Callback timer

4 files changed, 362 insertions, 67 deletions

diff --git a/erts/emulator/beam/erl_hl_timer.c b/erts/emulator/beam/erl_hl_timer.c
index 0cb75a8b5f..8eacb921fe 100644
--- a/erts/emulator/beam/erl_hl_timer.c
+++ b/erts/emulator/beam/erl_hl_timer.c
@@ -81,6 +81,13 @@ static void hdbg_chk_srv(ErtsHLTimerService *srv);
 #error "ERTS_REF_NUMBERS changed. Update me..."
 #endif
 
+typedef enum {
+    ERTS_TMR_BIF,
+    ERTS_TMR_PROC,
+    ERTS_TMR_PORT,
+    ERTS_TMR_CALLBACK
+} ErtsTmrType;
+
 #define ERTS_BIF_TIMER_SHORT_TIME 5000
 
 #ifdef ERTS_SMP
@@ -97,8 +104,9 @@ static void hdbg_chk_srv(ErtsHLTimerService *srv);
 #define ERTS_TMR_ROFLG_REG_NAME		(((Uint32) 1) << 13)
 #define ERTS_TMR_ROFLG_PROC		(((Uint32) 1) << 14)
 #define ERTS_TMR_ROFLG_PORT		(((Uint32) 1) << 15)
+#define ERTS_TMR_ROFLG_CALLBACK		(((Uint32) 1) << 16)
 #ifdef ERTS_BTM_ACCESSOR_SUPPORT
-#define ERTS_TMR_ROFLG_ABIF_TMR		(((Uint32) 1) << 16)
+#define ERTS_TMR_ROFLG_ABIF_TMR		(((Uint32) 1) << 17)
 #endif
 
 #define ERTS_TMR_ROFLG_SID_MASK	\
@@ -143,6 +151,7 @@ typedef struct {
     Uint32 roflgs;
     erts_smp_atomic32_t refc;
     union {
+	void *arg;
 	erts_atomic_t next;
     } u;
 } ErtsTmrHead;
@@ -158,6 +167,7 @@ struct ErtsHLTimer_ {
 	Process *proc;
 	Port *port;
 	Eterm name;
+	void (*callback)(void *);
     } receiver;
 
 #ifdef ERTS_HLT_HARD_DEBUG
@@ -192,7 +202,10 @@ struct ErtsHLTimer_ {
 
 typedef struct {
     ErtsTmrHead head; /* NEED to be first! */
-    void *p;
+    union {
+	void *p;
+	void (*callback)(void *);
+    } u;
     ErtsTWheelTimer tw_tmr;
 } ErtsTWTimer;
 
@@ -348,8 +361,8 @@ refn_is_lt(Uint32 *x, Uint32 *y)
 #define ERTS_RBT_WANT_SMALLEST
 #define ERTS_RBT_WANT_LOOKUP_INSERT
 #define ERTS_RBT_WANT_REPLACE
+#define ERTS_RBT_WANT_FOREACH
 #ifdef ERTS_HLT_HARD_DEBUG
-#  define ERTS_RBT_WANT_FOREACH
 #  define ERTS_RBT_WANT_LOOKUP
 #endif
 #define ERTS_RBT_UNDEF
@@ -460,8 +473,6 @@ same_time_list_foreach_destroy_yielding(ErtsHLTimer **root,
     }    
 }
 
-#ifdef ERTS_HLT_HARD_DEBUG
-
 static ERTS_INLINE void
 same_time_list_foreach(ErtsHLTimer *root,
 		       void (*op)(ErtsHLTimer *, void *),
@@ -476,6 +487,8 @@ same_time_list_foreach(ErtsHLTimer *root,
     }
 }
 
