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// Copyright 2016 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "time_zone_impl.h"
#include <mutex>
#include <string>
#include <unordered_map>
#include <utility>
#include "time_zone_fixed.h"
namespace absl {
namespace time_internal {
namespace cctz {
namespace {
// time_zone::Impls are linked into a map to support fast lookup by name.
using TimeZoneImplByName =
std::unordered_map<std::string, const time_zone::Impl*>;
TimeZoneImplByName* time_zone_map = nullptr;
// Mutual exclusion for time_zone_map.
std::mutex time_zone_mutex;
} // namespace
time_zone time_zone::Impl::UTC() {
return time_zone(UTCImpl());
}
bool time_zone::Impl::LoadTimeZone(const std::string& name, time_zone* tz) {
const time_zone::Impl* const utc_impl = UTCImpl();
// First check for UTC (which is never a key in time_zone_map).
auto offset = seconds::zero();
if (FixedOffsetFromName(name, &offset) && offset == seconds::zero()) {
*tz = time_zone(utc_impl);
return true;
}
// Then check, under a shared lock, whether the time zone has already
// been loaded. This is the common path. TODO: Move to shared_mutex.
{
std::lock_guard<std::mutex> lock(time_zone_mutex);
if (time_zone_map != nullptr) {
TimeZoneImplByName::const_iterator itr = time_zone_map->find(name);
if (itr != time_zone_map->end()) {
*tz = time_zone(itr->second);
return itr->second != utc_impl;
}
}
}
// Now check again, under an exclusive lock.
std::lock_guard<std::mutex> lock(time_zone_mutex);
if (time_zone_map == nullptr) time_zone_map = new TimeZoneImplByName;
const Impl*& impl = (*time_zone_map)[name];
if (impl == nullptr) {
// The first thread in loads the new time zone.
Impl* new_impl = new Impl(name);
new_impl->zone_ = TimeZoneIf::Load(new_impl->name_);
if (new_impl->zone_ == nullptr) {
delete new_impl; // free the nascent Impl
impl = utc_impl; // and fallback to UTC
} else {
impl = new_impl; // install new time zone
}
}
*tz = time_zone(impl);
return impl != utc_impl;
}
const time_zone::Impl& time_zone::Impl::get(const time_zone& tz) {
if (tz.impl_ == nullptr) {
// Dereferencing an implicit-UTC time_zone is expected to be
// rare, so we don't mind paying a small synchronization cost.
return *UTCImpl();
}
return *tz.impl_;
}
void time_zone::Impl::ClearTimeZoneMapTestOnly() {
std::lock_guard<std::mutex> lock(time_zone_mutex);
if (time_zone_map != nullptr) {
// Existing time_zone::Impl* entries are in the wild, so we simply
// leak them. Future requests will result in reloading the data.
time_zone_map->clear();
}
}
time_zone::Impl::Impl(const std::string& name) : name_(name) {}
const time_zone::Impl* time_zone::Impl::UTCImpl() {
static Impl* utc_impl = [] {
Impl* impl = new Impl("UTC");
impl->zone_ = TimeZoneIf::Load(impl->name_); // never fails
return impl;
}();
return utc_impl;
}
} // namespace cctz
} // namespace time_internal
} // namespace absl
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