From 9feb93758fd0305c261b524c13ab026e555948a1 Mon Sep 17 00:00:00 2001
From: Samy Al Bahra <sbahra@appnexus.com>
Date: Thu, 6 Oct 2011 11:09:35 -0400
Subject: [PATCH] ck_brlock: Add trylock variants with user-defined spin
 factor.

---
 include/ck_brlock.h | 55 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/include/ck_brlock.h b/include/ck_brlock.h
index cf44e64..0bace4e 100644
--- a/include/ck_brlock.h
+++ b/include/ck_brlock.h
@@ -102,6 +102,33 @@ ck_brlock_write_unlock(struct ck_brlock *br)
 	return;
 }
 
+CK_CC_INLINE static bool
+ck_brlock_write_trylock(struct ck_brlock *br, unsigned int factor)
+{
+	struct ck_brlock_reader *cursor;
+	unsigned int steps = 0;
+
+	while (ck_pr_fas_uint(&br->writer, true) == true) {
+		if (++steps >= factor)
+			return false;
+
+		ck_pr_stall();
+	}
+
+	for (cursor = br->readers; cursor != NULL; cursor = cursor->next) {
+		while (ck_pr_load_uint(&cursor->n_readers) != 0) {
+			if (++steps >= factor) {
+				ck_brlock_write_unlock(br);
+				return false;
+			}
+
+			ck_pr_stall();
+		}
+	}
+
+	return true;
+}
+
 CK_CC_INLINE static void
 ck_brlock_read_register(struct ck_brlock *br, struct ck_brlock_reader *reader)
 {
@@ -159,6 +186,34 @@ ck_brlock_read_lock(struct ck_brlock *br, struct ck_brlock_reader *reader)
 	return;
 }
 
+CK_CC_INLINE static bool
+ck_brlock_read_trylock(struct ck_brlock *br, struct ck_brlock_reader *reader, unsigned int factor)
+{
+	unsigned int steps = 0;
+
+	for (;;) {
+		while (ck_pr_load_uint(&br->writer) == true) {
+			if (++steps >= factor)
+				return false;
+
+			ck_pr_stall();
+		}
+
+		ck_pr_store_uint(&reader->n_readers, reader->n_readers + 1);
+		ck_pr_fence_strict_memory();
+
+		if (ck_pr_load_uint(&br->writer) == false)
+			break;
+
+		ck_pr_store_uint(&reader->n_readers, reader->n_readers - 1);
+
+		if (++steps >= factor)
+			return false;
+	}
+
+	return true;
+}
+
 CK_CC_INLINE static void
 ck_brlock_read_unlock(struct ck_brlock_reader *reader)
 {