Creation of LTS branch "lts_2018_12_18"20181200

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GitOrigin-RevId: 44b0fafc62d9b8f192e8180cbe9c4b806b339d57
Change-Id: I2c427b5b41b2d34101922048b00f3d9dafcb498d

29 files changed, 614 insertions, 337 deletions

diff --git a/absl/synchronization/BUILD.bazel b/absl/synchronization/BUILD.bazel
index 372874e1..e63b1d16 100644
--- a/absl/synchronization/BUILD.bazel
+++ b/absl/synchronization/BUILD.bazel
@@ -88,6 +88,9 @@ cc_test(
     size = "small",
     srcs = ["barrier_test.cc"],
     copts = ABSL_TEST_COPTS,
+    tags = [
+        "no_test_wasm",
+    ],
     deps = [
         ":synchronization",
         "//absl/time",
@@ -100,6 +103,9 @@ cc_test(
     size = "small",
     srcs = ["blocking_counter_test.cc"],
     copts = ABSL_TEST_COPTS,
+    tags = [
+        "no_test_wasm",
+    ],
     deps = [
         ":synchronization",
         "//absl/time",
@@ -138,6 +144,9 @@ cc_library(
     name = "thread_pool",
     testonly = 1,
     hdrs = ["internal/thread_pool.h"],
+    visibility = [
+        "//absl:__subpackages__",
+    ],
     deps = [
         ":synchronization",
         "//absl/base:core_headers",
@@ -149,6 +158,7 @@ cc_test(
     size = "large",
     srcs = ["mutex_test.cc"],
     copts = ABSL_TEST_COPTS,
+    shard_count = 25,
     deps = [
         ":synchronization",
         ":thread_pool",
@@ -160,18 +170,32 @@ cc_test(
     ],
 )
 
-cc_test(
-    name = "mutex_benchmark",
+cc_library(
+    name = "mutex_benchmark_common",
+    testonly = 1,
     srcs = ["mutex_benchmark.cc"],
-    copts = ABSL_TEST_COPTS,
-    tags = ["benchmark"],
-    visibility = ["//visibility:private"],
+    copts = ABSL_DEFAULT_COPTS,
+    visibility = [
+        "//absl/synchronization:__pkg__",
+    ],
     deps = [
         ":synchronization",
         ":thread_pool",
         "//absl/base",
+        "//absl/base:base_internal",
         "@com_github_google_benchmark//:benchmark_main",
     ],
+    alwayslink = 1,
+)
+
+cc_binary(
+    name = "mutex_benchmark",
+    testonly = 1,
+    copts = ABSL_DEFAULT_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":mutex_benchmark_common",
+    ],
 )
 
 cc_test(
@@ -205,6 +229,7 @@ cc_test(
     name = "per_thread_sem_test",
     size = "medium",
     copts = ABSL_TEST_COPTS,
+    tags = ["no_test_wasm"],
     deps = [
         ":per_thread_sem_test_common",
         ":synchronization",
@@ -225,6 +250,7 @@ cc_test(
         "//absl:windows": [],
         "//conditions:default": ["-pthread"],
     }),
+    tags = ["no_test_ios_x86_64"],
     deps = [
         ":synchronization",
         "//absl/base",
diff --git a/absl/synchronization/CMakeLists.txt b/absl/synchronization/CMakeLists.txt
index c19f5725..de0d7b7d 100644
--- a/absl/synchronization/CMakeLists.txt
+++ b/absl/synchronization/CMakeLists.txt
@@ -34,7 +34,7 @@ list(APPEND SYNCHRONIZATION_INTERNAL_HEADERS
 
 
 # synchronization library
-list(APPEND SYNCHRONIZATION_SRC 
+list(APPEND SYNCHRONIZATION_SRC
   "barrier.cc"
   "blocking_counter.cc"
   "internal/create_thread_identity.cc"
diff --git a/absl/synchronization/barrier.cc b/absl/synchronization/barrier.cc
index 545bb891..ee66c240 100644
--- a/absl/synchronization/barrier.cc
+++ b/absl/synchronization/barrier.cc
@@ -18,7 +18,7 @@
 #include "absl/synchronization/mutex.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 
 // Return whether int *arg is zero.
 static bool IsZero(void *arg) {
@@ -48,5 +48,5 @@ bool Barrier::Block() {
   return this->num_to_exit_ == 0;
 }
 
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/synchronization/barrier.h b/absl/synchronization/barrier.h
index ccae0a4c..77ac3602 100644
--- a/absl/synchronization/barrier.h
+++ b/absl/synchronization/barrier.h
@@ -23,7 +23,7 @@
 #include "absl/synchronization/mutex.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 
 // Barrier
 //
@@ -74,6 +74,6 @@ class Barrier {
   int num_to_exit_ GUARDED_BY(lock_);
 };
 
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 #endif  // ABSL_SYNCHRONIZATION_BARRIER_H_
diff --git a/absl/synchronization/blocking_counter.cc b/absl/synchronization/blocking_counter.cc
index f998099a..82d889a9 100644
--- a/absl/synchronization/blocking_counter.cc
+++ b/absl/synchronization/blocking_counter.cc
@@ -17,7 +17,7 @@
 #include "absl/base/internal/raw_logging.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 
 // Return whether int *arg is zero.
 static bool IsZero(void *arg) {
@@ -53,5 +53,5 @@ void BlockingCounter::Wait() {
   // after we return from this method.
 }
 
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/synchronization/blocking_counter.h b/absl/synchronization/blocking_counter.h
index 08b6f58c..554e396c 100644
--- a/absl/synchronization/blocking_counter.h
+++ b/absl/synchronization/blocking_counter.h
@@ -24,7 +24,7 @@
 #include "absl/synchronization/mutex.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 
 // BlockingCounter
 //
@@ -93,7 +93,7 @@ class BlockingCounter {
   int num_waiting_ GUARDED_BY(lock_);
 };
 
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_SYNCHRONIZATION_BLOCKING_COUNTER_H_
diff --git a/absl/synchronization/blocking_counter_test.cc b/absl/synchronization/blocking_counter_test.cc
index 486aa9b1..b3b55dd7 100644
--- a/absl/synchronization/blocking_counter_test.cc
+++ b/absl/synchronization/blocking_counter_test.cc
@@ -22,7 +22,7 @@
 #include "absl/time/time.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace {
 
 void PauseAndDecreaseCounter(BlockingCounter* counter, int* done) {
@@ -64,5 +64,5 @@ TEST(BlockingCounterTest, BasicFunctionality) {
 }
 
 }  // namespace
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/synchronization/internal/create_thread_identity.cc b/absl/synchronization/internal/create_thread_identity.cc
index 38cc7e2f..f27f16da 100644
--- a/absl/synchronization/internal/create_thread_identity.cc
+++ b/absl/synchronization/internal/create_thread_identity.cc
@@ -27,7 +27,7 @@
 #include "absl/synchronization/internal/per_thread_sem.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace synchronization_internal {
 
 // ThreadIdentity storage is persistent, we maintain a free-list of previously
@@ -108,7 +108,7 @@ base_internal::ThreadIdentity* CreateThreadIdentity() {
 }
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_LOW_LEVEL_ALLOC_MISSING
diff --git a/absl/synchronization/internal/create_thread_identity.h b/absl/synchronization/internal/create_thread_identity.h
index 05b5f7e1..1132d516 100644
--- a/absl/synchronization/internal/create_thread_identity.h
+++ b/absl/synchronization/internal/create_thread_identity.h
@@ -29,7 +29,7 @@
 #include "absl/base/port.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace synchronization_internal {
 
