1 /*
2  * Copyright (C) 2023 The Android Open Source Project
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 "berberis/runtime_primitives/signal_queue.h"
18 
19 #include <atomic>
20 
21 #include "berberis/base/forever_pool.h"
22 
23 namespace berberis {
24 
AllocSignal()25 siginfo_t* SignalQueue::AllocSignal() {
26   Node* node = ForeverPool<Node>::Alloc();
27   return &node->info;
28 }
29 
EnqueueSignal(siginfo_t * info)30 void SignalQueue::EnqueueSignal(siginfo_t* info) {
31   Node* node = reinterpret_cast<Node*>(info);
32   Node* produced = produced_.load(std::memory_order_relaxed);
33   do {
34     node->next = produced;
35   } while (!produced_.compare_exchange_weak(produced, node, std::memory_order_release));
36 }
37 
DequeueSignalUnsafe()38 siginfo_t* SignalQueue::DequeueSignalUnsafe() {
39   // Pick everything produced so far.
40   Node* produced = produced_.exchange(nullptr, std::memory_order_acquire);
41 
42   // Put in front of consumed.
43   if (produced) {
44     Node* last = produced;
45     while (last->next) {
46       last = last->next;
47     }
48     last->next = consumed_;
49     consumed_ = produced;
50   }
51 
52   if (!consumed_) {
53     return nullptr;
54   }
55 
56   // Consumed is in reverse order of arrival.
57   Node** best_p = &consumed_;
58   for (Node** curr_p = &consumed_->next; *curr_p; curr_p = &(*curr_p)->next) {
59     // As the list is in reverse order, use '<=' to get last match.
60     if ((*curr_p)->info.si_signo <= (*best_p)->info.si_signo) {
61       best_p = curr_p;
62     }
63   }
64 
65   Node* best = *best_p;
66   *best_p = best->next;
67 
68   return &best->info;
69 }
70 
FreeSignal(siginfo_t * info)71 void SignalQueue::FreeSignal(siginfo_t* info) {
72   ForeverPool<Node>::Free(reinterpret_cast<Node*>(info));
73 }
74 
75 }  // namespace berberis
76