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      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.
     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