Task Executors: Prepare for new TaskExecutor protocol

include/swift/ABI/Executor.h

@@ -28,8 +28,9 @@ class AsyncTask;
 class DefaultActor;
 class Job;
 class SerialExecutorWitnessTable;
+class TaskExecutorWitnessTable;
 
-/// An unmanaged reference to an executor.
+/// An unmanaged reference to a serial executor.
 ///
 /// This type corresponds to the type Optional<Builtin.Executor> in
 /// Swift.  The representation of nil in Optional<Builtin.Executor>
@@ -53,7 +54,7 @@ class SerialExecutorWitnessTable;
 ///   bits off before accessing the witness table, so setting them
 ///   in the future should back-deploy as long as the witness table
 ///   reference is still present.
-class ExecutorRef {
+class SerialExecutorRef {
   HeapObject *Identity; // Not necessarily Swift reference-countable
   uintptr_t Implementation;
 
@@ -79,7 +80,7 @@ class ExecutorRef {
 
   static_assert(static_cast<uintptr_t>(ExecutorKind::Ordinary) == 0);
 
-  constexpr ExecutorRef(HeapObject *identity, uintptr_t implementation)
+  constexpr SerialExecutorRef(HeapObject *identity, uintptr_t implementation)
     : Identity(identity), Implementation(implementation) {}
 
 public:
@@ -88,35 +89,35 @@ class ExecutorRef {
   /// environment, it's presumed to be okay to switch synchronously
   /// to an actor.  As an executor request, this represents a request
   /// to drop whatever the current actor is.
-  constexpr static ExecutorRef generic() {
-    return ExecutorRef(nullptr, 0);
+  constexpr static SerialExecutorRef generic() {
+    return SerialExecutorRef(nullptr, 0);
   }
 
   /// Given a pointer to a default actor, return an executor reference
   /// for it.
-  static ExecutorRef forDefaultActor(DefaultActor *actor) {
+  static SerialExecutorRef forDefaultActor(DefaultActor *actor) {
     assert(actor);
-    return ExecutorRef(actor, 0);
+    return SerialExecutorRef(actor, 0);
   }
 
   /// Given a pointer to a serial executor and its SerialExecutor
   /// conformance, return an executor reference for it.
-  static ExecutorRef forOrdinary(HeapObject *identity,
+  static SerialExecutorRef forOrdinary(HeapObject *identity,
                            const SerialExecutorWitnessTable *witnessTable) {
     assert(identity);
     assert(witnessTable);
     auto wtable = reinterpret_cast<uintptr_t>(witnessTable) |
         static_cast<uintptr_t>(ExecutorKind::Ordinary);
-    return ExecutorRef(identity, wtable);
+    return SerialExecutorRef(identity, wtable);
   }
 
-  static ExecutorRef forComplexEquality(HeapObject *identity,
+  static SerialExecutorRef forComplexEquality(HeapObject *identity,
                                         const SerialExecutorWitnessTable *witnessTable) {
     assert(identity);
     assert(witnessTable);
     auto wtable = reinterpret_cast<uintptr_t>(witnessTable) |
                   static_cast<uintptr_t>(ExecutorKind::ComplexEquality);
-    return ExecutorRef(identity, wtable);
+    return SerialExecutorRef(identity, wtable);
   }
 
   HeapObject *getIdentity() const {
@@ -162,7 +163,7 @@ class ExecutorRef {
 
   /// Do we have to do any work to start running as the requested
   /// executor?
-  bool mustSwitchToRun(ExecutorRef newExecutor) const {
+  bool mustSwitchToRun(SerialExecutorRef newExecutor) const {
     return Identity != newExecutor.Identity;
   }
 
@@ -174,10 +175,94 @@ class ExecutorRef {
     return Implementation & WitnessTableMask;
   }
 
