[PATCH 8/8] rpctrace: use condition variable to keep messages in sequence

[Brent Baccala]

---
 utils/rpctrace.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/utils/rpctrace.c b/utils/rpctrace.c
index 88b5e38..09911b3 100644
--- a/utils/rpctrace.c
+++ b/utils/rpctrace.c
@@ -131,6 +131,8 @@ struct traced_info
   mach_msg_type_name_t type;
   char *name;                  /* null or a string describing this */
   task_t task;                 /* The task who has the right. */
+  mach_port_seqno_t seqno;      /* next RPC to be processed on this port */
+  pthread_cond_t sequencer;     /* used to sequence RPCs when they are 
processed out-of-order */
 };
 
 /* Each traced port has one receiver info and multiple send wrappers.
@@ -366,6 +368,8 @@ new_send_wrapper (struct receiver_info *receive, task_t 
task,
             receive->forward, TRACED_INFO (info)->pi.port_right, task2pid 
(task));
   TRACED_INFO (info)->type = MACH_MSG_TYPE_MOVE_SEND;
   TRACED_INFO (info)->task = task;
+  TRACED_INFO (info)->seqno = 0;
+  pthread_cond_init(& TRACED_INFO(info)->sequencer, NULL);
   info->receive_right = receive;
   info->next = receive->next;
   receive->next = info;
@@ -396,6 +400,8 @@ new_send_once_wrapper (mach_port_t right, mach_port_t 
*wrapper_right, task_t tas
                               sizeof *info, &info);
       assert_perror (err);
       TRACED_INFO (info)->name = 0;
+      TRACED_INFO (info)->seqno = 0;
+      pthread_cond_init(& TRACED_INFO(info)->sequencer, NULL);
     }
 
   info->forward = right;
@@ -1207,6 +1213,11 @@ trace_and_forward (mach_msg_header_t *inp, 
mach_msg_header_t *outp)
 
   msgid = msgid_info (inp->msgh_id);
 
+  while (inp->msgh_seqno != TRACED_INFO (info)->seqno)
+    {
+      pthread_cond_wait (& TRACED_INFO (info)->sequencer, &tracelock);
+    }
+
   /* Determine message's destination task */
 
   if (INFO_SEND_ONCE(info))
@@ -1370,7 +1381,13 @@ trace_and_forward (mach_msg_header_t *inp, 
mach_msg_header_t *outp)
        }
     }
 
-  /* Unlock prior to sending message to avoid deadlocks in the kernel */
+  /* Advance our sequence number and signal any other thread waiting
+   * to process the next message on this port.
+   */
+  TRACED_INFO (info)->seqno = inp->msgh_seqno + 1;
+  pthread_cond_broadcast (& TRACED_INFO (info)->sequencer);
+
+  /* Unlock prior to resending message to avoid deadlocks in the kernel */
   ports_port_deref (info);
   pthread_mutex_unlock(&tracelock);
 
-- 
2.6.4