backport memory pressure callback to 1.9 (#114)

src/gc.c

@@ -40,6 +40,7 @@ static jl_gc_callback_list_t *gc_cblist_pre_gc;
 static jl_gc_callback_list_t *gc_cblist_post_gc;
 static jl_gc_callback_list_t *gc_cblist_notify_external_alloc;
 static jl_gc_callback_list_t *gc_cblist_notify_external_free;
+static jl_gc_callback_list_t *gc_cblist_notify_gc_pressure;
 
 #define gc_invoke_callbacks(ty, list, args) \
  do { \
@@ -126,6 +127,14 @@ JL_DLLEXPORT void jl_gc_set_cb_notify_external_free(jl_gc_cb_notify_external_fre
  jl_gc_deregister_callback(&gc_cblist_notify_external_free, (jl_gc_cb_func_t)cb);
 }
 
+JL_DLLEXPORT void jl_gc_set_cb_notify_gc_pressure(jl_gc_cb_notify_gc_pressure_t cb, int enable)
+ {
+ if (enable)
+ jl_gc_register_callback(&gc_cblist_notify_gc_pressure, (jl_gc_cb_func_t)cb);
+ else
+ jl_gc_deregister_callback(&gc_cblist_notify_gc_pressure, (jl_gc_cb_func_t)cb);
+ }
+
 // Protect all access to `finalizer_list_marked` and `to_finalize`.
 // For accessing `ptls->finalizers`, the lock is needed if a thread
 // is going to realloc the buffer (of its own list) or accessing the
@@ -767,6 +776,7 @@ static void gc_sweep_foreign_objs(void)
 }
 
 // GC knobs and self-measurement variables
+static int under_memory_pressure;
 static int64_t last_gc_total_bytes = 0;
 
 // max_total_memory is a suggestion. We try very hard to stay
@@ -3544,6 +3554,7 @@ static int _jl_gc_collect(jl_ptls_t ptls, jl_gc_collection_t collection)
  else {
  // We can't stay under our goal so let's go back to
  // the minimum interval and hope things get better
+ under_memory_pressure = 1;
  gc_num.interval = default_collect_interval;
  }
  }
@@ -3647,6 +3658,12 @@ JL_DLLEXPORT void jl_gc_collect(jl_gc_collection_t collection)
 
  gc_invoke_callbacks(jl_gc_cb_post_gc_t,
  gc_cblist_post_gc, (collection));
+
+ if (under_memory_pressure) {
+ gc_invoke_callbacks(jl_gc_cb_notify_gc_pressure_t,
+ gc_cblist_notify_gc_pressure, ());
+ }
+ under_memory_pressure = 0;
 #ifdef _OS_WINDOWS_
  SetLastError(last_error);
 #endif

src/julia_gcext.h

@@ -34,6 +34,10 @@ JL_DLLEXPORT void jl_gc_set_cb_notify_external_alloc(jl_gc_cb_notify_external_al
 JL_DLLEXPORT void jl_gc_set_cb_notify_external_free(jl_gc_cb_notify_external_free_t cb,
  int enable);
 
+// Memory pressure callback
+typedef void (*jl_gc_cb_notify_gc_pressure_t)(void);
+JL_DLLEXPORT void jl_gc_set_cb_notify_gc_pressure(jl_gc_cb_notify_gc_pressure_t cb, int enable);
+
 // Types for custom mark and sweep functions.
 typedef uintptr_t (*jl_markfunc_t)(jl_ptls_t, jl_value_t *obj);
 typedef void (*jl_sweepfunc_t)(jl_value_t *obj);