correctly account for cycle starts

src/execution_context.mli

@@ -25,5 +25,6 @@ val create_like
 val find_local : t -> 'a Univ_map.Key.t -> 'a option
 val with_local : t -> 'a Univ_map.Key.t -> 'a option -> t
 val with_tid : t -> int -> t
+
 val record_backtrace : t -> t
 

src/scheduler0.ml

@@ -7,8 +7,10 @@ let events t = t.time_source.events
 
 let set_execution_context t execution_context =
   (* Avoid a caml_modify in most cases. *)
+  (* XXX: see where job_queue also modifies current_execution_context *)
   if not (phys_equal t.current_execution_context execution_context)
   then (
-    if t.current_execution_context.tid <> execution_context.tid then (!Tracing.fns).trace_thread_switch execution_context ;
+    if t.current_execution_context.tid <> execution_context.tid then (!Tracing.fns).trace_thread_switch execution_context 
+    else if t.cycle_started then ((!Tracing.fns).trace_thread_switch execution_context; t.cycle_started <- false) ;
     t.current_execution_context <- execution_context )
 ;;

src/scheduler1.ml

@@ -120,6 +120,7 @@ type t = Scheduler0.t =
   ; mutable check_invariants                    : bool
   ; mutable max_num_jobs_per_priority_per_cycle : Max_num_jobs_per_priority_per_cycle.t
   ; mutable record_backtraces                   : bool
+  ; mutable cycle_started : bool
   ; mutable on_start_of_cycle                   : unit -> unit
   ; mutable on_end_of_cycle                     : unit -> unit }
 [@@deriving fields, sexp_of]
@@ -172,6 +173,7 @@ let invariant t : unit =
       ~check_invariants:ignore
       ~max_num_jobs_per_priority_per_cycle:ignore
       ~record_backtraces:ignore
+      ~cycle_started:ignore
       ~on_start_of_cycle:ignore
       ~on_end_of_cycle:ignore
     ;
@@ -243,6 +245,7 @@ let create () =
     ; check_invariants                     = Async_kernel_config.check_invariants
     ; max_num_jobs_per_priority_per_cycle  = Async_kernel_config.max_num_jobs_per_priority_per_cycle
     ; record_backtraces                    = Async_kernel_config.record_backtraces
+    ; cycle_started = false
     ; on_start_of_cycle                    = Fn.id
     ; on_end_of_cycle                      = Fn.id }
   and events = Timing_wheel_ns.create ~config:Async_kernel_config.timing_wheel_config ~start:now

src/types.ml

@@ -175,6 +175,7 @@ and Scheduler : sig
     ; mutable check_invariants                    : bool
     ; mutable max_num_jobs_per_priority_per_cycle : Max_num_jobs_per_priority_per_cycle.t
     ; mutable record_backtraces                   : bool
+    ; mutable cycle_started : bool
     ; mutable on_start_of_cycle                   : unit -> unit
     ; mutable on_end_of_cycle                     : unit -> unit }
 end = Scheduler