1 /*
2  * Copyright (C) 2018 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 #ifndef INCLUDE_PERFETTO_BASE_EVENT_H_
18 #define INCLUDE_PERFETTO_BASE_EVENT_H_
19 
20 #include "perfetto/base/build_config.h"
21 #include "perfetto/base/scoped_file.h"
22 
23 #if PERFETTO_BUILDFLAG(PERFETTO_OS_LINUX) || \
24     PERFETTO_BUILDFLAG(PERFETTO_OS_ANDROID)
25 #define PERFETTO_USE_EVENTFD() 1
26 #else
27 #define PERFETTO_USE_EVENTFD() 0
28 #endif
29 
30 namespace perfetto {
31 namespace base {
32 
33 // A waitable event that can be used with poll/select.
34 // This is really a wrapper around eventfd_create with a pipe-based fallback
35 // for other platforms where eventfd is not supported.
36 class Event {
37  public:
38   Event();
39   ~Event();
40   Event(Event&&) noexcept = default;
41   Event& operator=(Event&&) = default;
42 
43   // The non-blocking file descriptor that can be polled to wait for the event.
fd()44   int fd() const { return fd_.get(); }
45 
46   // Can be called from any thread.
47   void Notify();
48 
49   // Can be called from any thread. If more Notify() are queued a Clear() call
50   // can clear all of them (up to 16 per call).
51   void Clear();
52 
53  private:
54   // The eventfd, when eventfd is supported, otherwise this is the read end of
55   // the pipe for fallback mode.
56   ScopedFile fd_;
57 
58 #if !PERFETTO_USE_EVENTFD()
59   // The write end of the wakeup pipe.
60   ScopedFile write_fd_;
61 #endif
62 };
63 
64 }  // namespace base
65 }  // namespace perfetto
66 
67 #endif  // INCLUDE_PERFETTO_BASE_EVENT_H_
68