1 /*
2  * Copyright (C) 2020 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/LICENSE2.0
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 #pragma once
18 
19 #include <pthread.h>
20 
21 #include <android-base/macros.h>
22 #include <android-base/thread_annotations.h>
23 
24 // As of the end of May 2020, std::shared_mutex is *not* simply a pthread_rwlock, but rather a
25 // combination of std::mutex and std::condition variable, which is obviously less efficient.  This
26 // immitates what std::shared_mutex should be doing and is compatible with RAII thread wrappers.
27 
28 class SHARED_CAPABILITY("mutex") RwLock {
29   public:
RwLock()30     RwLock() {}
~RwLock()31     ~RwLock() {}
32 
lock()33     void lock() ACQUIRE() { pthread_rwlock_wrlock(&rwlock_); }
lock_shared()34     void lock_shared() ACQUIRE_SHARED() { pthread_rwlock_rdlock(&rwlock_); }
35 
unlock()36     void unlock() RELEASE() { pthread_rwlock_unlock(&rwlock_); }
37 
38   private:
39     pthread_rwlock_t rwlock_ = PTHREAD_RWLOCK_INITIALIZER;
40 };
41 
42 // std::shared_lock does not have thread annotations, so we need our own.
43 
44 class SCOPED_CAPABILITY SharedLock {
45   public:
SharedLock(RwLock & lock)46     explicit SharedLock(RwLock& lock) ACQUIRE_SHARED(lock) : lock_(lock) { lock_.lock_shared(); }
RELEASE()47     ~SharedLock() RELEASE() { lock_.unlock(); }
48 
lock_shared()49     void lock_shared() ACQUIRE_SHARED() { lock_.lock_shared(); }
unlock()50     void unlock() RELEASE() { lock_.unlock(); }
51 
52     DISALLOW_IMPLICIT_CONSTRUCTORS(SharedLock);
53 
54   private:
55     RwLock& lock_;
56 };
57