1 /* Copyright (c) 2009, Google Inc. 2 * All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions are 6 * met: 7 * 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 11 * copyright notice, this list of conditions and the following disclaimer 12 * in the documentation and/or other materials provided with the 13 * distribution. 14 * * Neither the name of Google Inc. nor the names of its 15 * contributors may be used to endorse or promote products derived from 16 * this software without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 19 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 20 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 21 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 22 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 28 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29 * 30 * --- 31 * This file is a Linux-specific part of spinlock_internal.cc 32 */ 33 34 #include <errno.h> 35 #include <sched.h> 36 #include <time.h> 37 #include <limits.h> 38 #include "base/linux_syscall_support.h" 39 40 #define FUTEX_WAIT 0 41 #define FUTEX_WAKE 1 42 #define FUTEX_PRIVATE_FLAG 128 43 44 static bool have_futex; 45 static int futex_private_flag = FUTEX_PRIVATE_FLAG; 46 47 namespace { 48 static struct InitModule { 49 InitModule() { 50 int x = 0; 51 // futexes are ints, so we can use them only when 52 // that's the same size as the lockword_ in SpinLock. 53 #ifdef __arm__ 54 // ARM linux doesn't support sys_futex1(void*, int, int, struct timespec*); 55 have_futex = 0; 56 #else 57 have_futex = (sizeof (Atomic32) == sizeof (int) && 58 sys_futex(&x, FUTEX_WAKE, 1, 0) >= 0); 59 #endif 60 if (have_futex && 61 sys_futex(&x, FUTEX_WAKE | futex_private_flag, 1, 0) < 0) { 62 futex_private_flag = 0; 63 } 64 } 65 } init_module; 66 67 } // anonymous namespace 68 69 70 namespace base { 71 namespace internal { 72 73 void SpinLockDelay(volatile Atomic32 *w, int32 value, int loop) { 74 if (loop != 0) { 75 int save_errno = errno; 76 struct timespec tm; 77 tm.tv_sec = 0; 78 if (have_futex) { 79 tm.tv_nsec = base::internal::SuggestedDelayNS(loop); 80 } else { 81 tm.tv_nsec = 2000001; // above 2ms so linux 2.4 doesn't spin 82 } 83 if (have_futex) { 84 tm.tv_nsec *= 16; // increase the delay; we expect explicit wakeups 85 sys_futex(reinterpret_cast<int *>(const_cast<Atomic32 *>(w)), 86 FUTEX_WAIT | futex_private_flag, 87 value, reinterpret_cast<struct kernel_timespec *>(&tm)); 88 } else { 89 nanosleep(&tm, NULL); 90 } 91 errno = save_errno; 92 } 93 } 94 95 void SpinLockWake(volatile Atomic32 *w, bool all) { 96 if (have_futex) { 97 sys_futex(reinterpret_cast<int *>(const_cast<Atomic32 *>(w)), 98 FUTEX_WAKE | futex_private_flag, all? INT_MAX : 1, 0); 99 } 100 } 101 102 } // namespace internal 103 } // namespace base 104
