Adjust heartbeat behavior

src/gc.c

@@ -3734,6 +3734,9 @@ static int _jl_gc_collect(jl_ptls_t ptls, jl_gc_collection_t collection)
     return recollect;
 }
 
+extern int jl_heartbeat_pause(void);
+extern int jl_heartbeat_resume(void);
+
 JL_DLLEXPORT void jl_gc_collect(jl_gc_collection_t collection)
 {
     JL_PROBE_GC_BEGIN(collection);
@@ -3775,6 +3778,7 @@ JL_DLLEXPORT void jl_gc_collect(jl_gc_collection_t collection)
     // existence of the thread in the jl_n_threads count.
     //
     // TODO: concurrently queue objects
+    jl_heartbeat_pause();
     jl_fence();
     gc_n_threads = jl_atomic_load_acquire(&jl_n_threads);
     gc_all_tls_states = jl_atomic_load_relaxed(&jl_all_tls_states);
@@ -3806,6 +3810,7 @@ JL_DLLEXPORT void jl_gc_collect(jl_gc_collection_t collection)
 
     gc_n_threads = 0;
     gc_all_tls_states = NULL;
+    jl_heartbeat_resume();
     jl_safepoint_end_gc();
     jl_gc_state_set(ptls, old_state, JL_GC_STATE_WAITING);
     JL_PROBE_GC_END();

src/stackwalk.c

@@ -1166,10 +1166,20 @@ JL_DLLEXPORT void jl_print_backtrace(void) JL_NOTSAFEPOINT
 }
 
 extern int gc_first_tid;
+extern int jl_inside_heartbeat_thread(void);
+extern int jl_heartbeat_pause(void);
+extern int jl_heartbeat_resume(void);
 
-// Print backtraces for all live tasks, for all threads, to jl_safe_printf stderr
+// Print backtraces for all live tasks, for all threads, to jl_safe_printf
+// stderr. This can take a _long_ time!
 JL_DLLEXPORT void jl_print_task_backtraces(int show_done) JL_NOTSAFEPOINT
 {
+    // disable heartbeats to prevent heartbeat loss while running this,
+    // unless this is called from the heartbeat thread
+    if (!jl_inside_heartbeat_thread()) {
+        jl_heartbeat_pause();
+    }
+
     size_t nthreads = jl_atomic_load_acquire(&jl_n_threads);
     jl_ptls_t *allstates = jl_atomic_load_relaxed(&jl_all_tls_states);
     int ctid = -1;
@@ -1232,6 +1242,10 @@ JL_DLLEXPORT void jl_print_task_backtraces(int show_done) JL_NOTSAFEPOINT
         jl_safe_printf("thread (%d) ==== End thread %d\n", ctid, ptls2->tid + 1);
     }
     jl_safe_printf("thread (%d) ++++ Done\n", ctid);
+
+    if (!jl_inside_heartbeat_thread()) {
+        jl_heartbeat_resume();
+    }
 }
 
 #ifdef __cplusplus

src/threading.c

@@ -1008,6 +1008,40 @@ JL_DLLEXPORT int jl_heartbeat_enable(int heartbeat_s, int show_tasks_after_n,
     return 0;
 }
 
+// temporarily pause the heartbeat thread
+JL_DLLEXPORT int jl_heartbeat_pause(void)
+{
+    if (!heartbeat_enabled) {
+        return -1;
+    }
+    heartbeat_enabled = 0;
+    return 0;
+}
+
+// resume the paused heartbeat thread
+JL_DLLEXPORT int jl_heartbeat_resume(void)
+{
+    // cannot resume if the heartbeat thread is already running
+    if (heartbeat_enabled) {
+        return -1;
+    }
+
+    // cannot resume if we weren't paused (disabled != paused)
+    if (heartbeat_interval_s == 0) {
+        return -1;
+    }
+
+    // heartbeat thread must be ready
+    if (uv_sem_trywait(&heartbeat_off_sem) != 0) {
+        return -1;
+    }
+    n_hbs_missed = 0;
+    n_hbs_recvd = 0;
+    heartbeat_enabled = 1;
+    uv_sem_post(&heartbeat_on_sem); // wake the heartbeat thread
+    return 0;
+}
+
 // heartbeat
 JL_DLLEXPORT void jl_heartbeat(void)
 {
@@ -1099,7 +1133,7 @@ void jl_heartbeat_threadfun(void *arg)
             uv_sem_post(&heartbeat_off_sem);
 
             // sleep the thread here; this semaphore is posted in
-            // jl_heartbeat_enable()
+            // jl_heartbeat_enable() or jl_heartbeat_resume()
             uv_sem_wait(&heartbeat_on_sem);
 
             // Set the sleep duration.
@@ -1111,7 +1145,7 @@ void jl_heartbeat_threadfun(void *arg)
         // heartbeat is enabled; sleep, waiting for the desired interval
         sleep_for(s, ns);
 
-        // if heartbeats were turned off while we were sleeping, reset
+        // if heartbeats were turned off/paused while we were sleeping, reset
         if (!heartbeat_enabled) {
             continue;
         }
@@ -1122,13 +1156,15 @@ void jl_heartbeat_threadfun(void *arg)
         tchb = jl_hrtime() - t0;
 
         // adjust the next sleep duration based on how long the heartbeat
-        // check took
+        // check took, but if it took too long then use the normal duration
         rs = 1;
         while (tchb > 1e9) {
             rs++;
             tchb -= 1e9;
         }
-        s = heartbeat_interval_s - rs;
+        if (rs < heartbeat_interval_s) {
+            s = heartbeat_interval_s - rs;
+        }
         ns = 1e9 - tchb;
     }
 }
@@ -1150,6 +1186,16 @@ JL_DLLEXPORT int jl_heartbeat_enable(int heartbeat_s, int show_tasks_after_n,
     return -1;
 }
 
+JL_DLLEXPORT int jl_heartbeat_pause(void)
+{
+    return -1;
+}
+
+JL_DLLEXPORT int jl_heartbeat_resume(void)
+{
+    return -1;
+}
+
 JL_DLLEXPORT void jl_heartbeat(void)
 {
 }