File 2551-pause_proc_timer-1-n-Introduce-ErtsPausedProcTimer-t.patch of Package erlang
From ffc80937c0662e2668956b581587419246242de5 Mon Sep 17 00:00:00 2001
From: Daniel Gorin <danielgo@meta.com>
Date: Wed, 27 Nov 2024 12:47:12 +0000
Subject: [PATCH 1/2] [pause_proc_timer][1/n] Introduce ErtsPausedProcTimer
type and operations
We want a way to "pause" a proc timer when suspending a process, and
"resume" it later. We will do this as follows.
* Pausing a proc timer means:
1. Cancelling the current timer in `common.timer`, if any.
2. Storing in `common.timer` instead how much time was left in the
timer. To compute the time left, we need to inspect the current
timer.
3. Flagging in the `Process` struct that the timer is paused. This is
so that we know later that we need to resume the timer when resuming
the process.
* Resuming a proc timer then amounts to:
1. Creating a new proc timer based on the time left that was stored
in `common.timer`.
2. Clear all the flags in the `Process` struct
* When cancelling a proc timer, we now need to check if it is paused
(in which case, it can just be ignored)
So here we introduce a `ErtsPausedProcTimer` type, that will contain the
time remaining on a paused timer, and a header that is shared with all
other timer types (so that we can safely insert it in `common.timer`).
We also introduce the functions to pause a proc timer and resume it.
At this point nothing calls these functions, this happens in the next
commits.
---
erts/emulator/beam/erl_alloc.types | 1 +
erts/emulator/beam/erl_hl_timer.c | 113 +++++++++++++++++++++++++++++
erts/emulator/beam/erl_hl_timer.h | 2 +
3 files changed, 116 insertions(+)
diff --git a/erts/emulator/beam/erl_alloc.types b/erts/emulator/beam/erl_alloc.types
index 4938e184ca..6da8eb7822 100644
--- a/erts/emulator/beam/erl_alloc.types
+++ b/erts/emulator/beam/erl_alloc.types
@@ -135,6 +135,7 @@ type TIMER_SERVICE LONG_LIVED SYSTEM timer_service
type LL_PTIMER FIXED_SIZE PROCESSES ll_ptimer
type HL_PTIMER FIXED_SIZE PROCESSES hl_ptimer
type BIF_TIMER FIXED_SIZE PROCESSES bif_timer
+type PAUSED_TIMER STANDARD PROCESSES paused_timer
type TIMER_REQUEST SHORT_LIVED PROCESSES timer_request
type BTM_YIELD_STATE SHORT_LIVED PROCESSES btm_yield_state
type REG_TABLE STANDARD SYSTEM reg_tab
diff --git a/erts/emulator/beam/erl_hl_timer.c b/erts/emulator/beam/erl_hl_timer.c
index f77b6fd604..c4a574055c 100644
--- a/erts/emulator/beam/erl_hl_timer.c
+++ b/erts/emulator/beam/erl_hl_timer.c
@@ -100,6 +100,7 @@ typedef enum {
#define ERTS_TMR_ROFLG_PROC (((Uint32) 1) << 15)
#define ERTS_TMR_ROFLG_PORT (((Uint32) 1) << 16)
#define ERTS_TMR_ROFLG_CALLBACK (((Uint32) 1) << 17)
+#define ERTS_TMR_ROFLG_PAUSED (((Uint32) 1) << 18)
#define ERTS_TMR_ROFLG_SID_MASK \
(ERTS_TMR_ROFLG_HLT - (Uint32) 1)
@@ -205,6 +206,12 @@ typedef union {
ErtsBifTimer btm;
} ErtsTimer;
+typedef struct {
+ ErtsTmrHead head; /* NEED to be first! */
+ Sint64 time_left_in_msec;
+ int count;
+} ErtsPausedProcTimer;
+
typedef ErtsTimer *(*ErtsCreateTimerFunc)(ErtsSchedulerData *esdp,
ErtsMonotonicTime timeout_pos,
int short_time, ErtsTmrType type,
@@ -950,6 +957,54 @@ create_tw_timer(ErtsSchedulerData *esdp,
return (ErtsTimer *) tmr;
}
+/*
+ * Paused proc timers
+ */
+static ERTS_INLINE ErtsPausedProcTimer *
+create_paused_proc_timer(Process *c_p)
+{
+ ErtsPausedProcTimer *result = NULL;
+ erts_aint_t itmr = erts_atomic_read_nob(&c_p->common.timer);
+
