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Diffstat (limited to 'source/blender/blenlib/BLI_compute_context.hh')
-rw-r--r-- | source/blender/blenlib/BLI_compute_context.hh | 173 |
1 files changed, 173 insertions, 0 deletions
diff --git a/source/blender/blenlib/BLI_compute_context.hh b/source/blender/blenlib/BLI_compute_context.hh new file mode 100644 index 00000000000..fc6858ad6a9 --- /dev/null +++ b/source/blender/blenlib/BLI_compute_context.hh @@ -0,0 +1,173 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ + +#pragma once + +/** \file + * \ingroup bli + * + * When logging computed values, we generally want to know where the value was computed. For + * example, geometry nodes logs socket values so that they can be displayed in the ui. For that we + * can combine the logged value with a `ComputeContext`, which identifies the place where the value + * was computed. + * + * This is not a trivial problem because e.g. just storing storing a pointer to the socket a value + * belongs to is not enough. That's because the same socket may correspond to many different values + * when the socket is used in a node group that is used multiple times. In this case, not only does + * the socket has to be stored but also the entire nested node group path that led to the + * evaluation of the socket. + * + * Storing the entire "context path" for every logged value is not feasible, because that path can + * become quite long. So that would need much more memory, more compute overhead and makes it + * complicated to compare if two contexts are the same. If the identifier for a compute context + * would have a variable size, it would also be much harder to create a map from context to values. + * + * The solution implemented below uses the following key ideas: + * - Every compute context can be hashed to a unique fixed size value (`ComputeContextHash`). While + * technically there could be hash collisions, the hashing algorithm has to be chosen to make + * that practically impossible. This way an entire context path, possibly consisting of many + * nested contexts, is represented by a single value that can be stored easily. + * - A nested compute context is build as singly linked list, where every compute context has a + * pointer to the parent compute context. Note that a link in the other direction is not possible + * because the same parent compute context may be used by many different children which possibly + * run on different threads. + */ + +#include "BLI_array.hh" +#include "BLI_linear_allocator.hh" +#include "BLI_stack.hh" +#include "BLI_string_ref.hh" + +namespace blender { + +/** + * A hash that uniquely identifies a specific (non-fixed-size) compute context. The hash has to + * have enough bits to make collisions practically impossible. + */ +struct ComputeContextHash { + static constexpr int64_t HashSizeInBytes = 16; + uint64_t v1 = 0; + uint64_t v2 = 0; + + uint64_t hash() const + { + return v1; + } + + friend bool operator==(const ComputeContextHash &a, const ComputeContextHash &b) + { + return a.v1 == b.v1 && a.v2 == b.v2; + } + + void mix_in(const void *data, int64_t len); + + friend std::ostream &operator<<(std::ostream &stream, const ComputeContextHash &hash); +}; + +static_assert(sizeof(ComputeContextHash) == ComputeContextHash::HashSizeInBytes); + +/** + * Identifies the context in which a computation happens. This context can be used to identify + * values logged during the computation. For more details, see the comment at the top of the file. + * + * This class should be subclassed to implement specific contexts. + */ +class ComputeContext { + private: + /** + * Only used for debugging currently. + */ + const char *static_type_; + /** + * Pointer to the context that this context is child of. That allows nesting compute contexts. + */ + const ComputeContext *parent_ = nullptr; + + protected: + /** + * The hash that uniquely identifies this context. It's a combined hash of this context as well + * as all the parent contexts. + */ + ComputeContextHash hash_; + + public: + ComputeContext(const char *static_type, const ComputeContext *parent) + : static_type_(static_type), parent_(parent) + { + if (parent != nullptr) { + hash_ = parent_->hash_; + } + } + virtual ~ComputeContext() = default; + + const ComputeContextHash &hash() const + { + return hash_; + } + + const char *static_type() const + { + return static_type_; + } + + const ComputeContext *parent() const + { + return parent_; + } + + /** + * Print the entire nested context stack. + */ + void print_stack(std::ostream &stream, StringRef name) const; + + /** + * Print information about this specific context. This has to be implemented by each subclass. + */ + virtual void print_current_in_line(std::ostream &stream) const = 0; + + friend std::ostream &operator<<(std::ostream &stream, const ComputeContext &compute_context); +}; + +/** + * Utility class to build a context stack in one place. This is typically used to get the hash that + * corresponds to a specific nested compute context, in order to look up corresponding logged + * values. + */ +class ComputeContextBuilder { + private: + LinearAllocator<> allocator_; + Stack<destruct_ptr<ComputeContext>> contexts_; + + public: + bool is_empty() const + { + return contexts_.is_empty(); + } + + const ComputeContext *current() const + { + if (contexts_.is_empty()) { + return nullptr; + } + return contexts_.peek().get(); + } + + const ComputeContextHash hash() const + { + BLI_assert(!contexts_.is_empty()); + return this->current()->hash(); + } + + template<typename T, typename... Args> void push(Args &&...args) + { + const ComputeContext *current = this->current(); + destruct_ptr<T> context = allocator_.construct<T>(current, std::forward<Args>(args)...); + contexts_.push(std::move(context)); + } + + void pop() + { + contexts_.pop(); + } +}; + +} // namespace blender |