+#ifdef ERTS_HLT_HARD_DEBUG
+
 static ERTS_INLINE ErtsHLTimer *
 same_time_list_lookup(ErtsHLTimer *root, ErtsHLTimer *x)
 {
@@ -761,9 +774,9 @@ schedule_tw_timer_destroy(ErtsTWTimer *tmr)
      * dropped at once...
      */
     if (tmr->head.roflgs & ERTS_TMR_ROFLG_PROC)
-	erts_proc_dec_refc((Process *) tmr->p);
-    else
-	erts_port_dec_refc((Port *) tmr->p);
+	erts_proc_dec_refc((Process *) tmr->u.p);
+    else if (tmr->head.roflgs & ERTS_TMR_ROFLG_PORT)
+	erts_port_dec_refc((Port *) tmr->u.p);
 
     erts_schedule_thr_prgr_later_cleanup_op(
 	scheduled_tw_timer_destroy,
@@ -785,7 +798,7 @@ static void
 tw_proc_timeout(void *vtwtp)
 {
     ErtsTWTimer *twtp = (ErtsTWTimer *) vtwtp;
-    Process *proc = (Process *) twtp->p;
+    Process *proc = (Process *) twtp->u.p;
     if (proc_timeout_common(proc, vtwtp))
 	tw_timer_dec_refc(twtp);
     tw_timer_dec_refc(twtp);
@@ -795,7 +808,7 @@ static void
 tw_port_timeout(void *vtwtp)
 {
     ErtsTWTimer *twtp = (ErtsTWTimer *) vtwtp;
-    Port *port = (Port *) twtp->p;
+    Port *port = (Port *) twtp->u.p;
     if (port_timeout_common(port, vtwtp))
 	tw_timer_dec_refc(twtp);
     tw_timer_dec_refc(twtp);
@@ -815,13 +828,26 @@ cancel_tw_timer(ErtsSchedulerData *esdp, ErtsTWTimer *tmr)
     erts_twheel_cancel_timer(esdp->timer_wheel, &tmr->tw_tmr);
 }
 
+static void
+tw_callback_timeout(void *vtwtp)
+{
+    ErtsTWTimer *twtp = (ErtsTWTimer *) vtwtp;
+    void (*callback)(void *) = twtp->u.callback;
+    void *arg = twtp->head.u.arg;
+    tw_timer_dec_refc(twtp);
+    (*callback)(arg);
+}
+
 static ErtsTWTimer *
 create_tw_timer(ErtsSchedulerData *esdp, 
-		void *p, int is_proc,
+		ErtsTmrType type, void *p,
+		void (*callback)(void *), void *arg,
 		ErtsMonotonicTime timeout_pos)
 {
     ErtsTWTimer *tmr;
     void (*timeout_func)(void *);
+    void (*cancel_func)(void *);
+    erts_aint32_t refc;
 
     tmr = tw_timer_alloc();
     erts_twheel_init_timer(&tmr->tw_tmr);
@@ -829,24 +855,48 @@ create_tw_timer(ErtsSchedulerData *esdp,
     tmr->head.roflgs = (Uint32) esdp->no;
     ERTS_HLT_ASSERT((tmr->head.roflgs
 		     & ~ERTS_TMR_ROFLG_SID_MASK) == 0);
-    tmr->p = p;
-    if (is_proc) {
+
+    switch (type) {
+
+    case ERTS_TMR_PROC:
+	tmr->u.p = p;
 	tmr->head.roflgs |= ERTS_TMR_ROFLG_PROC;
 	timeout_func = tw_proc_timeout;
+	cancel_func = tw_ptimer_cancel;
 	erts_proc_inc_refc((Process *) p);
-    }
-    else {
+	refc = 2;
+	break;
+
+    case ERTS_TMR_PORT:
+	tmr->u.p = p;
 	tmr->head.roflgs |= ERTS_TMR_ROFLG_PORT;
 	timeout_func = tw_port_timeout;
+	cancel_func = tw_ptimer_cancel;
 	erts_port_inc_refc((Port *) p);
+	refc = 2;
+	break;
+
+    case ERTS_TMR_CALLBACK:
+	tmr->head.u.arg = arg;
+	tmr->u.callback = callback;
+
+	tmr->head.roflgs |= ERTS_TMR_ROFLG_CALLBACK;
+	timeout_func = tw_callback_timeout;
+	cancel_func = NULL;
+	refc = 1;
+	break;
+
+    default:
+	ERTS_INTERNAL_ERROR("Unsupported timer type");
+	return NULL;
     }
 
