[Concurrency] Remove EventableExecutor, alter asSchedulable.

EventableExecutor is being removed, for now, but hopefully will
return in some form in the future.

The `asSchedulable` implementation needs to change for reasons of
ABI stability.

rdar://141348916

Author: al45tair

stdlib/public/Concurrency/DispatchExecutor.swift

@@ -25,8 +25,6 @@ import Swift
 
 @available(SwiftStdlib 6.2, *)
 public class DispatchMainExecutor: RunLoopExecutor, @unchecked Sendable {
-  public typealias AsSchedulable = DispatchMainExecutor
-
   var threaded = false
 
   public init() {}
@@ -61,6 +59,10 @@ extension DispatchMainExecutor: SerialExecutor {
 
 @available(SwiftStdlib 6.2, *)
 extension DispatchMainExecutor: SchedulableExecutor {
+  public var asSchedulable: SchedulableExecutor? {
+    return self
+  }
+
   public func enqueue<C: Clock>(_ job: consuming ExecutorJob,
                                 at instant: C.Instant,
                                 tolerance: C.Duration? = nil,
@@ -83,36 +85,6 @@ extension DispatchMainExecutor: SchedulableExecutor {
   }
 }
 
-@available(SwiftStdlib 6.2, *)
-extension DispatchMainExecutor: EventableExecutor {
-
-  /// Register a new event with a given handler.
-  public func registerEvent(
-    handler: @escaping @Sendable () -> ()
-  ) -> ExecutorEvent {
-    let source = unsafe _createDispatchEvent(handler: handler)
-
-    // Stash the pointer in the id of the ExecutorEvent struct
-    let eventId = unsafe unsafeBitCast(source, to: Int.self)
-    return ExecutorEvent(id: eventId)
-  }
-
-  /// Deregister the given event.
-  public func deregister(event: ExecutorEvent) {
-    // Extract the source and cancel it
-    let source = unsafe unsafeBitCast(event.id, to: OpaquePointer.self)
-    unsafe _destroyDispatchEvent(source)
-  }
-
-  /// Notify the executor of an event.
-  public func notify(event: ExecutorEvent) {
-    // Extract the source, but don't release it
-    let source = unsafe unsafeBitCast(event.id, to: OpaquePointer.self)
-    unsafe _signalDispatchEvent(source)
-  }
-
-}
-
 @available(SwiftStdlib 6.2, *)
 extension DispatchMainExecutor: MainExecutor {}
 
@@ -121,9 +93,6 @@ extension DispatchMainExecutor: MainExecutor {}
 @available(SwiftStdlib 6.2, *)
 public class DispatchGlobalTaskExecutor: TaskExecutor, SchedulableExecutor,
                                          @unchecked Sendable {
-
-  public typealias AsSchedulable = DispatchGlobalTaskExecutor
-
   public init() {}
 
   public func enqueue(_ job: consuming ExecutorJob) {

stdlib/public/Concurrency/Executor.swift

@@ -16,13 +16,6 @@ import Swift
 @available(SwiftStdlib 5.1, *)
 public protocol Executor: AnyObject, Sendable {
 
-  /// This Executor type as a schedulable executor.
-  ///
-  /// If the conforming type also conforms to `SchedulableExecutor`, then this is
-  /// bound to `Self`. Otherwise, it is an uninhabited type (such as Never).
-  @available(SwiftStdlib 6.2, *)
-  associatedtype AsSchedulable: SchedulableExecutor = SchedulableExecutorNever
-
   // Since lack move-only type support in the SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY configuration
   // Do not deprecate the UnownedJob enqueue in that configuration just yet - as we cannot introduce the replacements.
   #if !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
@@ -55,23 +48,8 @@ public protocol Executor: AnyObject, Sendable {
   #endif
 }
 
