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Diffstat (limited to 'third_party/abseil_cpp/absl/synchronization/internal/graphcycles.cc')
| -rw-r--r-- | third_party/abseil_cpp/absl/synchronization/internal/graphcycles.cc | 697 |
1 files changed, 0 insertions, 697 deletions
diff --git a/third_party/abseil_cpp/absl/synchronization/internal/graphcycles.cc b/third_party/abseil_cpp/absl/synchronization/internal/graphcycles.cc deleted file mode 100644 index 19f9aab5b1..0000000000 --- a/third_party/abseil_cpp/absl/synchronization/internal/graphcycles.cc +++ /dev/null @@ -1,697 +0,0 @@ -// Copyright 2017 The Abseil Authors. -// -// Licensed under the Apache License, Version 2.0 (the "License"); -// you may not use this file except in compliance with the License. -// You may obtain a copy of the License at -// -// https://www.apache.org/licenses/LICENSE-2.0 -// -// Unless required by applicable law or agreed to in writing, software -// distributed under the License is distributed on an "AS IS" BASIS, -// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. -// See the License for the specific language governing permissions and -// limitations under the License. - -// GraphCycles provides incremental cycle detection on a dynamic -// graph using the following algorithm: -// -// A dynamic topological sort algorithm for directed acyclic graphs -// David J. Pearce, Paul H. J. Kelly -// Journal of Experimental Algorithmics (JEA) JEA Homepage archive -// Volume 11, 2006, Article No. 1.7 -// -// Brief summary of the algorithm: -// -// (1) Maintain a rank for each node that is consistent -// with the topological sort of the graph. I.e., path from x to y -// implies rank[x] < rank[y]. -// (2) When a new edge (x->y) is inserted, do nothing if rank[x] < rank[y]. -// (3) Otherwise: adjust ranks in the neighborhood of x and y. - -#include "absl/base/attributes.h" -// This file is a no-op if the required LowLevelAlloc support is missing. -#include "absl/base/internal/low_level_alloc.h" -#ifndef ABSL_LOW_LEVEL_ALLOC_MISSING - -#include "absl/synchronization/internal/graphcycles.h" - -#include <algorithm> -#include <array> -#include "absl/base/internal/hide_ptr.h" -#include "absl/base/internal/raw_logging.h" -#include "absl/base/internal/spinlock.h" - -// Do not use STL. This module does not use standard memory allocation. - -namespace absl { -ABSL_NAMESPACE_BEGIN -namespace synchronization_internal { - -namespace { - -// Avoid LowLevelAlloc's default arena since it calls malloc hooks in -// which people are doing things like acquiring Mutexes. -ABSL_CONST_INIT static absl::base_internal::SpinLock arena_mu( - absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY); -ABSL_CONST_INIT static base_internal::LowLevelAlloc::Arena* arena; - -static void InitArenaIfNecessary() { - arena_mu.Lock(); - if (arena == nullptr) { - arena = base_internal::LowLevelAlloc::NewArena(0); - } - arena_mu.Unlock(); -} - -// Number of inlined elements in Vec. Hash table implementation -// relies on this being a power of two. -static const uint32_t kInline = 8; - -// A simple LowLevelAlloc based resizable vector with inlined storage -// for a few elements. T must be a plain type since constructor -// and destructor are not run on elements of type T managed by Vec. -template <typename T> -class Vec { - public: - Vec() { Init(); } - ~Vec() { Discard(); } - - void clear() { - Discard(); - Init(); - } - - bool empty() const { return size_ == 0; } - uint32_t size() const { return size_; } - T* begin() { return ptr_; } - T* end() { return ptr_ + size_; } - const T& operator[](uint32_t i) const { return ptr_[i]; } - T& operator[](uint32_t i) { return ptr_[i]; } - const T& back() const { return ptr_[size_-1]; } - void pop_back() { size_--; } - - void push_back(const T& v) { - if (size_ == capacity_) Grow(size_ + 1); - ptr_[size_] = v; - size_++; - } - - void resize(uint32_t n) { - if (n > capacity_) Grow(n); - size_ = n; - } - - void fill(const T& val) { - for (uint32_t i = 0; i < size(); i++) { - ptr_[i] = val; - } - } - - // Guarantees src is empty at end. - // Provided for the hash table resizing code below. - void MoveFrom(Vec<T>* src) { - if (src->ptr_ == src->space_) { - // Need to actually copy - resize(src->size_); - std::copy(src->ptr_, src->ptr_ + src->size_, ptr_); - src->size_ = 0; - } else { - Discard(); - ptr_ = src->ptr_; - size_ = src->size_; - capacity_ = src->capacity_; - src->Init(); - } - } - - private: - T* ptr_; - T space_[kInline]; - uint32_t size_; - uint32_t capacity_; - - void Init() { - ptr_ = space_; - size_ = 0; - capacity_ = kInline; - } - - void Discard() { - if (ptr_ != space_) base_internal::LowLevelAlloc::Free(ptr_); - } - - void Grow(uint32_t n) { - while (capacity_ < n) { - capacity_ *= 2; - } - size_t request = static_cast<size_t>(capacity_) * sizeof(T); - T* copy = static_cast<T*>( - base_internal::LowLevelAlloc::AllocWithArena(request, arena)); - std::copy(ptr_, ptr_ + size_, copy); - Discard(); - ptr_ = copy; - } - - Vec(const Vec&) = delete; - Vec& operator=(const Vec&) = delete; -}; - -// A hash set of non-negative int32_t that uses Vec for its underlying storage. -class NodeSet { - public: - NodeSet() { Init(); } - - void clear() { Init(); } - bool contains(int32_t v) const { return table_[FindIndex(v)] == v; } - - bool insert(int32_t v) { - uint32_t i = FindIndex(v); - if (table_[i] == v) { - return false; - } - if (table_[i] == kEmpty) { - // Only inserting over an empty cell increases the number of occupied - // slots. - occupied_++; - } - table_[i] = v; - // Double when 75% full. - if (occupied_ >= table_.size() - table_.size()/4) Grow(); - return true; - } - - void erase(uint32_t v) { - uint32_t i = FindIndex(v); - if (static_cast<uint32_t>(table_[i]) == v) { - table_[i] = kDel; - } - } - - // Iteration: is done via HASH_FOR_EACH - // Example: - // HASH_FOR_EACH(elem, node->out) { ... } -#define HASH_FOR_EACH(elem, eset) \ - for (int32_t elem, _cursor = 0; (eset).Next(&_cursor, &elem); ) - bool Next(int32_t* cursor, int32_t* elem) { - while (static_cast<uint32_t>(*cursor) < table_.size()) { - int32_t v = table_[*cursor]; - (*cursor)++; - if (v >= 0) { - *elem = v; - return true; - } - } - return false; - } - - private: - enum : int32_t { kEmpty = -1, kDel = -2 }; - Vec<int32_t> table_; - uint32_t occupied_; // Count of non-empty slots (includes deleted slots) - - static uint32_t Hash(uint32_t a) { return a * 41; } - - // Return index for storing v. May return an empty index or deleted index - int FindIndex(int32_t v) const { - // Search starting at hash index. - const