2 files changed, 19 insertions, 1 deletions
diff --git a/erts/emulator/beam/erl_nif.c b/erts/emulator/beam/erl_nif.c
index b2bd28fcbb..349d9bf13a 100644
--- a/erts/emulator/beam/erl_nif.c
+++ b/erts/emulator/beam/erl_nif.c
@@ -1083,6 +1083,17 @@ int enif_get_local_pid(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifPid* pid)
     return 0;
 }
 
+void enif_set_pid_undefined(ErlNifPid* pid)
+{
+    pid->pid = am_undefined;
+}
+
+int enif_is_pid_undefined(const ErlNifPid* pid)
+{
+    ASSERT(pid->pid == am_undefined || is_internal_pid(pid->pid));
+    return pid->pid == am_undefined;
+}
+
 int enif_get_local_port(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifPort* port)
 {
     if (is_internal_port(term)) {
@@ -3341,6 +3352,9 @@ int enif_monitor_process(ErlNifEnv* env, void* obj, const ErlNifPid* target_pid,
     }
     ASSERT(rsrc->type->down);
 
+    if (target_pid->pid == am_undefined)
+        return 1;
+
     ref = erts_make_ref_in_buffer(tmp);
 
     mdp = erts_monitor_create(ERTS_MON_TYPE_RESOURCE, ref,
diff --git a/erts/emulator/beam/erl_nif_api_funcs.h b/erts/emulator/beam/erl_nif_api_funcs.h
index 4ea6a2f7b0..8ab454c8dd 100644
--- a/erts/emulator/beam/erl_nif_api_funcs.h
+++ b/erts/emulator/beam/erl_nif_api_funcs.h
@@ -212,7 +212,8 @@ ERL_NIF_API_FUNC_DECL(int,enif_make_map_from_arrays,(ErlNifEnv *env, ERL_NIF_TER
 
 ERL_NIF_API_FUNC_DECL(int,enif_select_x,(ErlNifEnv* env, ErlNifEvent e, enum ErlNifSelectFlags flags, void* obj, const ErlNifPid* pid, ERL_NIF_TERM msg, ErlNifEnv* msg_env));
 ERL_NIF_API_FUNC_DECL(ERL_NIF_TERM,enif_make_monitor_term,(ErlNifEnv* env, const ErlNifMonitor*));
-
+ERL_NIF_API_FUNC_DECL(void,enif_set_pid_undefined,(ErlNifPid* pid));
+ERL_NIF_API_FUNC_DECL(int,enif_is_pid_undefined,(const ErlNifPid* pid));
 
 /*
 ** ADD NEW ENTRIES HERE (before this comment) !!!
@@ -398,6 +399,8 @@ ERL_NIF_API_FUNC_DECL(ERL_NIF_TERM,enif_make_monitor_term,(ErlNifEnv* env, const
 #  define enif_make_map_from_arrays ERL_NIF_API_FUNC_MACRO(enif_make_map_from_arrays)
 #  define enif_select_x ERL_NIF_API_FUNC_MACRO(enif_select_x)
 #  define enif_make_monitor_term ERL_NIF_API_FUNC_MACRO(enif_make_monitor_term)
+#  define enif_set_pid_undefined ERL_NIF_API_FUNC_MACRO(enif_set_pid_undefined)
+#  define enif_is_pid_undefined ERL_NIF_API_FUNC_MACRO(enif_is_pid_undefined)
 
 /*
 ** ADD NEW ENTRIES HERE (before this comment)
@@ -629,6 +632,7 @@ static ERL_NIF_INLINE ERL_NIF_TERM enif_make_list9(ErlNifEnv* env,
 #ifndef enif_make_pid
 
 #  define enif_make_pid(ENV, PID) ((void)(ENV),(const ERL_NIF_TERM)((PID)->pid))
+#  define enif_compare_pids(A, B) (enif_compare((A)->pid,(B)->pid))
 #  define enif_select_read(ENV, E, OBJ, PID, MSG, MSG_ENV) \
     enif_select_x(ENV, E, ERL_NIF_SELECT_READ | ERL_NIF_SELECT_CUSTOM_MSG, \
                   OBJ, PID, MSG, MSG_ENV)