[SE-0304] Clean up handling of task priorities.

Author: DougGregor

stdlib/public/Concurrency/Task.cpp

@@ -496,15 +496,18 @@ static AsyncTaskAndContext swift_task_create_commonImpl(
 
     if (currentTask)
       jobFlags.setPriority(currentTask->getPriority());
-    else
-      // FIXME: Ideally, this should be setting priority based on
-      // swift_task_getCurrentThreadPriority(). However, that creates
-      // priority differences which lead to different kinds of hangs
-      // Temporarily use Unspecified to work around that.
-      // See also: PR #37939.
-      jobFlags.setPriority(JobPriority::Unspecified);
+    else if (taskCreateFlags.inheritContext())
+      jobFlags.setPriority(swift_task_getCurrentThreadPriority());
   }
 
+  // Adjust user-interactive priorities down to user-initiated.
+  if (jobFlags.getPriority() == JobPriority::UserInteractive)
+    jobFlags.setPriority(JobPriority::UserInitiated);
+
+  // If there is still no job priority, use the default priority.
+  if (jobFlags.getPriority() == JobPriority::Unspecified)
+    jobFlags.setPriority(JobPriority::Default);
+
   // Figure out the size of the header.
   size_t headerSize = sizeof(AsyncTask);
   if (parent) {

stdlib/public/Concurrency/Task.swift

@@ -269,7 +269,7 @@ extension Task where Success == Never, Failure == Never {
       }
 
       // Otherwise, query the system.
-      return TaskPriority(rawValue: UInt8(0))
+      return TaskPriority(rawValue: UInt8(_getCurrentThreadPriority()))
     }
   }
 }
@@ -632,11 +632,10 @@ extension Task where Success == Never, Failure == Never {
   /// As such,
   /// this method isn't necessarily a way to avoid resource starvation.
   public static func yield() async {
-    let currentTask = Builtin.getCurrentAsyncTask()
-    let priority = getJobFlags(currentTask).priority ?? Task.currentPriority._downgradeUserInteractive
-
     return await Builtin.withUnsafeContinuation { (continuation: Builtin.RawUnsafeContinuation) -> Void in
-      let job = _taskCreateNullaryContinuationJob(priority: Int(priority.rawValue), continuation: continuation)
+      let job = _taskCreateNullaryContinuationJob(
+          priority: Int(Task.currentPriority.rawValue),
+          continuation: continuation)
       _enqueueJobGlobal(job)
     }
   }
@@ -708,7 +707,8 @@ public struct UnsafeCurrentTask {
   /// - SeeAlso: `TaskPriority`
   /// - SeeAlso: `Task.currentPriority`
   public var priority: TaskPriority {
-    getJobFlags(_task).priority ?? .unspecified
+    getJobFlags(_task).priority ?? TaskPriority(
+        rawValue: UInt8(_getCurrentThreadPriority()))
   }
 
   /// Cancel the current task.

stdlib/public/Concurrency/TaskSleep.swift

@@ -19,11 +19,10 @@ extension Task where Success == Never, Failure == Never {
   ///
   /// This function does _not_ block the underlying thread.
   public static func sleep(_ duration: UInt64) async {
-    let currentTask = Builtin.getCurrentAsyncTask()
-    let priority = getJobFlags(currentTask).priority ?? Task.currentPriority._downgradeUserInteractive
-
     return await Builtin.withUnsafeContinuation { (continuation: Builtin.RawUnsafeContinuation) -> Void in
-      let job = _taskCreateNullaryContinuationJob(priority: Int(priority.rawValue), continuation: continuation)
+      let job = _taskCreateNullaryContinuationJob(
+          priority: Int(Task.currentPriority.rawValue),
+          continuation: continuation)
       _enqueueJobGlobalWithDelay(duration, job)
     }
   }

test/Concurrency/Runtime/async_task_priority_current.swift

@@ -13,7 +13,7 @@ import Dispatch
 @available(SwiftStdlib 5.5, *)
 func test_detach() async {
   let a1 = Task.currentPriority
-  print("a1: \(a1)") // CHECK: TaskPriority(rawValue: 0)
+  print("a1: \(a1)") // CHECK: TaskPriority(rawValue: 21)
 
   // Note: remember to detach using a higher priority, otherwise a lower one
   // might be escalated by the get() and we could see `default` in the detached
@@ -24,7 +24,7 @@ func test_detach() async {
   }.get()
 
   let a3 = Task.currentPriority
-  print("a3: \(a3)") // CHECK: a3: TaskPriority(rawValue: 0)
+  print("a3: \(a3)") // CHECK: a3: TaskPriority(rawValue: 21)
 }
 
 @available(SwiftStdlib 5.5, *)