Change heartbeat thread controls

When enabling heartbeats, the user must specify:
- heartbeat_s: jl_heartbeat() must be called at least once every heartbeat_s; if it
  isn't, a one-line heartbeat loss report is printed
- show_tasks_after_n: after these many heartbeat_s have passed without jl_heartbeat()
  being called, print task backtraces and stop all reporting
- reset_after_n: after these many heartbeat_s have passed with jl_heartbeat()
  being called, print a heartbeats recovered message and reset reporting

src/threading.c

@@ -865,9 +865,9 @@ volatile int heartbeat_enabled;
 uv_sem_t heartbeat_on_sem,              // jl_heartbeat_enable -> thread
          heartbeat_off_sem;             // thread -> jl_heartbeat_enable
 int heartbeat_interval_s,
-    n_loss_reports,
-    reset_reporting_s;
-int last_report_s, report_interval_s, n_reported;
+    tasks_after_n,
+    reset_tasks_after_n;
+int tasks_showed, n_hbs_missed, n_hbs_recvd;
 _Atomic(int) heartbeats;
 
 JL_DLLEXPORT void jl_print_task_backtraces(int show_done) JL_NOTSAFEPOINT;
@@ -886,21 +886,19 @@ void jl_init_heartbeat(void)
 
 // enable/disable heartbeats
 // heartbeat_s: interval within which jl_heartbeat() must be called
-// n_reports: for one heartbeat loss interval, how many times to report
-// reset_reporting_after_s: how long to wait after a heartbeat loss
-//     interval and a return to steady heartbeats, before resetting
-//     reporting behavior
+// show_tasks_after_n: number of heartbeats missed before printing task backtraces
+// reset_after_n: number of heartbeats after which to reset
 //
 // When disabling heartbeats, the heartbeat thread must wake up,
 // find out that heartbeats are now diabled, and reset. For now, we
 // handle this by preventing re-enabling of heartbeats until this
 // completes.
-JL_DLLEXPORT int jl_heartbeat_enable(int heartbeat_s, int n_reports,
-                                     int reset_reporting_after_s)
+JL_DLLEXPORT int jl_heartbeat_enable(int heartbeat_s, int show_tasks_after_n,
+                                     int reset_after_n)
 {
     if (heartbeat_s <= 0) {
         heartbeat_enabled = 0;
-        heartbeat_interval_s = n_loss_reports = reset_reporting_s = 0;
+        heartbeat_interval_s = tasks_after_n = reset_tasks_after_n = 0;
     }
     else {
         // must disable before enabling
@@ -914,10 +912,11 @@ JL_DLLEXPORT int jl_heartbeat_enable(int heartbeat_s, int n_reports,
 
         jl_atomic_store_relaxed(&heartbeats, 0);
         heartbeat_interval_s = heartbeat_s;
-        n_loss_reports = n_reports;
-        reset_reporting_s = reset_reporting_after_s;
-        last_report_s = 0;
-        report_interval_s = heartbeat_interval_s;
+        tasks_after_n = show_tasks_after_n;
+        reset_tasks_after_n = reset_after_n;
+        tasks_showed = 0;
+        n_hbs_missed = 0;
+        n_hbs_recvd = 0;
         heartbeat_enabled = 1;
         uv_sem_post(&heartbeat_on_sem); // wake the heartbeat thread
     }
@@ -953,44 +952,42 @@ void sleep_for(int secs, int nsecs)
 uint8_t check_heartbeats(uint8_t gc_state)
 {
     int hb = jl_atomic_exchange(&heartbeats, 0);
-    uint64_t curr_s = jl_hrtime() / 1e9;
 
     if (hb <= 0) {
-        // we didn't get a heartbeat in the last interval; should we report?
-        if (n_reported < n_loss_reports &&
-                curr_s - last_report_s >= report_interval_s) {
-            jl_task_t *ct = jl_current_task;
-            jl_ptls_t ptls = ct->ptls;
-
-            // exit GC-safe region to report then re-enter
-            jl_gc_safe_leave(ptls, gc_state);
-            jl_safe_printf("==== heartbeat loss ====\n");
-            jl_print_task_backtraces(0);
-            gc_state = jl_gc_safe_enter(ptls);
-
-            // we've reported
-            n_reported++;
-
-            // record the reporting time _after_ the report
-            last_report_s = jl_hrtime() / 1e9;
-
-            // double the reporting interval up to a maximum
-            if (report_interval_s < 60 * heartbeat_interval_s) {
-                report_interval_s *= 2;
+        // we didn't get a heartbeat
+        n_hbs_recvd = 0;
+        n_hbs_missed++;
+
+        // if we've printed task backtraces already, do nothing
+        if (!tasks_showed) {
+            // otherwise, at least show this message
+            jl_safe_printf("==== heartbeat loss (%ds) ====\n",
+                           n_hbs_missed * heartbeat_interval_s);
+            // if we've missed enough heartbeats, print task backtraces
+            if (n_hbs_missed >= tasks_after_n) {
+                jl_task_t *ct = jl_current_task;
+                jl_ptls_t ptls = ct->ptls;
+
+                // exit GC-safe region to report then re-enter
+                jl_gc_safe_leave(ptls, gc_state);
+                jl_print_task_backtraces(0);
+                gc_state = jl_gc_safe_enter(ptls);
+
+                // we printed task backtraces
+                tasks_showed = 1;
             }
         }
-        // no heartbeats, don't change reporting state
-        return gc_state;
     }
     else {
-        // we got a heartbeat; reset the report count
-        n_reported = 0;
-    }
-
-    // reset the reporting interval only once we're steadily getting
-    // heartbeats for the requested reset interval
-    if (curr_s - reset_reporting_s > last_report_s) {
-        report_interval_s = heartbeat_interval_s;
+        // got a heartbeat
+        n_hbs_recvd++;
+        // if we'd printed task backtraces, check for reset
+        if (tasks_showed && n_hbs_recvd >= reset_tasks_after_n) {
+            tasks_showed = 0;
+            jl_safe_printf("==== heartbeats recovered (lost for %ds) ====\n",
+                           n_hbs_missed * heartbeat_interval_s);
+        }
+        n_hbs_missed = 0;
     }
 
     return gc_state;
@@ -999,7 +996,7 @@ uint8_t check_heartbeats(uint8_t gc_state)
 // heartbeat thread function
 void jl_heartbeat_threadfun(void *arg)
 {
-    int s, ns = 1e9 - 1, rs;
+    int s = 59, ns = 1e9 - 1, rs;
     uint64_t t0, tchb;
 
     // We need a TLS because backtraces are accumulated into ptls->bt_size
@@ -1057,8 +1054,8 @@ void jl_init_heartbeat(void)
 {
 }
 
-JL_DLLEXPORT int jl_heartbeat_enable(int heartbeat_s, int n_reports,
-                                     int reset_reporting_after_s)
+JL_DLLEXPORT int jl_heartbeat_enable(int heartbeat_s, int show_tasks_after_n,
+                                     int reset_after_n)
 {
     return -1;
 }