Make length/1 yielding

The guard BIF `length/1` would calculate the length of the list in one
go without yielding, even if the list was were long. To make it even
worse, the call to `length/1` would only cost a single reduction.

This commit reimplements `length/1` so that it eats a number of
reductions proportional to the length of the list, and yields if the
available reductions run out.

1 files changed, 5 insertions, 0 deletions

diff --git a/erts/emulator/beam/global.h b/erts/emulator/beam/global.h
index 322981ca1d..77b5a3ca05 100644
--- a/erts/emulator/beam/global.h
+++ b/erts/emulator/beam/global.h
@@ -891,6 +891,11 @@ void erts_init_bif(void);
 Eterm erl_send(Process *p, Eterm to, Eterm msg);
 int erts_set_group_leader(Process *proc, Eterm new_gl);
 
+/* erl_bif_guard.c */
+
+void erts_init_bif_guard(void);
+Eterm erts_trapping_length_1(Process* p, Eterm* args);
+
 /* erl_bif_op.c */
 
 Eterm erl_is_function(Process* p, Eterm arg1, Eterm arg2);