From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 12 Jun 2024 20:36:54 +0000 (-0400)
Subject: wfcqueue: make cds_wfcq_empty arguments const
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=c07754115fc26ba7157c70e013b2e3c73236c657;p=urcu.git

wfcqueue: make cds_wfcq_empty arguments const

cds_wfcq_empty does not modify its arguments. Hence, they can be marked
as `const`.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I0b14acf21ca0a59bbdda4eb701b83a66e8837d57
---

diff --git a/include/urcu/static/wfcqueue.h b/include/urcu/static/wfcqueue.h
index 26741ae..2799c61 100644
--- a/include/urcu/static/wfcqueue.h
+++ b/include/urcu/static/wfcqueue.h
@@ -133,10 +133,10 @@ static inline void ___cds_wfcq_init(struct __cds_wfcq_head *head,
  * make a queue appear empty if an enqueuer is preempted for a long time
  * between xchg() and setting the previous node's next pointer.
  */
-static inline bool _cds_wfcq_empty(cds_wfcq_head_ptr_t u_head,
-		struct cds_wfcq_tail *tail)
+static inline bool _cds_wfcq_empty(cds_wfcq_head_const_ptr_t u_head,
+		const struct cds_wfcq_tail *tail)
 {
-	struct __cds_wfcq_head *head = u_head._h;
+	const struct __cds_wfcq_head *head = u_head._h;
 	/*
 	 * Queue is empty if no node is pointed by head->node.next nor
 	 * tail->p. Even though the tail->p check is sufficient to find
@@ -283,7 +283,7 @@ ___cds_wfcq_first(cds_wfcq_head_ptr_t u_head,
 	struct __cds_wfcq_head *head = u_head._h;
 	struct cds_wfcq_node *node;
 
-	if (_cds_wfcq_empty(__cds_wfcq_head_cast(head), tail))
+	if (_cds_wfcq_empty(__cds_wfcq_head_const_cast(head), tail))
 		return NULL;
 	node = ___cds_wfcq_node_sync_next(&head->node, blocking);
 
@@ -399,7 +399,7 @@ ___cds_wfcq_dequeue_with_state(cds_wfcq_head_ptr_t u_head,
 	if (state)
 		*state = 0;
 
-	if (_cds_wfcq_empty(__cds_wfcq_head_cast(head), tail)) {
+	if (_cds_wfcq_empty(__cds_wfcq_head_const_cast(head), tail)) {
 		return NULL;
 	}
 
@@ -530,7 +530,7 @@ ___cds_wfcq_splice(
 	 * Initial emptiness check to speed up cases where queue is
 	 * empty: only require loads to check if queue is empty.
 	 */
-	if (_cds_wfcq_empty(__cds_wfcq_head_cast(src_q_head), src_q_tail))
+	if (_cds_wfcq_empty(__cds_wfcq_head_const_cast(src_q_head), src_q_tail))
 		return CDS_WFCQ_RET_SRC_EMPTY;
 
 	for (;;) {
diff --git a/include/urcu/wfcqueue.h b/include/urcu/wfcqueue.h
index bba5c55..5a4add4 100644
--- a/include/urcu/wfcqueue.h
+++ b/include/urcu/wfcqueue.h
@@ -78,6 +78,11 @@ typedef union {
 	struct __cds_wfcq_head *_h;
 	struct cds_wfcq_head *h;
 } __attribute__((__transparent_union__)) cds_wfcq_head_ptr_t;
+
+typedef union {
+	const struct __cds_wfcq_head *_h;
+	const struct cds_wfcq_head *h;
+} __attribute__((__transparent_union__)) cds_wfcq_head_const_ptr_t;
 #if defined(__clang__)
 #pragma clang diagnostic pop
 #endif
@@ -100,6 +105,25 @@ static inline struct cds_wfcq_head *cds_wfcq_head_cast(struct cds_wfcq_head *hea
 {
 	return head;
 }
+
+/*
+ * This static inline is only present for compatibility with C++. It is
+ * effect-less in C.
+ */
+static inline const struct __cds_wfcq_head *__cds_wfcq_head_const_cast(const struct __cds_wfcq_head *head)
+{
+	return head;
+}
+
+/*
+ * This static inline is only present for compatibility with C++. It is
+ * effect-less in C.
+ */
+static inline const struct cds_wfcq_head *cds_wfcq_head_const_cast(const struct cds_wfcq_head *head)
+{
+	return head;
+}
+
 #else /* #ifndef __cplusplus */
 