 // Allocates and attaches a ThreadIdentity object for the calling thread.
@@ -50,6 +50,6 @@ inline base_internal::ThreadIdentity* GetOrCreateCurrentThreadIdentity() {
 }
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 #endif  // ABSL_SYNCHRONIZATION_INTERNAL_CREATE_THREAD_IDENTITY_H_
diff --git a/absl/synchronization/internal/graphcycles.cc b/absl/synchronization/internal/graphcycles.cc
index 5a015844..139be0f5 100644
--- a/absl/synchronization/internal/graphcycles.cc
+++ b/absl/synchronization/internal/graphcycles.cc
@@ -44,7 +44,7 @@
 // Do not use STL.   This module does not use standard memory allocation.
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace synchronization_internal {
 
 namespace {
@@ -205,8 +205,7 @@ class NodeSet {
   }
 
  private:
-  static const int32_t kEmpty;
-  static const int32_t kDel;
+  enum : int32_t { kEmpty = -1, kDel = -2 };
   Vec<int32_t> table_;
   uint32_t occupied_;     // Count of non-empty slots (includes deleted slots)
 
@@ -256,9 +255,6 @@ class NodeSet {
   NodeSet& operator=(const NodeSet&) = delete;
 };
 
-const int32_t NodeSet::kEmpty = -1;
-const int32_t NodeSet::kDel = -2;
-
 // We encode a node index and a node version in GraphId.  The version
 // number is incremented when the GraphId is freed which automatically
 // invalidates all copies of the GraphId.
@@ -695,7 +691,7 @@ int GraphCycles::GetStackTrace(GraphId id, void*** ptr) {
 }
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_LOW_LEVEL_ALLOC_MISSING
diff --git a/absl/synchronization/internal/graphcycles.h b/absl/synchronization/internal/graphcycles.h
index e43ae26b..6609ea06 100644
--- a/absl/synchronization/internal/graphcycles.h
+++ b/absl/synchronization/internal/graphcycles.h
@@ -41,7 +41,7 @@
 #include <cstdint>
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace synchronization_internal {
 
 // Opaque identifier for a graph node.
@@ -133,7 +133,7 @@ class GraphCycles {
 };
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif
diff --git a/absl/synchronization/internal/graphcycles_test.cc b/absl/synchronization/internal/graphcycles_test.cc
index 09332bad..4dc2bdc5 100644
--- a/absl/synchronization/internal/graphcycles_test.cc
+++ b/absl/synchronization/internal/graphcycles_test.cc
@@ -25,7 +25,7 @@
 #include "absl/base/macros.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace synchronization_internal {
 
 // We emulate a GraphCycles object with a node vector and an edge vector.
@@ -460,5 +460,5 @@ TEST_F(GraphCyclesTest, ManyEdges) {
 }
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/synchronization/internal/kernel_timeout.h b/absl/synchronization/internal/kernel_timeout.h
index 3d3dc0cb..34ae94ec 100644
--- a/absl/synchronization/internal/kernel_timeout.h
+++ b/absl/synchronization/internal/kernel_timeout.h
@@ -25,9 +25,6 @@
 #ifndef ABSL_SYNCHRONIZATION_INTERNAL_KERNEL_TIMEOUT_H_
 #define ABSL_SYNCHRONIZATION_INTERNAL_KERNEL_TIMEOUT_H_
 
-#ifdef _WIN32
-#include <intsafe.h>
-#endif
 #include <time.h>
 #include <algorithm>
 #include <limits>
@@ -37,7 +34,7 @@
 #include "absl/time/time.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace synchronization_internal {
 
 class Futex;
@@ -80,7 +77,7 @@ class KernelTimeout {
     if (x <= 0) x = 1;
     // A time larger than what can be represented to the kernel is treated
     // as no timeout.
-    if (x == std::numeric_limits<int64_t>::max()) x = 0;
+    if (x == (std::numeric_limits<int64_t>::max)()) x = 0;
     return x;
   }
 
@@ -94,7 +91,7 @@ class KernelTimeout {
           ERROR,
           "Tried to create a timespec from a non-timeout; never do this.");
       // But we'll try to continue sanely.  no-timeout ~= saturated timeout.
-      n = std::numeric_limits<int64_t>::max();
+      n = (std::numeric_limits<int64_t>::max)();
     }
 
     // Kernel APIs validate timespecs as being at or after the epoch,
@@ -105,7 +102,7 @@ class KernelTimeout {
 
     struct timespec abstime;
     int64_t seconds = std::min(n / kNanosPerSecond,
-                             int64_t{std::numeric_limits<time_t>::max()});
+                             int64_t{(std::numeric_limits<time_t>::max)()});
     abstime.tv_sec = static_cast<time_t>(seconds);
     abstime.tv_nsec =
         static_cast<decltype(abstime.tv_nsec)>(n % kNanosPerSecond);
@@ -118,9 +115,14 @@ class KernelTimeout {
   // Windows. Callers should recognize that the return value is a
   // relative duration (it should be recomputed by calling this method
   // in the case of a spurious wakeup).
-  DWORD InMillisecondsFromNow() const {
+  // This header file may be included transitively by public header files,
+  // so we define our own DWORD and INFINITE instead of getting them from
+  // <intsafe.h> and <WinBase.h>.
+  typedef unsigned long DWord;  // NOLINT
+  DWord InMillisecondsFromNow() const {
+    constexpr DWord kInfinite = (std::numeric_limits<DWord>::max)();
     if (!has_timeout()) {
-      return INFINITE;
+      return kInfinite;
     }
     // The use of absl::Now() to convert from absolute time to
     // relative time means that absl::Now() cannot use anything that
@@ -129,13 +131,13 @@ class KernelTimeout {
     if (ns_ >= now) {
       // Round up so that Now() + ms_from_now >= ns_.
       constexpr uint64_t max_nanos =
-          std::numeric_limits<int64_t>::max() - 999999u;
+          (std::numeric_limits<int64_t>::max)() - 999999u;
       uint64_t ms_from_now =
           (std::min<uint64_t>(max_nanos, ns_ - now) + 999999u) / 1000000u;
-      if (ms_from_now > std::numeric_limits<DWORD>::max()) {
-        return INFINITE;
+      if (ms_from_now > kInfinite) {
+        return kInfinite;
       }
-      return static_cast<DWORD>(ms_from_now);
+      return static_cast<DWord>(ms_from_now);
     }
     return 0;
   }
@@ -146,6 +148,6 @@ class KernelTimeout {
 };
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 #endif  // ABSL_SYNCHRONIZATION_INTERNAL_KERNEL_TIMEOUT_H_
diff --git a/absl/synchronization/internal/mutex_nonprod.cc b/absl/synchronization/internal/mutex_nonprod.cc
index a8071a96..4b0b8bcd 100644
--- a/absl/synchronization/internal/mutex_nonprod.cc
+++ b/absl/synchronization/internal/mutex_nonprod.cc
@@ -31,7 +31,7 @@
 #include "absl/time/time.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace synchronization_internal {
 
 namespace {
@@ -316,5 +316,5 @@ bool Condition::Eval() const {
 
 void RegisterSymbolizer(bool (*)(const void*, char*, int)) {}
 
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/synchronization/internal/mutex_nonprod.inc b/absl/synchronization/internal/mutex_nonprod.inc
index 2d06285f..0ae4c0ea 100644
--- a/absl/synchronization/internal/mutex_nonprod.inc
+++ b/absl/synchronization/internal/mutex_nonprod.inc
@@ -36,7 +36,7 @@
 #endif
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 class Condition;
 
 namespace synchronization_internal {
@@ -254,5 +254,5 @@ class SynchronizationStorage {
 };
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/synchronization/internal/per_thread_sem.cc b/absl/synchronization/internal/per_thread_sem.cc
index 53b789d6..9de2d136 100644
--- a/absl/synchronization/internal/per_thread_sem.cc
+++ b/absl/synchronization/internal/per_thread_sem.cc
@@ -25,7 +25,7 @@
 #include "absl/synchronization/internal/waiter.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace synchronization_internal {
 
 void PerThreadSem::SetThreadBlockedCounter(std::atomic<int> *counter) {
@@ -59,7 +59,7 @@ void PerThreadSem::Tick(base_internal::ThreadIdentity *identity) {
 }
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 extern "C" {
diff --git a/absl/synchronization/internal/per_thread_sem.h b/absl/synchronization/internal/per_thread_sem.h
index fc64f768..6efd5951 100644
--- a/absl/synchronization/internal/per_thread_sem.h
+++ b/absl/synchronization/internal/per_thread_sem.h
@@ -32,7 +32,7 @@
 #include "absl/synchronization/internal/kernel_timeout.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 
 class Mutex;
 
