refcount.c++ (3461B)
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 && !defined(__clang__) 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 && !defined(__clang__) 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 && !defined(__clang__) 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