1 | //===- ThreadSafeAllocator.h ------------------------------------*- C++ -*-===// |
2 | // |
3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
4 | // See https://llvm.org/LICENSE.txt for license information. |
5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
6 | // |
7 | //===----------------------------------------------------------------------===// |
8 | |
9 | #ifndef LLVM_SUPPORT_THREADSAFEALLOCATOR_H |
10 | #define LLVM_SUPPORT_THREADSAFEALLOCATOR_H |
11 | |
12 | #include "llvm/ADT/STLExtras.h" |
13 | #include "llvm/Support/Allocator.h" |
14 | #include <atomic> |
15 | |
16 | namespace llvm { |
17 | |
18 | /// Thread-safe allocator adaptor. Uses a spin lock on the assumption that |
19 | /// contention here is extremely rare. |
20 | /// |
21 | /// TODO: Using a spin lock on every allocation can be quite expensive when |
22 | /// contention is high. Since this is mainly used for BumpPtrAllocator and |
23 | /// SpecificBumpPtrAllocator, it'd be better to have a specific thread-safe |
24 | /// BumpPtrAllocator implementation that only use a fair lock when allocating a |
25 | /// new slab but otherwise using atomic and be lock-free. |
26 | template <class AllocatorType> class ThreadSafeAllocator { |
27 | struct LockGuard { |
28 | LockGuard(std::atomic_flag &Flag) : Flag(Flag) { |
29 | if (LLVM_UNLIKELY(Flag.test_and_set(std::memory_order_acquire))) |
30 | while (Flag.test_and_set(m: std::memory_order_acquire)) { |
31 | } |
32 | } |
33 | ~LockGuard() { Flag.clear(m: std::memory_order_release); } |
34 | std::atomic_flag &Flag; |
35 | }; |
36 | |
37 | public: |
38 | auto Allocate(size_t N) { |
39 | return applyLocked([N](AllocatorType &Alloc) { return Alloc.Allocate(N); }); |
40 | } |
41 | |
42 | auto Allocate(size_t Size, size_t Align) { |
43 | return applyLocked([Size, Align](AllocatorType &Alloc) { |
44 | return Alloc.Allocate(Size, Align); |
45 | }); |
46 | } |
47 | |
48 | template <typename FnT, |
49 | typename T = typename llvm::function_traits<FnT>::result_t> |
50 | T applyLocked(FnT Fn) { |
51 | LockGuard Lock(Flag); |
52 | return Fn(Alloc); |
53 | } |
54 | |
55 | private: |
56 | AllocatorType Alloc; |
57 | std::atomic_flag Flag = ATOMIC_FLAG_INIT; |
58 | }; |
59 | |
60 | } // namespace llvm |
61 | |
62 | #endif // LLVM_SUPPORT_THREADSAFEALLOCATOR_H |
63 | |