+ while (futex_async(&gp_futex, FUTEX_WAIT, -1,
+ NULL, NULL, 0)) {
+ switch (errno) {
+ case EWOULDBLOCK:
+ /* Value already changed. */
+ return;
+ case EINTR:
+ /* Retry if interrupted by signal. */
+ break; /* Get out of switch. */
+ default:
+ /* Unexpected error. */
+ urcu_die(errno);
+ }
+ }
+}
+
+/*
+ * Always called with rcu_registry lock held. Releases this lock between
+ * iterations and grabs it again. Holds the lock when it returns.
+ */
+void update_counter_and_wait(void)
+{
+ CDS_LIST_HEAD(qsreaders);
+ unsigned int wait_loops = 0;
+ struct rcu_reader *index, *tmp;
+#ifdef HAS_INCOHERENT_CACHES
+ unsigned int wait_gp_loops = 0;
+#endif /* HAS_INCOHERENT_CACHES */
+
+ /* Switch parity: 0 -> 1, 1 -> 0 */
+ CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
+
+ /*
+ * Must commit rcu_gp_ctr update to memory before waiting for quiescent
+ * state. Failure to do so could result in the writer waiting forever
+ * while new readers are always accessing data (no progress). Enforce
+ * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr.
+ */
+ cmm_barrier();
+
+ /*
+ *
+ * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
+ * model easier to understand. It does not have a big performance impact
+ * anyway, given this is the write-side.
+ */
+ cmm_smp_mb();
+