@@ -81,7 +81,7 @@ class PerThreadSem {
 };
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 // In some build configurations we pass --detect-odr-violations to the
diff --git a/absl/synchronization/internal/per_thread_sem_test.cc b/absl/synchronization/internal/per_thread_sem_test.cc
index 63c8e56a..18b2458b 100644
--- a/absl/synchronization/internal/per_thread_sem_test.cc
+++ b/absl/synchronization/internal/per_thread_sem_test.cc
@@ -33,7 +33,7 @@
 // primitives which might use PerThreadSem, most notably absl::Mutex.
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace synchronization_internal {
 
 class SimpleSemaphore {
@@ -154,12 +154,15 @@ TEST_F(PerThreadSemTest, WithTimeout) {
 
 TEST_F(PerThreadSemTest, Timeouts) {
   absl::Time timeout = absl::Now() + absl::Milliseconds(50);
+  // Allow for a slight early return, to account for quality of implementation
+  // issues on various platforms.
+  const absl::Duration slop = absl::Microseconds(200);
   EXPECT_FALSE(Wait(timeout));
-  EXPECT_LE(timeout, absl::Now());
+  EXPECT_LE(timeout, absl::Now() + slop);
 
   absl::Time negative_timeout = absl::UnixEpoch() - absl::Milliseconds(100);
   EXPECT_FALSE(Wait(negative_timeout));
-  EXPECT_LE(negative_timeout, absl::Now());  // trivially true :)
+  EXPECT_LE(negative_timeout, absl::Now() + slop);  // trivially true :)
 
   Post(GetOrCreateCurrentThreadIdentity());
   // The wait here has an expired timeout, but we have a wake to consume,
@@ -170,5 +173,5 @@ TEST_F(PerThreadSemTest, Timeouts) {
 }  // namespace
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/synchronization/internal/thread_pool.h b/absl/synchronization/internal/thread_pool.h
index 82dedbf5..66c7546b 100644
--- a/absl/synchronization/internal/thread_pool.h
+++ b/absl/synchronization/internal/thread_pool.h
@@ -25,7 +25,7 @@
 #include "absl/synchronization/mutex.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace synchronization_internal {
 
 // A simple ThreadPool implementation for tests.
@@ -86,7 +86,7 @@ class ThreadPool {
 };
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_SYNCHRONIZATION_INTERNAL_THREAD_POOL_H_
diff --git a/absl/synchronization/internal/waiter.cc b/absl/synchronization/internal/waiter.cc
index ad86acce..76fdd861 100644
--- a/absl/synchronization/internal/waiter.cc
+++ b/absl/synchronization/internal/waiter.cc
@@ -46,7 +46,7 @@
 #include "absl/synchronization/internal/kernel_timeout.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace synchronization_internal {
 
 static void MaybeBecomeIdle() {
@@ -410,5 +410,5 @@ void Waiter::Poke() {
 #endif
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/synchronization/internal/waiter.h b/absl/synchronization/internal/waiter.h
index 1c284c0a..2b737260 100644
--- a/absl/synchronization/internal/waiter.h
+++ b/absl/synchronization/internal/waiter.h
@@ -53,7 +53,7 @@
 #endif
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace synchronization_internal {
 
 // Waiter is an OS-specific semaphore.
@@ -135,7 +135,7 @@ class Waiter {
 };
 
 }  // namespace synchronization_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_SYNCHRONIZATION_INTERNAL_WAITER_H_
diff --git a/absl/synchronization/lifetime_test.cc b/absl/synchronization/lifetime_test.cc
index 90c9009b..b7360c29 100644
--- a/absl/synchronization/lifetime_test.cc
+++ b/absl/synchronization/lifetime_test.cc
@@ -72,23 +72,19 @@ void ThreadTwo(absl::Mutex* mutex, absl::CondVar* condvar,
 // Launch thread 1 and thread 2, and block on their completion.
 // If any of 'mutex', 'condvar', or 'notification' is nullptr, use a locally
 // constructed instance instead.
-void RunTests(absl::Mutex* mutex, absl::CondVar* condvar,
-              absl::Notification* notification) {
+void RunTests(absl::Mutex* mutex, absl::CondVar* condvar) {
   absl::Mutex default_mutex;
   absl::CondVar default_condvar;
-  absl::Notification default_notification;
+  absl::Notification notification;
   if (!mutex) {
     mutex = &default_mutex;
   }
   if (!condvar) {
     condvar = &default_condvar;
   }
-  if (!notification) {
-    notification = &default_notification;
-  }
   bool state = false;
-  std::thread thread_one(ThreadOne, mutex, condvar, notification, &state);
-  std::thread thread_two(ThreadTwo, mutex, condvar, notification, &state);
+  std::thread thread_one(ThreadOne, mutex, condvar, &notification, &state);
+  std::thread thread_two(ThreadTwo, mutex, condvar, &notification, &state);
   thread_one.join();
   thread_two.join();
 }
@@ -96,8 +92,7 @@ void RunTests(absl::Mutex* mutex, absl::CondVar* condvar,
 void TestLocals() {
   absl::Mutex mutex;
   absl::CondVar condvar;
-  absl::Notification notification;
-  RunTests(&mutex, &condvar, &notification);
+  RunTests(&mutex, &condvar);
 }
 
 // Global variables during start and termination
diff --git a/absl/synchronization/mutex.cc b/absl/synchronization/mutex.cc
index 14e24a76..9f8d6cd7 100644
--- a/absl/synchronization/mutex.cc
+++ b/absl/synchronization/mutex.cc
@@ -71,7 +71,7 @@ ABSL_ATTRIBUTE_WEAK void AbslInternalMutexYield() { std::this_thread::yield(); }
 }  // extern "C"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 
 namespace {
 
@@ -299,7 +299,7 @@ static struct SynchEvent {     // this is a trivial hash table for the events
 // set "bits" in the word there (waiting until lockbit is clear before doing
 // so), and return a refcounted reference that will remain valid until
 // UnrefSynchEvent() is called.  If a new SynchEvent is allocated,
-// the std::string name is copied into it.
+// the string name is copied into it.
 // When used with a mutex, the caller should also ensure that kMuEvent
 // is set in the mutex word, and similarly for condition variables and kCVEvent.
 static SynchEvent *EnsureSynchEvent(std::atomic<intptr_t> *addr,
@@ -1828,8 +1828,8 @@ bool Mutex::LockSlowWithDeadline(MuHow how, const Condition *cond,
          cond == nullptr || EvalConditionAnnotated(cond, this, true, how);
 }
 
-// RAW_CHECK_FMT() takes a condition, a printf-style format std::string, and
-// the printf-style argument list.   The format std::string must be a literal.
+// RAW_CHECK_FMT() takes a condition, a printf-style format string, and
+// the printf-style argument list.   The format string must be a literal.
 // Arguments after the first are not evaluated unless the condition is true.
 #define RAW_CHECK_FMT(cond, ...)                                   \
   do {                                                             \
@@ -1976,7 +1976,7 @@ void Mutex::LockSlowLoop(SynchWaitParams *waitp, int flags) {
 // Unlock this mutex, which is held by the current thread.
 // If waitp is non-zero, it must be the wait parameters for the current thread
 // which holds the lock but is not runnable because its condition is false
-// or it n the process of blocking on a condition variable; it must requeue
+// or it is in the process of blocking on a condition variable; it must requeue
 // itself on the mutex/condvar to wait for its condition to become true.
 void Mutex::UnlockSlow(SynchWaitParams *waitp) {
   intptr_t v = mu_.load(std::memory_order_relaxed);
@@ -2685,5 +2685,5 @@ bool Condition::GuaranteedEqual(const Condition *a, const Condition *b) {
          a->arg_ == b->arg_ && a->method_ == b->method_;
 }
 
