4 files changed, 17 insertions, 0 deletions
diff --git a/include/grpc/impl/codegen/atm.h b/include/grpc/impl/codegen/atm.h
index 5589d5d411..ae00fb0f16 100644
--- a/include/grpc/impl/codegen/atm.h
+++ b/include/grpc/impl/codegen/atm.h
@@ -75,6 +75,9 @@
    int gpr_atm_no_barrier_cas(gpr_atm *p, gpr_atm o, gpr_atm n);
    int gpr_atm_acq_cas(gpr_atm *p, gpr_atm o, gpr_atm n);
    int gpr_atm_rel_cas(gpr_atm *p, gpr_atm o, gpr_atm n);
+
+   // Atomically, set *p=n and return the old value of *p
+   gpr_atm gpr_atm_full_xchg(gpr_atm *p, gpr_atm n);
 */
 
 #include <grpc/impl/codegen/port_platform.h>
diff --git a/include/grpc/impl/codegen/atm_gcc_atomic.h b/include/grpc/impl/codegen/atm_gcc_atomic.h
index 8caf7edbde..7d4ae98cf7 100644
--- a/include/grpc/impl/codegen/atm_gcc_atomic.h
+++ b/include/grpc/impl/codegen/atm_gcc_atomic.h
@@ -69,4 +69,6 @@ static __inline int gpr_atm_rel_cas(gpr_atm *p, gpr_atm o, gpr_atm n) {
                                      __ATOMIC_RELAXED);
 }
 
+#define gpr_atm_full_xchg(p, n) __atomic_exchange_n((p), (n), __ATOMIC_ACQ_REL)
+
 #endif /* GRPC_IMPL_CODEGEN_ATM_GCC_ATOMIC_H */
diff --git a/include/grpc/impl/codegen/atm_gcc_sync.h b/include/grpc/impl/codegen/atm_gcc_sync.h
index 915b09fb0c..9aa2b43189 100644
--- a/include/grpc/impl/codegen/atm_gcc_sync.h
+++ b/include/grpc/impl/codegen/atm_gcc_sync.h
@@ -84,4 +84,12 @@ static __inline void gpr_atm_no_barrier_store(gpr_atm *p, gpr_atm value) {
 #define gpr_atm_acq_cas(p, o, n) (__sync_bool_compare_and_swap((p), (o), (n)))
 #define gpr_atm_rel_cas(p, o, n) gpr_atm_acq_cas((p), (o), (n))
 
+static __inline gpr_atm gpr_atm_full_xchg(gpr_atm *p, gpr_atm n) {
+  gpr_atm cur;
+  do {
+    cur = gpr_atm_acq_load(p);
+  } while (!gpr_atm_rel_cas(p, cur, n));
+  return cur;
+}
+
 #endif /* GRPC_IMPL_CODEGEN_ATM_GCC_SYNC_H */
diff --git a/include/grpc/impl/codegen/atm_windows.h b/include/grpc/impl/codegen/atm_windows.h
index d5fa8c0f62..0ab70b95c4 100644
--- a/include/grpc/impl/codegen/atm_windows.h
+++ b/include/grpc/impl/codegen/atm_windows.h
@@ -122,4 +122,8 @@ static __inline gpr_atm gpr_atm_full_fetch_add(gpr_atm *p, gpr_atm delta) {
   return old;
 }
 
+static __inline gpr_atm gpr_atm_full_xchg(gpr_atm *p, gpr_atm n) {
+  return (gpr_atm)InterlockedExchangePointer((PVOID *)p, (PVOID)n);
+}
+
 #endif /* GRPC_IMPL_CODEGEN_ATM_WINDOWS_H */