-  bool operator==(ExecutorRef other) const {
+  bool operator==(SerialExecutorRef other) const {
     return Identity == other.Identity;
   }
-  bool operator!=(ExecutorRef other) const {
+  bool operator!=(SerialExecutorRef other) const {
+    return !(*this == other);
+  }
+};
+
+class TaskExecutorRef {
+  HeapObject *Identity; // Not necessarily Swift reference-countable
+  uintptr_t Implementation;
+
+  // We future-proof the ABI here by masking the low bits off the
+  // implementation pointer before using it as a witness table.
+  //
+  // We have 3 bits for future use remaining here.
+  enum: uintptr_t {
+    WitnessTableMask = ~uintptr_t(alignof(void*) - 1)
+  };
+
+  /// The kind is stored in the free bits in the `Implementation` witness table reference.
+  enum class TaskExecutorKind : uintptr_t {
+    /// Ordinary executor.
+    Ordinary = 0b00,
+  };
+
+  static_assert(static_cast<uintptr_t>(TaskExecutorKind::Ordinary) == 0);
+
+  constexpr TaskExecutorRef(HeapObject *identity, uintptr_t implementation)
+    : Identity(identity), Implementation(implementation) {}
+
+public:
+
+  constexpr static TaskExecutorRef undefined() {
+    return TaskExecutorRef(nullptr, 0);
+  }
+
+  /// Given a pointer to a serial executor and its TaskExecutor
+  /// conformance, return an executor reference for it.
+  static TaskExecutorRef forOrdinary(HeapObject *identity,
+                           const SerialExecutorWitnessTable *witnessTable) {
+    assert(identity);
+    assert(witnessTable);
+    auto wtable = reinterpret_cast<uintptr_t>(witnessTable) |
+        static_cast<uintptr_t>(TaskExecutorKind::Ordinary);
+    return TaskExecutorRef(identity, wtable);
+  }
+
+  HeapObject *getIdentity() const {
+    return Identity;
+  }
+
+  /// Is this the generic executor reference?
+  bool isUndefined() const {
+    return Identity == 0;
+  }
+
+  TaskExecutorKind getExecutorKind() const {
+    return static_cast<TaskExecutorKind>(Implementation & ~WitnessTableMask);
+  }
+
+  /// Is this an ordinary executor reference?
+  /// These executor references are the default kind, and have no special treatment elsewhere in the system.
+  bool isOrdinary() const {
+    return getExecutorKind() == TaskExecutorKind::Ordinary;
+  }
+
+  const TaskExecutorWitnessTable *getTaskExecutorWitnessTable() const {
+    assert(!isUndefined());
+    auto table = Implementation & WitnessTableMask;
+    return reinterpret_cast<const TaskExecutorWitnessTable*>(table);
+  }
+
+//  /// Do we have to do any work to start running as the requested
+//  /// executor?
+//  bool mustSwitchToRun(TaskExecutorRef newExecutor) const {
+//    return Identity != newExecutor.Identity;
+//  }
+
+  /// Get the raw value of the Implementation field, for tracing.
+  uintptr_t getRawImplementation() const {
+    return Implementation & WitnessTableMask;
+  }
+
+  bool operator==(TaskExecutorRef other) const {
+    return Identity == other.Identity;
+  }
+  bool operator!=(TaskExecutorRef other) const {
     return !(*this == other);
   }
 };

include/swift/ABI/Task.h

@@ -400,7 +400,7 @@ class AsyncTask : public Job {
 public:
   /// Flag that the task is to be enqueued on the provided executor and actually
   /// enqueue it
-  void flagAsAndEnqueueOnExecutor(ExecutorRef newExecutor);
+  void flagAsAndEnqueueOnExecutor(SerialExecutorRef newExecutor);
 
   /// Flag that this task is now completed. This normally does not do anything
   /// but can be used to locally insert logging.
@@ -790,7 +790,7 @@ class ContinuationAsyncContext : public AsyncContext {
 
   /// The executor that should be resumed to.
   /// Public ABI.
-  ExecutorRef ResumeToExecutor;
+  SerialExecutorRef ResumeToExecutor;
 
 #if defined(SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY)
   /// In a task-to-thread model, instead of voluntarily descheduling the task

include/swift/ABI/TaskOptions.h

@@ -82,14 +82,14 @@ class TaskGroupTaskOptionRecord : public TaskOptionRecord {
 /// executor should be used instead, most often this may mean the global
 /// concurrent executor, or the enclosing actor's executor.
 class ExecutorTaskOptionRecord : public TaskOptionRecord {
-  const ExecutorRef Executor;
+  const SerialExecutorRef Executor;
 
 public:
-  ExecutorTaskOptionRecord(ExecutorRef executor)
+  ExecutorTaskOptionRecord(SerialExecutorRef executor)
     : TaskOptionRecord(TaskOptionRecordKind::Executor),
       Executor(executor) {}
 
-  ExecutorRef getExecutor() const {
+  SerialExecutorRef getExecutor() const {
     return Executor;
   }
 

include/swift/ABI/TaskStatus.h

@@ -321,7 +321,7 @@ class TaskDependencyStatusRecord : public TaskStatusRecord {
     // (potentially intrusively), so that the appropriate escalation effect
     // (which may be different for each type of executor) can happen if a task
     // is escalated while enqueued.
-    ExecutorRef Executor;
+    SerialExecutorRef Executor;
   } DependentOn;
 
   // Enum specifying the type of dependency this task has
@@ -359,7 +359,7 @@ class TaskDependencyStatusRecord : public TaskStatusRecord {
       DependentOn.TaskGroup = taskGroup;
   }
 