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/synchronization/mutex.h b/absl/synchronization/mutex.h
index b5276037..ce97707f 100644
--- a/absl/synchronization/mutex.h
+++ b/absl/synchronization/mutex.h
@@ -24,7 +24,7 @@
 // Unlike a `std::mutex`, the Abseil `Mutex` provides the following additional
 // features:
 //   * Conditional predicates intrinsic to the `Mutex` object
-//   * Reader/writer locks, in addition to standard exclusive/writer locks
+//   * Shared/reader locks, in addition to standard exclusive/writer locks
 //   * Deadlock detection and debug support.
 //
 // The following helper classes are also defined within this file:
@@ -81,7 +81,7 @@
 #endif
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 
 class Condition;
 struct SynchWaitParams;
@@ -291,7 +291,7 @@ class LOCKABLE Mutex {
   // Mutex::ReaderLockWhen()
   // Mutex::WriterLockWhen()
   //
-  // Blocks until simultaneously both `cond` is `true` and this` Mutex` can
+  // Blocks until simultaneously both `cond` is `true` and this `Mutex` can
   // be acquired, then atomically acquires this `Mutex`. `LockWhen()` is
   // logically equivalent to `*Lock(); Await();` though they may have different
   // performance characteristics.
@@ -559,7 +559,7 @@ class SCOPED_LOCKABLE ReaderMutexLock {
 // WriterMutexLock
 //
 // The `WriterMutexLock` is a helper class, like `MutexLock`, which acquires and
-// releases a write (exclusive) lock on a `Mutex` va RAII.
+// releases a write (exclusive) lock on a `Mutex` via RAII.
 class SCOPED_LOCKABLE WriterMutexLock {
  public:
   explicit WriterMutexLock(Mutex *mu) EXCLUSIVE_LOCK_FUNCTION(mu)
@@ -585,7 +585,7 @@ class SCOPED_LOCKABLE WriterMutexLock {
 // -----------------------------------------------------------------------------
 //
 // As noted above, `Mutex` contains a number of member functions which take a
-// `Condition` as a argument; clients can wait for conditions to become `true`
+// `Condition` as an argument; clients can wait for conditions to become `true`
 // before attempting to acquire the mutex. These sections are known as
 // "condition critical" sections. To use a `Condition`, you simply need to
 // construct it, and use within an appropriate `Mutex` member function;
@@ -963,7 +963,7 @@ void RegisterMutexTracer(void (*fn)(const char *msg, const void *obj,
 //
 // The function pointer registered here will be called here on various CondVar
 // events.  The callback is given an opaque handle to the CondVar object and
-// a std::string identifying the event.  This is thread-safe, but only a single
+// a string identifying the event.  This is thread-safe, but only a single
 // tracer can be registered.
 //
 // Events that can be sent are "Wait", "Unwait", "Signal wakeup", and
@@ -1015,7 +1015,7 @@ enum class OnDeadlockCycle {
 // the manner chosen here.
 void SetMutexDeadlockDetectionMode(OnDeadlockCycle mode);
 
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 // In some build configurations we pass --detect-odr-violations to the
diff --git a/absl/synchronization/mutex_benchmark.cc b/absl/synchronization/mutex_benchmark.cc
index 30a52355..2652bb97 100644
--- a/absl/synchronization/mutex_benchmark.cc
+++ b/absl/synchronization/mutex_benchmark.cc
@@ -12,16 +12,154 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#include <cstdint>
+#include <mutex>  // NOLINT(build/c++11)
 #include <vector>
 
-#include "benchmark/benchmark.h"
-#include "absl/base/internal/sysinfo.h"
+#include "absl/base/internal/cycleclock.h"
+#include "absl/base/internal/spinlock.h"
 #include "absl/synchronization/blocking_counter.h"
 #include "absl/synchronization/internal/thread_pool.h"
 #include "absl/synchronization/mutex.h"
+#include "benchmark/benchmark.h"
 
 namespace {
 
+void BM_Mutex(benchmark::State& state) {
+  static absl::Mutex* mu = new absl::Mutex;
+  for (auto _ : state) {
+    absl::MutexLock lock(mu);
+  }
+}
+BENCHMARK(BM_Mutex)->UseRealTime()->Threads(1)->ThreadPerCpu();
+
+static void DelayNs(int64_t ns, int* data) {
+  int64_t end = absl::base_internal::CycleClock::Now() +
+                ns * absl::base_internal::CycleClock::Frequency() / 1e9;
+  while (absl::base_internal::CycleClock::Now() < end) {
+    ++(*data);
+    benchmark::DoNotOptimize(*data);
+  }
+}
+
+template <typename MutexType>
+class RaiiLocker {
+ public:
+  explicit RaiiLocker(MutexType* mu) : mu_(mu) { mu_->Lock(); }
+  ~RaiiLocker() { mu_->Unlock(); }
+ private:
+  MutexType* mu_;
+};
+
+template <>
+class RaiiLocker<std::mutex> {
+ public:
+  explicit RaiiLocker(std::mutex* mu) : mu_(mu) { mu_->lock(); }
+  ~RaiiLocker() { mu_->unlock(); }
+ private:
+  std::mutex* mu_;
+};
+
+template <typename MutexType>
+void BM_Contended(benchmark::State& state) {
+  struct Shared {
+    MutexType mu;
+    int data = 0;
+  };
+  static auto* shared = new Shared;
+  int local = 0;
+  for (auto _ : state) {
+    // Here we model both local work outside of the critical section as well as
+    // some work inside of the critical section. The idea is to capture some
+    // more or less realisitic contention levels.
+    // If contention is too low, the benchmark won't measure anything useful.
+    // If contention is unrealistically high, the benchmark will favor
+    // bad mutex implementations that block and otherwise distract threads
+    // from the mutex and shared state for as much as possible.
+    // To achieve this amount of local work is multiplied by number of threads
+    // to keep ratio between local work and critical section approximately
+    // equal regardless of number of threads.
+    DelayNs(100 * state.threads, &local);
+    RaiiLocker<MutexType> locker(&shared->mu);
+    DelayNs(state.range(0), &shared->data);
+  }
+}
+
+BENCHMARK_TEMPLATE(BM_Contended, absl::Mutex)
+    ->UseRealTime()
+    // ThreadPerCpu poorly handles non-power-of-two CPU counts.
+    ->Threads(1)
+    ->Threads(2)
+    ->Threads(4)
+    ->Threads(6)
+    ->Threads(8)
+    ->Threads(12)
+    ->Threads(16)
+    ->Threads(24)
+    ->Threads(32)
+    ->Threads(48)
+    ->Threads(64)
+    ->Threads(96)
+    ->Threads(128)
+    ->Threads(192)
+    ->Threads(256)
+    // Some empirically chosen amounts of work in critical section.
+    // 1 is low contention, 200 is high contention and few values in between.
+    ->Arg(1)
+    ->Arg(20)
+    ->Arg(50)
+    ->Arg(200);
+
+BENCHMARK_TEMPLATE(BM_Contended, absl::base_internal::SpinLock)
+    ->UseRealTime()
+    // ThreadPerCpu poorly handles non-power-of-two CPU counts.
+    ->Threads(1)
+    ->Threads(2)
+    ->Threads(4)
+    ->Threads(6)
+    ->Threads(8)
+    ->Threads(12)
+    ->Threads(16)
+    ->Threads(24)
+    ->Threads(32)
+    ->Threads(48)
+    ->Threads(64)
+    ->Threads(96)
+    ->Threads(128)
+    ->Threads(192)
+    ->Threads(256)
+    // Some empirically chosen amounts of work in critical section.
+    // 1 is low contention, 200 is high contention and few values in between.
+    ->Arg(1)
+    ->Arg(20)
+    ->Arg(50)
+    ->Arg(200);
+
+BENCHMARK_TEMPLATE(BM_Contended, std::mutex)
+    ->UseRealTime()
+    // ThreadPerCpu poorly handles non-power-of-two CPU counts.
+    ->Threads(1)
+    ->Threads(2)
+    ->Threads(4)
+    ->Threads(6)
+    ->Threads(8)
+    ->Threads(12)
+    ->Threads(16)
+    ->Threads(24)
+    ->Threads(32)
+    ->Threads(48)
+    ->Threads(64)
+    ->Threads(96)
+    ->Threads(128)
+    ->Threads(192)
+    ->Threads(256)
+    // Some empirically chosen amounts of work in critical section.
+    // 1 is low contention, 200 is high contention and few values in between.
+    ->Arg(1)
+    ->Arg(20)
+    ->Arg(50)
+    ->Arg(200);
+
 // Measure the overhead of conditions on mutex release (when they must be
 // evaluated).  Mutex has (some) support for equivalence classes allowing
 // Conditions with the same function/argument to potentially not be multiply
@@ -74,21 +212,12 @@ void BM_ConditionWaiters(benchmark::State& state) {
   mu.Unlock();
 }
 
