Merge pull request #37474 from rjmccall/merge-abi-2-into-5.5

Merge the concurrency-5.5-abi-2 branch into release/5.5

Author: rjmccall

include/swift/ABI/AsyncLet.h

@@ -0,0 +1,52 @@
+//===--- AsyncLet.h - ABI structures for async let -00-----------*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Swift ABI describing task groups.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_ABI_TASK_ASYNC_LET_H
+#define SWIFT_ABI_TASK_ASYNC_LET_H
+
+#include "swift/ABI/Task.h"
+#include "swift/ABI/HeapObject.h"
+#include "swift/Runtime/Concurrency.h"
+#include "swift/Runtime/Config.h"
+#include "swift/Basic/RelativePointer.h"
+#include "swift/Basic/STLExtras.h"
+
+namespace swift {
+
+/// Represents an in-flight `async let`, i.e. the Task that is computing the
+/// result of the async let, along with the awaited status and other metadata.
+class alignas(Alignment_AsyncLet) AsyncLet {
+public:
+  // These constructors do not initialize the AsyncLet instance, and the
+  // destructor does not destroy the AsyncLet instance; you must call
+  // swift_asyncLet_{start,end} yourself.
+  constexpr AsyncLet()
+    : PrivateData{} {}
+
+  // FIXME: not sure how many words we should reserve
+  void *PrivateData[NumWords_AsyncLet];
+
+  // TODO: we could offer a "was awaited on" check here
+
+  /// Returns the child task that is associated with this async let.
+  /// The tasks completion is used to fulfil the value represented by this async let.
+  AsyncTask *getTask() const;
+
+};
+
+} // end namespace swift
+
+#endif // SWIFT_ABI_TASK_ASYNC_LET_H

include/swift/ABI/Executor.h

@@ -27,25 +27,42 @@ class AsyncContext;
 class AsyncTask;
 class DefaultActor;
 class Job;
-
-/// FIXME: only exists for the quick-and-dirty MainActor implementation.
-SWIFT_EXPORT_FROM(swift_Concurrency)
-Metadata* MainActorMetadata;
+class SerialExecutorWitnessTable;
 
 /// An unmanaged reference to an executor.
 ///
-/// The representation is two words: identity and implementation.
-/// The identity word is a reference to the executor object; for
-/// default actors, this is the actor object.  The implementation
-/// word describes how the executor works; it carries a witness table
-/// as well as a small number of bits indicating various special
-/// implementation properties.  As an exception to both of these
-/// rules, a null identity represents a generic executor and
-/// implies a null implementation word.
+/// This type corresponds to the type Optional<Builtin.Executor> in
+/// Swift.  The representation of nil in Optional<Builtin.Executor>
+/// aligns with what this type calls the generic executor, so the
+/// notional subtype of this type which is never generic corresponds
+/// to the type Builtin.Executor.
+///
+/// An executor reference is divided into two pieces:
+///
+/// - The identity, which is just a (potentially ObjC) object
+///   reference; when this is null, the reference is generic.
+///   Equality of executor references is based solely on equality
+///   of identity.
+///
+/// - The implementation, which is an optional reference to a
+///   witness table for the SerialExecutor protocol.  When this
+///   is null, but the identity is non-null, the reference is to
+///   a default actor.  The low bits of the implementation pointer
+///   are reserved for the use of marking interesting properties
+///   about the executor's implementation.  The runtime masks these
+///   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 {
   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.
+  enum: uintptr_t {
+    WitnessTableMask = ~uintptr_t(alignof(void*) - 1)
+  };
+
   constexpr ExecutorRef(HeapObject *identity, uintptr_t implementation)
     : Identity(identity), Implementation(implementation) {}
 
@@ -58,23 +75,11 @@ class ExecutorRef {
     return ExecutorRef(nullptr, 0);
   }
 
