Get pending events in random

Nowadays, we select events to be reported to GDB in random, however
that is not enough when many GDBserver internal events (not reported
to GDB) are generated.

GDBserver pulls all events out of kernel via waitpid, and leave them
pending.  When goes through threads which have pending events,
GDBserver uses find_inferior to find the first thread which has
pending event, and consumes it.  Note that find_inferior always
iterate threads in a fixed order.  If multiple threads keep hitting
GDBserver breakpoints, range stepping with single-step breakpoint for
example, threads in the head of the thread list are more likely to be
processed and threads in the tail are starved.  This causes some timeout
fails in gdb.threads/non-stop-fair-events.exp when range stepping is
enabled on arm-linux.

This patch fixes this issue by randomly selecting pending events.  It
adds a new function find_inferior_in_random, which iterates threads
which have pending events randomly.

gdb/gdbserver:

2016-10-27  Yao Qi  <yao.qi@linaro.org>

	* inferiors.c (find_inferior_in_random): New function.
	* inferiors.h (find_inferior_in_random): Declare.
	* linux-low.c (linux_wait_for_event_filtered): Call
	find_inferior_in_random instead of find_inferior.

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index d43a96a0aee375ea26a1802547e5e36903b9dbce..c6bc016ce819a3fe90572d6d6d5c7e04ebb058c7 100644 (file)
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,10 @@
+2016-10-27  Yao Qi  <yao.qi@linaro.org>
+
+       * inferiors.c (find_inferior_in_random): New function.
+       * inferiors.h (find_inferior_in_random): Declare.
+       * linux-low.c (linux_wait_for_event_filtered): Call
+       find_inferior_in_random instead of find_inferior.
+
 2016-10-27  Yao Qi  <yao.qi@linaro.org>
 
        * linux-low.c (linux_wait_1): If single-step breakpoints are

diff --git a/gdb/gdbserver/inferiors.c b/gdb/gdbserver/inferiors.c
index 7888f3c18525682555acda2019361f3c06054122..574a7ba7d57082534589f78b9232a5233bb6f312 100644 (file)
--- a/gdb/gdbserver/inferiors.c
+++ b/gdb/gdbserver/inferiors.c
@@ -248,6 +248,51 @@ find_inferior (struct inferior_list *list,
   return NULL;
 }
 
+/* Find the random inferior_list_entry E in LIST for which FUNC (E, ARG)
+   returns non-zero.  If no entry is found then return NULL.  */
+
+struct inferior_list_entry *
+find_inferior_in_random (struct inferior_list *list,
+                        int (*func) (struct inferior_list_entry *, void *),
+                        void *arg)
+{
+  struct inferior_list_entry *inf = list->head;
+  int count = 0;
+  int random_selector;
+
+  /* First count how many interesting entries we have.  */
+  while (inf != NULL)
+    {
+      struct inferior_list_entry *next;
+
+      next = inf->next;
+      if ((*func) (inf, arg))
+       count++;
+      inf = next;
+    }
+
+  if (count == 0)
+    return NULL;
+
+  /* Now randomly pick an entry out of those.  */
+  random_selector = (int)
+    ((count * (double) rand ()) / (RAND_MAX + 1.0));
+
+  inf = list->head;
+  while (inf != NULL)
+    {
+      struct inferior_list_entry *next;
+
+      next = inf->next;
+      if ((*func) (inf, arg) && (random_selector-- == 0))
+       return inf;
+      inf = next;
+    }
+
+  gdb_assert_not_reached ("failed to find an inferior in random.");
+  return NULL;
+}
+
 struct inferior_list_entry *
 find_inferior_id (struct inferior_list *list, ptid_t id)
 {

diff --git a/gdb/gdbserver/inferiors.h b/gdb/gdbserver/inferiors.h
index 65ab1c6fc60828b05fdae47ba4b67b2452088d24..6ea7a999d592c6c6c23e83429fbeacfdc89a97be 100644 (file)
--- a/gdb/gdbserver/inferiors.h
+++ b/gdb/gdbserver/inferiors.h
@@ -154,6 +154,11 @@ struct inferior_list_entry *find_inferior
       void *arg);
 struct inferior_list_entry *find_inferior_id (struct inferior_list *list,
                                              ptid_t id);
+struct inferior_list_entry *
+  find_inferior_in_random (struct inferior_list *,
+                          int (*func) (struct inferior_list_entry *,
+                                       void *),
+                          void *arg);
 
 void *inferior_target_data (struct thread_info *);
 void set_inferior_target_data (struct thread_info *, void *);

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index a463774971bac7bcb5992e474ae9cc9c1c07f037..5dcf376ecf63401e399f63d6ff8fcb4a4fc12fd6 100644 (file)
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -2700,7 +2700,8 @@ linux_wait_for_event_filtered (ptid_t wait_ptid, ptid_t filter_ptid,
   if (ptid_equal (filter_ptid, minus_one_ptid) || ptid_is_pid (filter_ptid))
     {
       event_thread = (struct thread_info *)
-       find_inferior (&all_threads, status_pending_p_callback, &filter_ptid);
+       find_inferior_in_random (&all_threads, status_pending_p_callback,
+                                &filter_ptid);
       if (event_thread != NULL)
        event_child = get_thread_lwp (event_thread);
       if (debug_threads && event_thread)
@@ -2811,7 +2812,8 @@ linux_wait_for_event_filtered (ptid_t wait_ptid, ptid_t filter_ptid,
       /* ... and find an LWP with a status to report to the core, if
         any.  */
       event_thread = (struct thread_info *)
-       find_inferior (&all_threads, status_pending_p_callback, &filter_ptid);
+       find_inferior_in_random (&all_threads, status_pending_p_callback,
+                                &filter_ptid);
       if (event_thread != NULL)
        {
          event_child = get_thread_lwp (event_thread);