-    erts_smp_atomic32_init_nob(&tmr->head.refc, 2);
+    erts_smp_atomic32_init_nob(&tmr->head.refc, refc);
 
     erts_twheel_set_timer(esdp->timer_wheel,
 			  &tmr->tw_tmr,
 			  timeout_func,
-			  tw_ptimer_cancel,
+			  cancel_func,
 			  tmr,
 			  timeout_pos);
 
@@ -994,17 +1044,15 @@ hlt_delete_abtm(ErtsHLTimer *tmr)
 static ErtsHLTimer *
 create_hl_timer(ErtsSchedulerData *esdp,
 		ErtsMonotonicTime timeout_pos,
-		int short_time, int is_bif_tmr,
+		int short_time, ErtsTmrType type,
 		void *rcvrp, Eterm rcvr, Eterm acsr,
-		Eterm msg, Uint32 *refn)
+		Eterm msg, Uint32 *refn,
+		void (*callback)(void *), void *arg)
 {
     ErtsHLTimerService *srv = esdp->timer_service;
     ErtsHLTimer *tmr, *st_tmr;
     erts_aint32_t refc;
     Uint32 roflgs;
-#ifdef ERTS_BTM_ACCESSOR_SUPPORT
-    int is_abif_tmr = is_bif_tmr && is_value(acsr) && acsr != rcvr;
-#endif
 
     check_canceled_queue(esdp, srv);
 
@@ -1012,45 +1060,69 @@ create_hl_timer(ErtsSchedulerData *esdp,
 
     roflgs = ((Uint32) esdp->no) | ERTS_TMR_ROFLG_HLT;
 
-    if (!is_bif_tmr)
+    if (type != ERTS_TMR_BIF) {
+
 	tmr = erts_alloc(ERTS_ALC_T_HL_PTIMER,
 			 ERTS_HL_PTIMER_SIZE);
-    else if (short_time) {
-	tmr = bif_timer_pre_alloc();
-	if (!tmr)
-	    goto alloc_bif_timer;
-	roflgs |= ERTS_TMR_ROFLG_PRE_ALC;
-    }
-    else {
-    alloc_bif_timer:
-#ifdef ERTS_BTM_ACCESSOR_SUPPORT
-	if (is_abif_tmr)
-	    tmr = erts_alloc(ERTS_ALC_T_ABIF_TIMER,
-			     ERTS_ABIF_TIMER_SIZE);
-	else
-#endif
-	    tmr = erts_alloc(ERTS_ALC_T_BIF_TIMER,
-			     ERTS_BIF_TIMER_SIZE);
-    }
+	tmr->timeout = timeout_pos;
 
-    tmr->timeout = timeout_pos;
+	switch (type) {
+
+	case ERTS_TMR_PROC:
+	    ERTS_HLT_ASSERT(is_internal_pid(rcvr));
 
-    if (!is_bif_tmr) {
-	if (is_internal_pid(rcvr)) {
 	    erts_proc_inc_refc((Process *) rcvrp);
 	    tmr->receiver.proc = (Process *) rcvrp;
 	    roflgs |= ERTS_TMR_ROFLG_PROC;
-	}
-	else {
-	    erts_port_inc_refc((Port *) rcvrp);
+	    refc = 2;
+	    break;
+
+	case ERTS_TMR_PORT:
 	    ERTS_HLT_ASSERT(is_internal_port(rcvr));
+	    erts_port_inc_refc((Port *) rcvrp);
 	    tmr->receiver.port = (Port *) rcvrp;
 	    roflgs |= ERTS_TMR_ROFLG_PORT;
+	    refc = 2;
+	    break;
+
+	case ERTS_TMR_CALLBACK:
+	    roflgs |= ERTS_TMR_ROFLG_CALLBACK;
+	    tmr->receiver.callback = callback;
+	    tmr->head.u.arg = arg;
+	    refc = 1;
+	    break;
+
+	default:
+	    ERTS_INTERNAL_ERROR("Unsupported timer type");
+	    return NULL;
 	}
-	refc = 2;
+
     }
-    else {
+    else { /* ERTS_TMR_BIF */
 	Uint hsz;
+#ifdef ERTS_BTM_ACCESSOR_SUPPORT
+	int is_abif_tmr = is_value(acsr) && acsr != rcvr;
+#endif
+
+	if (short_time) {
+	    tmr = bif_timer_pre_alloc();
+	    if (!tmr)
+		goto alloc_bif_timer;
+	    roflgs |= ERTS_TMR_ROFLG_PRE_ALC;
+	}
+	else {
+	alloc_bif_timer:
+#ifdef ERTS_BTM_ACCESSOR_SUPPORT
+	    if (is_abif_tmr)
+		tmr = erts_alloc(ERTS_ALC_T_ABIF_TIMER,
+				 ERTS_ABIF_TIMER_SIZE);
+	    else
+#endif
+		tmr = erts_alloc(ERTS_ALC_T_BIF_TIMER,
+				 ERTS_BIF_TIMER_SIZE);
+	}
+
+	tmr->timeout = timeout_pos;
 
