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DeltaTree2::Cursor now reconstructs current item on-demand, caches it in an Optional member, and does not initialize it when a cursor is copied.

This commit is contained in:
Steve Atherton 2021-05-25 01:31:50 -07:00
parent 7f411934b4
commit 3451c2242f
1 changed files with 18 additions and 25 deletions
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43
fdbserver/DeltaTree.h
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@ -1046,9 +1046,10 @@ public:
Cursor(DecodeCache* cache, DeltaTree2* tree) : cache(cache), tree(tree), nodeIndex(-1) {}
Cursor(DecodeCache* cache, DeltaTree2* tree, int nodeIndex) : cache(cache), tree(tree), nodeIndex(nodeIndex) {
updateItem();
}
Cursor(DecodeCache* cache, DeltaTree2* tree, int nodeIndex) : cache(cache), tree(tree), nodeIndex(nodeIndex) {}
// Copy constructor does not copy item because normally a copied cursor will be immediately moved.
Cursor(const Cursor& c) : cache(c.cache), tree(c.tree), nodeIndex(c.nodeIndex) {}
int rootIndex() {
if (!cache->empty()) {
@ -1062,7 +1063,7 @@ public:
DeltaTree2* tree;
DecodeCache* cache;
int nodeIndex;
T item;
mutable Optional<T> item;
Node* node() const { return tree->nodeAt(cache->get(nodeIndex).nodeOffset); }
@ -1071,7 +1072,7 @@ public:
return format("Cursor{nodeIndex=-1}");
}
return format("Cursor{item=%s indexItem=%s nodeIndex=%d decodedNode=%s node=%s ",
item.toString().c_str(),
item.present() ? item.get().toString().c_str() : "<absent>",
get(cache->get(nodeIndex)).toString().c_str(),
nodeIndex,
cache->get(nodeIndex).toString().c_str(),
@ -1103,23 +1104,20 @@ public:
return delta.apply(cache->arena, base, decoded.partial);
}
private:
inline void updateItem() { item = get(cache->get(nodeIndex)); }
public:
// Get the item at the cursor
// Behavior is undefined if the cursor is not valid.
// If the cursor is moved, the reference object returned will be modified to
// the cursor's new current item.
const T& get() const { return item; }
void switchTree(DeltaTree2* newTree) {
tree = newTree;
if (nodeIndex != -1) {
updateItem();
const T& get() const {
if (!item.present()) {
item = get(cache->get(nodeIndex));
}
return item.get();
}
void switchTree(DeltaTree2* newTree) { tree = newTree; }
// If the cursor is valid, return a reference to the cursor's internal T.
// Otherwise, returns a reference to the cache's upper boundary.
const T& getOrUpperBound() const { return valid() ? get() : cache->upperBound; }
@ -1224,13 +1222,14 @@ public:
// Does not skip/avoid deleted nodes.
int seek(const T& s, int skipLen = 0) {
nodeIndex = -1;
item.reset();
deltatree_printf("seek(%s) start %s\n", s.toString().c_str(), toString().c_str());
int nIndex = rootIndex();
int cmp = 0;
while (nIndex != -1) {
nodeIndex = nIndex;
updateItem();
item.reset();
cmp = s.compare(get(), skipLen);
deltatree_printf("seek(%s) loop cmp=%d %s\n", s.toString().c_str(), cmp, toString().c_str());
if (cmp == 0) {
@ -1249,11 +1248,11 @@ public:
bool moveFirst() {
nodeIndex = -1;
item.reset();
int nIndex = rootIndex();
deltatree_printf("moveFirst start %s\n", toString().c_str());
while (nIndex != -1) {
nodeIndex = nIndex;
updateItem();
deltatree_printf("moveFirst moved %s\n", toString().c_str());
nIndex = getLeftChildIndex(nIndex);
}
@ -1262,11 +1261,11 @@ public:
bool moveLast() {
nodeIndex = -1;
item.reset();
int nIndex = rootIndex();
deltatree_printf("moveLast start %s\n", toString().c_str());
while (nIndex != -1) {
nodeIndex = nIndex;
updateItem();
deltatree_printf("moveLast moved %s\n", toString().c_str());
nIndex = getRightChildIndex(nIndex);
}
@ -1276,21 +1275,18 @@ public:
// Try to move to next node, sees deleted nodes.
void _moveNext() {
deltatree_printf("_moveNext start %s\n", toString().c_str());
item.reset();
// Try to go right
int nIndex = getRightChildIndex(nodeIndex);
// If we couldn't go right, then the answer is our next ancestor
if (nIndex == -1) {
nodeIndex = cache->get(nodeIndex).rightParentIndex;
if (nodeIndex != -1) {
updateItem();
}
deltatree_printf("_moveNext move1 %s\n", toString().c_str());
} else {
// Go left as far as possible
do {
nodeIndex = nIndex;
updateItem();
deltatree_printf("_moveNext move2 %s\n", toString().c_str());
nIndex = getLeftChildIndex(nodeIndex);
} while (nIndex != -1);
@ -1300,20 +1296,17 @@ public:
// Try to move to previous node, sees deleted nodes.
void _movePrev() {
deltatree_printf("_movePrev start %s\n", toString().c_str());
item.reset();
// Try to go left
int nIndex = getLeftChildIndex(nodeIndex);
// If we couldn't go left, then the answer is our prev ancestor
if (nIndex == -1) {
nodeIndex = cache->get(nodeIndex).leftParentIndex;
if (nodeIndex != -1) {
updateItem();
}
deltatree_printf("_movePrev move1 %s\n", toString().c_str());
} else {
// Go right as far as possible
do {
nodeIndex = nIndex;
updateItem();
deltatree_printf("_movePrev move2 %s\n", toString().c_str());
nIndex = getRightChildIndex(nodeIndex);
} while (nIndex != -1);