mirror of
https://github.com/apple/swift.git
synced 2025-12-21 12:14:44 +01:00
38 lines
1.5 KiB
C++
38 lines
1.5 KiB
C++
//===--- Once.cpp - Runtime support for lazy initialization ----------------==//
|
|
//
|
|
// This source file is part of the Swift.org open source project
|
|
//
|
|
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
|
|
// Licensed under Apache License v2.0 with Runtime Library Exception
|
|
//
|
|
// See http://swift.org/LICENSE.txt for license information
|
|
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// Swift runtime functions in support of lazy initialization.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "swift/Runtime/Once.h"
|
|
#include <dispatch/dispatch.h>
|
|
#include <type_traits>
|
|
|
|
using namespace swift;
|
|
|
|
static_assert(std::is_same<swift_once_t, dispatch_once_t>::value,
|
|
"swift_once_t and dispatch_once_t must stay in sync");
|
|
|
|
/// Runs the given function with the given context argument exactly once.
|
|
/// The predicate argument must point to a global or static variable of static
|
|
/// extent of type swift_once_t.
|
|
|
|
void swift::swift_once(swift_once_t *predicate, void (*fn)(HeapObject *ctx),
|
|
HeapObject *ctx) {
|
|
// Swift convention passes ctx in here at +1, but 'fn' should also consume
|
|
// its argument at +1, so calling it exactly once should perfectly balance
|
|
// the retain count without any additional work.
|
|
dispatch_once_f(predicate, reinterpret_cast<void*>(ctx),
|
|
reinterpret_cast<dispatch_function_t>(fn));
|
|
}
|