uint32_t mask = table_.size() - 1; - uint32_t i = Hash(v) & mask; - int deleted_index = -1; // If >= 0, index of first deleted element we see - while (true) { - int32_t e = table_[i]; - if (v == e) { - return i; - } else if (e == kEmpty) { - // Return any previously encountered deleted slot. - return (deleted_index >= 0) ? deleted_index : i; - } else if (e == kDel && deleted_index < 0) { - // Keep searching since v might be present later. - deleted_index = i; - } - i = (i + 1) & mask; // Linear probing; quadratic is slightly slower. - } - } - - void Init() { - table_.clear(); - table_.resize(kInline); - table_.fill(kEmpty); - occupied_ = 0; - } - - void Grow() { - Vec<int32_t> copy; - copy.MoveFrom(&table_); - occupied_ = 0; - table_.resize(copy.size() * 2); - table_.fill(kEmpty); - - for (const auto& e : copy) { - if (e >= 0) insert(e); - } - } - - NodeSet(const NodeSet&) = delete; - NodeSet& operator=(const NodeSet&) = delete; -}; - -// We encode a node index and a node version in GraphId. The version -// number is incremented when the GraphId is freed which automatically -// invalidates all copies of the GraphId. - -inline GraphId MakeId(int32_t index, uint32_t version) { - GraphId g; - g.handle = - (static_cast<uint64_t>(version) << 32) | static_cast<uint32_t>(index); - return g; -} - -inline int32_t NodeIndex(GraphId id) { - return static_cast<uint32_t>(id.handle & 0xfffffffful); -} - -inline uint32_t NodeVersion(GraphId id) { - return static_cast<uint32_t>(id.handle >> 32); -} - -struct Node { - int32_t rank; // rank number assigned by Pearce-Kelly algorithm - uint32_t version; // Current version number - int32_t next_hash; // Next entry in hash table - bool visited; // Temporary marker used by depth-first-search - uintptr_t masked_ptr; // User-supplied pointer - NodeSet in; // List of immediate predecessor nodes in graph - NodeSet out; // List of immediate successor nodes in graph - int priority; // Priority of recorded stack trace. - int nstack; // Depth of recorded stack trace. - void* stack[40]; // stack[0,nstack-1] holds stack trace for node. -}; - -// Hash table for pointer to node index lookups. -class PointerMap { - public: - explicit PointerMap(const Vec<Node*>* nodes) : nodes_(nodes) { - table_.fill(-1); - } - - int32_t Find(void* ptr) { - auto masked = base_internal::HidePtr(ptr); - for (int32_t i = table_[Hash(ptr)]; i != -1;) { - Node* n = (*nodes_)[i]; - if (n->masked_ptr == masked) return i; - i = n->next_hash; - } - return -1; - } - - void Add(void* ptr, int32_t i) { - int32_t* head = &table_[Hash(ptr)]; - (*nodes_)[i]->next_hash = *head; - *head = i; - } - - int32_t Remove(void* ptr) { - // Advance through linked list while keeping track of the - // predecessor slot that points to the current entry. - auto masked = base_internal::HidePtr(ptr); - for (int32_t* slot = &table_[Hash(ptr)]; *slot != -1; ) { - int32_t index = *slot; - Node* n = (*nodes_)[index]; - if (n->masked_ptr == masked) { - *slot = n->next_hash; // Remove n from linked list - n->next_hash = -1; - return index; - } - slot = &n->next_hash; - } - return -1; - } - - private: - // Number of buckets in hash table for pointer lookups. - static constexpr uint32_t kHashTableSize = 8171; // should be prime - - const