-#ifdef THREAD_SANITIZER
-// ThreadSanitizer can't handle 8192 threads.
-constexpr int kMaxConditionWaiters = 2048;
-#else
+// Some configurations have higher thread limits than others.
+#if defined(__linux__) && !defined(THREAD_SANITIZER)
 constexpr int kMaxConditionWaiters = 8192;
+#else
+constexpr int kMaxConditionWaiters = 1024;
 #endif
 BENCHMARK(BM_ConditionWaiters)->RangePair(0, 2, 1, kMaxConditionWaiters);
 
-void BM_ContendedMutex(benchmark::State& state) {
-  static absl::Mutex* mu = new absl::Mutex;
-  for (auto _ : state) {
-    absl::MutexLock lock(mu);
-  }
-}
-BENCHMARK(BM_ContendedMutex)->Threads(1);
-BENCHMARK(BM_ContendedMutex)->ThreadPerCpu();
-
 }  // namespace
diff --git a/absl/synchronization/mutex_test.cc b/absl/synchronization/mutex_test.cc
index 53b93784..b2820e20 100644
--- a/absl/synchronization/mutex_test.cc
+++ b/absl/synchronization/mutex_test.cc
@@ -29,6 +29,7 @@
 #include <vector>
 
 #include "gtest/gtest.h"
+#include "absl/base/attributes.h"
 #include "absl/base/internal/raw_logging.h"
 #include "absl/base/internal/sysinfo.h"
 #include "absl/memory/memory.h"
@@ -54,8 +55,8 @@ CreateDefaultPool() {
 // Hack to schedule a function to run on a thread pool thread after a
 // duration has elapsed.
 static void ScheduleAfter(absl::synchronization_internal::ThreadPool *tp,
-                          const std::function<void()> &func,
-                          absl::Duration after) {
+                          absl::Duration after,
+                          const std::function<void()> &func) {
   tp->Schedule([func, after] {
     absl::SleepFor(after);
     func();
@@ -1150,249 +1151,369 @@ TEST(Mutex, DeadlockIdBug) NO_THREAD_SAFETY_ANALYSIS {
 // and so never expires/passes, and one that will expire/pass in the near
 // future.
 
-// Encapsulate a Mutex-protected bool with its associated Condition/CondVar.
-class Cond {
- public:
-  explicit Cond(bool use_deadline) : use_deadline_(use_deadline), c_(&b_) {}
-
-  void Set(bool v) {
-    absl::MutexLock lock(&mu_);
-    b_ = v;
+static absl::Duration TimeoutTestAllowedSchedulingDelay() {
+  // Note: we use a function here because Microsoft Visual Studio fails to
+  // properly initialize constexpr static absl::Duration variables.
+  return absl::Milliseconds(150);
+}
+
+// Returns true if `actual_delay` is close enough to `expected_delay` to pass
+// the timeouts/deadlines test.  Otherwise, logs warnings and returns false.
+ABSL_MUST_USE_RESULT
+static bool DelayIsWithinBounds(absl::Duration expected_delay,
+                                absl::Duration actual_delay) {
+  bool pass = true;
+  // Do not allow the observed delay to be less than expected.  This may occur
+  // in practice due to clock skew or when the synchronization primitives use a
+  // different clock than absl::Now(), but these cases should be handled by the
+  // the retry mechanism in each TimeoutTest.
+  if (actual_delay < expected_delay) {
+    ABSL_RAW_LOG(WARNING,
+                 "Actual delay %s was too short, expected %s (difference %s)",
+                 absl::FormatDuration(actual_delay).c_str(),
+                 absl::FormatDuration(expected_delay).c_str(),
+                 absl::FormatDuration(actual_delay - expected_delay).c_str());
+    pass = false;
   }
-
-  bool AwaitWithTimeout(absl::Duration timeout) {
-    absl::MutexLock lock(&mu_);
-    return use_deadline_ ? mu_.AwaitWithDeadline(c_, absl::Now() + timeout)
-                         : mu_.AwaitWithTimeout(c_, timeout);
+  // If the expected delay is <= zero then allow a small error tolerance, since
+  // we do not expect context switches to occur during test execution.
+  // Otherwise, thread scheduling delays may be substantial in rare cases, so
+  // tolerate up to kTimeoutTestAllowedSchedulingDelay of error.
+  absl::Duration tolerance = expected_delay <= absl::ZeroDuration()
+                                 ? absl::Milliseconds(10)
+                                 : TimeoutTestAllowedSchedulingDelay();
+  if (actual_delay > expected_delay + tolerance) {
+    ABSL_RAW_LOG(WARNING,
+                 "Actual delay %s was too long, expected %s (difference %s)",
+                 absl::FormatDuration(actual_delay).c_str(),
+                 absl::FormatDuration(expected_delay).c_str(),
+                 absl::FormatDuration(actual_delay - expected_delay).c_str());
+    pass = false;
   }
+  return pass;
+}
+
+// Parameters for TimeoutTest, below.
+struct TimeoutTestParam {
+  // The file and line number (used for logging purposes only).
+  const char *from_file;
+  int from_line;
+
+  // Should the absolute deadline API based on absl::Time be tested?  If false,
+  // the relative deadline API based on absl::Duration is tested.
+  bool use_absolute_deadline;
+
+  // The deadline/timeout used when calling the API being tested
+  // (e.g. Mutex::LockWhenWithDeadline).
+  absl::Duration wait_timeout;
+
+  // The delay before the condition will be set true by the test code.  If zero
+  // or negative, the condition is set true immediately (before calling the API
+  // being tested).  Otherwise, if infinite, the condition is never set true.
+  // Otherwise a closure is scheduled for the future that sets the condition
+  // true.
+  absl::Duration satisfy_condition_delay;
+
+  // The expected result of the condition after the call to the API being
+  // tested. Generally `true` means the condition was true when the API returns,
+  // `false` indicates an expected timeout.
+  bool expected_result;
+
+  // The expected delay before the API under test returns.  This is inherently
+  // flaky, so some slop is allowed (see `DelayIsWithinBounds` above), and the
+  // test keeps trying indefinitely until this constraint passes.
+  absl::Duration expected_delay;
+};
 
