MINOR: pattern: add pat_ref_may_commit() helper function

pat_ref_may_commit() may be used to know if a given generation ID id still
valid, which means it may still be committed at some point. Else it means
that another pending generation ID older than the tested one was already
committed and thus other generations ID below this one are stale and must
be regenerated.

diff --git a/include/haproxy/pattern.h b/include/haproxy/pattern.h
index 2b1235853ccb8d4ba5e547f8345567c2f0bcd58a..a4af1087538b6d75de2489b4788dc79cf4b4cf0e 100644 (file)
--- a/include/haproxy/pattern.h
+++ b/include/haproxy/pattern.h
@@ -229,6 +229,27 @@ static inline void pat_ref_giveup(struct pat_ref *ref, unsigned int gen)
        HA_ATOMIC_CAS(&ref->next_gen, &gen, gen - 1);
 }
 
+/* Checks if the provided <gen> number is valid in the sense that it may
+ * still be committed. Indeed, multiple gen numbers may be created in parallel,
+ * but once one of them gets committed, pending generation numbers below the
+ * new current one are not valid anymore (they should be recreated).
+ *
+ * It is not strictly mandatory to call this function under lock if the caller
+ * uses this info as an opportunistic hint, otherwise, when consistency is
+ * required, <ref> lock should be held as commit operation is also performed
+ * under the lock.
+ *
+ * The function returns 1 if <gen> is still valid, and 0 otherwise
+ */
+static inline int pat_ref_may_commit(struct pat_ref *ref, unsigned int gen)
+{
+       unsigned int curr_gen = HA_ATOMIC_LOAD(&ref->curr_gen);
+
+       if ((int)(gen - curr_gen) > 0)
+               return 1;
+       return 0;
+}
+
 /* Commit the whole pattern reference by updating the generation number or
  * failing in case someone else managed to do it meanwhile. While this could
  * be done using a CAS, it must instead be called with the PATREF_LOCK held in
@@ -239,7 +260,7 @@ static inline void pat_ref_giveup(struct pat_ref *ref, unsigned int gen)
  */
 static inline int pat_ref_commit(struct pat_ref *ref, unsigned int gen)
 {
-       if ((int)(gen - ref->curr_gen) > 0) {
+       if (pat_ref_may_commit(ref, gen)) {
                ref->curr_gen = gen;
                event_hdl_publish(&ref->e_subs, EVENT_HDL_SUB_PAT_REF_COMMIT, NULL);
        }