1 #pragma once 2 3 /* 4 * Copyright (C) 2017 The Android Open Source Project 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 #include <unistd.h> 20 #include <linux/futex.h> 21 #include <sys/syscall.h> 22 23 24 // Signaling mechanism that allows threads to signal changes to shared 25 // memory and to wait for signals. 26 27 namespace vsoc { 28 /** 29 * Defines the strategy for signaling among threads on a single kernel. 30 */ 31 namespace SingleSidedSignal { 32 /** 33 * Waits for a signal, assuming the the word at addr matches expected_state. 34 * Will return immediately if the value does not match. 35 * Callers must be equipped to cope with spurious returns. 36 */ 37 static void AwaitSignal(uint32_t expected_state, uint32_t* uaddr) { 38 syscall(SYS_futex, uaddr, FUTEX_WAIT, expected_state, nullptr, nullptr, 0); 39 } 40 41 /** 42 * Sends a signal to every thread in AwaitSignal() using the address in 43 * uaddr. 44 */ 45 static void Signal(std::atomic<uint32_t>* uaddr) { 46 syscall(SYS_futex, reinterpret_cast<int32_t*>(uaddr), FUTEX_WAKE, -1, nullptr, 47 nullptr, 0); 48 } 49 } // namespace SingleSidedSignal 50 } // namespace vsoc 51