-/// Uninhabited class type to indicate we don't support scheduling.
-@available(SwiftStdlib 6.2, *)
-public class SchedulableExecutorNever {
-  private init(_ n: Never) {}
-}
-
 @available(SwiftStdlib 6.2, *)
-extension SchedulableExecutorNever: SchedulableExecutor, @unchecked Sendable {
-
-  public func enqueue(_ job: consuming ExecutorJob) {
-    fatalError("This should never be reached")
-  }
-
-}
-
-@available(SwiftStdlib 6.2, *)
-public protocol SchedulableExecutor: Executor where Self.AsSchedulable == Self {
+public protocol SchedulableExecutor: Executor {
 
   #if !$Embedded
 
@@ -123,17 +101,13 @@ public protocol SchedulableExecutor: Executor where Self.AsSchedulable == Self {
 extension Executor {
   /// Return this executable as a SchedulableExecutor, or nil if that is
   /// unsupported.
+  ///
+  /// Executors that implement SchedulableExecutor should provide their
+  /// own copy of this method, which will allow the compiler to avoid a
+  /// potentially expensive runtime cast.
   @available(SwiftStdlib 6.2, *)
-  var asSchedulable: AsSchedulable? {
-    #if !$Embedded
-    if Self.self == AsSchedulable.self {
-      return _identityCast(self, to: AsSchedulable.self)
-    } else {
-      return nil
-    }
-    #else
-    return nil
-    #endif
+  var asSchedulable: SchedulableExecutor? {
+    return self as? SchedulableExecutor
   }
 }
 
@@ -536,71 +510,17 @@ public protocol RunLoopExecutor: Executor {
 @available(SwiftStdlib 6.2, *)
 extension RunLoopExecutor {
 
-  public func run(until condition: () -> Bool) throws {
+  public func runUntil(_ condition: () -> Bool) throws {
     fatalError("run(until condition:) not supported on this executor")
   }
 
 }
 
 
-/// Represents an event registered with an `EventableExecutor`.
-@available(SwiftStdlib 6.2, *)
-public struct ExecutorEvent: Identifiable, Comparable, Sendable {
-  public typealias ID = Int
-
-  public var id: Self.ID
-
-  public init(id: Self.ID) {
-    self.id = id
-  }
-
-  public static func < (lhs: Self, rhs: Self) -> Bool {
-    return lhs.id < rhs.id
-  }
-  public static func == (lhs: Self, rhs: Self) -> Bool {
-    return lhs.id == rhs.id
-  }
-}
-
-
-/// An executor that has support for coalesced events.
-@available(SwiftStdlib 6.2, *)
-public protocol EventableExecutor {
-
-  /// Register a new event with a given handler.
-  ///
-  /// Notifying the executor of the event will cause the executor to
-  /// execute the handler, however the executor is free to coalesce multiple
-  /// event notifications, and is also free to execute the handler at a time
-  /// of its choosing.
-  ///
-  /// Parameters
-  ///
-  /// - handler:  The handler to call when the event fires.
-  ///
-  /// Returns a new opaque `Event`.
-  func registerEvent(handler: @escaping @Sendable () -> ()) -> ExecutorEvent
-
-  /// Deregister the given event.
-  ///
-  /// After this function returns, there will be no further executions of the
-  /// handler for the given event.
-  func deregister(event: ExecutorEvent)
-
-  /// Notify the executor of an event.
-  ///
-  /// This will trigger, at some future point, the execution of the associated
-  /// event handler.  Prior to that time, multiple calls to `notify` may be
-  /// coalesced and result in a single invocation of the event handler.
-  func notify(event: ExecutorEvent)
-
-}
-
-
 /// The main executor must conform to these three protocols; we have to
 /// make this a protocol for compatibility with Embedded Swift.
 @available(SwiftStdlib 6.2, *)
-public protocol MainExecutor: RunLoopExecutor, SerialExecutor, EventableExecutor {
+public protocol MainExecutor: RunLoopExecutor, SerialExecutor {
 }
 
