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to use it. ConcurrentReadableHashMap is lock-free for readers, with writers using a lock to ensure mutual exclusion amongst each other. The intent is to eventually replace all uses ConcurrentMap with ConcurrentReadableHashMap. ConcurrentReadableHashMap provides for relatively quick lookups by using a hash table. Rearders perform an atomic increment/decrement in order to inform writers that there are active readers. The design attempts to minimize wasted memory by storing the actual elements out-of-line, and having the table store indices into a separate array of elements. The protocol conformance cache now uses ConcurrentReadableHashMap, which provides faster lookups and less memory use than the previous ConcurrentMap implementation. The previous implementation caches ProtocolConformanceDescriptors and extracts the WitnessTable after the cache lookup. The new implementation directly caches the WitnessTable, removing an extra step (potentially a quite slow one) from the fast path. The previous implementation used a generational scheme to detect when negative cache entries became obsolete due to new dynamic libraries being loaded, and update them in place. The new implementation just clears the entire cache when libraries are loaded, greatly simplifying the code and saving the memory needed to track the current generation in each negative cache entry. This means we need to re-cache all requested conformances after loading a dynamic library, but loading libraries at runtime is rare and slow anyway. rdar://problem/67268325
67 lines
2.1 KiB
C++
67 lines
2.1 KiB
C++
//===--- RuntimeInternals.h - Runtime Internal Structures -------*- C++ -*-===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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//
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// Runtime data structures that Reflection inspects externally.
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//
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// FIXME: Ideally the original definitions would be templatized on a Runtime
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// parameter and we could use the original definitions in both the runtime and
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// in Reflection.
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//
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//===----------------------------------------------------------------------===//
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#ifndef SWIFT_REFLECTION_RUNTIME_INTERNALS_H
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#define SWIFT_REFLECTION_RUNTIME_INTERNALS_H
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namespace swift {
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namespace reflection {
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template <typename Runtime>
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struct ConformanceNode {
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typename Runtime::StoredPointer Left, Right;
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typename Runtime::StoredPointer Type;
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typename Runtime::StoredPointer Proto;
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typename Runtime::StoredPointer Description;
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typename Runtime::StoredSize FailureGeneration;
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};
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template <typename Runtime>
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struct MetadataAllocation {
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uint16_t Tag;
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typename Runtime::StoredPointer Ptr;
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unsigned Size;
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};
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template <typename Runtime> struct MetadataCacheNode {
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typename Runtime::StoredPointer Left;
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typename Runtime::StoredPointer Right;
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};
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template <typename Runtime> struct ConcurrentHashMap {
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typename Runtime::StoredSize ReaderCount;
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typename Runtime::StoredSize ElementCount;
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typename Runtime::StoredPointer Elements;
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typename Runtime::StoredPointer Indices;
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// We'll ignore the remaining fields for now....
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};
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template <typename Runtime> struct ConformanceCacheEntry {
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typename Runtime::StoredPointer Type;
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typename Runtime::StoredPointer Proto;
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typename Runtime::StoredPointer Witness;
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};
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} // end namespace reflection
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} // end namespace swift
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#endif // SWIFT_REFLECTION_RUNTIME_INTERNALS_H
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