Revert "[atomic] Make pointer get op relaxed instead of acquire"
This reverts commit b1e5650c67266dc158f22355fed206cd1c413f70.
After lots of head-scratching and finally finding the only truly
readable source to be the good old:
https://www.kernel.org/doc/Documentation/memory-barriers.txt
I've convinced myself that we need consume memory-ordering on get().
The location of memory-barrier in a load should be after, not before
the load. That needs fixing. I'll do that separately.
diff --git a/src/hb-atomic-private.hh b/src/hb-atomic-private.hh
index c860582..02cf6f3 100644
--- a/src/hb-atomic-private.hh
+++ b/src/hb-atomic-private.hh
@@ -40,19 +40,20 @@
/* We need external help for these */
#if defined(hb_atomic_int_impl_add) \
+ && defined(hb_atomic_ptr_impl_get) \
&& defined(hb_atomic_ptr_impl_cmpexch)
/* Defined externally, i.e. in config.h; must have typedef'ed hb_atomic_int_impl_t as well. */
-#elif !defined(HB_NO_MT) && defined(__ATOMIC_RELAXED)
+#elif !defined(HB_NO_MT) && defined(__ATOMIC_ACQUIRE)
/* C++11-style GCC primitives. */
typedef int hb_atomic_int_impl_t;
#define hb_atomic_int_impl_add(AI, V) __atomic_fetch_add (&(AI), (V), __ATOMIC_ACQ_REL)
-#define hb_atomic_ptr_impl_get(P) __atomic_load_n ((P), __ATOMIC_RELAXED)
+#define hb_atomic_ptr_impl_get(P) __atomic_load_n ((P), __ATOMIC_ACQUIRE)
static inline bool
_hb_atomic_ptr_impl_cmplexch (const void **P, const void *O_, const void *N)
{
@@ -70,7 +71,7 @@
typedef int hb_atomic_int_impl_t;
#define hb_atomic_int_impl_add(AI, V) (reinterpret_cast<std::atomic<int> *> (&AI)->fetch_add ((V), std::memory_order_acq_rel))
-#define hb_atomic_ptr_impl_get(P) (reinterpret_cast<std::atomic<void*> *> (P)->load (std::memory_order_relaxed))
+#define hb_atomic_ptr_impl_get(P) (reinterpret_cast<std::atomic<void*> *> (P)->load (std::memory_order_acquire))
static inline bool
_hb_atomic_ptr_impl_cmplexch (const void **P, const void *O_, const void *N)
{
@@ -84,9 +85,22 @@
#include <windows.h>
+/* MinGW has a convoluted history of supporting MemoryBarrier
+ * properly. As such, define a function to wrap the whole
+ * thing. */
+static inline void _HBMemoryBarrier (void) {
+#if !defined(MemoryBarrier)
+ long dummy = 0;
+ InterlockedExchange (&dummy, 1);
+#else
+ MemoryBarrier ();
+#endif
+}
+
typedef LONG hb_atomic_int_impl_t;
#define hb_atomic_int_impl_add(AI, V) InterlockedExchangeAdd (&(AI), (V))
+#define hb_atomic_ptr_impl_get(P) (_HBMemoryBarrier (), (void *) *(P))
#define hb_atomic_ptr_impl_cmpexch(P,O,N) (InterlockedCompareExchangePointer ((void **) (P), (void *) (N), (void *) (O)) == (void *) (O))
@@ -95,6 +109,7 @@
typedef int hb_atomic_int_impl_t;
#define hb_atomic_int_impl_add(AI, V) __sync_fetch_and_add (&(AI), (V))
+#define hb_atomic_ptr_impl_get(P) (void *) (__sync_synchronize (), *(P))
#define hb_atomic_ptr_impl_cmpexch(P,O,N) __sync_bool_compare_and_swap ((P), (O), (N))
@@ -104,9 +119,10 @@
#include <mbarrier.h>
typedef unsigned int hb_atomic_int_impl_t;
-#define hb_atomic_int_impl_add(AI, V) (({__machine_rw_barrier ();}), atomic_add_int_nv (&(AI), (V)) - (V))
+#define hb_atomic_int_impl_add(AI, V) ( ({__machine_rw_barrier ();}), atomic_add_int_nv (&(AI), (V)) - (V))
-#define hb_atomic_ptr_impl_cmpexch(P,O,N) (({__machine_rw_barrier ();}), atomic_cas_ptr ((void **) (P), (void *) (O), (void *) (N)) == (void *) (O) ? true : false)
+#define hb_atomic_ptr_impl_get(P) ( ({__machine_rw_barrier ();}), (void *) *(P))
+#define hb_atomic_ptr_impl_cmpexch(P,O,N) ( ({__machine_rw_barrier ();}), atomic_cas_ptr ((void **) (P), (void *) (O), (void *) (N)) == (void *) (O) ? true : false)
#elif !defined(HB_NO_MT) && defined(__APPLE__)
@@ -122,6 +138,7 @@
typedef int32_t hb_atomic_int_impl_t;
#define hb_atomic_int_impl_add(AI, V) (OSAtomicAdd32Barrier ((V), &(AI)) - (V))
+#define hb_atomic_ptr_impl_get(P) (OSMemoryBarrier (), (void *) *(P))
#if (MAC_OS_X_VERSION_MIN_REQUIRED > MAC_OS_X_VERSION_10_4 || __IPHONE_VERSION_MIN_REQUIRED >= 20100)
#define hb_atomic_ptr_impl_cmpexch(P,O,N) OSAtomicCompareAndSwapPtrBarrier ((void *) (O), (void *) (N), (void **) (P))
#else
@@ -154,6 +171,7 @@
typedef int hb_atomic_int_impl_t;
#define hb_atomic_int_impl_add(AI, V) _hb_fetch_and_add (&(AI), (V))
+#define hb_atomic_ptr_impl_get(P) (__sync(), (void *) *(P))
#define hb_atomic_ptr_impl_cmpexch(P,O,N) _hb_compare_and_swaplp ((long*)(P), (long)(O), (long)(N))
#elif !defined(HB_NO_MT)
@@ -163,6 +181,7 @@
typedef volatile int hb_atomic_int_impl_t;
#define hb_atomic_int_impl_add(AI, V) (((AI) += (V)) - (V))
+#define hb_atomic_ptr_impl_get(P) ((void *) *(P))
#define hb_atomic_ptr_impl_cmpexch(P,O,N) (* (void * volatile *) (P) == (void *) (O) ? (* (void * volatile *) (P) = (void *) (N), true) : false)
@@ -171,16 +190,13 @@
typedef int hb_atomic_int_impl_t;
#define hb_atomic_int_impl_add(AI, V) (((AI) += (V)) - (V))
+#define hb_atomic_ptr_impl_get(P) ((void *) *(P))
#define hb_atomic_ptr_impl_cmpexch(P,O,N) (* (void **) (P) == (void *) (O) ? (* (void **) (P) = (void *) (N), true) : false)
#endif
-#ifndef hb_atomic_ptr_impl_get
-#define hb_atomic_ptr_impl_get(P) ((void *) *(P))
-#endif
-
#ifndef HB_ATOMIC_INT_INIT
#define HB_ATOMIC_INT_INIT(V) {V}
#endif
