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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
62 lines
2.7 KiB
C++
62 lines
2.7 KiB
C++
//===--- CompatibiltyOverride.h - Back-deploying compatibility fixes --*- 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 - 2018 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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// Support back-deploying compatibility fixes for newer apps running on older runtimes.
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//
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//===----------------------------------------------------------------------===//
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#ifndef COMPATIBILITY_OVERRIDE_H
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#define COMPATIBILITY_OVERRIDE_H
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#include "../../public/runtime/Private.h"
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#include "swift/Runtime/Metadata.h"
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#include "swift/Runtime/Once.h"
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#include <type_traits>
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namespace swift {
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#define COMPATIBILITY_UNPAREN(...) __VA_ARGS__
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#define OVERRIDE(name, ret, attrs, ccAttrs, namespace, typedArgs, namedArgs) \
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ccAttrs typedef ret (*Original_ ## name) typedArgs;
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#include "CompatibilityOverride.def"
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#define OVERRIDE(name, ret, attrs, ccAttrs, namespace, typedArgs, namedArgs) \
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ccAttrs typedef ret (*Override_ ## name)(COMPATIBILITY_UNPAREN typedArgs, \
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Original_ ## name originalImpl);
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#include "CompatibilityOverride.def"
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#define OVERRIDE(name, ret, attrs, ccAttrs, namespace, typedArgs, namedArgs) \
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Override_ ## name getOverride_ ## name();
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#include "CompatibilityOverride.def"
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/// Used to define an override point. The override point #defines the appropriate
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/// OVERRIDE macro from CompatibilityOverride.def to this macro, then includes
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/// the file to generate the override points. The original implementation of the
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/// functionality must be available as swift_funcNameHereImpl.
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#define COMPATIBILITY_OVERRIDE(name, ret, attrs, ccAttrs, namespace, typedArgs, namedArgs) \
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attrs ccAttrs ret namespace swift_ ## name typedArgs { \
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static Override_ ## name Override; \
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static swift_once_t Predicate; \
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swift_once(&Predicate, [](void *) { \
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Override = getOverride_ ## name(); \
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}, nullptr); \
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if (Override != nullptr) \
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return Override(COMPATIBILITY_UNPAREN namedArgs, swift_ ## name ## Impl); \
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return swift_ ## name ## Impl namedArgs; \
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}
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} /* end namespace swift */
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#endif /* COMPATIBILITY_OVERRIDE_H */
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