1 /* 2 * Copyright (C) 2015 The Android Open Source Project 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * * Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * * Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in 12 * the documentation and/or other materials provided with the 13 * distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS 22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 #ifndef _BIONIC_LOCK_H 29 #define _BIONIC_LOCK_H 30 31 #include <stdatomic.h> 32 #include "private/bionic_futex.h" 33 34 class Lock { 35 private: 36 enum LockState { 37 Unlocked = 0, 38 LockedWithoutWaiter, 39 LockedWithWaiter, 40 }; 41 _Atomic(LockState) state; 42 bool process_shared; 43 44 public: 45 Lock(bool process_shared = false) { 46 init(process_shared); 47 } 48 49 void init(bool process_shared) { 50 atomic_init(&state, Unlocked); 51 this->process_shared = process_shared; 52 } 53 54 void lock() { 55 LockState old_state = Unlocked; 56 if (__predict_true(atomic_compare_exchange_strong_explicit(&state, &old_state, 57 LockedWithoutWaiter, memory_order_acquire, memory_order_relaxed))) { 58 return; 59 } 60 while (atomic_exchange_explicit(&state, LockedWithWaiter, memory_order_acquire) != Unlocked) { 61 // TODO: As the critical section is brief, it is a better choice to spin a few times befor sleeping. 62 __futex_wait_ex(&state, process_shared, LockedWithWaiter, NULL); 63 } 64 return; 65 } 66 67 void unlock() { 68 if (atomic_exchange_explicit(&state, Unlocked, memory_order_release) == LockedWithWaiter) { 69 __futex_wake_ex(&state, process_shared, 1); 70 } 71 } 72 }; 73 74 #endif // _BIONIC_LOCK_H 75