-  bool LockWhenWithTimeout(absl::Duration timeout) {
-    bool b = use_deadline_ ? mu_.LockWhenWithDeadline(c_, absl::Now() + timeout)
-                           : mu_.LockWhenWithTimeout(c_, timeout);
-    mu_.Unlock();
-    return b;
+// Print a `TimeoutTestParam` to a debug log.
+std::ostream &operator<<(std::ostream &os, const TimeoutTestParam &param) {
+  return os << "from: " << param.from_file << ":" << param.from_line
+            << " use_absolute_deadline: "
+            << (param.use_absolute_deadline ? "true" : "false")
+            << " wait_timeout: " << param.wait_timeout
+            << " satisfy_condition_delay: " << param.satisfy_condition_delay
+            << " expected_result: "
+            << (param.expected_result ? "true" : "false")
+            << " expected_delay: " << param.expected_delay;
+}
+
+std::string FormatString(const TimeoutTestParam &param) {
+  std::ostringstream os;
+  os << param;
+  return os.str();
+}
+
+// Like `thread::Executor::ScheduleAt` except:
+// a) Delays zero or negative are executed immediately in the current thread.
+// b) Infinite delays are never scheduled.
+// c) Calls this test's `ScheduleAt` helper instead of using `pool` directly.
+static void RunAfterDelay(absl::Duration delay,
+                          absl::synchronization_internal::ThreadPool *pool,
+                          const std::function<void()> &callback) {
+  if (delay <= absl::ZeroDuration()) {
+    callback();  // immediate
+  } else if (delay != absl::InfiniteDuration()) {
+    ScheduleAfter(pool, delay, callback);
   }
+}
 
-  bool ReaderLockWhenWithTimeout(absl::Duration timeout) {
-    bool b = use_deadline_
-                 ? mu_.ReaderLockWhenWithDeadline(c_, absl::Now() + timeout)
-                 : mu_.ReaderLockWhenWithTimeout(c_, timeout);
-    mu_.ReaderUnlock();
-    return b;
-  }
+class TimeoutTest : public ::testing::Test,
+                    public ::testing::WithParamInterface<TimeoutTestParam> {};
 
-  void Await() {
-    absl::MutexLock lock(&mu_);
-    mu_.Await(c_);
-  }
+std::vector<TimeoutTestParam> MakeTimeoutTestParamValues() {
+  // The `finite` delay is a finite, relatively short, delay.  We make it larger
+  // than our allowed scheduling delay (slop factor) to avoid confusion when
+  // diagnosing test failures.  The other constants here have clear meanings.
+  const absl::Duration finite = 3 * TimeoutTestAllowedSchedulingDelay();
+  const absl::Duration never = absl::InfiniteDuration();
+  const absl::Duration negative = -absl::InfiniteDuration();
+  const absl::Duration immediate = absl::ZeroDuration();
 
-  void Signal(bool v) {
-    absl::MutexLock lock(&mu_);
-    b_ = v;
-    cv_.Signal();
+  // Every test case is run twice; once using the absolute deadline API and once
+  // using the relative timeout API.
+  std::vector<TimeoutTestParam> values;
+  for (bool use_absolute_deadline : {false, true}) {
+    // Tests with a negative timeout (deadline in the past), which should
+    // immediately return current state of the condition.
+
+    // The condition is already true:
+    values.push_back(TimeoutTestParam{
+        __FILE__, __LINE__, use_absolute_deadline,
+        negative,   // wait_timeout
+        immediate,  // satisfy_condition_delay
+        true,       // expected_result
+        immediate,  // expected_delay
+    });
+
+    // The condition becomes true, but the timeout has already expired:
+    values.push_back(TimeoutTestParam{
+        __FILE__, __LINE__, use_absolute_deadline,
+        negative,  // wait_timeout
+        finite,    // satisfy_condition_delay
+        false,     // expected_result
+        immediate  // expected_delay
+    });
+
+    // The condition never becomes true:
+    values.push_back(TimeoutTestParam{
+        __FILE__, __LINE__, use_absolute_deadline,
+        negative,  // wait_timeout
+        never,     // satisfy_condition_delay
+        false,     // expected_result
+        immediate  // expected_delay
+    });
+
+    // Tests with an infinite timeout (deadline in the infinite future), which
+    // should only return when the condition becomes true.
+
+    // The condition is already true:
+    values.push_back(TimeoutTestParam{
+        __FILE__, __LINE__, use_absolute_deadline,
+        never,      // wait_timeout
+        immediate,  // satisfy_condition_delay
+        true,       // expected_result
+        immediate   // expected_delay
+    });
+
+    // The condition becomes true before the (infinite) expiry:
+    values.push_back(TimeoutTestParam{
+        __FILE__, __LINE__, use_absolute_deadline,
+        never,   // wait_timeout
+        finite,  // satisfy_condition_delay
+        true,    // expected_result
+        finite,  // expected_delay
+    });
+
+    // Tests with a (small) finite timeout (deadline soon), with the condition
+    // becoming true both before and after its expiry.
+
+    // The condition is already true:
+    values.push_back(TimeoutTestParam{
+        __FILE__, __LINE__, use_absolute_deadline,
+        never,      // wait_timeout
+        immediate,  // satisfy_condition_delay
+        true,       // expected_result
+        immediate   // expected_delay
+    });
+
+    // The condition becomes true before the expiry:
+    values.push_back(TimeoutTestParam{
+        __FILE__, __LINE__, use_absolute_deadline,
+        finite * 2,  // wait_timeout
+        finite,      // satisfy_condition_delay
+        true,        // expected_result
+        finite       // expected_delay
+    });
+
+    // The condition becomes true, but the timeout has already expired:
+    values.push_back(TimeoutTestParam{
+        __FILE__, __LINE__, use_absolute_deadline,
+        finite,      // wait_timeout
+        finite * 2,  // satisfy_condition_delay
+        false,       // expected_result
+        finite       // expected_delay
+    });
+
+    // The condition never becomes true:
+    values.push_back(TimeoutTestParam{
+        __FILE__, __LINE__, use_absolute_deadline,
+        finite,  // wait_timeout
+        never,   // satisfy_condition_delay
+        false,   // expected_result
+        finite   // expected_delay
+    });
   }
-
-  bool WaitWithTimeout(absl::Duration timeout) {
-    absl::MutexLock lock(&mu_);
-    absl::Time deadline = absl::Now() + timeout;
-    if (use_deadline_) {
-      while (!b_ && !cv_.WaitWithDeadline(&mu_, deadline)) {
-      }
-    } else {
-      while (!b_ && !cv_.WaitWithTimeout(&mu_, timeout)) {
-        timeout = deadline - absl::Now();  // recompute timeout
-      }
+  return values;
+}
+
+// Instantiate `TimeoutTest` with `MakeTimeoutTestParamValues()`.
+INSTANTIATE_TEST_CASE_P(All, TimeoutTest,
+                        testing::ValuesIn(MakeTimeoutTestParamValues()));
+
+TEST_P(TimeoutTest, Await) {
+  const TimeoutTestParam params = GetParam();
+  ABSL_RAW_LOG(INFO, "Params: %s", FormatString(params).c_str());
+
+  // Because this test asserts bounds on scheduling delays it is flaky.  To
+  // compensate it loops forever until it passes.  Failures express as test
+  // timeouts, in which case the test log can be used to diagnose the issue.
+  for (int attempt = 1;; ++attempt) {
+    ABSL_RAW_LOG(INFO, "Attempt %d", attempt);
+
+    absl::Mutex mu;
+    bool value = false;  // condition value (under mu)
+
+    std::unique_ptr<absl::synchronization_internal::ThreadPool> pool =
+        CreateDefaultPool();
+    RunAfterDelay(params.satisfy_condition_delay, pool.get(), [&] {
+      absl::MutexLock l(&mu);
+      value = true;
+    });
+
+    absl::MutexLock lock(&mu);
+    absl::Time start_time = absl::Now();
+    absl::Condition cond(&value);
+    bool result =
+        params.use_absolute_deadline
+            ? mu.AwaitWithDeadline(cond, start_time + params.wait_timeout)
+            : mu.AwaitWithTimeout(cond, params.wait_timeout);
+    if (DelayIsWithinBounds(params.expected_delay, absl::Now() - start_time)) {
+      EXPECT_EQ(params.expected_result, result);
+      break;
     }
-    return b_;
-  }
-
-  void Wait() {
-    absl::MutexLock lock(&mu_);
-    while (!b_) cv_.Wait(&mu_);
-  }
-
- private:
-  const bool use_deadline_;
-
-  bool b_;
-  absl::Condition c_;
-  absl::CondVar cv_;
-  absl::Mutex mu_;
-};
-
-class OperationTimer {
- public:
-  OperationTimer() : start_(absl::Now()) {}
-  absl::Duration Get() const { return absl::Now() - start_; }
-
- private:
-  const absl::Time start_;
-};
-
-static void CheckResults(bool exp_result, bool act_result,
-                         absl::Duration exp_duration,
-                         absl::Duration act_duration) {
-  ABSL_RAW_CHECK(exp_result == act_result, "CheckResults failed");
-  // Allow for some worse-case scheduling delay and clock skew.
-  if ((exp_duration - absl::Milliseconds(40) > act_duration) ||
-      (exp_duration + absl::Milliseconds(150) < act_duration)) {
-    ABSL_RAW_LOG(FATAL, "CheckResults failed: operation took %s, expected %s",
-                 absl::FormatDuration(act_duration).c_str(),
-                 absl::FormatDuration(exp_duration).c_str());
   }
 }
 
