Linux native thread create/exit events support

A following patch (fix for gdb/19828) makes linux-nat.c add threads to
GDB's thread list earlier in the "attach" sequence, and that causes a
surprising regression on
gdb.threads/attach-many-short-lived-threads.exp on my machine.  The
extra "thread x exited" handling and traffic slows down that test
enough that GDB core has trouble keeping up with new threads that are
spawned while trying to stop existing ones.

I saw the exact same issue with remote/gdbserver a while ago and fixed
it in 65706a29bac5 (Remote thread create/exit events) so part of the
fix here is the exact same -- add support for thread created events to
gdb/linux-nat.c.  infrun.c:stop_all_threads enables those events when
it tries to stop threads, which ensures that new threads never get a
chance to themselves start new threads, thus fixing the race.

gdb/
2016-05-24  Pedro Alves  <palves@redhat.com>

	PR gdb/19828
	* linux-nat.c (report_thread_events): New global.
	(linux_handle_extended_wait): Report
	TARGET_WAITKIND_THREAD_CREATED if thread event reporting is
	enabled.
	(wait_lwp, linux_nat_filter_event): Report all thread exits if
	thread event reporting is enabled.  Remove comment.
	(filter_exit_event): New function.
	(linux_nat_wait_1): Use it.
	(linux_nat_thread_events): New function.
	(linux_nat_add_target): Install it as target_thread_events method.

1 files changed, 8 insertions, 6 deletions

diff --git a/gdb/linux-thread-db.c b/gdb/linux-thread-db.c
index 284e331..2300c81 100644
--- a/gdb/linux-thread-db.c
+++ b/gdb/linux-thread-db.c
@@ -1116,12 +1116,14 @@ thread_db_wait (struct target_ops *ops,
 
   ptid = beneath->to_wait (beneath, ptid, ourstatus, options);
 
-  if (ourstatus->kind == TARGET_WAITKIND_IGNORE)
-    return ptid;
-
-  if (ourstatus->kind == TARGET_WAITKIND_EXITED
-      || ourstatus->kind == TARGET_WAITKIND_SIGNALLED)
-    return ptid;
+  switch (ourstatus->kind)
+    {
+    case TARGET_WAITKIND_IGNORE:
+    case TARGET_WAITKIND_EXITED:
+    case TARGET_WAITKIND_THREAD_EXITED:
+    case TARGET_WAITKIND_SIGNALLED:
+      return ptid;
+    }
 
   info = get_thread_db_info (ptid_get_pid (ptid));