erts: Implement recv_mark/1 and recv_set/1 for real

The recv_mark/1 instruction will both save the current
position in the message queue and a mark (the address of the
loop_rec/2 instruction just following the recv_set/1
instruction). The recv_mark/1 instruction will only
use the saved position if the mark is correct.

The reason for saving and verifying the mark is that
the compiler does not need to guarantee that no other
receive instruction can be executed in between the
recv_mark/1 and recv_set/1 instructions (the mark will
be cleared by the remove_message/0 instruction when a message
is removed from the message queue). That means that arbitrary
function calls in between those instruction can be allowed.

1 files changed, 8 insertions, 0 deletions

diff --git a/erts/emulator/beam/erl_message.h b/erts/emulator/beam/erl_message.h
index 459c6363aa..489dee7b37 100644
--- a/erts/emulator/beam/erl_message.h
+++ b/erts/emulator/beam/erl_message.h
@@ -75,6 +75,13 @@ typedef struct {
     ErlMessage** last;  /* point to the last next pointer */
     ErlMessage** save;
     int len;            /* queue length */
+
+    /*
+     * The following two fields are used by the recv_mark/1 and
+     * recv_set/1 instructions.
+     */
+    BeamInstr* mark;		/* address to rec_loop/2 instruction */
+    ErlMessage** saved_last;	/* saved last pointer */
 } ErlMessageQueue;
 
 #ifdef ERTS_SMP
@@ -137,6 +144,7 @@ do {							\
      (p)->msg.len--; \
      if (__mp == NULL) \
          (p)->msg.last = (p)->msg.save; \
+     (p)->msg.mark = 0; \
 } while(0)
 
 /* Reset message save point (after receive match) */