MINOR: listener: pre-compute some thread counts per bind_conf
In order to quickly pick a thread ID when accepting a connection, we'll
need to know certain pre-computed values derived from the thread mask,
which are counts of bits per position multiples of 1, 2, 4, 8, 16 and
32. In practice it is sufficient to compute only the 4 first ones and
store them in the bind_conf. We update the count every time the
bind_thread value is adjusted.
The fields in the bind_conf struct have been moved around a little bit
to make it easier to group all thread bit values into the same cache
line.
The function used to return a thread number is bind_map_thread_id(),
and it maps a number between 0 and 31/63 to a thread ID between 0 and
31/63, starting from the left.
diff --git a/src/listener.c b/src/listener.c
index f642eb4..fb527ab 100644
--- a/src/listener.c
+++ b/src/listener.c
@@ -802,6 +802,33 @@
}
}
+/* recompute the bit counts per parity for the bind_thread value. This will be
+ * used to quickly map a thread number from 1 to #thread to a thread ID among
+ * the ones bound. This is the preparation phase of the bit rank counting algo
+ * described here: https://graphics.stanford.edu/~seander/bithacks.html
+ */
+void bind_recount_thread_bits(struct bind_conf *conf)
+{
+ unsigned long m;
+
+ m = thread_mask(conf->bind_thread);
+ conf->thr_count = my_popcountl(m);
+ mask_prep_rank_map(m, &conf->thr_2, &conf->thr_4, &conf->thr_8, &conf->thr_16);
+}
+
+/* Report the ID of thread <r> in bind_conf <conf> according to its thread_mask.
+ * <r> must be between 0 and LONGBITS-1. This makes use of the pre-computed
+ * bits resulting from bind_recount_thread_bits. See this function for more
+ * info.
+ */
+unsigned int bind_map_thread_id(const struct bind_conf *conf, unsigned int r)
+{
+ unsigned long m;
+
+ m = thread_mask(conf->bind_thread);
+ return mask_find_rank_bit_fast(r, m, conf->thr_2, conf->thr_4, conf->thr_8, conf->thr_16);
+}
+
/************************************************************************/
/* All supported sample and ACL keywords must be declared here. */
/************************************************************************/
@@ -1012,6 +1039,7 @@
conf->bind_proc |= proc;
conf->bind_thread |= thread;
+ bind_recount_thread_bits(conf);
return 0;
}