 /*
@@ -121,6 +145,27 @@ static inline cds_wfcq_head_ptr_t cds_wfcq_head_cast(struct cds_wfcq_head *head)
 	cds_wfcq_head_ptr_t ret = { .h = head };
 	return ret;
 }
+
+/*
+ * This static inline is used by internally in the static inline
+ * implementation of the API.
+ */
+static inline cds_wfcq_head_const_ptr_t __cds_wfcq_head_const_cast(const struct __cds_wfcq_head *head)
+{
+	cds_wfcq_head_const_ptr_t ret = { ._h = head };
+	return ret;
+}
+
+/*
+ * This static inline is used by internally in the static inline
+ * implementation of the API.
+ */
+static inline cds_wfcq_head_const_ptr_t cds_wfcq_head_const_cast(const struct cds_wfcq_head *head)
+{
+	cds_wfcq_head_const_ptr_t ret = { .h = head };
+	return ret;
+}
+
 #endif /* #else #ifndef __cplusplus */
 
 struct cds_wfcq_tail {
@@ -238,8 +283,8 @@ extern void __cds_wfcq_init(struct __cds_wfcq_head *head,
  *
  * No memory barrier is issued. No mutual exclusion is required.
  */
-extern bool cds_wfcq_empty(cds_wfcq_head_ptr_t head,
-		struct cds_wfcq_tail *tail);
+extern bool cds_wfcq_empty(cds_wfcq_head_const_ptr_t head,
+		const struct cds_wfcq_tail *tail);
 
 /*
  * cds_wfcq_dequeue_lock: take the dequeue mutual exclusion lock.
@@ -500,10 +545,22 @@ static inline cds_wfcq_head_ptr_t cds_wfcq_head_cast_cpp(struct cds_wfcq_head *h
 	return ret;
 }
 
+static inline cds_wfcq_head_const_ptr_t cds_wfcq_head_const_cast_cpp(const struct __cds_wfcq_head *head)
+{
+	cds_wfcq_head_const_ptr_t ret = { ._h = head };
+	return ret;
+}
+
+static inline cds_wfcq_head_const_ptr_t cds_wfcq_head_const_cast_cpp(const struct cds_wfcq_head *head)
+{
+	cds_wfcq_head_const_ptr_t ret = { .h = head };
+	return ret;
+}
+
 template<typename T> static inline bool cds_wfcq_empty(T head,
-		struct cds_wfcq_tail *tail)
+		const struct cds_wfcq_tail *tail)
 {
-	return cds_wfcq_empty(cds_wfcq_head_cast_cpp(head), tail);
+	return cds_wfcq_empty(cds_wfcq_head_const_cast_cpp(head), tail);
 }
 
 template<typename T> static inline bool cds_wfcq_enqueue(T head,
diff --git a/src/wfcqueue.c b/src/wfcqueue.c
index ff05510..294b266 100644
--- a/src/wfcqueue.c
+++ b/src/wfcqueue.c
@@ -38,8 +38,8 @@ void __cds_wfcq_init(struct __cds_wfcq_head *head,
 	___cds_wfcq_init(head, tail);
 }
 
-bool cds_wfcq_empty(cds_wfcq_head_ptr_t head,
-		struct cds_wfcq_tail *tail)
+bool cds_wfcq_empty(cds_wfcq_head_const_ptr_t head,
+		const struct cds_wfcq_tail *tail)
 
 {
 	return _cds_wfcq_empty(head, tail);