Revert changes except the switch to a Memory

base/task.jl

@@ -922,31 +922,29 @@ end
 
 const StickyWorkqueue = IntrusiveLinkedListSynchronized{Task}
 global Workqueues::Memory{StickyWorkqueue} = Memory{StickyWorkqueue}([StickyWorkqueue()])
-const Workqueue = (@atomic :acquire Base.Workqueues)[1] # default work queue is thread 1 // TODO: deprecate this variable
+const Workqueues_lock = Threads.SpinLock()
+const Workqueue = Workqueues[1] # default work queue is thread 1 // TODO: deprecate this variable
 
 function workqueue_for(tid::Int)
-    qs = @atomic :acquire Base.Workqueues
+    qs = Workqueues
     if length(qs) >= tid && isassigned(qs, tid)
-        return @inbounds qs[tid] # This assumes that threads don't get deleted and that once an index is set
-                                 # all following Workqueue Memorys have the same queues at those indices
+        return @inbounds qs[tid]
     end
-    while length(qs) < tid
-        # slow path to allocate it
-        nt = Threads.maxthreadid()
-        @assert tid <= nt
-        new_qs = copyto!(typeof(qs)(undef, length(qs) + nt - 1), qs) # This overallocates by nt-1
-        xchg = @atomicreplace :acquire_release :acquire Base.Workqueues qs => new_qs
-        if xchg.success
-            qs = new_qs
-            break
-        else
-            qs = xchg.old
+    # slow path to allocate it
+    @assert tid > 0
+    l = Workqueues_lock
+    @lock l begin
+        qs = Workqueues
+        if length(qs) < tid
+            nt = Threads.maxthreadid()
+            @assert tid <= nt
+            global Workqueues = qs = copyto!(typeof(qs)(undef, length(qs) + nt - 1), qs)
         end
+        if !isassigned(qs, tid)
+            @inbounds qs[tid] = StickyWorkqueue()
+        end
+        return @inbounds qs[tid]
     end
-    if !isassigned(qs, tid)
-        @inbounds qs[tid] = StickyWorkqueue()
-    end
-    return @inbounds qs[tid]
 end
 
 function enq_work(t::Task)