MDEV-6693 - Atomic operations with explicit memory barrier

Added API for atomic operations with explicit memory barrier. Only gcc
atomic builtins are currently supported. If they're unavailable, fall
back to atomic operations with implicit full memory barrier.

include/my_atomic.h

@@ -20,27 +20,86 @@
   This header defines five atomic operations:
 
   my_atomic_add#(&var, what)
+  my_atomic_add#_explicit(&var, what, memory_order)
     'Fetch and Add'
     add 'what' to *var, and return the old value of *var
+    All memory orders are valid.
 
   my_atomic_fas#(&var, what)
+  my_atomic_fas#_explicit(&var, what, memory_order)
     'Fetch And Store'
     store 'what' in *var, and return the old value of *var
+    All memory orders are valid.
 
   my_atomic_cas#(&var, &old, new)
+  my_atomic_cas#_weak_explicit(&var, &old, new, succ, fail)
+  my_atomic_cas#_strong_explicit(&var, &old, new, succ, fail)
     'Compare And Swap'
     if *var is equal to *old, then store 'new' in *var, and return TRUE
     otherwise store *var in *old, and return FALSE
+    succ - the memory synchronization ordering for the read-modify-write
+    operation if the comparison succeeds. All memory orders are valid.
+    fail - the memory synchronization ordering for the load operation if the
+    comparison fails. Cannot be MY_MEMORY_ORDER_RELEASE or
+    MY_MEMORY_ORDER_ACQ_REL and cannot specify stronger ordering than succ.
+
+    The weak form is allowed to fail spuriously, that is, act as if *var != *old
+    even if they are equal. When a compare-and-exchange is in a loop, the weak
+    version will yield better performance on some platforms. When a weak
+    compare-and-exchange would require a loop and a strong one would not, the
+    strong one is preferable.
 
   my_atomic_load#(&var)
+  my_atomic_load#_explicit(&var, memory_order)
     return *var
+    Order must be one of MY_MEMORY_ORDER_RELAXED, MY_MEMORY_ORDER_CONSUME,
+    MY_MEMORY_ORDER_ACQUIRE, MY_MEMORY_ORDER_SEQ_CST.
 
   my_atomic_store#(&var, what)
+  my_atomic_store#_explicit(&var, what, memory_order)
     store 'what' in *var
+    Order must be one of MY_MEMORY_ORDER_RELAXED, MY_MEMORY_ORDER_RELEASE,
+    MY_MEMORY_ORDER_SEQ_CST.
 
   '#' is substituted by a size suffix - 8, 16, 32, 64, or ptr
   (e.g. my_atomic_add8, my_atomic_fas32, my_atomic_casptr).
 
+  The first version orders memory accesses according to MY_MEMORY_ORDER_SEQ_CST,
+  the second version (with _explicit suffix) orders memory accesses according to
+  given memory order.
+
+  memory_order specifies how non-atomic memory accesses are to be ordered around
+  an atomic operation:
+
+  MY_MEMORY_ORDER_RELAXED - there are no constraints on reordering of memory
+                            accesses around the atomic variable.
+  MY_MEMORY_ORDER_CONSUME - no reads in the current thread dependent on the
+                            value currently loaded can be reordered before this
+                            load. This ensures that writes to dependent
+                            variables in other threads that release the same
+                            atomic variable are visible in the current thread.
+                            On most platforms, this affects compiler
+                            optimization only.
+  MY_MEMORY_ORDER_ACQUIRE - no reads in the current thread can be reordered
+                            before this load. This ensures that all writes in
+                            other threads that release the same atomic variable
+                            are visible in the current thread.
+  MY_MEMORY_ORDER_RELEASE - no writes in the current thread can be reordered
+                            after this store. This ensures that all writes in
+                            the current thread are visible in other threads that
+                            acquire the same atomic variable.
+  MY_MEMORY_ORDER_ACQ_REL - no reads in the current thread can be reordered
+                            before this load as well as no writes in the current
+                            thread can be reordered after this store. The
+                            operation is read-modify-write operation. It is
+                            ensured that all writes in another threads that
+                            release the same atomic variable are visible before
+                            the modification and the modification is visible in
+                            other threads that acquire the same atomic variable.
+  MY_MEMORY_ORDER_SEQ_CST - The operation has the same semantics as
+                            acquire-release operation, and additionally has
+                            sequentially-consistent operation ordering.
+
   NOTE This operations are not always atomic, so they always must be
   enclosed in my_atomic_rwlock_rdlock(lock)/my_atomic_rwlock_rdunlock(lock)
   or my_atomic_rwlock_wrlock(lock)/my_atomic_rwlock_wrunlock(lock).
@@ -50,7 +109,7 @@
   On architectures where these operations are really atomic, rwlocks will
   be optimized away.
   8- and 16-bit atomics aren't implemented for windows (see generic-msvc.h),
-  but can be added, if necessary. 
+  but can be added, if necessary.
 */
 
 #ifndef my_atomic_rwlock_init
@@ -283,4 +342,79 @@ extern int my_atomic_initialize();
 