 	roflgs |= ERTS_TMR_ROFLG_BIF_TMR;
 	if (is_internal_pid(rcvr)) {
@@ -1081,6 +1153,7 @@ create_hl_timer(ErtsSchedulerData *esdp,
 	tmr->btm.refn[2] = refn[2];
 
 	tmr->btm.proc_tree.parent = ERTS_HLT_PFIELD_NOT_IN_TABLE;
+
 #ifdef ERTS_BTM_ACCESSOR_SUPPORT
 	if (is_abif_tmr) {
 	    Process *aproc;
@@ -1097,6 +1170,8 @@ create_hl_timer(ErtsSchedulerData *esdp,
 	    }
 	}
 #endif
+
+	btm_rbt_insert(&srv->btm_tree, tmr);
     }
 
     tmr->head.roflgs = roflgs;
@@ -1124,9 +1199,6 @@ create_hl_timer(ErtsSchedulerData *esdp,
     if (st_tmr)
 	same_time_list_insert(&st_tmr->time.tree.same_time, tmr);
 
-    if (is_bif_tmr)
-	btm_rbt_insert(&srv->btm_tree, tmr);
-
 #ifdef ERTS_HLT_HARD_DEBUG
     tmr->pending_timeout = 0;
 #endif
@@ -1231,10 +1303,13 @@ static void hlt_timeout(ErtsHLTimer *tmr, void *vsrv)
 	    hlt_bif_timer_timeout(tmr, roflgs);
 	else if (roflgs & ERTS_TMR_ROFLG_PROC)
 	    hlt_proc_timeout(tmr);
-	else {
-	    ERTS_HLT_ASSERT(roflgs & ERTS_TMR_ROFLG_PORT);
+	else if (roflgs & ERTS_TMR_ROFLG_PORT)
 	    hlt_port_timeout(tmr);
+	else {
+	    ERTS_HLT_ASSERT(roflgs & ERTS_TMR_ROFLG_CALLBACK);
+	    (*tmr->receiver.callback)(tmr->head.u.arg);
 	}
+
     }
 
     tmr->time.tree.parent = ERTS_HLT_PFIELD_NOT_IN_TABLE;
@@ -1700,8 +1775,9 @@ setup_bif_timer(Process *c_p, ErtsMonotonicTime timeout_pos,
 
     tmo_msg = wrap ? TUPLE3(tmp_hp, am_timeout, ref, msg) : msg;
 
-    tmr = create_hl_timer(esdp, timeout_pos, short_time, 1, NULL, 
-			  rcvr, acsr, tmo_msg, internal_ref_numbers(ref));
+    tmr = create_hl_timer(esdp, timeout_pos, short_time,
+			  ERTS_TMR_BIF, NULL,  rcvr, acsr, tmo_msg,
+			  internal_ref_numbers(ref), NULL, NULL);
 
     UnUseTmpHeap(4, c_p);
 