-  /// FIXME: only exists for the quick-and-dirty MainActor implementation.
-  /// NOTE: I didn't go with Executor::forMainActor(DefaultActor*) because
-  /// __swift_run_job_main_executor can't take more than one argument.
-  static ExecutorRef mainExecutor() {
-    auto identity = getMainActorIdentity();
-    return ExecutorRef(identity, 0);
-  }
-  static HeapObject *getMainActorIdentity() {
-    return reinterpret_cast<HeapObject*>(
-                                   ExecutorRefFlags::MainActorIdentity);
-  }
-
   /// Given a pointer to a default actor, return an executor reference
   /// for it.
   static ExecutorRef forDefaultActor(DefaultActor *actor) {
     assert(actor);
-    return ExecutorRef(actor, unsigned(ExecutorRefFlags::DefaultActor));
+    return ExecutorRef(actor, 0);
   }
 
   HeapObject *getIdentity() const {
@@ -86,37 +91,29 @@ class ExecutorRef {
     return Identity == 0;
   }
 
-  /// FIXME: only exists for the quick-and-dirty MainActor implementation.
-  bool isMainExecutor() const {
-    if (Identity == getMainActorIdentity())
-      return true;
-
-    if (Identity == nullptr || MainActorMetadata == nullptr)
-      return false;
-
-    Metadata const* metadata = swift_getObjectType(Identity);
-    return metadata == MainActorMetadata;
-  }
-
   /// Is this a default-actor executor reference?
   bool isDefaultActor() const {
-    return Implementation & unsigned(ExecutorRefFlags::DefaultActor);
+    return !isGeneric() && Implementation == 0;
   }
   DefaultActor *getDefaultActor() const {
     assert(isDefaultActor());
     return reinterpret_cast<DefaultActor*>(Identity);
   }
 
+  const SerialExecutorWitnessTable *getSerialExecutorWitnessTable() const {
+    assert(!isGeneric() && !isDefaultActor());
+    auto table = Implementation & WitnessTableMask;
+    return reinterpret_cast<const SerialExecutorWitnessTable*>(table);
+  }
+
   /// Do we have to do any work to start running as the requested
   /// executor?
   bool mustSwitchToRun(ExecutorRef newExecutor) const {
     return Identity != newExecutor.Identity;
   }
 
   bool operator==(ExecutorRef other) const {
-    return Identity == other.Identity
-    /// FIXME: only exists for the quick-and-dirty MainActor implementation.
-          || (isMainExecutor() && other.isMainExecutor());
+    return Identity == other.Identity;
   }
   bool operator!=(ExecutorRef other) const {
     return !(*this == other);

include/swift/ABI/MetadataValues.h

@@ -49,6 +49,9 @@ enum {
 
   /// The number of words in a task group.
   NumWords_TaskGroup = 32,
+
+  /// The number of words in an AsyncLet (flags + task pointer)
+  NumWords_AsyncLet = 8, // TODO: not sure how much is enough, these likely could be pretty small
 };
 
 struct InProcess;
@@ -127,6 +130,9 @@ const size_t Alignment_DefaultActor = MaximumAlignment;
 /// The alignment of a TaskGroup.
 const size_t Alignment_TaskGroup = MaximumAlignment;
 
+/// The alignment of an AsyncLet.
+const size_t Alignment_AsyncLet = MaximumAlignment;
+
 /// Flags stored in the value-witness table.
 template <typename int_type>
 class TargetValueWitnessFlags {
@@ -1994,7 +2000,7 @@ enum class JobPriority : size_t {
 };
 
 /// Flags for schedulable jobs.
-class JobFlags : public FlagSet<size_t> {
+class JobFlags : public FlagSet<uint32_t> {
 public:
   enum {
     Kind           = 0,
@@ -2013,7 +2019,7 @@ class JobFlags : public FlagSet<size_t> {
     Task_IsContinuingAsyncTask      = 27,
   };
 