 #endif
 
+#ifdef __ATOMIC_SEQ_CST
+#define MY_MEMORY_ORDER_RELAXED __ATOMIC_RELAXED
+#define MY_MEMORY_ORDER_CONSUME __ATOMIC_CONSUME
+#define MY_MEMORY_ORDER_ACQUIRE __ATOMIC_ACQUIRE
+#define MY_MEMORY_ORDER_RELEASE __ATOMIC_RELEASE
+#define MY_MEMORY_ORDER_ACQ_REL __ATOMIC_ACQ_REL
+#define MY_MEMORY_ORDER_SEQ_CST __ATOMIC_SEQ_CST
+
+#define my_atomic_store32_explicit(P, D, O) __atomic_store_n((P), (D), (O))
+#define my_atomic_store64_explicit(P, D, O) __atomic_store_n((P), (D), (O))
+#define my_atomic_storeptr_explicit(P, D, O) __atomic_store_n((P), (D), (O))
+
+#define my_atomic_load32_explicit(P, O) __atomic_load_n((P), (O))
+#define my_atomic_load64_explicit(P, O) __atomic_load_n((P), (O))
+#define my_atomic_loadptr_explicit(P, O) __atomic_load_n((P), (O))
+
+#define my_atomic_fas32_explicit(P, D, O) __atomic_exchange_n((P), (D), (O))
+#define my_atomic_fas64_explicit(P, D, O) __atomic_exchange_n((P), (D), (O))
+#define my_atomic_fasptr_explicit(P, D, O) __atomic_exchange_n((P), (D), (O))
+
+#define my_atomic_add32_explicit(P, A, O) __atomic_fetch_add((P), (A), (O))
+#define my_atomic_add64_explicit(P, A, O) __atomic_fetch_add((P), (A), (O))
+
+#define my_atomic_cas32_weak_explicit(P, E, D, S, F) \
+  __atomic_compare_exchange_n((P), (E), (D), true, (S), (F))
+#define my_atomic_cas64_weak_explicit(P, E, D, S, F) \
+  __atomic_compare_exchange_n((P), (E), (D), true, (S), (F))
+#define my_atomic_casptr_weak_explicit(P, E, D, S, F) \
+  __atomic_compare_exchange_n((P), (E), (D), true, (S), (F))
+
+#define my_atomic_cas32_strong_explicit(P, E, D, S, F) \
+  __atomic_compare_exchange_n((P), (E), (D), false, (S), (F))
+#define my_atomic_cas64_strong_explicit(P, E, D, S, F) \
+  __atomic_compare_exchange_n((P), (E), (D), false, (S), (F))
+#define my_atomic_casptr_strong_explicit(P, E, D, S, F) \
+  __atomic_compare_exchange_n((P), (E), (D), false, (S), (F))
+#else
+#define MY_MEMORY_ORDER_RELAXED
+#define MY_MEMORY_ORDER_CONSUME
+#define MY_MEMORY_ORDER_ACQUIRE
+#define MY_MEMORY_ORDER_RELEASE
+#define MY_MEMORY_ORDER_ACQ_REL
+#define MY_MEMORY_ORDER_SEQ_CST
+
+#define my_atomic_store32_explicit(P, D, O) my_atomic_store32((P), (D))
+#define my_atomic_store64_explicit(P, D, O) my_atomic_store64((P), (D))
+#define my_atomic_storeptr_explicit(P, D, O) my_atomic_storeptr((P), (D))
+
+#define my_atomic_load32_explicit(P, O) my_atomic_load32((P))
+#define my_atomic_load64_explicit(P, O) my_atomic_load64((P))
+#define my_atomic_loadptr_explicit(P, O) my_atomic_loadptr((P))
+
+#define my_atomic_fas32_explicit(P, D, O) my_atomic_fas32((P), (D))
+#define my_atomic_fas64_explicit(P, D, O) my_atomic_fas64((P), (D))
+#define my_atomic_fasptr_explicit(P, D, O) my_atomic_fasptr((P), (D))
+
+#define my_atomic_add32_explicit(P, A, O) my_atomic_add32((P), (A))
+#define my_atomic_add64_explicit(P, A, O) my_atomic_add64((P), (A))
+#define my_atomic_addptr_explicit(P, A, O) my_atomic_addptr((P), (A))
+
+#define my_atomic_cas32_weak_explicit(P, E, D, S, F) \
+  my_atomic_cas32((P), (E), (D))
+#define my_atomic_cas64_weak_explicit(P, E, D, S, F) \
+  my_atomic_cas64((P), (E), (D))
+#define my_atomic_casptr_weak_explicit(P, E, D, S, F) \
+  my_atomic_casptr((P), (E), (D))
+
+#define my_atomic_cas32_strong_explicit(P, E, D, S, F) \
+  my_atomic_cas32((P), (E), (D))
+#define my_atomic_cas64_strong_explicit(P, E, D, S, F) \
+  my_atomic_cas64((P), (E), (D))
+#define my_atomic_casptr_strong_explicit(P, E, D, S, F) \
+  my_atomic_casptr((P), (E), (D))
+#endif
+
 #endif /* MY_ATOMIC_INCLUDED */