Vec<Node*>* nodes_; - std::array<int32_t, kHashTableSize> table_; - - static uint32_t Hash(void* ptr) { - return reinterpret_cast<uintptr_t>(ptr) % kHashTableSize; - } -}; - -} // namespace - -struct GraphCycles::Rep { - Vec<Node*> nodes_; - Vec<int32_t> free_nodes_; // Indices for unused entries in nodes_ - PointerMap ptrmap_; - - // Temporary state. - Vec<int32_t> deltaf_; // Results of forward DFS - Vec<int32_t> deltab_; // Results of backward DFS - Vec<int32_t> list_; // All nodes to reprocess - Vec<int32_t> merged_; // Rank values to assign to list_ entries - Vec<int32_t> stack_; // Emulates recursion stack for depth-first searches - - Rep() : ptrmap_(&nodes_) {} -}; - -static Node* FindNode(GraphCycles::Rep* rep, GraphId id) { - Node* n = rep->nodes_[NodeIndex(id)]; - return (n->version == NodeVersion(id)) ? n : nullptr; -} - -GraphCycles::GraphCycles() { - InitArenaIfNecessary(); - rep_ = new (base_internal::LowLevelAlloc::AllocWithArena(sizeof(Rep), arena)) - Rep; -} - -GraphCycles::~GraphCycles() { - for (auto* node : rep_->nodes_) { - node->Node::~Node(); - base_internal::LowLevelAlloc::Free(node); - } - rep_->Rep::~Rep(); - base_internal::LowLevelAlloc::Free(rep_); -} - -bool GraphCycles::CheckInvariants() const { - Rep* r = rep_; - NodeSet ranks; // Set of ranks seen so far. - for (uint32_t x = 0; x < r->nodes_.size(); x++) { - Node* nx = r->nodes_[x]; - void* ptr = base_internal::UnhidePtr<void>(nx->masked_ptr); - if (ptr != nullptr && static_cast<uint32_t>(r->ptrmap_.Find(ptr)) != x) { - ABSL_RAW_LOG(FATAL, "Did not find live node in hash table %u %p", x, ptr); - } - if (nx->visited) { - ABSL_RAW_LOG(FATAL, "Did not clear visited marker on node %u", x); - } - if (!ranks.insert(nx->rank)) { - ABSL_RAW_LOG(FATAL, "Duplicate occurrence of rank %d", nx->rank); - } - HASH_FOR_EACH(y, nx->out) { - Node* ny = r->nodes_[y]; - if (nx->rank >= ny->rank) { - ABSL_RAW_LOG(FATAL, "Edge %u->%d has bad rank assignment %d->%d", x, y, - nx->rank, ny->rank); - } - } - } - return true; -} - -GraphId GraphCycles::GetId(void* ptr) { - int32_t i = rep_->ptrmap_.Find(ptr); - if (i != -1) { - return MakeId(i, rep_->nodes_[i]->version); - } else if (rep_->free_nodes_.empty()) { - Node* n = - new (base_internal::LowLevelAlloc::AllocWithArena(sizeof(Node), arena)) - Node; - n->version = 1; // Avoid 0 since it is used by InvalidGraphId() - n->visited = false; - n->rank = rep_->nodes_.size(); - n->masked_ptr = base_internal::HidePtr(ptr); - n->nstack = 0; - n->priority = 0; - rep_->nodes_.push_back(n); - rep_->ptrmap_.Add(ptr, n->rank); - return MakeId(n->rank, n->version); - } else { - // Preserve preceding rank since the set of ranks in use must be - // a permutation of [0,rep_->nodes_.size()-1]. - int32_t r = rep_->free_nodes_.back(); - rep_->free_nodes_.pop_back(); - Node* n = rep_->nodes_[r]; - n->masked_ptr = base_internal::HidePtr(ptr); - n->nstack = 0; - n->priority = 0; - rep_->ptrmap_.Add(ptr, r); - return MakeId(r, n->version); - } -} - -void GraphCycles::RemoveNode(void* ptr) { - int32_t i = rep_->ptrmap_.Remove(ptr); - if (i == -1) { - return; - } - Node* x = rep_->nodes_[i]; - HASH_FOR_EACH(y, x->out) { - rep_->nodes_[y]->in.erase(i); - } - HASH_FOR_EACH(y, x->in) { - rep_->nodes_[y]->out.erase(i); - } - x->in.clear(); - x->out.clear(); - x->masked_ptr = base_internal::HidePtr<void>(nullptr); - if (x->version == std::numeric_limits<uint32_t>::max()) { - // Cannot use x any more - } else { - x->version++; // Invalidates all copies of node. - rep_->free_nodes_.push_back(i); - } -} - -void* GraphCycles::Ptr(GraphId id) { - Node* n = FindNode(rep_, id); - return n == nullptr ? nullptr - : base_internal::UnhidePtr<void>(n->masked_ptr); -} - -bool GraphCycles::HasNode(GraphId node) { - return FindNode(rep_, node) != nullptr; -} - -bool GraphCycles::HasEdge(GraphId x, GraphId y) const { - Node* xn = FindNode(rep_, x); - return xn && FindNode(rep_, y) && xn->out.contains(NodeIndex(y)); -} - -void GraphCycles::RemoveEdge(GraphId x, GraphId y) { - Node* xn = FindNode(rep_, x); - Node* yn = FindNode(rep_, y); - if (xn && yn) { - xn->out.erase(NodeIndex(y)); - yn->in.erase(NodeIndex(x)); - // No need to update the rank assignment since a previous valid - // rank assignment remains valid after an edge deletion. - } -} - -static bool ForwardDFS(GraphCycles::Rep* r, int32_t n, int32_t upper_bound); -static void BackwardDFS(GraphCycles::Rep* r, int32_t n, int32_t lower_bound); -static void Reorder(GraphCycles::Rep* r); -static void Sort(const Vec<Node*>&, Vec<int32_t>* delta); -static void MoveToList( - GraphCycles::Rep* r, Vec<int32_t>* src, Vec<int32_t>* dst); - -bool GraphCycles::InsertEdge(GraphId idx, GraphId idy) { - Rep* r = rep_; - const int32_t x = NodeIndex(idx); - const int32_t y = NodeIndex(idy); - Node* nx = FindNode(r, idx); - Node* ny = FindNode(r, idy); - if (nx == nullptr || ny == nullptr) return true; // Expired ids - - if (nx == ny) return false; // Self edge - if (!nx->out.insert(y)) { - // Edge already exists. - return true; - } - - ny->in.insert(x); - - if (nx->rank <= ny->rank) { - // New edge is consistent with existing rank assignment. - return true; - } - - // Current rank assignments are incompatible with the new edge. Recompute. - // We only need to consider nodes that fall in the range [ny->rank,nx->rank]. - if (!ForwardDFS(r, y, nx->rank)) { - // Found a cycle. Undo the insertion and tell caller. - nx->out.erase(y); - ny->in.erase(x); - // Since we do not call Reorder() on this path, clear any visited - // markers left by ForwardDFS. - for (const auto& d : r->deltaf_) { - r->nodes_[d]->visited = false; - } - return false; - } - BackwardDFS(r, x, ny->rank); - Reorder(r); - return true; -} - -static bool ForwardDFS(GraphCycles::Rep* r, int32_t n, int32_t upper_bound) { - // Avoid recursion since stack space might be limited. - // We instead keep a stack of nodes to visit. - r->deltaf_.clear(); - r->stack_.clear(); - r->stack_.push_back(n); - while (!r->stack_.empty()) { - n = r->stack_.back(); - r->stack_.pop_back(); - Node* nn = r->nodes_[n]; - if (nn->visited) continue; - - nn->visited = true; - r->deltaf_.push_back(n); - - HASH_FOR_EACH(w, nn->out) { - Node* nw = r->nodes_[w]; - if (nw->rank == upper_bound) { - return false; // Cycle - } - if (!nw->visited && nw->rank < upper_bound) { - r->stack_.push_back(w); - } - } - } - return true; -} - -static void BackwardDFS(GraphCycles::Rep* r, int32_t n, int32_t lower_bound) { - r->deltab_.clear(); - r->stack_.clear(); - r->stack_.push_back(n); - while (!r->stack_.empty()) { - n = r->stack_.back(); - r->stack_.pop_back(); - Node* nn = r->nodes_[n]; - if (nn->visited) continue; - - nn->visited = true; - r->deltab_.push_back(n); - - HASH_FOR_EACH(w, nn->in) { - Node* nw = r->nodes_[w]; - if (!nw->visited && lower_bound < nw->rank) { - r->stack_.push_back(w); - } - } - } -} - -static void Reorder(GraphCycles::Rep* r) { - Sort(r->nodes_, &r->deltab_); - Sort(r->nodes_, &r->deltaf_); - - // Adds contents of delta lists to list_ (backwards deltas first). - r->list_.clear(); - MoveToList(r, &r->deltab_, &r->list_); - MoveToList(r, &r->deltaf_, &r->list_); - - // Produce sorted list of all ranks that will be reassigned. - r->merged_.resize(r->deltab_.size() + r->deltaf_.size()); - std::merge(r->deltab_.begin(), r->deltab_.end(), - r->deltaf_.begin(), r->deltaf_.end(), - r->merged_.begin()); - - // Assign the ranks in order to the collected list. - for (uint32_t i = 0; i < r->list_.size(); i++) { - r->nodes_[r->list_[i]]->rank = r->merged_[i]; - } -} - -static void Sort(const Vec<Node*>& nodes, Vec<int32_t>* delta) { - struct ByRank { - const Vec<Node*>* nodes; - bool operator()(int32_t a, int32_t b) const { - return (*nodes)[a]->rank < (*nodes)[b]->rank; - } - }; - ByRank cmp; - cmp.nodes = &nodes; - std::sort(delta->begin(), delta->end(), cmp); -} - -static void MoveToList( - GraphCycles::Rep* r, Vec<int32_t>* src, Vec<int32_t>* dst) { - for (auto& v : *src) { - int32_t w = v; - v = r->nodes_[w]->rank; // Replace v entry with its rank - r->nodes_[w]->visited = false; // Prepare for future DFS calls - dst->push_back(w); - } -} - -int GraphCycles::FindPath(GraphId idx, GraphId idy, int max_path_len, - GraphId path[]) const { - Rep* r = rep_; - if (FindNode(r, idx) == nullptr || FindNode(r, idy) == nullptr) return 0; - const int32_t x = NodeIndex(idx); - const int32_t y = NodeIndex(idy); - - // Forward depth first search starting at x until we hit y. - // As we descend into a node, we push it onto the path. - // As we leave a node, we remove it from the path. - int path_len = 0; - - NodeSet seen; - r->stack_.clear(); - r->stack_.push_back(x); - while (!r->stack_.empty()) { - int32_t n = r->stack_.back(); - r->stack_.pop_back(); - if (n < 0) { - // Marker to indicate that we are leaving a node - path_len--; - continue; - } - - if (path_len < max_path_len) { - path[path_len] = MakeId(n, rep_->nodes_[n]->version); - } - path_len++; - r->stack_.push_back(-1); // Will remove tentative path entry - - if (n == y) { - return path_len; - } - - HASH_FOR_EACH(w, r->nodes_[n]->out) { - if (seen.insert(w)) { - r->stack_.push_back(w); - } - } - } - - return 0; -} - -bool GraphCycles::IsReachable(GraphId x, GraphId y) const { - return FindPath(x, y, 0, nullptr) > 0; -} - -void GraphCycles::UpdateStackTrace(GraphId id, int priority, - int (*get_stack_trace)(void** stack, int)) { - Node* n = FindNode(rep_, id); - if (n == nullptr || n->priority >= priority) { - return; - } - n->nstack = (*get_stack_trace)(n->stack, ABSL_ARRAYSIZE(n->stack)); - n->priority = priority; -} - -int GraphCycles::GetStackTrace(GraphId id, void*** ptr) { - Node* n = FindNode(rep_, id); - if (n == nullptr) { - *ptr = nullptr; - return 0; - } else { - *ptr = n->stack; - return n->nstack; - } -} - -} // namespace synchronization_internal -ABSL_NAMESPACE_END -} // namespace absl - -#endif // ABSL_LOW_LEVEL_ALLOC_MISSING |