-  TaskDependencyStatusRecord(AsyncTask *waitingTask, ExecutorRef executor) :
+  TaskDependencyStatusRecord(AsyncTask *waitingTask, SerialExecutorRef executor) :
     TaskStatusRecord(TaskStatusRecordKind::TaskDependency),
         DependencyKind(EnqueuedOnExecutor), WaitingTask(waitingTask) {
       DependentOn.Executor = executor;
@@ -369,7 +369,7 @@ class TaskDependencyStatusRecord : public TaskStatusRecord {
     return record->getKind() == TaskStatusRecordKind::TaskDependency;
   }
 
-  void updateDependencyToEnqueuedOn(ExecutorRef executor) {
+  void updateDependencyToEnqueuedOn(SerialExecutorRef executor) {
     DependencyKind = EnqueuedOnExecutor;
     DependentOn.Executor = executor;
   }

include/swift/AST/ASTSynthesis.h

@@ -50,6 +50,7 @@ enum SingletonTypeSynthesizer {
   _void,
   _word,
   _serialExecutor,
+  _taskExecutor,
 };
 inline Type synthesizeType(SynthesisContext &SC,
                            SingletonTypeSynthesizer kind) {
@@ -69,6 +70,9 @@ inline Type synthesizeType(SynthesisContext &SC,
   case _serialExecutor:
     return SC.Context.getProtocol(KnownProtocolKind::SerialExecutor)
       ->getDeclaredInterfaceType();
+  case _taskExecutor:
+    return SC.Context.getProtocol(KnownProtocolKind::TaskExecutor)
+      ->getDeclaredInterfaceType();
   }
 }
 

include/swift/AST/Builtins.def

@@ -874,7 +874,7 @@ BUILTIN_MISC_OPERATION_WITH_SILGEN(Alignof, "alignof", "n", Special)
 
 // getCurrentExecutor: () async -> Builtin.Executor?
 //
-// Retrieve the ExecutorRef on which the current asynchronous
+// Retrieve the SerialExecutorRef on which the current asynchronous
 // function is executing, or nil if the function isn't running
 // anywhere in particular.
 BUILTIN_MISC_OPERATION_WITH_SILGEN(GetCurrentExecutor, "getCurrentExecutor", "", Special)

include/swift/AST/KnownProtocols.def

@@ -86,6 +86,7 @@ PROTOCOL(FixedWidthInteger)
 PROTOCOL(RangeReplaceableCollection)
 PROTOCOL(Executor)
 PROTOCOL(SerialExecutor)
+PROTOCOL(TaskExecutor)
 PROTOCOL(GlobalActor)
 
 PROTOCOL_(BridgedNSError)

include/swift/AST/KnownSDKTypes.def

@@ -44,6 +44,7 @@ KNOWN_SDK_TYPE_DECL(Concurrency, Job, StructDecl, 0) // TODO: remove in favor of
 KNOWN_SDK_TYPE_DECL(Concurrency, ExecutorJob, StructDecl, 0)
 KNOWN_SDK_TYPE_DECL(Concurrency, UnownedJob, StructDecl, 0)
 KNOWN_SDK_TYPE_DECL(Concurrency, Executor, NominalTypeDecl, 0)
+KNOWN_SDK_TYPE_DECL(Concurrency, TaskExecutor, NominalTypeDecl, 0)
 KNOWN_SDK_TYPE_DECL(Concurrency, SerialExecutor, NominalTypeDecl, 0)
 KNOWN_SDK_TYPE_DECL(Concurrency, UnownedSerialExecutor, NominalTypeDecl, 0)
 

include/swift/AST/Types.h

@@ -1693,7 +1693,7 @@ class BuiltinRawUnsafeContinuationType : public BuiltinType {
 DEFINE_EMPTY_CAN_TYPE_WRAPPER(BuiltinRawUnsafeContinuationType, BuiltinType)
 
 /// BuiltinExecutorType - The builtin executor-ref type.  In C, this
-/// is the ExecutorRef struct type.
+/// is the SerialExecutorRef struct type.
 class BuiltinExecutorType : public BuiltinType {
   friend class ASTContext;
   BuiltinExecutorType(const ASTContext &C)

include/swift/Demangling/StandardTypesMangling.def

@@ -88,6 +88,7 @@ STANDARD_TYPE_CONCURRENCY(Protocol, F, Executor)
 STANDARD_TYPE_CONCURRENCY(Protocol, f, SerialExecutor)
 STANDARD_TYPE_CONCURRENCY(Structure, G, TaskGroup)
 STANDARD_TYPE_CONCURRENCY(Structure, g, ThrowingTaskGroup)
+STANDARD_TYPE_CONCURRENCY(Protocol, h, TaskExecutor)
 STANDARD_TYPE_CONCURRENCY(Protocol, I, AsyncIteratorProtocol)
 STANDARD_TYPE_CONCURRENCY(Protocol, i, AsyncSequence)
 STANDARD_TYPE_CONCURRENCY(Structure, J, UnownedJob)

include/swift/Runtime/Concurrency.h

@@ -660,7 +660,7 @@ void swift_task_localsCopyTo(AsyncTask* target);
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swiftasync)
 void swift_task_switch(SWIFT_ASYNC_CONTEXT AsyncContext *resumeToContext,
                        TaskContinuationFunction *resumeFunction,
-                       ExecutorRef newExecutor);
+                       SerialExecutorRef newExecutor);
 
