util/u_atomic: add p_atomic_xchg
The closest to it in the old-style gcc builtins is __sync_lock_test_and_set,
however, that is only guaranteed to work with values 0 and 1 and only
provides an acquire barrier. I also don't know about other OSes, so we
provide a simple & stupid emulation via p_atomic_cmpxchg.
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
diff --git a/src/util/u_atomic.h b/src/util/u_atomic.h
index 2a5bbae..c6d4bde 100644
--- a/src/util/u_atomic.h
+++ b/src/util/u_atomic.h
@@ -12,6 +12,7 @@
#define U_ATOMIC_H
#include <stdbool.h>
+#include <stdint.h>
/* Favor OS-provided implementations.
*
@@ -47,6 +48,8 @@
#define p_atomic_add(v, i) (void) __atomic_add_fetch((v), (i), __ATOMIC_ACQ_REL)
#define p_atomic_inc_return(v) __atomic_add_fetch((v), 1, __ATOMIC_ACQ_REL)
#define p_atomic_dec_return(v) __atomic_sub_fetch((v), 1, __ATOMIC_ACQ_REL)
+#define p_atomic_xchg(v, i) __atomic_exchange_n((v), (i), __ATOMIC_ACQ_REL)
+#define PIPE_NATIVE_ATOMIC_XCHG
#else
@@ -220,6 +223,33 @@
#error "No pipe_atomic implementation selected"
#endif
+#ifndef PIPE_NATIVE_ATOMIC_XCHG
+static inline uint32_t p_atomic_xchg_32(uint32_t *v, uint32_t i)
+{
+ uint32_t actual = p_atomic_read(v);
+ uint32_t expected;
+ do {
+ expected = actual;
+ actual = p_atomic_cmpxchg(v, expected, i);
+ } while (expected != actual);
+ return actual;
+}
+static inline uint64_t p_atomic_xchg_64(uint64_t *v, uint64_t i)
+{
+ uint64_t actual = p_atomic_read(v);
+ uint64_t expected;
+ do {
+ expected = actual;
+ actual = p_atomic_cmpxchg(v, expected, i);
+ } while (expected != actual);
+ return actual;
+}
+
+#define p_atomic_xchg(v, i) ((__typeof(*(v))) \
+ sizeof(*(v)) == sizeof(uint32_t) ? p_atomic_xchg_32((uint32_t *)(v), (uint32_t)(i)) : \
+ sizeof(*(v)) == sizeof(uint64_t) ? p_atomic_xchg_64((uint64_t *)(v), (uint64_t)(i)) : \
+ (assert(!"should not get here"), 0))
+#endif
#endif /* U_ATOMIC_H */