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//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2023 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for Swift project authors
//
internal import _TestingInternals
/// A type that wraps a value requiring access from a synchronous caller during
/// concurrent execution.
///
/// Instances of this type use a lock to synchronize access to their raw values.
/// The lock is not recursive.
///
/// Instances of this type can be used to synchronize access to shared data from
/// a synchronous caller. Wherever possible, use actor isolation or other Swift
/// concurrency tools.
///
/// This type is not part of the public interface of the testing library.
///
/// - Bug: The state protected by this type should instead be protected using
/// actor isolation, but actor-isolated functions cannot be called from
/// synchronous functions. ([83888717](rdar://83888717))
struct Locked<T>: RawRepresentable, Sendable where T: Sendable {
/// The platform-specific type to use for locking.
///
/// It would be preferable to implement this lock in Swift, however there is
/// no standard lock or mutex type available across all platforms that is
/// visible in Swift. C11 has a standard `mtx_t` type, but it is not widely
/// supported and so cannot be relied upon.
///
/// To keep the implementation of this type as simple as possible,
/// `pthread_mutex_t` is used on Apple platforms instead of `os_unfair_lock`
/// or `OSAllocatedUnfairLock`.
#if SWT_TARGET_OS_APPLE || os(Linux) || (os(WASI) && compiler(>=6.1) && _runtime(_multithreaded))
private typealias _Lock = pthread_mutex_t
#elseif os(Windows)
private typealias _Lock = SRWLOCK
#elseif os(WASI)
// No locks on WASI without multithreaded runtime.
private typealias _Lock = Void
#else
#warning("Platform-specific implementation missing: locking unavailable")
private typealias _Lock = Void
#endif
/// A type providing heap-allocated storage for an instance of ``Locked``.
private final class _Storage: ManagedBuffer<T, _Lock> {
deinit {
withUnsafeMutablePointerToElements { lock in
#if SWT_TARGET_OS_APPLE || os(Linux) || (os(WASI) && compiler(>=6.1) && _runtime(_multithreaded))
_ = pthread_mutex_destroy(lock)
#elseif os(Windows)
// No deinitialization needed.
#elseif os(WASI)
// No locks on WASI without multithreaded runtime.
#else
#warning("Platform-specific implementation missing: locking unavailable")
#endif
}
}
}
/// Storage for the underlying lock and wrapped value.
private nonisolated(unsafe) var _storage: ManagedBuffer<T, _Lock>
init(rawValue: T) {
_storage = _Storage.create(minimumCapacity: 1, makingHeaderWith: { _ in rawValue })
_storage.withUnsafeMutablePointerToElements { lock in
#if SWT_TARGET_OS_APPLE || os(Linux) || (os(WASI) && compiler(>=6.1) && _runtime(_multithreaded))
_ = pthread_mutex_init(lock, nil)
#elseif os(Windows)
InitializeSRWLock(lock)
#elseif os(WASI)
// No locks on WASI without multithreaded runtime.
#else
#warning("Platform-specific implementation missing: locking unavailable")
#endif
}
}
var rawValue: T {
withLock { $0 }
}
/// Acquire the lock and invoke a function while it is held.
///
/// - Parameters:
/// - body: A closure to invoke while the lock is held.
///
/// - Returns: Whatever is returned by `body`.
///
/// - Throws: Whatever is thrown by `body`.
///
/// This function can be used to synchronize access to shared data from a
/// synchronous caller. Wherever possible, use actor isolation or other Swift
/// concurrency tools.
nonmutating func withLock<R>(_ body: (inout T) throws -> R) rethrows -> R {
try _storage.withUnsafeMutablePointers { rawValue, lock in
#if SWT_TARGET_OS_APPLE || os(Linux) || (os(WASI) && compiler(>=6.1) && _runtime(_multithreaded))
_ = pthread_mutex_lock(lock)
defer {
_ = pthread_mutex_unlock(lock)
}
#elseif os(Windows)
AcquireSRWLockExclusive(lock)
defer {
ReleaseSRWLockExclusive(lock)
}
#elseif os(WASI)
// No locks on WASI without multithreaded runtime.
#else
#warning("Platform-specific implementation missing: locking unavailable")
#endif
return try body(&rawValue.pointee)
}
}
#if SWT_TARGET_OS_APPLE || os(Linux) || (os(WASI) && compiler(>=6.1) && _runtime(_multithreaded))
/// Acquire the lock and invoke a function while it is held, yielding both the
/// protected value and a reference to the lock itself.
///
/// - Parameters:
/// - body: A closure to invoke while the lock is held.
///
/// - Returns: Whatever is returned by `body`.
///
/// - Throws: Whatever is thrown by `body`.
///
/// This function is equivalent to ``withLock(_:)`` except that the closure
/// passed to it also takes a reference to the underlying platform lock. This
/// function can be used when platform-specific functionality such as a
/// `pthread_cond_t` is needed. Because the caller has direct access to the
/// lock and is able to unlock and re-lock it, it is unsafe to modify the
/// protected value.
///
/// - Warning: Callers that unlock the lock _must_ lock it again before the
/// closure returns. If the lock is not acquired when `body` returns, the
/// effect is undefined.
nonmutating func withUnsafeUnderlyingLock<R>(_ body: (UnsafeMutablePointer<pthread_mutex_t>, T) throws -> R) rethrows -> R {
try withLock { value in
try _storage.withUnsafeMutablePointerToElements { lock in
try body(lock, value)
}
}
}
#endif
}
extension Locked where T: AdditiveArithmetic {
/// Add something to the current wrapped value of this instance.
///
/// - Parameters:
/// - addend: The value to add.
///
/// - Returns: The sum of ``rawValue`` and `addend`.
@discardableResult func add(_ addend: T) -> T {
withLock { rawValue in
let result = rawValue + addend
rawValue = result
return result
}
}
}
extension Locked where T: Numeric {
/// Increment the current wrapped value of this instance.
///
/// - Returns: The sum of ``rawValue`` and `1`.
///
/// This function is exactly equivalent to `add(1)`.
@discardableResult func increment() -> T {
add(1)
}
/// Decrement the current wrapped value of this instance.
///
/// - Returns: The sum of ``rawValue`` and `-1`.
///
/// This function is exactly equivalent to `add(-1)`.
@discardableResult func decrement() -> T {
add(-1)
}
}
extension Locked {
/// Initialize an instance of this type with a raw value of `nil`.
init<V>() where T == V? {
self.init(rawValue: nil)
}
/// Initialize an instance of this type with a raw value of `[:]`.
init<K, V>() where T == Dictionary<K, V> {
self.init(rawValue: [:])
}
}
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