-static void TestAwaitTimeout(Cond *cp, absl::Duration timeout, bool exp_result,
-                             absl::Duration exp_duration) {
-  OperationTimer t;
-  bool act_result = cp->AwaitWithTimeout(timeout);
-  CheckResults(exp_result, act_result, exp_duration, t.Get());
-}
-
-static void TestLockWhenTimeout(Cond *cp, absl::Duration timeout,
-                                bool exp_result, absl::Duration exp_duration) {
-  OperationTimer t;
-  bool act_result = cp->LockWhenWithTimeout(timeout);
-  CheckResults(exp_result, act_result, exp_duration, t.Get());
-}
+TEST_P(TimeoutTest, LockWhen) {
+  const TimeoutTestParam params = GetParam();
+  ABSL_RAW_LOG(INFO, "Params: %s", FormatString(params).c_str());
+
+  // Because this test asserts bounds on scheduling delays it is flaky.  To
+  // compensate it loops forever until it passes.  Failures express as test
+  // timeouts, in which case the test log can be used to diagnose the issue.
+  for (int attempt = 1;; ++attempt) {
+    ABSL_RAW_LOG(INFO, "Attempt %d", attempt);
+
+    absl::Mutex mu;
+    bool value = false;  // condition value (under mu)
+
+    std::unique_ptr<absl::synchronization_internal::ThreadPool> pool =
+        CreateDefaultPool();
+    RunAfterDelay(params.satisfy_condition_delay, pool.get(), [&] {
+      absl::MutexLock l(&mu);
+      value = true;
+    });
+
+    absl::Time start_time = absl::Now();
+    absl::Condition cond(&value);
+    bool result =
+        params.use_absolute_deadline
+            ? mu.LockWhenWithDeadline(cond, start_time + params.wait_timeout)
+            : mu.LockWhenWithTimeout(cond, params.wait_timeout);
+    mu.Unlock();
 
-static void TestReaderLockWhenTimeout(Cond *cp, absl::Duration timeout,
-                                      bool exp_result,
-                                      absl::Duration exp_duration) {
-  OperationTimer t;
-  bool act_result = cp->ReaderLockWhenWithTimeout(timeout);
-  CheckResults(exp_result, act_result, exp_duration, t.Get());
+    if (DelayIsWithinBounds(params.expected_delay, absl::Now() - start_time)) {
+      EXPECT_EQ(params.expected_result, result);
+      break;
+    }
+  }
 }
 
-static void TestWaitTimeout(Cond *cp, absl::Duration timeout, bool exp_result,
-                            absl::Duration exp_duration) {
-  OperationTimer t;
-  bool act_result = cp->WaitWithTimeout(timeout);
-  CheckResults(exp_result, act_result, exp_duration, t.Get());
+TEST_P(TimeoutTest, ReaderLockWhen) {
+  const TimeoutTestParam params = GetParam();
+  ABSL_RAW_LOG(INFO, "Params: %s", FormatString(params).c_str());
+
+  // Because this test asserts bounds on scheduling delays it is flaky.  To
+  // compensate it loops forever until it passes.  Failures express as test
+  // timeouts, in which case the test log can be used to diagnose the issue.
+  for (int attempt = 0;; ++attempt) {
+    ABSL_RAW_LOG(INFO, "Attempt %d", attempt);
+
+    absl::Mutex mu;
+    bool value = false;  // condition value (under mu)
+
+    std::unique_ptr<absl::synchronization_internal::ThreadPool> pool =
+        CreateDefaultPool();
+    RunAfterDelay(params.satisfy_condition_delay, pool.get(), [&] {
+      absl::MutexLock l(&mu);
+      value = true;
+    });
+
+    absl::Time start_time = absl::Now();
+    bool result =
+        params.use_absolute_deadline
+            ? mu.ReaderLockWhenWithDeadline(absl::Condition(&value),
+                                            start_time + params.wait_timeout)
+            : mu.ReaderLockWhenWithTimeout(absl::Condition(&value),
+                                           params.wait_timeout);
+    mu.ReaderUnlock();
+
+    if (DelayIsWithinBounds(params.expected_delay, absl::Now() - start_time)) {
+      EXPECT_EQ(params.expected_result, result);
+      break;
+    }
+  }
 }
 
-// Tests with a negative timeout (deadline in the past), which should
-// immediately return the current state of the condition.
-static void TestNegativeTimeouts(absl::synchronization_internal::ThreadPool *tp,
-                                 Cond *cp) {
-  const absl::Duration negative = -absl::InfiniteDuration();
-  const absl::Duration immediate = absl::ZeroDuration();
-
-  // The condition is already true:
-  cp->Set(true);
-  TestAwaitTimeout(cp, negative, true, immediate);
-  TestLockWhenTimeout(cp, negative, true, immediate);
-  TestReaderLockWhenTimeout(cp, negative, true, immediate);
-  TestWaitTimeout(cp, negative, true, immediate);
-
-  // The condition becomes true, but the timeout has already expired:
-  const absl::Duration delay = absl::Milliseconds(200);
-  cp->Set(false);
-  ScheduleAfter(tp, std::bind(&Cond::Set, cp, true), 3 * delay);
-  TestAwaitTimeout(cp, negative, false, immediate);
-  TestLockWhenTimeout(cp, negative, false, immediate);
-  TestReaderLockWhenTimeout(cp, negative, false, immediate);
-  cp->Await();  // wait for the scheduled Set() to complete
-  cp->Set(false);
-  ScheduleAfter(tp, std::bind(&Cond::Signal, cp, true), delay);
-  TestWaitTimeout(cp, negative, false, immediate);
-  cp->Wait();  // wait for the scheduled Signal() to complete
-
-  // The condition never becomes true:
-  cp->Set(false);
-  TestAwaitTimeout(cp, negative, false, immediate);
-  TestLockWhenTimeout(cp, negative, false, immediate);
-  TestReaderLockWhenTimeout(cp, negative, false, immediate);
-  TestWaitTimeout(cp, negative, false, immediate);
-}
-
-// Tests with an infinite timeout (deadline in the infinite future), which
-// should only return when the condition becomes true.
-static void TestInfiniteTimeouts(absl::synchronization_internal::ThreadPool *tp,
-                                 Cond *cp) {
-  const absl::Duration infinite = absl::InfiniteDuration();
-  const absl::Duration immediate = absl::ZeroDuration();
-
-  // The condition is already true:
-  cp->Set(true);
-  TestAwaitTimeout(cp, infinite, true, immediate);
-  TestLockWhenTimeout(cp, infinite, true, immediate);
-  TestReaderLockWhenTimeout(cp, infinite, true, immediate);
-  TestWaitTimeout(cp, infinite, true, immediate);
-
-  // The condition becomes true before the (infinite) expiry:
-  const absl::Duration delay = absl::Milliseconds(200);
-  cp->Set(false);
-  ScheduleAfter(tp, std::bind(&Cond::Set, cp, true), delay);
-  TestAwaitTimeout(cp, infinite, true, delay);
-  cp->Set(false);
-  ScheduleAfter(tp, std::bind(&Cond::Set, cp, true), delay);
-  TestLockWhenTimeout(cp, infinite, true, delay);
-  cp->Set(false);
-  ScheduleAfter(tp, std::bind(&Cond::Set, cp, true), delay);
-  TestReaderLockWhenTimeout(cp, infinite, true, delay);
-  cp->Set(false);
-  ScheduleAfter(tp, std::bind(&Cond::Signal, cp, true), delay);
-  TestWaitTimeout(cp, infinite, true, delay);
-}
-
-// Tests with a (small) finite timeout (deadline soon), with the condition
-// becoming true both before and after its expiry.
-static void TestFiniteTimeouts(absl::synchronization_internal::ThreadPool *tp,
-                               Cond *cp) {
-  const absl::Duration finite = absl::Milliseconds(400);
-  const absl::Duration immediate = absl::ZeroDuration();
+TEST_P(TimeoutTest, Wait) {
+  const TimeoutTestParam params = GetParam();
+  ABSL_RAW_LOG(INFO, "Params: %s", FormatString(params).c_str());
+
+  // Because this test asserts bounds on scheduling delays it is flaky.  To
+  // compensate it loops forever until it passes.  Failures express as test
+  // timeouts, in which case the test log can be used to diagnose the issue.
+  for (int attempt = 0;; ++attempt) {
+    ABSL_RAW_LOG(INFO, "Attempt %d", attempt);
+
+    absl::Mutex mu;
+    bool value = false;  // condition value (under mu)
+    absl::CondVar cv;    // signals a change of `value`
+
+    std::unique_ptr<absl::synchronization_internal::ThreadPool> pool =
+        CreateDefaultPool();
+    RunAfterDelay(params.satisfy_condition_delay, pool.get(), [&] {
+      absl::MutexLock l(&mu);
+      value = true;
+      cv.Signal();
+    });
+
+    absl::MutexLock lock(&mu);
+    absl::Time start_time = absl::Now();
+    absl::Duration timeout = params.wait_timeout;
+    absl::Time deadline = start_time + timeout;
+    while (!value) {
+      if (params.use_absolute_deadline ? cv.WaitWithDeadline(&mu, deadline)
+                                       : cv.WaitWithTimeout(&mu, timeout)) {
+        break;  // deadline/timeout exceeded
+      }
+      timeout = deadline - absl::Now();  // recompute
+    }
+    bool result = value;  // note: `mu` is still held
 
