1/*
2 * Copyright 2016-present Facebook, Inc.
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 <folly/ClockGettimeWrappers.h>
18#include <folly/Likely.h>
19#include <folly/portability/Time.h>
20
21#include <chrono>
22
23#include <time.h>
24
25#ifndef _WIN32
26#define _GNU_SOURCE 1
27#include <dlfcn.h>
28#endif
29
30namespace folly {
31namespace chrono {
32
33static int64_t clock_gettime_ns_fallback(clockid_t clock) {
34 struct timespec ts;
35 int r = clock_gettime(clock, &ts);
36 if (UNLIKELY(r != 0)) {
37 // Mimic what __clock_gettime_ns does (even though this can be a legit
38 // value).
39 return -1;
40 }
41 std::chrono::nanoseconds result =
42 std::chrono::seconds(ts.tv_sec) + std::chrono::nanoseconds(ts.tv_nsec);
43 return result.count();
44}
45
46// Initialize with default behavior, which we might override on Linux hosts
47// with VDSO support.
48int (*clock_gettime)(clockid_t, timespec* ts) = &::clock_gettime;
49int64_t (*clock_gettime_ns)(clockid_t) = &clock_gettime_ns_fallback;
50
51#ifdef FOLLY_HAVE_LINUX_VDSO
52
53namespace {
54
55struct VdsoInitializer {
56 VdsoInitializer() {
57 m_handle = dlopen("linux-vdso.so.1", RTLD_LAZY | RTLD_LOCAL | RTLD_NOLOAD);
58 if (!m_handle) {
59 return;
60 }
61
62 void* p = dlsym(m_handle, "__vdso_clock_gettime");
63 if (p) {
64 folly::chrono::clock_gettime = (int (*)(clockid_t, timespec*))p;
65 }
66 p = dlsym(m_handle, "__vdso_clock_gettime_ns");
67 if (p) {
68 folly::chrono::clock_gettime_ns = (int64_t(*)(clockid_t))p;
69 }
70 }
71
72 ~VdsoInitializer() {
73 if (m_handle) {
74 clock_gettime = &::clock_gettime;
75 clock_gettime_ns = &clock_gettime_ns_fallback;
76 dlclose(m_handle);
77 }
78 }
79
80 private:
81 void* m_handle;
82};
83
84static const VdsoInitializer vdso_initializer;
85} // namespace
86
87#endif
88} // namespace chrono
89} // namespace folly
90