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 <mutex>
18#include <string>
19#include <unordered_map>
20#include <utility>
21
22#include "time_zone_fixed.h"
23
24namespace absl {
25namespace time_internal {
26namespace cctz {
27
28namespace {
29
30// time_zone::Impls are linked into a map to support fast lookup by name.
31using TimeZoneImplByName =
32 std::unordered_map<std::string, const time_zone::Impl*>;
33TimeZoneImplByName* time_zone_map = nullptr;
34
35// Mutual exclusion for time_zone_map.
36std::mutex time_zone_mutex;
37
38} // namespace
39
40time_zone time_zone::Impl::UTC() {
41 return time_zone(UTCImpl());
42}
43
44bool time_zone::Impl::LoadTimeZone(const std::string& name, time_zone* tz) {
45 const time_zone::Impl* const utc_impl = UTCImpl();
46
47 // First check for UTC (which is never a key in time_zone_map).
48 auto offset = seconds::zero();
49 if (FixedOffsetFromName(name, &offset) && offset == seconds::zero()) {
50 *tz = time_zone(utc_impl);
51 return true;
52 }
53
54 // Then check, under a shared lock, whether the time zone has already
55 // been loaded. This is the common path. TODO: Move to shared_mutex.
56 {
57 std::lock_guard<std::mutex> lock(time_zone_mutex);
58 if (time_zone_map != nullptr) {
59 TimeZoneImplByName::const_iterator itr = time_zone_map->find(name);
60 if (itr != time_zone_map->end()) {
61 *tz = time_zone(itr->second);
62 return itr->second != utc_impl;
63 }
64 }
65 }
66
67 // Now check again, under an exclusive lock.
68 std::lock_guard<std::mutex> lock(time_zone_mutex);
69 if (time_zone_map == nullptr) time_zone_map = new TimeZoneImplByName;
70 const Impl*& impl = (*time_zone_map)[name];
71 if (impl == nullptr) {
72 // The first thread in loads the new time zone.
73 Impl* new_impl = new Impl(name);
74 new_impl->zone_ = TimeZoneIf::Load(new_impl->name_);
75 if (new_impl->zone_ == nullptr) {
76 delete new_impl; // free the nascent Impl
77 impl = utc_impl; // and fallback to UTC
78 } else {
79 impl = new_impl; // install new time zone
80 }
81 }
82 *tz = time_zone(impl);
83 return impl != utc_impl;
84}
85
86void time_zone::Impl::ClearTimeZoneMapTestOnly() {
87 std::lock_guard<std::mutex> lock(time_zone_mutex);
88 if (time_zone_map != nullptr) {
89 // Existing time_zone::Impl* entries are in the wild, so we simply
90 // leak them. Future requests will result in reloading the data.
91 time_zone_map->clear();
92 }
93}
94
95time_zone::Impl::Impl(const std::string& name) : name_(name) {}
96
97const time_zone::Impl* time_zone::Impl::UTCImpl() {
98 static Impl* utc_impl = [] {
99 Impl* impl = new Impl("UTC");
100 impl->zone_ = TimeZoneIf::Load(impl->name_); // never fails
101 return impl;
102 }();
103 return utc_impl;
104}
105
106} // namespace cctz
107} // namespace time_internal
108} // namespace absl
109