1 | /* |
2 | * Copyright 2018-present Facebook, Inc. |
3 | * |
4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
5 | * you may not use this file except in compliance with the License. |
6 | * You may obtain a copy of the License at |
7 | * |
8 | * http://www.apache.org/licenses/LICENSE-2.0 |
9 | * |
10 | * Unless required by applicable law or agreed to in writing, software |
11 | * distributed under the License is distributed on an "AS IS" BASIS, |
12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
13 | * See the License for the specific language governing permissions and |
14 | * limitations under the License. |
15 | */ |
16 | |
17 | #include <folly/Portability.h> |
18 | |
19 | #if FOLLY_HAS_COROUTINES |
20 | |
21 | #include <folly/experimental/coro/SharedMutex.h> |
22 | |
23 | using namespace folly::coro; |
24 | |
25 | SharedMutexFair::~SharedMutexFair() { |
26 | assert(state_->lockedFlagAndReaderCount_ == kUnlocked); |
27 | assert(state_->waitersHead_ == nullptr); |
28 | } |
29 | |
30 | bool SharedMutexFair::try_lock() noexcept { |
31 | auto lock = state_.contextualLock(); |
32 | if (lock->lockedFlagAndReaderCount_ == kUnlocked) { |
33 | lock->lockedFlagAndReaderCount_ = kExclusiveLockFlag; |
34 | return true; |
35 | } |
36 | return false; |
37 | } |
38 | |
39 | bool SharedMutexFair::try_lock_shared() noexcept { |
40 | auto lock = state_.contextualLock(); |
41 | if (lock->lockedFlagAndReaderCount_ == kUnlocked || |
42 | (lock->lockedFlagAndReaderCount_ >= kSharedLockCountIncrement && |
43 | lock->waitersHead_ == nullptr)) { |
44 | lock->lockedFlagAndReaderCount_ += kSharedLockCountIncrement; |
45 | return true; |
46 | } |
47 | return false; |
48 | } |
49 | |
50 | void SharedMutexFair::unlock() noexcept { |
51 | LockAwaiterBase* awaitersToResume = nullptr; |
52 | { |
53 | auto lockedState = state_.contextualLock(); |
54 | assert(lockedState->lockedFlagAndReaderCount_ == kExclusiveLockFlag); |
55 | awaitersToResume = unlockOrGetNextWaitersToResume(*lockedState); |
56 | } |
57 | |
58 | resumeWaiters(awaitersToResume); |
59 | } |
60 | |
61 | void SharedMutexFair::unlock_shared() noexcept { |
62 | LockAwaiterBase* awaitersToResume = nullptr; |
63 | { |
64 | auto lockedState = state_.contextualLock(); |
65 | assert(lockedState->lockedFlagAndReaderCount_ >= kSharedLockCountIncrement); |
66 | lockedState->lockedFlagAndReaderCount_ -= kSharedLockCountIncrement; |
67 | if (lockedState->lockedFlagAndReaderCount_ != kUnlocked) { |
68 | return; |
69 | } |
70 | |
71 | awaitersToResume = unlockOrGetNextWaitersToResume(*lockedState); |
72 | } |
73 | |
74 | resumeWaiters(awaitersToResume); |
75 | } |
76 | |
77 | SharedMutexFair::LockAwaiterBase* |
78 | SharedMutexFair::unlockOrGetNextWaitersToResume( |
79 | SharedMutexFair::State& state) noexcept { |
80 | auto* head = state.waitersHead_; |
81 | if (head != nullptr) { |
82 | if (head->lockType_ == LockType::EXCLUSIVE) { |
83 | state.waitersHead_ = std::exchange(head->nextAwaiter_, nullptr); |
84 | state.lockedFlagAndReaderCount_ = kExclusiveLockFlag; |
85 | } else { |
86 | std::size_t newState = kSharedLockCountIncrement; |
87 | |
88 | // Scan for a run of SHARED lock types. |
89 | auto* last = head; |
90 | auto* next = last->nextAwaiter_; |
91 | while (next != nullptr && next->lockType_ == LockType::SHARED) { |
92 | last = next; |
93 | next = next->nextAwaiter_; |
94 | newState += kSharedLockCountIncrement; |
95 | } |
96 | |
97 | last->nextAwaiter_ = nullptr; |
98 | state.lockedFlagAndReaderCount_ = newState; |
99 | state.waitersHead_ = next; |
100 | } |
101 | |
102 | if (state.waitersHead_ == nullptr) { |
103 | state.waitersTailNext_ = &state.waitersHead_; |
104 | } |
105 | } else { |
106 | state.lockedFlagAndReaderCount_ = kUnlocked; |
107 | } |
108 | |
109 | return head; |
110 | } |
111 | |
112 | void SharedMutexFair::resumeWaiters(LockAwaiterBase* awaiters) noexcept { |
113 | while (awaiters != nullptr) { |
114 | std::exchange(awaiters, awaiters->nextAwaiter_)->resume(); |
115 | } |
116 | } |
117 | |
118 | #endif |
119 | |