You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
142 lines
5.1 KiB
142 lines
5.1 KiB
// 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.
|
|
//
|
|
|
|
#ifndef ABSL_SYNCHRONIZATION_INTERNAL_GRAPHCYCLES_H_
|
|
#define ABSL_SYNCHRONIZATION_INTERNAL_GRAPHCYCLES_H_
|
|
|
|
// GraphCycles detects the introduction of a cycle into a directed
|
|
// graph that is being built up incrementally.
|
|
//
|
|
// Nodes are identified by small integers. It is not possible to
|
|
// record multiple edges with the same (source, destination) pair;
|
|
// requests to add an edge where one already exists are silently
|
|
// ignored.
|
|
//
|
|
// It is also not possible to introduce a cycle; an attempt to insert
|
|
// an edge that would introduce a cycle fails and returns false.
|
|
//
|
|
// GraphCycles uses no internal locking; calls into it should be
|
|
// serialized externally.
|
|
|
|
// Performance considerations:
|
|
// Works well on sparse graphs, poorly on dense graphs.
|
|
// Extra information is maintained incrementally to detect cycles quickly.
|
|
// InsertEdge() is very fast when the edge already exists, and reasonably fast
|
|
// otherwise.
|
|
// FindPath() is linear in the size of the graph.
|
|
// The current implementation uses O(|V|+|E|) space.
|
|
|
|
#include <cstdint>
|
|
|
|
#include "absl/base/config.h"
|
|
|
|
namespace absl {
|
|
ABSL_NAMESPACE_BEGIN
|
|
namespace synchronization_internal {
|
|
|
|
// Opaque identifier for a graph node.
|
|
struct GraphId {
|
|
uint64_t handle;
|
|
|
|
bool operator==(const GraphId& x) const { return handle == x.handle; }
|
|
bool operator!=(const GraphId& x) const { return handle != x.handle; }
|
|
};
|
|
|
|
// Return an invalid graph id that will never be assigned by GraphCycles.
|
|
inline GraphId InvalidGraphId() {
|
|
return GraphId{0};
|
|
}
|
|
|
|
class GraphCycles {
|
|
public:
|
|
GraphCycles();
|
|
~GraphCycles();
|
|
|
|
// Return the id to use for ptr, assigning one if necessary.
|
|
// Subsequent calls with the same ptr value will return the same id
|
|
// until Remove().
|
|
GraphId GetId(void* ptr);
|
|
|
|
// Remove "ptr" from the graph. Its corresponding node and all
|
|
// edges to and from it are removed.
|
|
void RemoveNode(void* ptr);
|
|
|
|
// Return the pointer associated with id, or nullptr if id is not
|
|
// currently in the graph.
|
|
void* Ptr(GraphId id);
|
|
|
|
// Attempt to insert an edge from source_node to dest_node. If the
|
|
// edge would introduce a cycle, return false without making any
|
|
// changes. Otherwise add the edge and return true.
|
|
bool InsertEdge(GraphId source_node, GraphId dest_node);
|
|
|
|
// Remove any edge that exists from source_node to dest_node.
|
|
void RemoveEdge(GraphId source_node, GraphId dest_node);
|
|
|
|
// Return whether node exists in the graph.
|
|
bool HasNode(GraphId node);
|
|
|
|
// Return whether there is an edge directly from source_node to dest_node.
|
|
bool HasEdge(GraphId source_node, GraphId dest_node) const;
|
|
|
|
// Return whether dest_node is reachable from source_node
|
|
// by following edges.
|
|
bool IsReachable(GraphId source_node, GraphId dest_node) const;
|
|
|
|
// Find a path from "source" to "dest". If such a path exists,
|
|
// place the nodes on the path in the array path[], and return
|
|
// the number of nodes on the path. If the path is longer than
|
|
// max_path_len nodes, only the first max_path_len nodes are placed
|
|
// in path[]. The client should compare the return value with
|
|
// max_path_len" to see when this occurs. If no path exists, return
|
|
// 0. Any valid path stored in path[] will start with "source" and
|
|
// end with "dest". There is no guarantee that the path is the
|
|
// shortest, but no node will appear twice in the path, except the
|
|
// source and destination node if they are identical; therefore, the
|
|
// return value is at most one greater than the number of nodes in
|
|
// the graph.
|
|
int FindPath(GraphId source, GraphId dest, int max_path_len,
|
|
GraphId path[]) const;
|
|
|
|
// Update the stack trace recorded for id with the current stack
|
|
// trace if the last time it was updated had a smaller priority
|
|
// than the priority passed on this call.
|
|
//
|
|
// *get_stack_trace is called to get the stack trace.
|
|
void UpdateStackTrace(GraphId id, int priority,
|
|
int (*get_stack_trace)(void**, int));
|
|
|
|
// Set *ptr to the beginning of the array that holds the recorded
|
|
// stack trace for id and return the depth of the stack trace.
|
|
int GetStackTrace(GraphId id, void*** ptr);
|
|
|
|
// Check internal invariants. Crashes on failure, returns true on success.
|
|
// Expensive: should only be called from graphcycles_test.cc.
|
|
bool CheckInvariants() const;
|
|
|
|
// ----------------------------------------------------
|
|
struct Rep;
|
|
private:
|
|
Rep *rep_; // opaque representation
|
|
GraphCycles(const GraphCycles&) = delete;
|
|
GraphCycles& operator=(const GraphCycles&) = delete;
|
|
};
|
|
|
|
} // namespace synchronization_internal
|
|
ABSL_NAMESPACE_END
|
|
} // namespace absl
|
|
|
|
#endif
|