[GC] Made the concurrency scheduler a constant PMC. This means that i…

…t never

gets collected by the end-of-the-world GC run before all tasks and timers and
events (which depend on it for their destruction) get collected and destroyed.
See RT #60622 for one example of that.

Of course, as it's a constant PMC now, it always needs its live flag cleared
just before it gets marked as live, otherwise it won't have a chance to perform
its custom marking of the PObjs to which it refers.  This is a workaround, but
the real fix is to figure out safe and consistent order of destruction, and
that's a much larger patch.

I also tidied some related code.

git-svn-id: https://svn.parrot.org/parrot/trunk@32841 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

src/gc/dod.c

@@ -298,8 +298,14 @@ Parrot_dod_trace_root(PARROT_INTERP, int trace_stack)
     pobject_lives(interp, (PObj *)interp->root_namespace);
 
     /* mark the concurrency scheduler */
-    if (interp->scheduler)
+    if (interp->scheduler) {
+        /* the scheduler is a constant PMC, but it's an aggregate
+         * clearing the live flag here forces it to mark its children
+         * but it won't get collected during global destruction before tasks do
+         * See RT #60622 for the symptom of that problem */
+        PObj_live_CLEAR((PObj *)interp->scheduler);
         pobject_lives(interp, (PObj *)interp->scheduler);
+    }
 
     /* s. packfile.c */
     mark_const_subs(interp);
@@ -323,8 +329,8 @@ Parrot_dod_trace_root(PARROT_INTERP, int trace_stack)
     Parrot_IOData_mark(interp, interp->piodata);
 
     /* quick check if we can already bail out */
-    if (arena_base->lazy_dod && arena_base->num_early_PMCs_seen >=
-            arena_base->num_early_DOD_PMCs)
+    if (arena_base->lazy_dod
+    &&  arena_base->num_early_PMCs_seen >= arena_base->num_early_DOD_PMCs)
         return 0;
 
     /* Find important stuff on the system stack */

src/inter_create.c

@@ -309,10 +309,7 @@ Note that C<exit_code> is ignored.
 void
 Parrot_really_destroy(PARROT_INTERP, SHIM(int exit_code), SHIM(void *arg))
 {
-
-    /*
-     * wait for threads to complete if needed; terminate the event loop
-     */
+    /* wait for threads to complete if needed; terminate the event loop */
     if (!interp->parent_interpreter) {
         Parrot_cx_runloop_end(interp);
         pt_join_threads(interp);
@@ -327,7 +324,7 @@ Parrot_really_destroy(PARROT_INTERP, SHIM(int exit_code), SHIM(void *arg))
      * Need to turn off DOD blocking, else things stay alive and IO
      * handles aren't closed
      */
-    interp->arena_base->DOD_block_level =
+    interp->arena_base->DOD_block_level    =
         interp->arena_base->GC_block_level = 0;
 
     if (Interp_trace_TEST(interp, ~0)) {
@@ -344,9 +341,9 @@ Parrot_really_destroy(PARROT_INTERP, SHIM(int exit_code), SHIM(void *arg))
     Parrot_do_dod_run(interp, GC_finish_FLAG);
 
 #if STM_PROFILE
-    if (interp->thread_data && interp->thread_data->stm_log &&
-            !interp->parent_interpreter &&
-                Interp_debug_TEST(interp, PARROT_THREAD_DEBUG_FLAG))
+    if (interp->thread_data && interp->thread_data->stm_log
+    && !interp->parent_interpreter
+    &&  Interp_debug_TEST(interp, PARROT_THREAD_DEBUG_FLAG))
         Parrot_STM_dump_profile(interp);
 #endif
 

src/pmc/parrotinterpreter.pmc

@@ -47,7 +47,8 @@ clone_interpreter(Parrot_Interp d, Parrot_Interp s, INTVAL flags)
     /* we block DOD runs while cloning since C<d> is not yet running */
     Parrot_block_GC_mark(d);
 
-    d->scheduler = pmc_new(d, enum_class_Scheduler);
+    /* create as constant to avoid order-of-destruction errors, RT #60622 */
+    d->scheduler = constant_pmc_new(d, enum_class_Scheduler);
     d->scheduler = VTABLE_share_ro(d, d->scheduler);
 
     if (flags & PARROT_CLONE_RUNOPS)

src/scheduler.c

@@ -72,7 +72,8 @@ Parrot_cx_init_scheduler(PARROT_INTERP)
         /* Add the very first interpreter to the list of interps. */
         pt_add_to_interpreters(interp, NULL);
 
-        scheduler = pmc_new(interp, enum_class_Scheduler);
+        /* create as constant to avoid order-of-destruction errors, RT #60622 */
+        scheduler = constant_pmc_new(interp, enum_class_Scheduler);
         scheduler = VTABLE_share_ro(interp, scheduler);
 
         interp->scheduler = scheduler;