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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef js_UbiNodePostOrder_h
#define js_UbiNodePostOrder_h
#include "mozilla/Attributes.h"
#include <utility>
#include "js/UbiNode.h"
#include "js/Vector.h"
namespace js {
class SystemAllocPolicy;
}
namespace JS {
class AutoCheckCannotGC;
namespace ubi {
/**
* A post-order depth-first traversal of `ubi::Node` graphs.
*
* No GC may occur while an instance of `PostOrder` is live.
*
* The `NodeVisitor` type provided to `PostOrder::traverse` must have the
* following member:
*
* bool operator()(Node& node)
*
* The node visitor method. This method is called once for each `node`
* reachable from the start set in post-order.
*
* This visitor function should return true on success, or false if an error
* occurs. A false return value terminates the traversal immediately, and
* causes `PostOrder::traverse` to return false.
*
* The `EdgeVisitor` type provided to `PostOrder::traverse` must have the
* following member:
*
* bool operator()(Node& origin, Edge& edge)
*
* The edge visitor method. This method is called once for each outgoing
* `edge` from `origin` that is reachable from the start set.
*
* NB: UNLIKE NODES, THERE IS NO GUARANTEED ORDER IN WHICH EDGES AND THEIR
* ORIGINS ARE VISITED!
*
* This visitor function should return true on success, or false if an error
* occurs. A false return value terminates the traversal immediately, and
* causes `PostOrder::traverse` to return false.
*/
struct PostOrder {
private:
struct OriginAndEdges {
Node origin;
EdgeVector edges;
OriginAndEdges(const Node& node, EdgeVector&& edges)
: origin(node), edges(std::move(edges)) {}
OriginAndEdges(const OriginAndEdges& rhs) = delete;
OriginAndEdges& operator=(const OriginAndEdges& rhs) = delete;
OriginAndEdges(OriginAndEdges&& rhs)
: origin(rhs.origin), edges(std::move(rhs.edges)) {
MOZ_ASSERT(&rhs != this, "self-move disallowed");
}
OriginAndEdges& operator=(OriginAndEdges&& rhs) {
this->~OriginAndEdges();
new (this) OriginAndEdges(std::move(rhs));
return *this;
}
};
using Stack = js::Vector<OriginAndEdges, 256, js::SystemAllocPolicy>;
using Set = js::HashSet<Node, js::DefaultHasher<Node>, js::SystemAllocPolicy>;
JSContext* cx;
Set seen;
Stack stack;
#ifdef DEBUG
bool traversed;
#endif
private:
[[nodiscard]] bool fillEdgesFromRange(EdgeVector& edges,
js::UniquePtr<EdgeRange>& range) {
MOZ_ASSERT(range);
for (; !range->empty(); range->popFront()) {
if (!edges.append(std::move(range->front()))) {
return false;
}
}
return true;
}
[[nodiscard]] bool pushForTraversing(const Node& node) {
EdgeVector edges;
auto range = node.edges(cx, /* wantNames */ false);
return range && fillEdgesFromRange(edges, range) &&
stack.append(OriginAndEdges(node, std::move(edges)));
}
public:
// Construct a post-order traversal object.
//
// The traversal asserts that no GC happens in its runtime during its
// lifetime via the `AutoCheckCannotGC&` parameter. We do nothing with it,
// other than require it to exist with a lifetime that encloses our own.
PostOrder(JSContext* cx, AutoCheckCannotGC&)
: cx(cx),
seen(),
stack()
#ifdef DEBUG
,
traversed(false)
#endif
{
}
// Add `node` as a starting point for the traversal. You may add
// as many starting points as you like. Returns false on OOM.
[[nodiscard]] bool addStart(const Node& node) {
if (!seen.put(node)) {
return false;
}
return pushForTraversing(node);
}
// Traverse the graph in post-order, starting with the set of nodes passed
// to `addStart` and applying `onNode::operator()` for each node in the
// graph and `onEdge::operator()` for each edge in the graph, as described
// above.
//
// This should be called only once per instance of this class.
//
// Return false on OOM or error return from `onNode::operator()` or
// `onEdge::operator()`.
template <typename NodeVisitor, typename EdgeVisitor>
[[nodiscard]] bool traverse(NodeVisitor onNode, EdgeVisitor onEdge) {
#ifdef DEBUG
MOZ_ASSERT(!traversed, "Can only traverse() once!");
traversed = true;
#endif
while (!stack.empty()) {
auto& origin = stack.back().origin;
auto& edges = stack.back().edges;
if (edges.empty()) {
if (!onNode(origin)) {
return false;
}
stack.popBack();
continue;
}
Edge edge = std::move(edges.back());
edges.popBack();
if (!onEdge(origin, edge)) {
return false;
}
auto ptr = seen.lookupForAdd(edge.referent);
// We've already seen this node, don't follow its edges.
if (ptr) {
continue;
}
// Mark the referent as seen and follow its edges.
if (!seen.add(ptr, edge.referent) || !pushForTraversing(edge.referent)) {
return false;
}
}
return true;
}
};
} // namespace ubi
} // namespace JS
#endif // js_UbiNodePostOrder_h