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 26741ae81d241ed04f1917b68e7755847c90490b..2799c61bb38b3c9f53610af50fad0d516445bf5f 100644 (file)
--- 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 bba5c558d96cef1015c2a3197c5fe43797356e9d..5a4add454f59df3e04f2f098e82d9cdc06955853 100644 (file)
--- 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 ff05510bd29d0f87aba4632bfcf92b8c34c43cc9..294b2662ba023115cc90c7fe921e93b6a6994be4 100644 (file)
--- 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);