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7b2a6e5e8d
This matches how dispatch_once works in C, dramatically cutting the cost of a global accessor by avoiding the runtime call in the hot path and giving the global a unique branch for the CPU to predict away. For now, only do this for Darwin; non-ObjC platforms don't necessarily expose their "done" value as ABI like ours do. While we're here, change "once" to take a thin function pointer. We don't ever emit global initializers with context dependencies, and this simplifies the runtime glue between swift_once and dispatch_once/std::call_once a bit. Swift SVN r28166
46 lines
1.3 KiB
C++
46 lines
1.3 KiB
C++
//===--- Once.h - Runtime support for lazy initialization ------*- 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 - 2015 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 http://swift.org/LICENSE.txt for license information
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// See http://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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// Swift runtime functions in support of lazy initialization.
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//
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//===----------------------------------------------------------------------===//
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#ifndef SWIFT_RUNTIME_ONCE_H
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#define SWIFT_RUNTIME_ONCE_H
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#include "swift/Runtime/HeapObject.h"
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#include <mutex>
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namespace swift {
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#ifdef __APPLE__
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// On OS X and iOS, swift_once_t matches dispatch_once_t.
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typedef long swift_once_t;
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#else
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// On other platforms swift_once_t is std::once_flag
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typedef std::once_flag swift_once_t;
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#endif
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/// Runs the given function with the given context argument exactly once.
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/// The predicate argument must point to a global or static variable of static
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/// extent of type swift_once_t.
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extern "C"
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void swift_once(swift_once_t *predicate, void (*fn)(void *));
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}
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#endif
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