-  // The condition is already true:
-  cp->Set(true);
-  TestAwaitTimeout(cp, finite, true, immediate);
-  TestLockWhenTimeout(cp, finite, true, immediate);
-  TestReaderLockWhenTimeout(cp, finite, true, immediate);
-  TestWaitTimeout(cp, finite, true, immediate);
-
-  // The condition becomes true before the expiry:
-  const absl::Duration delay1 = finite / 2;
-  cp->Set(false);
-  ScheduleAfter(tp, std::bind(&Cond::Set, cp, true), delay1);
-  TestAwaitTimeout(cp, finite, true, delay1);
-  cp->Set(false);
-  ScheduleAfter(tp, std::bind(&Cond::Set, cp, true), delay1);
-  TestLockWhenTimeout(cp, finite, true, delay1);
-  cp->Set(false);
-  ScheduleAfter(tp, std::bind(&Cond::Set, cp, true), delay1);
-  TestReaderLockWhenTimeout(cp, finite, true, delay1);
-  cp->Set(false);
-  ScheduleAfter(tp, std::bind(&Cond::Signal, cp, true), delay1);
-  TestWaitTimeout(cp, finite, true, delay1);
-
-  // The condition becomes true, but the timeout has already expired:
-  const absl::Duration delay2 = finite * 2;
-  cp->Set(false);
-  ScheduleAfter(tp, std::bind(&Cond::Set, cp, true), 3 * delay2);
-  TestAwaitTimeout(cp, finite, false, finite);
-  TestLockWhenTimeout(cp, finite, false, finite);
-  TestReaderLockWhenTimeout(cp, finite, false, finite);
-  cp->Await();  // wait for the scheduled Set() to complete
-  cp->Set(false);
-  ScheduleAfter(tp, std::bind(&Cond::Signal, cp, true), delay2);
-  TestWaitTimeout(cp, finite, false, finite);
-  cp->Wait();  // wait for the scheduled Signal() to complete
-
-  // The condition never becomes true:
-  cp->Set(false);
-  TestAwaitTimeout(cp, finite, false, finite);
-  TestLockWhenTimeout(cp, finite, false, finite);
-  TestReaderLockWhenTimeout(cp, finite, false, finite);
-  TestWaitTimeout(cp, finite, false, finite);
-}
-
-TEST(Mutex, Timeouts) {
-  auto tp = CreateDefaultPool();
-  for (bool use_deadline : {false, true}) {
-    Cond cond(use_deadline);
-    TestNegativeTimeouts(tp.get(), &cond);
-    TestInfiniteTimeouts(tp.get(), &cond);
-    TestFiniteTimeouts(tp.get(), &cond);
+    if (DelayIsWithinBounds(params.expected_delay, absl::Now() - start_time)) {
+      EXPECT_EQ(params.expected_result, result);
+      break;
+    }
   }
 }
 
diff --git a/absl/synchronization/notification.cc b/absl/synchronization/notification.cc
index a38acc5f..472b7a3e 100644
--- a/absl/synchronization/notification.cc
+++ b/absl/synchronization/notification.cc
@@ -22,7 +22,8 @@
 #include "absl/time/time.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
+
 void Notification::Notify() {
   MutexLock l(&this->mutex_);
 
@@ -82,5 +83,5 @@ bool Notification::WaitForNotificationWithDeadline(absl::Time deadline) const {
   return notified;
 }
 
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/synchronization/notification.h b/absl/synchronization/notification.h
index 99f8ee63..25821b18 100644
--- a/absl/synchronization/notification.h
+++ b/absl/synchronization/notification.h
@@ -52,11 +52,12 @@
 
 #include <atomic>
 
+#include "absl/base/macros.h"
 #include "absl/synchronization/mutex.h"
 #include "absl/time/time.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 
 // -----------------------------------------------------------------------------
 // Notification
@@ -109,6 +110,6 @@ class Notification {
   std::atomic<bool> notified_yet_;  // written under mutex_
 };
 
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 #endif  // ABSL_SYNCHRONIZATION_NOTIFICATION_H_
diff --git a/absl/synchronization/notification_test.cc b/absl/synchronization/notification_test.cc
index 83e17e34..d1b66743 100644
--- a/absl/synchronization/notification_test.cc
+++ b/absl/synchronization/notification_test.cc
@@ -21,7 +21,7 @@
 #include "absl/synchronization/mutex.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 
 // A thread-safe class that holds a counter.
 class ThreadSafeCounter {
@@ -72,10 +72,13 @@ static void BasicTests(bool notify_before_waiting, Notification* notification) {
       notification->WaitForNotificationWithTimeout(absl::Milliseconds(0)));
   EXPECT_FALSE(notification->WaitForNotificationWithDeadline(absl::Now()));
 
+  const absl::Duration delay = absl::Milliseconds(50);
+  // Allow for a slight early return, to account for quality of implementation
+  // issues on various platforms.
+  const absl::Duration slop = absl::Microseconds(200);
   absl::Time start = absl::Now();
-  EXPECT_FALSE(
-      notification->WaitForNotificationWithTimeout(absl::Milliseconds(50)));
-  EXPECT_LE(start + absl::Milliseconds(50), absl::Now());
+  EXPECT_FALSE(notification->WaitForNotificationWithTimeout(delay));
+  EXPECT_LE(start + delay, absl::Now() + slop);
 
   ThreadSafeCounter ready_counter;
   ThreadSafeCounter done_counter;
@@ -122,5 +125,5 @@ TEST(NotificationTest, SanityTest) {
   BasicTests(true, &local_notification2);
 }
 
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl