
|
|
recomputedSubtreeCount += n.children[i].subtreeCount
|
|
}
|
|
}
|
|
if recomputedSubtreeCount != n.subtreeCount {
|
|
panic(fmt.Sprintf("recomputed subtree count (%d) ≠ n.subtreeCount (%d)",
|
|
recomputedSubtreeCount, n.subtreeCount))
|
|
}
|
|
}
|
|
|
|
// btree is an implementation of a B-Tree.
|
|
//
|
|
// btree stores FileMetadata in an ordered structure, allowing easy insertion,
|
|
// removal, and iteration. The B-Tree stores items in order based on cmp. The
|
|
// first level of the LSM uses a cmp function that compares sequence numbers.
|
|
// All other levels compare using the FileMetadata.Smallest.
|
|
//
|
|
// Write operations are not safe for concurrent mutation by multiple
|
|
// goroutines, but Read operations are.
|
|
type btree struct {
|
|
root *node
|
|
cmp btreeCmp
|
|
}
|
|
|
|
// Release dereferences and clears the root node of the btree, removing all
|
|
// items from the btree. In doing so, it decrements contained file counts.
|
|
// It returns a slice of newly obsolete backing files, if any.
|
|
func (t *btree) Release() (obsolete []*FileBacking) {
|
|
if t.root != nil {
|
|
t.root.decRef(true /* contentsToo */, &obsolete)
|
|
t.root = nil
|
|
}
|
|
return obsolete
|
|
}
|
|
|
|
// Clone clones the btree, lazily. It does so in constant time.
|
|
func (t *btree) Clone() btree {
|
|
c := *t
|
|
if c.root != nil {
|
|
// Incrementing the reference count on the root node is sufficient to
|
|
// ensure that no node in the cloned tree can be mutated by an actor
|
|
// holding a reference to the original tree and vice versa. This
|
|
// property is upheld because the root node in the receiver btree and
|
|
// the returned btree will both necessarily have a reference count of at
|
|
// least 2 when this method returns. All tree mutations recursively
|
|
// acquire mutable node references (see mut) as they traverse down the
|
|
// tree. The act of acquiring a mutable node reference performs a clone
|
|
// if a node's reference count is greater than one. Cloning a node (see
|
|
// clone) increases the reference count on each of its children,
|
|
// ensuring that they have a reference count of at least 2. This, in
|
|
// turn, ensures that any of the child nodes that are modified will also
|
|
// be copied-on-write, recursively ensuring the immutability property
|
|
// over the entire tree.
|
|
c.root.incRef()
|
|
}
|
|
return c
|
|
}
|
|
|
|
// Delete removes the provided file from the tree.
|
|
// It returns true if the file now has a zero reference count.
|
|
func (t *btree) Delete(item *FileMetadata) (obsolete bool) {
|
|
if t.root == nil || t.root.count == 0 {
|
|
return false
|
|
}
|
|
if out := mut(&t.root).Remove(t.cmp, item); out != nil {
|
|
obsolete = out.Unref() == 0
|
|
}
|
|
if invariants.Enabled {
|
|
t.root.verifyInvariants()
|
|
}
|
|
if t.root.count == 0 {
|
|
old := t.root
|
|
if t.root.leaf {
|
|
t.root = nil
|
|
} else {
|
|
t.root = t.root.children[0]
|
|
}
|
|
old.decRef(false /* contentsToo */, nil)
|
|
}
|
|
return obsolete
|
|
}
|
|
|
|
// Insert adds the given item to the tree. If a item in the tree already
|
|
// equals the given one, Insert panics.
|
|
func (t *btree) Insert(item *FileMetadata) error {
|
|
if t.root == nil {
|
|
t.root = newLeafNode()
|
|
} else if t.root.count >= maxItems {
|
|
splitLa, splitNode := mut(&t.root).split(maxItems / 2)
|
|
newRoot := newNode()
|
|
newRoot.count = 1
|
|
newRoot.items[0] = splitLa
|
|
newRoot.children[0] = t.root
|
|
newRoot.children[1] = splitNode
|
|
newRoot.subtreeCount = t.root.subtreeCount + splitNode.subtreeCount + 1
|
|
t.root = newRoot
|
|
}
|
|
item.Ref()
|
|
err := mut(&t.root).Insert(t.cmp, item)
|
|
if invariants.Enabled {
|
|
t.root.verifyInvariants()
|
|
}
|
|
return err
|
|
}
|
|
|
|
// Iter returns a new iterator object. It is not safe to continue using an
|
|
// iterator after modifications are made to the tree. If modifications are made,
|
|
// create a new iterator.
|
|
func (t *btree) Iter() iterator {
|
|
return iterator{r: t.root, pos: -1, cmp: t.cmp}
|
|
}
|
|
|
|
// Count returns the number of files contained within the B-Tree.
|
|
func (t *btree) Count() int {
|
|
if t.root == nil {
|
|
return 0
|
|
}
|
|
return t.root.subtreeCount
|
|
}
|
|
|
|
// String returns a string description of the tree. The format is
|
|
// similar to the https://en.wikipedia.org/wiki/Newick_format.
|
|
func (t *btree) String() string {
|
|
if t.Count() == 0 {
|
|
return ";"
|
|
}
|
|
var b strings.Builder
|
|
t.root.writeString(&b)
|
|
return b.String()
|
|
}
|
|
|
|
func (n *node) writeString(b *strings.Builder) {
|
|
if n.leaf {
|
|
for i := int16(0); i < n.count; i++ {
|
|
if i != 0 {
|
|
b.WriteString(",")
|
|
}
|
|
b.WriteString(n.items[i].String())
|
|
}
|
|
return
|
|
}
|
|
for i := int16(0); i <= n.count; i++ {
|
|
b.WriteString("(")
|
|
n.children[i].writeString(b)
|
|
b.WriteString(")")
|
|
if i < n.count {
|
|
b.WriteString(n.items[i].String())
|
|
}
|
|
}
|
|
}
|
|
|
|
// iterStack represents a stack of (node, pos) tuples, which captures
|
|
// iteration state as an iterator descends a btree.
|
|
type iterStack struct {
|
|
// a contains aLen stack frames when an iterator stack is short enough.
|
|
// If the iterator stack overflows the capacity of iterStackArr, the stack
|
|
// is moved to s and aLen is set to -1.
|
|
a iterStackArr
|
|
aLen int16 // -1 when using s
|
|
s []iterFrame
|
|
}
|
|
|
|
// Used to avoid allocations for stacks below a certain size.
|
|
type iterStackArr [3]iterFrame
|
|
|
|
type iterFrame struct {
|
|
n *node
|
|
pos int16
|
|
}
|
|
|
|
func (is *iterStack) push(f iterFrame) {
|
|
if is.aLen == -1 {
|
|
is.s = append(is.s, f)
|
|
} else if int(is.aLen) == len(is.a) {
|
|
is.s = make([]iterFrame, int(is.aLen)+1, 2*int(is.aLen))
|
|
copy(is.s, is.a[:])
|
|
is.s[int(is.aLen)] = f
|
|
is.aLen = -1
|
|
} else {
|
|
is.a[is.aLen] = f
|
|
is.aLen++
|
|
}
|
|
}
|
|
|
|
func (is *iterStack) pop() iterFrame {
|
|
if is.aLen == -1 {
|
|
f := is.s[len(is.s)-1]
|
|
is.s = is.s[:len(is.s)-1]
|
|
return f
|
|
}
|
|
is.aLen--
|
|
return is.a[is.aLen]
|
|
}
|
|
|
|
func (is *iterStack) len() int {
|
|
if is.aLen == -1 {
|
|
return len(is.s)
|
|
}
|
|
return int(is.aLen)
|
|
}
|
|
|
|
func (is *iterStack) clone() iterStack {
|
|
// If the iterator is using the embedded iterStackArr, we only need to
|
|
// copy the struct itself.
|
|
if is.s == nil {
|
|
return *is
|
|
}
|
|
clone := *is
|
|
clone.s = make([]iterFrame, len(is.s))
|
|
copy(clone.s, is.s)
|
|
return clone
|
|
}
|
|
|
|
func (is *iterStack) nth(n int) (f iterFrame, ok bool) {
|
|
if is.aLen == -1 {
|
|
if n >= len(is.s) {
|
|
return f, false
|
|
}
|
|
return is.s[n], true
|
|
}
|
|
if int16(n) >= is.aLen {
|
|
return f, false
|
|
}
|
|
return is.a[n], true
|
|
}
|
|
|
|
func (is *iterStack) reset() {
|
|
if is.aLen == -1 {
|
|
is.s = is.s[:0]
|
|
} else {
|
|
is.aLen = 0
|
|
}
|
|
}
|
|
|
|
// iterator is responsible for search and traversal within a btree.
|
|
type iterator struct {
|
|
// the root node of the B-Tree.
|
|
r *node
|
|
// n and pos make up the current position of the iterator.
|
|
// If valid, n.items[pos] is the current value of the iterator.
|
|
//
|
|
// n may be nil iff i.r is nil.
|
|
n *node
|
|
pos int16
|
|
// cmp dictates the ordering of the FileMetadata.
|
|
cmp func(*FileMetadata, *FileMetadata) int
|
|
// a stack of n's ancestors within the B-Tree, alongside the position
|
|
// taken to arrive at n. If non-empty, the bottommost frame of the stack
|
|
// will always contain the B-Tree root.
|
|
s iterStack
|
|
}
|
|
|
|
// countLeft returns the count of files that are to the left of the current
|
|
// iterator position.
|
|
func (i *iterator) countLeft() int {
|
|
if i.r == nil {
|
|
return 0
|
|
}
|
|
|
|
// Each iterator has a stack of frames marking the path from the root node
|
|
// to the current iterator position. All files (n.items) and all subtrees
|
|
// (n.children) with indexes less than [pos] are to the left of the current
|
|
// iterator position.
|
|
//
|
|
// +------------------------+ -
|
|
// | Root pos:5 | |
|
|
// +------------------------+ | stack
|
|
// | Root/5 pos:3 | | frames
|
|
// +------------------------+ | [i.s]
|
|
// | Root/5/3 pos:9 | |
|
|
// +========================+ -
|
|
// | |
|
|
// | i.n: Root/5/3/9 i.pos:2|
|
|
// +------------------------+
|
|
//
|
|
var count int
|
|
// Walk all the ancestors in the iterator stack [i.s], tallying up all the
|
|
// files and subtrees to the left of the stack frame's position.
|
|
f, ok := i.s.nth(0)
|
|
for fi := 0; ok; fi++ {
|
|
// There are [f.pos] files contained within [f.n.items] that sort to the
|
|
// left of the subtree the iterator has descended.
|
|
count += int(f.pos)
|
|
// Any subtrees that fall before the stack frame's position are entirely
|
|
// to the left of the iterator's current position.
|
|
for j := int16(0); j < f.pos; j++ {
|
|
count += f.n.children[j].subtreeCount
|
|
}
|
|
f, ok = i.s.nth(fi + 1)
|
|
}
|
|
|
|
// The bottommost stack frame is inlined within the iterator struct. Again,
|
|
// [i.pos] files fall to the left of the current iterator position.
|
|
count += int(i.pos)
|
|
if !i.n.leaf {
|
|
// NB: Unlike above, we use a `<= i.pos` comparison. The iterator is
|
|
// positioned at item `i.n.items[i.pos]`, which sorts after everything
|
|
// in the subtree at `i.n.children[i.pos]`.
|
|
for j := int16(0); j <= i.pos; j++ {
|
|
count += i.n.children[j].subtreeCount
|
|
}
|
|
}
|
|
return count
|
|
}
|
|
|
|
func (i *iterator) clone() iterator {
|
|
c := *i
|
|
c.s = i.s.clone()
|
|
return c
|
|
}
|
|
|
|
func (i *iterator) reset() {
|
|
i.n = i.r
|
|
i.pos = -1
|
|
i.s.reset()
|
|
}
|
|
|
|
func (i iterator) String() string {
|
|
var buf bytes.Buffer
|
|
for n := 0; ; n++ {
|
|
f, ok := i.s.nth(n)
|
|
if !ok {
|
|
break
|
|
}
|
|
fmt.Fprintf(&buf, "%p: %02d/%02d\n", f.n, f.pos, f.n.count)
|
|
}
|
|
if i.r == nil {
|
|
fmt.Fprintf(&buf, "<nil>: %02d", i.pos)
|
|
} else {
|
|
fmt.Fprintf(&buf, "%p: %02d/%02d", i.n, i.pos, i.n.count)
|
|
}
|
|
return buf.String()
|
|
}
|
|
|
|
func cmpIter(a, b iterator) int {
|
|
if a.r != b.r {
|
|
panic("compared iterators from different btrees")
|
|
}
|
|
|
|
// Each iterator has a stack of frames marking the path from the root node
|
|
// to the current iterator position. We walk both paths formed by the
|
|
// iterators' stacks simultaneously, descending from the shared root node,
|
|
// always comparing nodes at the same level in the tree.
|
|
//
|
|
// If the iterators' paths ever diverge and point to different nodes, the
|
|
// iterators are not equal and we use the node positions to evaluate the
|
|
// comparison.
|
|
//
|
|
// If an iterator's stack ends, we stop descending and use its current
|
|
// node and position for the final comparison. One iterator's stack may
|
|
// end before another's if one iterator is positioned deeper in the tree.
|
|
//
|
|
// a b
|
|
// +------------------------+ +--------------------------+ -
|
|
// | Root pos:5 | = | Root pos:5 | |
|
|
// +------------------------+ +--------------------------+ | stack
|
|
// | Root/5 pos:3 | = | Root/5 pos:3 | | frames
|
|
// +------------------------+ +--------------------------+ |
|
|
// | Root/5/3 pos:9 | > | Root/5/3 pos:1 | |
|
|
// +========================+ +==========================+ -
|
|
// | | | |
|
|
// | a.n: Root/5/3/9 a.pos:2| | b.n: Root/5/3/1, b.pos:5 |
|
|
// +------------------------+ +--------------------------+
|
|
|
|
// Initialize with the iterator's current node and position. These are
|
|
// conceptually the most-recent/current frame of the iterator stack.
|
|
an, apos := a.n, a.pos
|
|
bn, bpos := b.n, b.pos
|
|
|
|
// aok, bok are set while traversing the iterator's path down the B-Tree.
|
|
// They're declared in the outer scope because they help distinguish the
|
|
// sentinel case when both iterators' first frame points to the last child
|
|
// of the root. If an iterator has no other frames in its stack, it's the
|
|
// end sentinel state which sorts after everything else.
|
|
var aok, bok bool
|
|
for i := 0; ; i++ {
|
|
var af, bf iterFrame
|
|
af, aok = a.s.nth(i)
|
|
bf, bok = b.s.nth(i)
|
|
if !aok || !bok {
|
|
if aok {
|
|
// Iterator a, unlike iterator b, still has a frame. Set an,
|
|
// apos so we compare using the frame from the stack.
|
|
an, apos = af.n, af.pos
|
|
}
|
|
if bok {
|
|
// Iterator b, unlike iterator a, still has a frame. Set bn,
|
|
// bpos so we compare using the frame from the stack.
|
|
bn, bpos = bf.n, bf.pos
|
|
}
|
|
break
|
|
}
|
|
|
|
// aok && bok
|
|
if af.n != bf.n {
|
|
panic("nonmatching nodes during btree iterator comparison")
|
|
}
|
|
if v := stdcmp.Compare(af.pos, bf.pos); v != 0 {
|
|
return v
|
|
}
|
|
// Otherwise continue up both iterators' stacks (equivalently, down the
|
|
// B-Tree away from the root).
|
|
}
|
|
|
|
if aok && bok {
|
|
panic("expected one or more stacks to have been exhausted")
|
|
}
|
|
if an != bn {
|
|
panic("nonmatching nodes during btree iterator comparison")
|
|
}
|
|
if v := stdcmp.Compare(apos, bpos); v != 0 {
|
|
return v
|
|
}
|
|
switch {
|
|
case aok:
|
|
// a is positioned at a leaf child at this position and b is at an
|
|
// end sentinel state.
|
|
return -1
|
|
case bok:
|
|
// b is positioned at a leaf child at this position and a is at an
|
|
// end sentinel state.
|
|
return +1
|
|
default:
|
|
return 0
|
|
}
|
|
}
|
|
|
|
func (i *iterator) descend(n *node, pos int16) {
|
|
i.s.push(iterFrame{n: n, pos: pos})
|
|
i.n = n.children[pos]
|
|
i.pos = 0
|
|
}
|
|
|
|
// ascend ascends up to the current node's parent and resets the position
|
|
// to the one previously set for this parent node.