 /// Mark a task for enqueue on a new executor and then enqueue it.
 ///
@@ -671,7 +671,7 @@ void swift_task_switch(SWIFT_ASYNC_CONTEXT AsyncContext *resumeToContext,
 /// synchronously when possible.
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
 void
-swift_task_enqueueTaskOnExecutor(AsyncTask *task, ExecutorRef executor);
+swift_task_enqueueTaskOnExecutor(AsyncTask *task, SerialExecutorRef executor);
 
 /// Enqueue the given job to run asynchronously on the given executor.
 ///
@@ -681,7 +681,7 @@ swift_task_enqueueTaskOnExecutor(AsyncTask *task, ExecutorRef executor);
 /// Generally you should call swift_task_switch to switch execution
 /// synchronously when possible.
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
-void swift_task_enqueue(Job *job, ExecutorRef executor);
+void swift_task_enqueue(Job *job, SerialExecutorRef executor);
 
 /// Enqueue the given job to run asynchronously on the global
 /// execution pool.
@@ -716,7 +716,7 @@ bool swift_task_isOnExecutor(
     const SerialExecutorWitnessTable *wtable);
 
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
-bool swift_executor_isComplexEquality(ExecutorRef ref);
+bool swift_executor_isComplexEquality(SerialExecutorRef ref);
 
 /// Return the 64bit TaskID (if the job is an AsyncTask),
 /// or the 32bits of the job Id otherwise.
@@ -886,27 +886,27 @@ void swift_task_asyncMainDrainQueue [[noreturn]]();
 /// Establish that the current thread is running as the given
 /// executor, then run a job.
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
-void swift_job_run(Job *job, ExecutorRef executor);
+void swift_job_run(Job *job, SerialExecutorRef executor);
 
 /// Return the current thread's active task reference.
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
 AsyncTask *swift_task_getCurrent(void);
 
 /// Return the current thread's active executor reference.
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
-ExecutorRef swift_task_getCurrentExecutor(void);
+SerialExecutorRef swift_task_getCurrentExecutor(void);
 
 /// Return the main-actor executor reference.
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
-ExecutorRef swift_task_getMainExecutor(void);
+SerialExecutorRef swift_task_getMainExecutor(void);
 
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
-bool swift_task_isCurrentExecutor(ExecutorRef executor);
+bool swift_task_isCurrentExecutor(SerialExecutorRef executor);
 
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
 void swift_task_reportUnexpectedExecutor(
     const unsigned char *file, uintptr_t fileLength, bool fileIsASCII,
-    uintptr_t line, ExecutorRef executor);
+    uintptr_t line, SerialExecutorRef executor);
 
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
 JobPriority swift_task_getCurrentThreadPriority(void);

include/swift/Runtime/RuntimeFunctions.def

@@ -2310,7 +2310,7 @@ FUNCTION(TaskCreate,
 
 // void swift_task_switch(AsyncContext *resumeContext,
 //                        TaskContinuationFunction *resumeFunction,
-//                        ExecutorRef newExecutor);
+//                        SerialExecutorRef newExecutor);
 FUNCTION(TaskSwitchFunc,
          swift_task_switch, SwiftAsyncCC,
          ConcurrencyAvailability,
@@ -2372,7 +2372,7 @@ FUNCTION(ContinuationThrowingResumeWithError,
          EFFECT(Concurrency),
          UNKNOWN_MEMEFFECTS)
 
-// ExecutorRef swift_task_getCurrentExecutor();
+// SerialExecutorRef swift_task_getCurrentExecutor();
 FUNCTION(TaskGetCurrentExecutor,
          swift_task_getCurrentExecutor, SwiftCC,
          ConcurrencyAvailability,
@@ -2382,7 +2382,7 @@ FUNCTION(TaskGetCurrentExecutor,
          EFFECT(Concurrency),
          MEMEFFECTS(ArgMemOnly))
 
-// ExecutorRef swift_task_getMainExecutor();
+// SerialExecutorRef swift_task_getMainExecutor();
 FUNCTION(TaskGetMainExecutor,
          swift_task_getMainExecutor, SwiftCC,
          ConcurrencyAvailability,