Use stdatomic.h for atomic_counter_t where available.

Closes ticket 23953.

1 files changed, 13 insertions, 6 deletions

diff --git a/src/common/compat_threads.c b/src/common/compat_threads.c
index 208d3138d9..e8a97f1254 100644
--- a/src/common/compat_threads.c
+++ b/src/common/compat_threads.c
@@ -352,12 +352,7 @@ alert_sockets_close(alert_sockets_t *socks)
   socks->read_fd = socks->write_fd = -1;
 }
 
-/*
- * XXXX We might be smart to move to compiler intrinsics or real atomic
- * XXXX operations at some point.  But not yet.
- *
- */
-
+#ifndef HAVE_STDATOMIC_H
 /** Initialize a new atomic counter with the value 0 */
 void
 atomic_counter_init(atomic_counter_t *counter)
@@ -397,4 +392,16 @@ atomic_counter_get(atomic_counter_t *counter)
   tor_mutex_release(&counter->mutex);
   return val;
 }
+/** Replace the value of an atomic counter; return the old one. */
+size_t
+atomic_counter_exchange(atomic_counter_t *counter, size_t newval)
+{
+  size_t oldval;
+  tor_mutex_acquire(&counter->mutex);
+  oldval = counter->val;
+  counter->val = newval;
+  tor_mutex_release(&counter->mutex);
+  return oldval;
+}
+#endif