1 /* 2 * Copyright (C) 2021 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 <memory> 18 19 #include <android-base/result.h> 20 #include <android-base/unique_fd.h> 21 #include <utils/Errors.h> 22 23 namespace android { 24 25 /** This is not a pipe. */ 26 class FdTrigger { 27 public: 28 /** Returns nullptr for error case */ 29 static std::unique_ptr<FdTrigger> make(); 30 31 /** 32 * Close the write end of the pipe so that the read end receives POLLHUP. 33 * Not threadsafe. 34 */ 35 void trigger(); 36 37 /** 38 * Check whether this has been triggered by checking the write end. Note: 39 * this has no internal locking, and it is inherently racey, but this is 40 * okay, because if we accidentally return false when a trigger has already 41 * happened, we can imagine that instead, the scheduler actually executed 42 * the code which is polling isTriggered earlier. 43 */ 44 [[nodiscard]] bool isTriggered(); 45 46 /** 47 * Poll for a read event. 48 * 49 * event - for pollfd 50 * 51 * Return: 52 * true - time to read! 53 * false - trigger happened 54 */ 55 [[nodiscard]] status_t triggerablePoll(base::borrowed_fd fd, int16_t event); 56 57 private: 58 base::unique_fd mWrite; 59 base::unique_fd mRead; 60 }; 61 } // namespace android 62