-  explicit JobFlags(size_t bits) : FlagSet(bits) {}
+  explicit JobFlags(uint32_t bits) : FlagSet(bits) {}
   JobFlags(JobKind kind) { setKind(kind); }
   JobFlags(JobKind kind, JobPriority priority) {
     setKind(kind);
@@ -2194,20 +2200,6 @@ enum class ContinuationStatus : size_t {
   Resumed = 2
 };
 
-/// Flags describing the executor implementation that are stored
-/// in the ExecutorRef.
-enum class ExecutorRefFlags : size_t {
-  // The number of bits available here is very limited because it's
-  // potentially just the alignment bits of a protocol witness table
-  // pointer
-
-  /// The executor is a default actor.
-  DefaultActor = 0x1,
-
-  /// TODO: remove this
-  MainActorIdentity = 0x2,
-};
-
 } // end namespace swift
 
 #endif // SWIFT_ABI_METADATAVALUES_H

include/swift/ABI/Task.h

@@ -39,7 +39,10 @@ class TaskGroup;
 extern FullMetadata<DispatchClassMetadata> jobHeapMetadata;
 
 /// A schedulable job.
-class alignas(2 * alignof(void*)) Job : public HeapObject {
+class alignas(2 * alignof(void*)) Job :
+  // For async-let tasks, the refcount bits are initialized as "immortal"
+  // because such a task is allocated with the parent's stack allocator.
+  public HeapObject {
 public:
   // Indices into SchedulerPrivate, for use by the runtime.
   enum {
@@ -65,6 +68,9 @@ class alignas(2 * alignof(void*)) Job : public HeapObject {
 
   JobFlags Flags;
 
+  // Derived classes can use this to store a Job Id.
+  uint32_t Id = 0;
+
   // We use this union to avoid having to do a second indirect branch
   // when resuming an asynchronous task, which we expect will be the
   // common case.
@@ -88,6 +94,14 @@ class alignas(2 * alignof(void*)) Job : public HeapObject {
     assert(isAsyncTask() && "wrong constructor for a non-task job");
   }
 
+  /// Create a job with "immortal" reference counts.
+  /// Used for async let tasks.
+  Job(JobFlags flags, TaskContinuationFunction *invoke,
+      const HeapMetadata *metadata, InlineRefCounts::Immortal_t immortal)
+      : HeapObject(metadata, immortal), Flags(flags), ResumeTask(invoke) {
+    assert(isAsyncTask() && "wrong constructor for a non-task job");
+  }
+
   bool isAsyncTask() const {
     return Flags.isAsyncTask();
   }
@@ -112,8 +126,13 @@ class alignas(2 * alignof(void*)) Job : public HeapObject {
 };
 
 // The compiler will eventually assume these.
+#if defined(__LP64__) || defined(_WIN64)
 static_assert(sizeof(Job) == 6 * sizeof(void*),
               "Job size is wrong");
+#else
+static_assert(sizeof(Job) == 8 * sizeof(void*),
+              "Job size is wrong");
+#endif
 static_assert(alignof(Job) == 2 * alignof(void*),
               "Job alignment is wrong");
 
@@ -220,8 +239,25 @@ class AsyncTask : public Job {
       Status(ActiveTaskStatus()),
       Local(TaskLocal::Storage()) {
     assert(flags.isAsyncTask());
+    Id = getNextTaskId();
+  }
+
+  /// Create a task with "immortal" reference counts.
+  /// Used for async let tasks.
+  AsyncTask(const HeapMetadata *metadata, InlineRefCounts::Immortal_t immortal,
+            JobFlags flags,
+            TaskContinuationFunction *run,
+            AsyncContext *initialContext)
+    : Job(flags, run, metadata, immortal),
+      ResumeContext(initialContext),
+      Status(ActiveTaskStatus()),
+      Local(TaskLocal::Storage()) {
+    assert(flags.isAsyncTask());
+    Id = getNextTaskId();
   }
 