@@ -2538,6 +2614,80 @@ BIF_RETTYPE read_timer_2(BIF_ALIST_2)
     return ret;
 }
 
+static void
+start_callback_timer(ErtsSchedulerData *esdp,
+		     int twt,
+		     ErtsMonotonicTime timeout_pos,
+		     void (*callback)(void *),
+		     void *arg)
+		     
+{
+    if (twt)
+	create_tw_timer(esdp, ERTS_TMR_CALLBACK, NULL,
+			callback, arg, timeout_pos);
+    else
+	create_hl_timer(esdp, timeout_pos, 0,
+			ERTS_TMR_CALLBACK, NULL,
+			NIL, THE_NON_VALUE, NIL,
+			NULL, callback, arg);
+}
+
+typedef struct {
+    int twt;
+    ErtsMonotonicTime timeout_pos;
+    void (*callback)(void *);
+    void *arg;
+} ErtsStartCallbackTimerRequest;
+
+static void
+scheduled_start_callback_timer(void *vsctr)
+{
+    ErtsStartCallbackTimerRequest *sctr
+	= (ErtsStartCallbackTimerRequest *) vsctr;
+
+    start_callback_timer(erts_get_scheduler_data(),
+			 sctr->twt,
+			 sctr->timeout_pos,
+			 sctr->callback,	
+			 sctr->arg);
+
+    erts_free(ERTS_ALC_T_TIMER_REQUEST, vsctr);
+}
+
+void
+erts_start_timer_callback(ErtsMonotonicTime tmo,
+			  void (*callback)(void *),
+			  void *arg)
+{
+    ErtsSchedulerData *esdp;
+    ErtsMonotonicTime timeout_pos;
+    int twt;
+
+    esdp = erts_get_scheduler_data();
+    timeout_pos = get_timeout_pos(erts_get_monotonic_time(esdp),
+				  tmo);
+    twt = tmo < ERTS_TIMER_WHEEL_MSEC;
+
+    if (esdp)
+	start_callback_timer(esdp,
+			     twt,
+			     timeout_pos,
+			     callback,
+			     arg);
+    else {
+	ErtsStartCallbackTimerRequest *sctr;
+	sctr = erts_alloc(ERTS_ALC_T_TIMER_REQUEST,
+			  sizeof(ErtsStartCallbackTimerRequest));
+	sctr->twt = twt;
+	sctr->timeout_pos = timeout_pos;
+	sctr->callback = callback;
+	sctr->arg = arg;
+	erts_schedule_misc_aux_work(1,
+				    scheduled_start_callback_timer,
+				    (void *) sctr);
+    }
+}
+
 /*
  * Process and Port timer functionality.
  *
@@ -2561,12 +2711,13 @@ set_proc_timer_common(Process *c_p, ErtsSchedulerData *esdp, Sint64 tmo,
 	c_p->flags &= ~F_TIMO;
 
 	if (tmo < ERTS_TIMER_WHEEL_MSEC)
-	    tmr = (void *) create_tw_timer(esdp, (void *) c_p, 1, timeout_pos);
+	    tmr = (void *) create_tw_timer(esdp, ERTS_TMR_PROC, (void *) c_p,
+					   NULL, NULL, timeout_pos);
 	else
-	    tmr = (void *) create_hl_timer(esdp, timeout_pos,
-					   short_time, 0, (void *) c_p,
+	    tmr = (void *) create_hl_timer(esdp, timeout_pos, short_time,
+					   ERTS_TMR_PROC, (void *) c_p,
 					   c_p->common.id, THE_NON_VALUE,
-					   NIL, NULL);
+					   NIL, NULL, NULL, NULL);
 	erts_smp_atomic_set_relb(&c_p->common.timer, (erts_aint_t) tmr);
     }
 }
@@ -2649,13 +2800,12 @@ erts_set_port_timer(Port *c_prt, Sint64 tmo)
     timeout_pos = get_timeout_pos(erts_get_monotonic_time(esdp), tmo);
 
     if (tmo < ERTS_TIMER_WHEEL_MSEC)
-	tmr = (void *) create_tw_timer(esdp, (void *) c_prt, 0,
-				       timeout_pos);
+	tmr = (void *) create_tw_timer(esdp, ERTS_TMR_PORT, (void *) c_prt,
+				       NULL, NULL, timeout_pos);
     else
-	tmr = (void *) create_hl_timer(esdp, timeout_pos, 0, 0,
-				       (void *) c_prt,
-				       c_prt->common.id, THE_NON_VALUE,
-				       NIL, NULL);
+	tmr = (void *) create_hl_timer(esdp, timeout_pos, 0, ERTS_TMR_PORT,
+				       (void *) c_prt, c_prt->common.id,
+				       THE_NON_VALUE, NIL, NULL, NULL, NULL);
     erts_smp_atomic_set_relb(&c_prt->common.timer, (erts_aint_t) tmr);
 }
 
