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Use find_thread_in_random in select_event_lwp 

I noticed that find_thread_in_random duplicates the code in
find_thread_in_random, so this patch changes the latter to use the
former.

There are two other spots in gdb that do this, but to unify all of
them would require switching some code from using the "iterate over"
idiom to using iterators.

Another possible improvement is that find_thread_in_random could be
made single-pass using reservoir sampling.

Tested by the buildbot.

gdb/gdbserver/ChangeLog
2019-04-09  Tom Tromey  <tromey@adacore.com>

	* linux-low.c (select_event_lwp): Use find_thread_in_random.
This commit is contained in:
Tom Tromey 2019-04-04 16:57:11 -06:00
parent 9ab8741a48
commit b0319eaaf9
2 changed files with 8 additions and 31 deletions
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4
gdb/gdbserver/ChangeLog
View File

@ -1,3 +1,7 @@
2019-04-09 Tom Tromey <tromey@adacore.com>
* linux-low.c (select_event_lwp): Use find_thread_in_random.
2019-04-08 Tom Tromey <tom@tromey.com>
* linux-low.c (linux_detach_one_lwp): Replace throw_exception with

35
gdb/gdbserver/linux-low.c
View File

@ -2828,7 +2828,6 @@ linux_wait_for_event (ptid_t ptid, int *wstatp, int options)
static void
select_event_lwp (struct lwp_info **orig_lp)
{
int random_selector;
struct thread_info *event_thread = NULL;
/* In all-stop, give preference to the LWP that is being
@ -2862,39 +2861,13 @@ select_event_lwp (struct lwp_info **orig_lp)
/* No single-stepping LWP. Select one at random, out of those
which have had events. */
/* First see how many events we have. */
int num_events = 0;
for_each_thread ([&] (thread_info *thread)
event_thread = find_thread_in_random ([&] (thread_info *thread)
{
lwp_info *lp = get_thread_lwp (thread);
/* Count only resumed LWPs that have an event pending. */
if (thread->last_status.kind == TARGET_WAITKIND_IGNORE
&& lp->status_pending_p)
num_events++;
});
gdb_assert (num_events > 0);
/* Now randomly pick a LWP out of those that have had
events. */
random_selector = (int)
((num_events * (double) rand ()) / (RAND_MAX + 1.0));
if (debug_threads && num_events > 1)
debug_printf ("SEL: Found %d SIGTRAP events, selecting #%d\n",
num_events, random_selector);
event_thread = find_thread ([&] (thread_info *thread)
{
lwp_info *lp = get_thread_lwp (thread);
/* Select only resumed LWPs that have an event pending. */
if (thread->last_status.kind == TARGET_WAITKIND_IGNORE
&& lp->status_pending_p)
if (random_selector-- == 0)
return true;
return false;
/* Only resumed LWPs that have an event pending. */
return (thread->last_status.kind == TARGET_WAITKIND_IGNORE
&& lp->status_pending_p);
});
}