 
@@ -719,6 +639,9 @@ extension Task where Success == Never, Failure == Never {
        let schedulable = taskExecutor.asSchedulable {
       return schedulable
     }
+    if let schedulable = defaultExecutor.asSchedulable {
+      return schedulable
+    }
     return nil
   }
 }

stdlib/public/Concurrency/PlatformExecutorEmbedded.swift

@@ -34,22 +34,12 @@ public final class EmbeddedMainExecutor: MainExecutor, @unchecked Sendable {
   public func run() throws {
   }
 
-  public func run(until condition: () -> Bool) throws {
+  public func runUntil(_ condition: () -> Bool) throws {
   }
 
   public func stop() {
   }
 
-  public func registerEvent(handler: @escaping () -> ()) -> ExecutorEvent {
-    return ExecutorEvent(id: 0)
-  }
-
-  public func deregister(event: ExecutorEvent) {
-  }
-
-  public func notify(event: ExecutorEvent) {
-  }
-
 }
 
 // .. Platform Task Executor ...................................................

stdlib/public/Concurrency/PlatformExecutorNone.swift

@@ -32,18 +32,6 @@ public class PlatformMainExecutor: MainExecutor, @unchecked Sendable {
     fatalError("There is no main executor implementation for this platform")
   }
 
-  public func registerEvent(handler: @escaping () -> ()) -> ExecutorEvent {
-    fatalError("There is no main executor implementation for this platform")
-  }
-
-  public func deregister(event: ExecutorEvent) {
-    fatalError("There is no main executor implementation for this platform")
-  }
-
-  public func notify(event: ExecutorEvent) {
-    fatalError("There is no main executor implementation for this platform")
-  }
-
 }
 
 // .. Platform Default Executor ................................................

stdlib/public/Concurrency/TaskSleep.swift

@@ -30,8 +30,6 @@ extension Task where Success == Never, Failure == Never {
 
       if #available(SwiftStdlib 6.2, *) {
         let executor = Task.currentSchedulableExecutor
-          ?? Task.defaultExecutor.asSchdulable
-
         #if !$Embedded
         executor!.enqueue(ExecutorJob(context: job),
                           after: .nanoseconds(duration),
@@ -272,7 +270,6 @@ extension Task where Success == Never, Failure == Never {
 
               if #available(SwiftStdlib 6.2, *) {
                 let executor = Task.currentSchedulableExecutor
-                  ?? Task.defaultExecutor.asSchedulable
                 let job = ExecutorJob(context: Builtin.convertTaskToJob(sleepTask))
                 #if !$Embedded
                 executor!.enqueue(job,

stdlib/public/Concurrency/TaskSleepDuration.swift

@@ -55,7 +55,7 @@ extension Task where Success == Never, Failure == Never {
               }
 
               if #available(SwiftStdlib 6.2, *) {
-                let executor = Task.currentSchdulableExecutor ?? Task.defaultExecutor.asSchedulable
+                let executor = Task.currentSchedulableExecutor
                 let job = ExecutorJob(context: Builtin.convertTaskToJob(sleepTask))
 
                 #if !$Embedded

test/Concurrency/Runtime/custom_main_executor.swift

@@ -59,16 +59,6 @@ final class SimpleMainExecutor: MainExecutor, @unchecked Sendable {
   func stop() {
     shouldStop = true
   }
-
-  func registerEvent(handler: @escaping @Sendable () -> ()) -> ExecutorEvent {
-    return ExecutorEvent(id: 0)
-  }
-
-  func deregister(event: ExecutorEvent) {
-  }
-
-  func notify(event: ExecutorEvent) {
-  }
 }
 
 @available(SwiftStdlib 6.2, *)

test/Concurrency/Runtime/sleep_executor.swift

@@ -20,7 +20,11 @@ actor MyActor {
 }
 
 @available(SwiftStdlib 6.2, *)
-final class TestExecutor: TaskExecutor, SchedulableExecutor @unchecked Sendable {
+final class TestExecutor: TaskExecutor, SchedulableExecutor, @unchecked Sendable {
+  var asSchedulable: SchedulableExecutor? {
+    return self
+  }
+
   public func enqueue(_ _job: consuming ExecutorJob) {
     let job = UnownedJob(_job)
     DispatchQueue.main.async {