@@ -2800,6 +2950,98 @@ erts_debug_bif_timer_foreach(void (*func)(Eterm,
     }
 }
 
+typedef struct {
+    void (*tclbk)(void *);
+    void (*func)(void *,
+		 ErtsMonotonicTime,
+		 void *);
+    void *arg;
+} ErtsDebugForeachCallbackTimer;
+
+static void
+debug_callback_timer_foreach_list(ErtsHLTimer *tmr, void *vdfct)
+{
+    ErtsDebugForeachCallbackTimer *dfct
+	= (ErtsDebugForeachCallbackTimer *) vdfct;
+
+    if ((tmr->head.roflgs & ERTS_TMR_ROFLG_CALLBACK)
+	&& (tmr->receiver.callback && dfct->tclbk))
+	(*dfct->func)(dfct->arg,
+		      tmr->timeout,
+		      tmr->head.u.arg);
+}
+
+static void
+debug_callback_timer_foreach(ErtsHLTimer *tmr, void *vdfct)
+{
+    ErtsDebugForeachCallbackTimer *dfct
+	= (ErtsDebugForeachCallbackTimer *) vdfct;
+
+    if (tmr->time.tree.same_time)
+	same_time_list_foreach(tmr->time.tree.same_time,
+			       debug_callback_timer_foreach_list,
+			       vdfct);
+
+    if ((tmr->head.roflgs & ERTS_TMR_ROFLG_CALLBACK)
+	&& (tmr->receiver.callback && dfct->tclbk))
+	(*dfct->func)(dfct->arg,
+		      tmr->timeout,
+		      tmr->head.u.arg);
+}
+
+static void
+debug_tw_callback_timer(void *vdfct,
+			ErtsMonotonicTime timeout_pos,
+			void *vtwtp)
+{
+    ErtsTWTimer *twtp = (ErtsTWTimer *) vtwtp;
+    ErtsDebugForeachCallbackTimer *dfct
+	= (ErtsDebugForeachCallbackTimer *) vdfct;
+
+    if (twtp->u.callback == dfct->tclbk)
+	(*dfct->func)(dfct->arg,
+		      timeout_pos,
+		      twtp->head.u.arg);
+}
+
+void
+erts_debug_callback_timer_foreach(void (*tclbk)(void *),
+				  void (*func)(void *,
+					       ErtsMonotonicTime,
+					       void *),
+				  void *arg)
+{
+    int six;
+    ErtsDebugForeachCallbackTimer dfct;
+
+    dfct.tclbk = tclbk;
+    dfct.func = func;
+    dfct.arg = arg;
+
+    if (!erts_smp_thr_progress_is_blocking())
+	ERTS_INTERNAL_ERROR("Not blocking thread progress");
+
+    for (six = 0; six < erts_no_schedulers; six++) {
+	ErtsHLTimerService *srv =
+	    erts_aligned_scheduler_data[six].esd.timer_service;
+	ErtsTimerWheel *twheel =
+	    erts_aligned_scheduler_data[six].esd.timer_wheel;
+
+	erts_twheel_debug_foreach(twheel,
+				  tw_callback_timeout,
+				  debug_tw_callback_timer,
+				  (void *) &dfct);
+
+	if (srv->yield.root)
+	    debug_callback_timer_foreach(srv->yield.root,
+					 (void *) &dfct);
+
+	time_rbt_foreach(srv->btm_tree,
+			 debug_callback_timer_foreach,
+			 (void *) &dfct);
+    }
+}
+
 #ifdef ERTS_HLT_HARD_DEBUG
 