|
|
func (i *iterator) ascend() {
|
|
f := i.s.pop()
|
|
i.n = f.n
|
|
i.pos = f.pos
|
|
}
|
|
|
|
// seek repositions the iterator over the first file for which fn returns
|
|
// true, mirroring the semantics of the standard library's sort.Search
|
|
// function. Like sort.Search, seek requires the iterator's B-Tree to be
|
|
// ordered such that fn returns false for some (possibly empty) prefix of the
|
|
// tree's files, and then true for the (possibly empty) remainder.
|
|
func (i *iterator) seek(fn func(*FileMetadata) bool) {
|
|
i.reset()
|
|
if i.r == nil {
|
|
return
|
|
}
|
|
|
|
for {
|
|
// Logic copied from sort.Search.
|
|
j, k := 0, int(i.n.count)
|
|
for j < k {
|
|
h := int(uint(j+k) >> 1) // avoid overflow when computing h
|
|
|
|
// j ≤ h < k
|
|
if !fn(i.n.items[h]) {
|
|
j = h + 1 // preserves f(j-1) == false
|
|
} else {
|
|
k = h // preserves f(k) == true
|
|
}
|
|
}
|
|
|
|
i.pos = int16(j)
|
|
if i.n.leaf {
|
|
if i.pos == i.n.count {
|
|
i.next()
|
|
}
|
|
return
|
|
}
|
|
i.descend(i.n, i.pos)
|
|
}
|
|
}
|
|
|
|
// first seeks to the first item in the btree.
|
|
func (i *iterator) first() {
|
|
i.reset()
|
|
if i.r == nil {
|
|
return
|
|
}
|
|
for !i.n.leaf {
|
|
i.descend(i.n, 0)
|
|
}
|
|
i.pos = 0
|
|
}
|
|
|
|
// last seeks to the last item in the btree.
|
|
func (i *iterator) last() {
|
|
i.reset()
|
|
if i.r == nil {
|
|
return
|
|
}
|
|
for !i.n.leaf {
|
|
i.descend(i.n, i.n.count)
|
|
}
|
|
i.pos = i.n.count - 1
|
|
}
|
|
|
|
// next positions the iterator to the item immediately following
|
|
// its current position.
|
|
func (i *iterator) next() {
|
|
if i.r == nil {
|
|
return
|
|
}
|
|
|
|
if i.n.leaf {
|
|
if i.pos < i.n.count {
|
|
i.pos++
|
|
}
|
|
if i.pos < i.n.count {
|
|
return
|
|
}
|
|
for i.s.len() > 0 && i.pos >= i.n.count {
|
|
i.ascend()
|
|
}
|
|
return
|
|
}
|
|
|
|
i.descend(i.n, i.pos+1)
|
|
for !i.n.leaf {
|
|
i.descend(i.n, 0)
|
|
}
|
|
i.pos = 0
|
|
}
|
|
|
|
// prev positions the iterator to the item immediately preceding
|
|
// its current position.
|
|
func (i *iterator) prev() {
|
|
if i.r == nil {
|
|
return
|
|
}
|
|
|
|
if i.n.leaf {
|
|
i.pos--
|
|
if i.pos >= 0 {
|
|
return
|
|
}
|
|
for i.s.len() > 0 && i.pos < 0 {
|
|
i.ascend()
|
|
i.pos--
|
|
}
|
|
return
|
|
}
|
|
|
|
i.descend(i.n, i.pos)
|
|
for !i.n.leaf {
|
|
i.descend(i.n, i.n.count)
|
|
}
|
|
i.pos = i.n.count - 1
|
|
}
|
|
|
|
// valid returns whether the iterator is positioned at a valid position.
|
|
func (i *iterator) valid() bool {
|
|
return i.r != nil && i.pos >= 0 && i.pos < i.n.count
|
|
}
|
|
|
|
// cur returns the item at the iterator's current position. It is illegal
|
|
// to call cur if the iterator is not valid.
|
|
func (i *iterator) cur() *FileMetadata {
|
|
if invariants.Enabled && !i.valid() {
|
|
panic("btree iterator.cur invoked on invalid iterator")
|
|
}
|
|
return i.n.items[i.pos]
|
|
}
|