1 // Copyright 2016 Google Inc. All Rights Reserved.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 #include "time_zone_impl.h"
16
17 #include <deque>
18 #include <mutex>
19 #include <string>
20 #include <unordered_map>
21 #include <utility>
22
23 #include "absl/base/config.h"
24 #include "time_zone_fixed.h"
25
26 namespace absl {
27 ABSL_NAMESPACE_BEGIN
28 namespace time_internal {
29 namespace cctz {
30
31 namespace {
32
33 // time_zone::Impls are linked into a map to support fast lookup by name.
34 using TimeZoneImplByName =
35 std::unordered_map<std::string, const time_zone::Impl*>;
36 TimeZoneImplByName* time_zone_map = nullptr;
37
38 // Mutual exclusion for time_zone_map.
TimeZoneMutex()39 std::mutex& TimeZoneMutex() {
40 // This mutex is intentionally "leaked" to avoid the static deinitialization
41 // order fiasco (std::mutex's destructor is not trivial on many platforms).
42 static std::mutex* time_zone_mutex = new std::mutex;
43 return *time_zone_mutex;
44 }
45
46 } // namespace
47
UTC()48 time_zone time_zone::Impl::UTC() { return time_zone(UTCImpl()); }
49
LoadTimeZone(const std::string & name,time_zone * tz)50 bool time_zone::Impl::LoadTimeZone(const std::string& name, time_zone* tz) {
51 const time_zone::Impl* const utc_impl = UTCImpl();
52
53 // First check for UTC (which is never a key in time_zone_map).
54 auto offset = seconds::zero();
55 if (FixedOffsetFromName(name, &offset) && offset == seconds::zero()) {
56 *tz = time_zone(utc_impl);
57 return true;
58 }
59
60 // Then check, under a shared lock, whether the time zone has already
61 // been loaded. This is the common path. TODO: Move to shared_mutex.
62 {
63 std::lock_guard<std::mutex> lock(TimeZoneMutex());
64 if (time_zone_map != nullptr) {
65 TimeZoneImplByName::const_iterator itr = time_zone_map->find(name);
66 if (itr != time_zone_map->end()) {
67 *tz = time_zone(itr->second);
68 return itr->second != utc_impl;
69 }
70 }
71 }
72
73 // Now check again, under an exclusive lock.
74 std::lock_guard<std::mutex> lock(TimeZoneMutex());
75 if (time_zone_map == nullptr) time_zone_map = new TimeZoneImplByName;
76 const Impl*& impl = (*time_zone_map)[name];
77 if (impl == nullptr) {
78 // The first thread in loads the new time zone.
79 Impl* new_impl = new Impl(name);
80 new_impl->zone_ = TimeZoneIf::Load(new_impl->name_);
81 if (new_impl->zone_ == nullptr) {
82 delete new_impl; // free the nascent Impl
83 impl = utc_impl; // and fallback to UTC
84 } else {
85 impl = new_impl; // install new time zone
86 }
87 }
88 *tz = time_zone(impl);
89 return impl != utc_impl;
90 }
91
ClearTimeZoneMapTestOnly()92 void time_zone::Impl::ClearTimeZoneMapTestOnly() {
93 std::lock_guard<std::mutex> lock(TimeZoneMutex());
94 if (time_zone_map != nullptr) {
95 // Existing time_zone::Impl* entries are in the wild, so we can't delete
96 // them. Instead, we move them to a private container, where they are
97 // logically unreachable but not "leaked". Future requests will result
98 // in reloading the data.
99 static auto* cleared = new std::deque<const time_zone::Impl*>;
100 for (const auto& element : *time_zone_map) {
101 cleared->push_back(element.second);
102 }
103 time_zone_map->clear();
104 }
105 }
106
Impl(const std::string & name)107 time_zone::Impl::Impl(const std::string& name) : name_(name) {}
108
UTCImpl()109 const time_zone::Impl* time_zone::Impl::UTCImpl() {
110 static Impl* utc_impl = [] {
111 Impl* impl = new Impl("UTC");
112 impl->zone_ = TimeZoneIf::Load(impl->name_); // never fails
113 return impl;
114 }();
115 return utc_impl;
116 }
117
118 } // namespace cctz
119 } // namespace time_internal
120 ABSL_NAMESPACE_END
121 } // namespace absl
122