 typedef struct {
diff --git a/erts/emulator/beam/erl_hl_timer.h b/erts/emulator/beam/erl_hl_timer.h
index 30889a71da..24c57fc873 100644
--- a/erts/emulator/beam/erl_hl_timer.h
+++ b/erts/emulator/beam/erl_hl_timer.h
@@ -59,7 +59,9 @@ int erts_cancel_bif_timers(Process *, ErtsBifTimers *, void **);
 int erts_detach_accessor_bif_timers(Process *, ErtsBifTimers *, void **);
 ErtsHLTimerService *erts_create_timer_service(void);
 void erts_hl_timer_init(void);
-
+void erts_start_timer_callback(ErtsMonotonicTime,
+			       void (*)(void *),
+			       void *);
 #ifdef ERTS_SMP
 void
 erts_handle_canceled_timers(void *vesdp,
@@ -76,5 +78,10 @@ void erts_debug_bif_timer_foreach(void (*func)(Eterm,
 					       ErlHeapFragment *,
 					       void *),
 				  void *arg);
-
+void
+erts_debug_callback_timer_foreach(void (*tclbk)(void *),
+				  void (*func)(void *,
+					       ErtsMonotonicTime,
+					       void *),
+				  void *arg);
 #endif /* ERL_HL_TIMER_H__ */
diff --git a/erts/emulator/beam/erl_time.h b/erts/emulator/beam/erl_time.h
index 4560cd23af..e64b86496a 100644
--- a/erts/emulator/beam/erl_time.h
+++ b/erts/emulator/beam/erl_time.h
@@ -453,4 +453,12 @@ ERTS_GLB_INLINE ErtsMonotonicTime erts_next_timeout_time(ErtsNextTimeoutRef nxt_
 
 #endif /* ERTS_GLB_INLINE_INCL_FUNC_DEF */
 
+void
+erts_twheel_debug_foreach(ErtsTimerWheel *tiw,
+			  void (*tclbk)(void *),
+			  void (*func)(void *,
+				       ErtsMonotonicTime,
+				       void *),
+			  void *arg);
+
 #endif /* timer wheel api */
diff --git a/erts/emulator/beam/time.c b/erts/emulator/beam/time.c
index 8bffdedb2b..fe7c5826f5 100644
--- a/erts/emulator/beam/time.c
+++ b/erts/emulator/beam/time.c
@@ -529,6 +529,9 @@ erts_create_timer_wheel(ErtsSchedulerData *esdp)
     tiw->next_timeout_time = mtime + ERTS_MONOTONIC_DAY;
     tiw->sentinel.next = &tiw->sentinel;
     tiw->sentinel.prev = &tiw->sentinel;
+    tiw->sentinel.u.func.timeout = NULL;
+    tiw->sentinel.u.func.cancel = NULL;
+    tiw->sentinel.u.func.arg = NULL;
     return tiw;
 }
 
@@ -624,6 +627,41 @@ erts_twheel_cancel_timer(ErtsTimerWheel *tiw, ErtsTWheelTimer *p)
     }
 }
 
+void
+erts_twheel_debug_foreach(ErtsTimerWheel *tiw,
+			  void (*tclbk)(void *),
+			  void (*func)(void *,
+				       ErtsMonotonicTime,
+				       void *),
+			  void *arg)
+{
+    ErtsTWheelTimer *tmr;
+    int ix;
+
+    tmr = tiw->sentinel.next;
+    while (tmr != &tiw->sentinel) {
+	if (tmr->u.func.timeout == tclbk)
+	    (*func)(arg, tmr->timeout_pos, tmr->u.func.arg);
+	tmr = tmr->next;
+    }
+
+    for (tmr = tiw->at_once.head; tmr; tmr = tmr->next) {
+	if (tmr->u.func.timeout == tclbk)
+	    (*func)(arg, tmr->timeout_pos, tmr->u.func.arg);
+    }
+
+    for (ix = 0; ix < ERTS_TIW_SIZE; ix++) {
+	tmr = tiw->w[ix];
+	if (tmr) {
+	    do {
+		if (tmr->u.func.timeout == tclbk)
+		    (*func)(arg, tmr->timeout_pos, tmr->u.func.arg);
+		tmr = tmr->next;
+	    } while (tmr != tiw->w[ix]);
+	}
+    }
+}
+
 #ifdef ERTS_TW_DEBUG
 void erts_p_slpq(void)
 {