From 2eba343b51e0923cd3fb919a6abd6120590fc059 Mon Sep 17 00:00:00 2001
From: Abseil Team <absl-team@google.com>
Date: Tue, 9 Jun 2020 08:17:12 -0700
Subject: Export of internal Abseil changes

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baf626d27ff1547776745f3b601cc42f703d4bdf by Greg Falcon <gfalcon@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 315486679

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39d4e7f9214c5a74e4ee4b8a7f4af26479925029 by Gennadiy Rozental <rogeeff@google.com>:

Avoid order dependant test cases.

PiperOrigin-RevId: 315327948

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8feb187703a28bb0c5cfc5dd6091e3faa90a8e61 by Gennadiy Rozental <rogeeff@google.com>:

Avoid order dependant test cases.

PiperOrigin-RevId: 315317018

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cffd8fddad15908ec9de7f21f65b20528972e3fa by Gennadiy Rozental <rogeeff@google.com>:

Avoid order dependant test cases.

PiperOrigin-RevId: 315311587

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48997a0ceb231b75c14eb4b1eb3b66af69e49f42 by Tom Manshreck <shreck@google.com>:

Nit: remove extra "the"

PiperOrigin-RevId: 314959763

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9516f44a4b5d3055427c95e80c8c04a6321e4221 by Gennadiy Rozental <rogeeff@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 314925147

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4f8691d74a4eb42ed03ef29c9588a01b78829941 by Abseil Team <absl-team@google.com>:

Uninclude util/bits/bits.h

PiperOrigin-RevId: 314858384

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02b42a8ec5e5561b29b4e5f93cc1482c3c72ef2d by Abseil Team <absl-team@google.com>:

Google-internal changes only.

PiperOrigin-RevId: 314855667

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146013d69dabafbe2030e23ced7b741d9e8d417c by Gennadiy Rozental <rogeeff@google.com>:

Uninclude util/bits/bits.h

PiperOrigin-RevId: 314838927
GitOrigin-RevId: baf626d27ff1547776745f3b601cc42f703d4bdf
Change-Id: I2602286fb13cf35a88bdd80fe0b44974d4388d46
---
 absl/time/internal/cctz/src/time_zone_impl.cc | 34 ++++++++++-----------------
 1 file changed, 13 insertions(+), 21 deletions(-)

(limited to 'absl/time/internal/cctz/src/time_zone_impl.cc')

diff --git a/absl/time/internal/cctz/src/time_zone_impl.cc b/absl/time/internal/cctz/src/time_zone_impl.cc
index 030ae0e1..f34e3aec 100644
--- a/absl/time/internal/cctz/src/time_zone_impl.cc
+++ b/absl/time/internal/cctz/src/time_zone_impl.cc
@@ -15,6 +15,7 @@
 #include "time_zone_impl.h"
 
 #include <deque>
+#include <memory>
 #include <mutex>
 #include <string>
 #include <unordered_map>
@@ -48,17 +49,16 @@ std::mutex& TimeZoneMutex() {
 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();
+  const Impl* const utc_impl = UTCImpl();
 
-  // First check for UTC (which is never a key in time_zone_map).
+  // 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.
+  // Check whether the time zone has already been loaded.
   {
     std::lock_guard<std::mutex> lock(TimeZoneMutex());
     if (time_zone_map != nullptr) {
@@ -70,20 +70,15 @@ bool time_zone::Impl::LoadTimeZone(const std::string& name, time_zone* tz) {
     }
   }
 
-  // Now check again, under an exclusive lock.
+  // Load the new time zone (outside the lock).
+  std::unique_ptr<const Impl> new_impl(new Impl(name));
+
+  // Add the new time zone to the map.
   std::lock_guard<std::mutex> lock(TimeZoneMutex());
   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
-    }
+  if (impl == nullptr) {  // this thread won any load race
+    impl = new_impl->zone_ ? new_impl.release() : utc_impl;
   }
   *tz = time_zone(impl);
   return impl != utc_impl;
@@ -104,14 +99,11 @@ void time_zone::Impl::ClearTimeZoneMapTestOnly() {
   }
 }
 
-time_zone::Impl::Impl(const std::string& name) : name_(name) {}
+time_zone::Impl::Impl(const std::string& name)
+    : name_(name), zone_(TimeZoneIf::Load(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;
-  }();
+  static const Impl* utc_impl = new Impl("UTC");  // never fails
   return utc_impl;
 }
 
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