+ if (itmr != ERTS_PTMR_NONE && itmr != ERTS_PTMR_TIMEDOUT) {
+ ErtsSchedulerData *esdp = erts_proc_sched_data(c_p);
+ ErtsTimer *tmr = (ErtsTimer *)itmr;
+
+ if (tmr->head.roflgs & ERTS_TMR_ROFLG_PAUSED) {
+ // The process timer was already paused, reuse the paused timer
+ ErtsPausedProcTimer *pptmr = (ErtsPausedProcTimer*) tmr;
+ pptmr->count++;
+ } else {
+ int is_hlt = !!(tmr->head.roflgs & ERTS_TMR_ROFLG_HLT);
+ ErtsMonotonicTime timeout_pos;
+
+ ASSERT(tmr->head.roflgs & ERTS_TMR_ROFLG_PROC);
+
+ result = erts_alloc(ERTS_ALC_T_PAUSED_TIMER,
+ sizeof(ErtsPausedProcTimer));
+ result->head.roflgs = tmr->head.roflgs | ERTS_TMR_ROFLG_PAUSED;
+ erts_atomic32_init_nob(&result->head.refc, 1);
+ result->head.receiver.proc = tmr->head.receiver.proc;
+
+ timeout_pos = (is_hlt
+ ? tmr->hlt.timeout
+ : erts_tweel_read_timeout(&tmr->twt.u.tw_tmr));
+ result->time_left_in_msec = get_time_left(esdp, timeout_pos);
+ result->count = 1;
+ }
+ }
+
+ return result;
+}
+
+static ERTS_INLINE void
+paused_proc_timer_dec_refc(ErtsPausedProcTimer *pptmr)
+{
+ if (erts_atomic32_dec_read_relb(&pptmr->head.refc) == 0) {
+ erts_free(ERTS_ALC_T_PAUSED_TIMER, (void *) pptmr);
+ }
+}
+
/*
* Basic high level timer stuff
*/
@@ -1665,6 +1720,11 @@ continue_cancel_ptimer(ErtsSchedulerData *esdp, ErtsTimer *tmr)
{
Uint32 sid = (tmr->head.roflgs & ERTS_TMR_ROFLG_SID_MASK);
+ if (tmr->head.roflgs & ERTS_TMR_ROFLG_PAUSED) {
+ paused_proc_timer_dec_refc((ErtsPausedProcTimer*) tmr);
+ return;
+ }
+
if (esdp->no != sid)
queue_canceled_timer(esdp, sid, tmr);
else
@@ -2714,6 +2774,59 @@ erts_cancel_proc_timer(Process *c_p)
(ErtsTimer *) tval);
}
+void
+erts_pause_proc_timer(Process *c_p)
+{
+ ErtsPausedProcTimer *pptmr;
+
+ ERTS_LC_ASSERT((ERTS_PROC_LOCK_MAIN | ERTS_PROC_LOCK_STATUS)
+ & erts_proc_lc_my_proc_locks(c_p));
+
+ pptmr = create_paused_proc_timer(c_p);
+ if (!pptmr) {
+ return;
+ }
+
+ CANCEL_TIMER(c_p);
+
+ erts_atomic_set_nob(&c_p->common.timer, (erts_aint_t) pptmr);
+}
+
+int
+erts_resume_paused_proc_timer(Process *c_p)
+{
+ erts_aint_t timer;
+ int resumed_timer = 0;
+
+ ERTS_LC_ASSERT((ERTS_PROC_LOCK_MAIN | ERTS_PROC_LOCK_STATUS)
+ & erts_proc_lc_my_proc_locks(c_p));
+
+ timer = erts_atomic_xchg_nob(&c_p->common.timer, ERTS_PTMR_NONE);
+
+ ASSERT(timer != ERTS_PTMR_TIMEDOUT);
+
+ if (timer != ERTS_PTMR_NONE) {
+ UWord tmo = 0;
+ ErtsPausedProcTimer *pptmr = (ErtsPausedProcTimer *)timer;
+
+ ASSERT(pptmr->head.roflgs & ERTS_TMR_ROFLG_PAUSED);
+
+ pptmr->count -= 1;
+ if (pptmr->count == 0) {
+ if (pptmr->time_left_in_msec > 0) {
+ ASSERT((pptmr->time_left_in_msec >> 32) == 0);
+ tmo = (UWord) pptmr->time_left_in_msec;
+ }
+
+ erts_set_proc_timer_uword(c_p, tmo);
+ paused_proc_timer_dec_refc(pptmr);
+ resumed_timer = 1;
+ }
+ }
+
+ return resumed_timer;
+}
+
void
erts_set_port_timer(Port *c_prt, Sint64 tmo)
{
diff --git a/erts/emulator/beam/erl_hl_timer.h b/erts/emulator/beam/erl_hl_timer.h
index 3a864a7330..78fcb2ac87 100644
--- a/erts/emulator/beam/erl_hl_timer.h
+++ b/erts/emulator/beam/erl_hl_timer.h
@@ -53,6 +53,8 @@ size_t erts_timer_type_size(ErtsAlcType_t type);
int erts_set_proc_timer_term(Process *, Eterm);
void erts_set_proc_timer_uword(Process *, UWord);
void erts_cancel_proc_timer(Process *);
+void erts_pause_proc_timer(Process *);
+int erts_resume_paused_proc_timer(Process *);
void erts_set_port_timer(Port *, Sint64);
void erts_cancel_port_timer(Port *);
Sint64 erts_read_port_timer(Port *);
--
2.43.0
