1 /*
2 * Copyright 2015 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8 #ifndef SkAtomics_sync_DEFINED
9 #define SkAtomics_sync_DEFINED
10
11 // This file is mostly a shim. We'd like to delete it. Please don't put much
12 // effort into maintaining it, and if you find bugs in it, the right fix is to
13 // delete this file and upgrade your compiler to something that supports
14 // __atomic builtins or std::atomic.
15
barrier(sk_memory_order mo)16 static inline void barrier(sk_memory_order mo) {
17 asm volatile("" : : : "memory"); // Prevents the compiler from reordering code.
18 #if SK_CPU_X86
19 // On x86, we generally don't need an extra memory barrier for loads or stores.
20 if (sk_memory_order_seq_cst == mo) { __sync_synchronize(); }
21 #else
22 // On other platforms (e.g. ARM) we do unless the memory order is relaxed.
23 if (sk_memory_order_relaxed != mo) { __sync_synchronize(); }
24 #endif
25 }
26
27 // These barriers only support our majority use cases: acquire and relaxed loads, release stores.
28 // For anything more complicated, please consider deleting this file and upgrading your compiler.
29
30 template <typename T>
sk_atomic_load(const T * ptr,sk_memory_order mo)31 T sk_atomic_load(const T* ptr, sk_memory_order mo) {
32 T val = *ptr;
33 barrier(mo);
34 return val;
35 }
36
37 template <typename T>
sk_atomic_store(T * ptr,T val,sk_memory_order mo)38 void sk_atomic_store(T* ptr, T val, sk_memory_order mo) {
39 barrier(mo);
40 *ptr = val;
41 }
42
43 template <typename T>
sk_atomic_fetch_add(T * ptr,T val,sk_memory_order)44 T sk_atomic_fetch_add(T* ptr, T val, sk_memory_order) {
45 return __sync_fetch_and_add(ptr, val);
46 }
47
48 template <typename T>
sk_atomic_compare_exchange(T * ptr,T * expected,T desired,sk_memory_order,sk_memory_order)49 bool sk_atomic_compare_exchange(T* ptr, T* expected, T desired, sk_memory_order, sk_memory_order) {
50 T prev = __sync_val_compare_and_swap(ptr, *expected, desired);
51 if (prev == *expected) {
52 return true;
53 }
54 *expected = prev;
55 return false;
56 }
57
58 template <typename T>
sk_atomic_exchange(T * ptr,T val,sk_memory_order)59 T sk_atomic_exchange(T* ptr, T val, sk_memory_order) {
60 // There is no __sync exchange. Emulate it with a CAS loop.
61 T prev;
62 do {
63 prev = sk_atomic_load(ptr);
64 } while(!sk_atomic_compare_exchange(ptr, &prev, val));
65 return prev;
66 }
67
68 #endif//SkAtomics_sync_DEFINED
69