1 | // Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors |
2 | // Licensed under the MIT License: |
3 | // |
4 | // Permission is hereby granted, free of charge, to any person obtaining a copy |
5 | // of this software and associated documentation files (the "Software"), to deal |
6 | // in the Software without restriction, including without limitation the rights |
7 | // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell |
8 | // copies of the Software, and to permit persons to whom the Software is |
9 | // furnished to do so, subject to the following conditions: |
10 | // |
11 | // The above copyright notice and this permission notice shall be included in |
12 | // all copies or substantial portions of the Software. |
13 | // |
14 | // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
15 | // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
16 | // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE |
17 | // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER |
18 | // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, |
19 | // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN |
20 | // THE SOFTWARE. |
21 | |
22 | #include "refcount.h" |
23 | #include "debug.h" |
24 | |
25 | #if _MSC_VER |
26 | // Annoyingly, MSVC only implements the C++ atomic libs, not the C libs, so the only useful |
27 | // thing we can get from <atomic> seems to be atomic_thread_fence... but that one function is |
28 | // indeed not implemented by the intrinsics, so... |
29 | #include <atomic> |
30 | #endif |
31 | |
32 | namespace kj { |
33 | |
34 | // ======================================================================================= |
35 | // Non-atomic (thread-unsafe) refcounting |
36 | |
37 | Refcounted::~Refcounted() noexcept(false) { |
38 | KJ_ASSERT(refcount == 0, "Refcounted object deleted with non-zero refcount." ); |
39 | } |
40 | |
41 | void Refcounted::disposeImpl(void* pointer) const { |
42 | if (--refcount == 0) { |
43 | delete this; |
44 | } |
45 | } |
46 | |
47 | // ======================================================================================= |
48 | // Atomic (thread-safe) refcounting |
49 | |
50 | AtomicRefcounted::~AtomicRefcounted() noexcept(false) { |
51 | KJ_ASSERT(refcount == 0, "Refcounted object deleted with non-zero refcount." ); |
52 | } |
53 | |
54 | void AtomicRefcounted::disposeImpl(void* pointer) const { |
55 | #if _MSC_VER |
56 | if (KJ_MSVC_INTERLOCKED(Decrement, rel)(&refcount) == 0) { |
57 | std::atomic_thread_fence(std::memory_order_acquire); |
58 | delete this; |
59 | } |
60 | #else |
61 | if (__atomic_sub_fetch(&refcount, 1, __ATOMIC_RELEASE) == 0) { |
62 | __atomic_thread_fence(__ATOMIC_ACQUIRE); |
63 | delete this; |
64 | } |
65 | #endif |
66 | } |
67 | |
68 | bool AtomicRefcounted::addRefWeakInternal() const { |
69 | #if _MSC_VER |
70 | long orig = refcount; |
71 | |
72 | for (;;) { |
73 | if (orig == 0) { |
74 | // Refcount already hit zero. Destructor is already running so we can't revive the object. |
75 | return false; |
76 | } |
77 | |
78 | unsigned long old = KJ_MSVC_INTERLOCKED(CompareExchange, nf)(&refcount, orig + 1, orig); |
79 | if (old == orig) { |
80 | return true; |
81 | } |
82 | orig = old; |
83 | } |
84 | #else |
85 | uint orig = __atomic_load_n(&refcount, __ATOMIC_RELAXED); |
86 | |
87 | for (;;) { |
88 | if (orig == 0) { |
89 | // Refcount already hit zero. Destructor is already running so we can't revive the object. |
90 | return false; |
91 | } |
92 | |
93 | if (__atomic_compare_exchange_n(&refcount, &orig, orig + 1, true, |
94 | __ATOMIC_RELAXED, __ATOMIC_RELAXED)) { |
95 | // Successfully incremented refcount without letting it hit zero. |
96 | return true; |
97 | } |
98 | } |
99 | #endif |
100 | } |
101 | |
102 | } // namespace kj |
103 | |