Add gpr_ref_is_unique

include/grpc/support/sync.h

@@ -164,6 +164,10 @@ GPRAPI void gpr_refn(gpr_refcount *r, int n);
    zero. .  Requires *r initialized. */
 GPRAPI int gpr_unref(gpr_refcount *r);
 
+/* Return non-zero iff the reference count of *r is one, and thus is owned
+   by exactly one object. */
+GPRAPI int gpr_ref_is_unique(gpr_refcount *r);
+
 /* --- Stats counters ---
 
    These calls act on the integral type gpr_stats_counter.  It requires no

src/core/lib/support/sync.c

@@ -113,6 +113,10 @@ int gpr_unref(gpr_refcount *r) {
   return prior == 1;
 }
 
+int gpr_ref_is_unique(gpr_refcount *r) {
+  return gpr_atm_acq_load(&r->count) == 1;
+}
+
 void gpr_stats_init(gpr_stats_counter *c, intptr_t n) {
   gpr_atm_rel_store(&c->value, n);
 }