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[embedded] Make embedded swift_once thread-safe

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This commit is contained in:
Kuba Mracek
2023-10-29 20:33:43 -07:00
parent 50a98d3055
commit b057417e52
2 changed files with 93 additions and 12 deletions
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39
stdlib/public/core/EmbeddedRuntime.swift
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@@ -196,23 +196,31 @@ fileprivate func refcountPointer(for object: UnsafeMutablePointer<HeapObject>) -
return UnsafeMutablePointer<Int>(UnsafeRawPointer(object).advanced(by: MemoryLayout<Int>.size)._rawValue)
}
fileprivate func loadRelaxed(_ refcount: UnsafeMutablePointer<Int>) -> Int {
Int(Builtin.atomicload_monotonic_Word(refcount._rawValue))
fileprivate func loadRelaxed(_ atomic: UnsafeMutablePointer<Int>) -> Int {
Int(Builtin.atomicload_monotonic_Word(atomic._rawValue))
}
fileprivate func loadAcquire(_ refcount: UnsafeMutablePointer<Int>) -> Int {
Int(Builtin.atomicload_acquire_Word(refcount._rawValue))
fileprivate func loadAcquire(_ atomic: UnsafeMutablePointer<Int>) -> Int {
Int(Builtin.atomicload_acquire_Word(atomic._rawValue))
}
fileprivate func subFetchAcquireRelease(_ refcount: UnsafeMutablePointer<Int>, n: Int) -> Int {
let oldValue = Int(Builtin.atomicrmw_sub_acqrel_Word(refcount._rawValue, n._builtinWordValue))
fileprivate func subFetchAcquireRelease(_ atomic: UnsafeMutablePointer<Int>, n: Int) -> Int {
let oldValue = Int(Builtin.atomicrmw_sub_acqrel_Word(atomic._rawValue, n._builtinWordValue))
return oldValue - n
}
fileprivate func addRelaxed(_ refcount: UnsafeMutablePointer<Int>, n: Int) {
_ = Builtin.atomicrmw_add_monotonic_Word(refcount._rawValue, n._builtinWordValue)
fileprivate func addRelaxed(_ atomic: UnsafeMutablePointer<Int>, n: Int) {
_ = Builtin.atomicrmw_add_monotonic_Word(atomic._rawValue, n._builtinWordValue)
}
fileprivate func compareExchangeRelaxed(_ atomic: UnsafeMutablePointer<Int>, expectedOldValue: Int, desiredNewValue: Int) -> Bool {
let (_, won) = Builtin.cmpxchg_monotonic_monotonic_Word(atomic._rawValue, expectedOldValue._builtinWordValue, desiredNewValue._builtinWordValue)
return Bool(won)
}
fileprivate func storeRelease(_ atomic: UnsafeMutablePointer<Int>, newValue: Int) {
Builtin.atomicstore_release_Word(atomic._rawValue, newValue._builtinWordValue)
}
/// Exclusivity checking
@@ -233,11 +241,18 @@ public func swift_endAccess(buffer: UnsafeMutableRawPointer) {
@_silgen_name("swift_once")
public func swift_once(predicate: UnsafeMutablePointer<Int>, fn: (@convention(c) (UnsafeMutableRawPointer)->()), context: UnsafeMutableRawPointer) {
// TODO/FIXME: The following only works in single-threaded environments.
if predicate.pointee == 0 {
predicate.pointee = 1
if loadAcquire(predicate) < 0 { return }
let won = compareExchangeRelaxed(predicate, expectedOldValue: 0, desiredNewValue: 1)
if won {
fn(context)
predicate.pointee = -1
storeRelease(predicate, newValue: -1)
return
}
// TODO: This should really use an OS provided lock
while loadAcquire(predicate) >= 0 {
// spin
}
}