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
44static bool have_futex;
45static int futex_private_flag = FUTEX_PRIVATE_FLAG;
46
47namespace {
48static 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
70namespace base {
71namespace internal {
72
73void 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
95void 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