//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2020 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 the list of Swift project authors
//
//===----------------------------------------------------------------------===//

import Swift
@_implementationOnly import _SwiftConcurrencyShims

/// Common protocol to which all actor classes conform.
///
/// The \c Actor protocol provides the core functionality of an actor class,
/// which involves enqueuing new partial tasks to be executed at some
/// point. Actor classes implicitly conform to this protocol as part of their
/// primary class definition.
public protocol Actor: AnyObject, ConcurrentValue {
  /// Enqueue a new partial task that will be executed in the actor's context.
  func enqueue(partialTask: PartialAsyncTask)
}

/// Called to initialize the default actor instance in an actor.
/// The implementation will call this within the actor's initializer.
@_silgen_name("swift_defaultActor_initialize")
public func _defaultActorInitialize(_ actor: AnyObject)

/// Called to destroy the default actor instance in an actor.
/// The implementation will call this within the actor's deinit.
@_silgen_name("swift_defaultActor_destroy")
public func _defaultActorDestroy(_ actor: AnyObject)

/// Called by the synthesized implementation of enqueue(partialTask:).
@_silgen_name("swift_defaultActor_enqueue")
public func _defaultActorEnqueue(partialTask: PartialAsyncTask,
                                 actor: AnyObject)

/// FIXME: only exists for the quick-and-dirty MainActor implementation.
@_silgen_name("swift_MainActor_register")
fileprivate func _registerMainActor(actor: AnyObject)

/// A singleton actor whose executor is equivalent to 
/// \c DispatchQueue.main, which is the main dispatch queue.
@globalActor public final class MainActor {
  public static let shared = _Impl()
  
  public actor _Impl {
    init() { _registerMainActor(actor: self) }
  }
}