+  ~AsyncTask();
+
   /// Given that we've already fully established the job context
   /// in the current thread, start running this task.  To establish
   /// the job context correctly, call swift_job_run or
@@ -481,13 +517,24 @@ class AsyncTask : public Job {
     return reinterpret_cast<AsyncTask *&>(
         SchedulerPrivate[NextWaitingTaskIndex]);
   }
+
+  /// Get the next non-zero Task ID.
+  uint32_t getNextTaskId() {
+    static std::atomic<uint32_t> Id(1);
+    uint32_t Next = Id.fetch_add(1, std::memory_order_relaxed);
+    if (Next == 0) Next = Id.fetch_add(1, std::memory_order_relaxed);
+    return Next;
+  }
 };
 
 // The compiler will eventually assume these.
 static_assert(sizeof(AsyncTask) == 14 * sizeof(void*),
               "AsyncTask size is wrong");
 static_assert(alignof(AsyncTask) == 2 * alignof(void*),
               "AsyncTask alignment is wrong");
+// Libc hardcodes this offset to extract the TaskID
+static_assert(offsetof(AsyncTask, Id) == 4 * sizeof(void *) + 4,
+              "AsyncTask::Id offset is wrong");
 
 SWIFT_CC(swiftasync)
 inline void Job::runInFullyEstablishedContext() {
@@ -608,13 +655,13 @@ class FutureAsyncContext : public AsyncContext {
 /// This matches the ABI of a closure `() async throws -> ()`
 using AsyncVoidClosureEntryPoint =
   SWIFT_CC(swiftasync)
-  void (SWIFT_ASYNC_CONTEXT AsyncContext *, SWIFT_CONTEXT HeapObject *);
+  void (SWIFT_ASYNC_CONTEXT AsyncContext *, SWIFT_CONTEXT void *);
 
 /// This matches the ABI of a closure `<T>() async throws -> T`
 using AsyncGenericClosureEntryPoint =
     SWIFT_CC(swiftasync)
     void(OpaqueValue *,
-         SWIFT_ASYNC_CONTEXT AsyncContext *, SWIFT_CONTEXT HeapObject *);
+         SWIFT_ASYNC_CONTEXT AsyncContext *, SWIFT_CONTEXT void *);
 
 /// This matches the ABI of the resume function of a closure
 ///  `() async throws -> ()`.
@@ -628,7 +675,7 @@ class AsyncContextPrefix {
   // passing the closure context instead of via the async context)
   AsyncVoidClosureEntryPoint *__ptrauth_swift_task_resume_function
       asyncEntryPoint;
-   HeapObject *closureContext;
+  void *closureContext;
   SwiftError *errorResult;
 };
 
@@ -641,7 +688,7 @@ class FutureAsyncContextPrefix {
   // passing the closure context instead of via the async context)
   AsyncGenericClosureEntryPoint *__ptrauth_swift_task_resume_function
       asyncEntryPoint;
-  HeapObject *closureContext;
+  void *closureContext;
   SwiftError *errorResult;
 };
 

include/swift/ABI/TaskGroup.h

@@ -29,8 +29,8 @@ namespace swift {
 /// The task group is responsible for maintaining dynamically created child tasks.
 class alignas(Alignment_TaskGroup) TaskGroup {
 public:
-  // These constructors do not initialize the actor instance, and the
-  // destructor does not destroy the actor instance; you must call
+  // These constructors do not initialize the group instance, and the
+  // destructor does not destroy the group instance; you must call
   // swift_taskGroup_{initialize,destroy} yourself.
   constexpr TaskGroup()
     : PrivateData{} {}
@@ -43,4 +43,4 @@ class alignas(Alignment_TaskGroup) TaskGroup {
 
 } // end namespace swift
 
-#endif
+#endif // SWIFT_ABI_TASK_GROUP_H