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dadcb04ae2
SWIFT_STDLIB_SINGLE_THREADED_RUNTIME is too much of a blunt instrument here. It covers both the Concurrency runtime and the rest of the runtime, but we'd like to be able to have e.g. a single-threaded Concurrency runtime while the rest of the runtime is still thread safe (for instance). So: rename it to SWIFT_STDLIB_SINGLE_THREADED_CONCURRENCY and make it just control the Concurrency runtime, then add a SWIFT_STDLIB_THREADING_PACKAGE setting at the CMake/build-script level, which defines SWIFT_STDLIB_THREADING_xxx where xxx depends on the chosen threading package. This is especially useful on systems where there may be a choice of threading package that you could use. rdar://90776105
68 lines
2.4 KiB
C++
68 lines
2.4 KiB
C++
//===--- Once.cpp - Runtime support for lazy initialization ---------------===//
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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 - 2017 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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// Swift runtime functions in support of lazy initialization.
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//
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//===----------------------------------------------------------------------===//
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#include "Private.h"
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#include "swift/Runtime/Once.h"
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#include "swift/Runtime/Debug.h"
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#include <type_traits>
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using namespace swift;
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#if SWIFT_STDLIB_THREADING_NONE
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// No dependencies on single-threaded environments.
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#elif SWIFT_STDLIB_THREADING_DARWIN
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// On macOS and iOS, swift_once is implemented using GCD.
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// The compiler emits an inline check matching the barrier-free inline fast
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// path of dispatch_once(). See SwiftTargetInfo.OnceDonePredicateValue.
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#include <dispatch/dispatch.h>
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static_assert(std::is_same<swift_once_t, dispatch_once_t>::value,
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"swift_once_t and dispatch_once_t must stay in sync");
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#else
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// On non-Darwin platforms we do not assume any barrier-free inline path
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// and SwiftTargetInfo.OnceDonePredicateValue is unset in the compiler.
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#endif
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// The compiler generates the swift_once_t values as word-sized zero-initialized
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// variables, so we want to make sure swift_once_t isn't larger than the
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// platform word or the function below might overwrite something it shouldn't.
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static_assert(sizeof(swift_once_t) <= sizeof(void*),
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"swift_once_t must be no larger than the platform word");
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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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void swift::swift_once(swift_once_t *predicate, void (*fn)(void *),
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void *context) {
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#ifdef SWIFT_STDLIB_THREADING_NONE
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if (! *predicate) {
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*predicate = true;
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fn(context);
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}
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#elif SWIFT_STDLIB_THREADING_DARWIN
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dispatch_once_f(predicate, context, fn);
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#elif defined(__CYGWIN__)
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_swift_once_f(predicate, context, fn);
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#else
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std::call_once(*predicate, fn, context);
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#endif
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}
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