mirror of
https://github.com/apple/swift.git
synced 2025-12-14 20:36:38 +01:00
53 lines
2.1 KiB
C++
53 lines
2.1 KiB
C++
//===--- Once.cpp - Runtime support for lazy initialization ---------------===//
|
|
//
|
|
// This source file is part of the Swift.org open source project
|
|
//
|
|
// Copyright (c) 2014 - 2016 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 "swift/Runtime/Debug.h"
|
|
#include <type_traits>
|
|
|
|
using namespace swift;
|
|
|
|
#ifdef __APPLE__
|
|
|
|
// On OS X and iOS, swift_once is implemented using GCD.
|
|
|
|
#include <dispatch/dispatch.h>
|
|
static_assert(std::is_same<swift_once_t, dispatch_once_t>::value,
|
|
"swift_once_t and dispatch_once_t must stay in sync");
|
|
#endif
|
|
// The compiler generates the swift_once_t values as word-sized zero-initialized
|
|
// variables, so we want to make sure swift_once_t isn't larger than the
|
|
// platform word or the function below might overwrite something it shouldn't.
|
|
static_assert(sizeof(swift_once_t) <= sizeof(void*),
|
|
"swift_once_t must be no larger than the platform word");
|
|
|
|
/// 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)(void *)) {
|
|
#if defined(__APPLE__)
|
|
dispatch_once_f(predicate, nullptr, fn);
|
|
#else
|
|
// FIXME: We're relying here on the coincidence that libstdc++ uses pthread's
|
|
// pthread_once, and that on glibc pthread_once follows a compatible init
|
|
// process (the token is a word that is atomically incremented from 0 to
|
|
// 1 to 2 during initialization) to work. We should implement our own version
|
|
// that we can rely on to continue to work that way.
|
|
// For more information, see rdar://problem/18499385
|
|
std::call_once(*predicate, [fn]() { fn(nullptr); });
|
|
#endif
|
|
}
|