From 512bbc050bb8d42ec9463dbc49eb90dc6ecb3ad4 Mon Sep 17 00:00:00 2001
From: Samy Al Bahra <sbahra@repnop.org>
Date: Sun, 8 Jul 2012 15:59:30 -0400
Subject: [PATCH] ck_rwlock: Add recursive trylock operations.

Unlike ck_rwlock, there is no spin factor associated with these.
---
 include/ck_rwlock.h                       | 29 +++++++++++++++++++++++
 regressions/ck_rwlock/validate/validate.c | 25 ++++++++++++++++++-
 2 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/include/ck_rwlock.h b/include/ck_rwlock.h
index 804112d..1bd4372 100644
--- a/include/ck_rwlock.h
+++ b/include/ck_rwlock.h
@@ -192,6 +192,28 @@ leave:
 	return;
 }
 
+CK_CC_INLINE static bool
+ck_rwlock_recursive_write_trylock(ck_rwlock_recursive_t *rw, unsigned int tid)
+{
+	unsigned int o;
+
+	o = ck_pr_load_uint(&rw->rw.writer);
+	if (o == tid)
+		goto leave;
+
+	if (ck_pr_cas_uint(&rw->rw.writer, 0, tid) == false)
+		return false;
+
+	if (ck_pr_load_uint(&rw->rw.n_readers) != 0) {
+		ck_pr_store_uint(&rw->rw.writer, 0);
+		return false;
+	}
+
+leave:
+	rw->wc++;
+	return true;
+}
+
 CK_CC_INLINE static void
 ck_rwlock_recursive_write_unlock(ck_rwlock_recursive_t *rw)
 {
@@ -210,6 +232,13 @@ ck_rwlock_recursive_read_lock(ck_rwlock_recursive_t *rw)
 	return;
 }
 
+CK_CC_INLINE static bool
+ck_rwlock_recursive_read_trylock(ck_rwlock_recursive_t *rw)
+{
+
+	return ck_rwlock_read_trylock(&rw->rw, 1);
+}
+
 CK_CC_INLINE static void
 ck_rwlock_recursive_read_unlock(ck_rwlock_recursive_t *rw)
 {
diff --git a/regressions/ck_rwlock/validate/validate.c b/regressions/ck_rwlock/validate/validate.c
index a944021..d51864a 100644
--- a/regressions/ck_rwlock/validate/validate.c
+++ b/regressions/ck_rwlock/validate/validate.c
@@ -64,10 +64,22 @@ thread_recursive(void *null CK_CC_UNUSED)
         }
 
 	while (i--) {
+		if ((i % 10000) == 0) {
+			while (ck_rwlock_recursive_write_trylock(&r_lock, t) == false)
+				ck_pr_stall();
+		} else {
+			ck_rwlock_recursive_write_lock(&r_lock, t);
+		}
+
 		ck_rwlock_recursive_write_lock(&r_lock, t);
 		ck_rwlock_recursive_write_lock(&r_lock, t);
 		ck_rwlock_recursive_write_lock(&r_lock, t);
-		ck_rwlock_recursive_write_lock(&r_lock, t);
+
+		if (ck_rwlock_recursive_write_trylock(&r_lock, t) == false) {
+			fprintf(stderr, "ERROR: write_trylock failed.\n");
+			exit(EXIT_FAILURE);
+		}
+
 		{
 			l = ck_pr_load_uint(&locked);
 			if (l != 0) {
@@ -109,7 +121,16 @@ thread_recursive(void *null CK_CC_UNUSED)
 		ck_rwlock_recursive_write_unlock(&r_lock);
 		ck_rwlock_recursive_write_unlock(&r_lock);
 		ck_rwlock_recursive_write_unlock(&r_lock);
+		ck_rwlock_recursive_write_unlock(&r_lock);
+
+		if ((i % 10000) == 0) {
+			while (ck_rwlock_recursive_read_trylock(&r_lock) == false)
+				ck_pr_stall();
+		} else {
+			ck_rwlock_recursive_read_lock(&r_lock);
+		}
 
+		ck_rwlock_recursive_read_lock(&r_lock);
 		ck_rwlock_recursive_read_lock(&r_lock);
 		{
 			l = ck_pr_load_uint(&locked);
@@ -119,6 +140,8 @@ thread_recursive(void *null CK_CC_UNUSED)
 			}
 		}
 		ck_rwlock_recursive_read_unlock(&r_lock);
+		ck_rwlock_recursive_read_unlock(&r_lock);
+		ck_rwlock_recursive_read_unlock(&r_lock);
 	}
 
 	return (NULL);