microsoft · StephanTLavavej · Oct 17, 2020 · Oct 13, 2020 · Oct 13, 2020 · Oct 13, 2020
diff --git a/README.md b/README.md
@@ -143,7 +143,7 @@ Just try to follow these rules, so we can spend more time fixing bugs and implem
 The STL uses boost-math headers to provide P0226R1 Mathematical Special Functions. We recommend using [vcpkg][] to
 acquire this dependency.
 
-1. Install Visual Studio 2019 16.8 Preview 3 or later.
+1. Install Visual Studio 2019 16.8 Preview 4 or later.
     * We recommend selecting "C++ CMake tools for Windows" in the VS Installer.
     This will ensure that you're using supported versions of CMake and Ninja.
     * Otherwise, install [CMake][] 3.17 or later, and [Ninja][] 1.8.2 or later.
@@ -158,7 +158,7 @@ acquire this dependency.
 
 # How To Build With A Native Tools Command Prompt
 
-1. Install Visual Studio 2019 16.8 Preview 3 or later.
+1. Install Visual Studio 2019 16.8 Preview 4 or later.
     * We recommend selecting "C++ CMake tools for Windows" in the VS Installer.
     This will ensure that you're using supported versions of CMake and Ninja.
     * Otherwise, install [CMake][] 3.17 or later, and [Ninja][] 1.8.2 or later.
@@ -235,7 +235,7 @@ C:\Users\username\Desktop>dumpbin /IMPORTS .\example.exe | findstr msvcp
 
 1. Follow either [How To Build With A Native Tools Command Prompt][] or [How To Build With The Visual Studio IDE][].
 2. Invoke `git submodule update --init llvm-project` at the root of the STL source tree.
-3. Acquire [Python][] 3.8 or newer and have it on the `PATH` (or run it directly using its absolute or relative path).
+3. Acquire [Python][] 3.9 or newer and have it on the `PATH` (or run it directly using its absolute or relative path).
 4. Have LLVM's `bin` directory on the `PATH` (so `clang-cl.exe` is available).
     * We recommend selecting "C++ Clang tools for Windows" in the VS Installer. This will automatically add LLVM to the
     `PATH` of the x86 and x64 Native Tools Command Prompts, and will ensure that you're using a supported version.

diff --git a/azure-devops/provision-image.ps1 b/azure-devops/provision-image.ps1
@@ -97,7 +97,7 @@ $Workloads = @(
 $ReleaseInPath = 'Preview'
 $Sku = 'Enterprise'
 $VisualStudioBootstrapperUrl = 'https://aka.ms/vs/16/pre/vs_enterprise.exe'
-$PythonUrl = 'https://www.python.org/ftp/python/3.8.5/python-3.8.5-amd64.exe'
+$PythonUrl = 'https://www.python.org/ftp/python/3.9.0/python-3.9.0-amd64.exe'
 
 $CudaUrl = `
   'https://developer.download.nvidia.com/compute/cuda/10.1/Prod/local_installers/cuda_10.1.243_426.00_win10.exe'

diff --git a/azure-pipelines.yml b/azure-pipelines.yml
@@ -6,7 +6,7 @@
 variables:
   tmpDir: 'D:\Temp'
 
-pool: 'StlBuild-2020-09-14'
+pool: 'StlBuild-2020-10-13'
 
 stages:
   - stage: Code_Format

diff --git a/stl/inc/condition_variable b/stl/inc/condition_variable
@@ -130,7 +130,7 @@ public:
     template <class _Lock, class _Rep, class _Period, class _Predicate>
     bool wait_for(_Lock& _Lck, const chrono::duration<_Rep, _Period>& _Rel_time, _Predicate _Pred) {
         // wait for signal with timeout and check predicate
-        return wait_until(_Lck, chrono::steady_clock::now() + _Rel_time, _STD move(_Pred));
+        return wait_until(_Lck, _To_absolute_time(_Rel_time), _STD move(_Pred));
     }
 
     template <class _Lock>
@@ -232,7 +232,7 @@ public:
 
     template <class _Lock, class _Rep, class _Period, class _Predicate>
     bool wait_for(_Lock& _Lck, stop_token _Stoken, const chrono::duration<_Rep, _Period>& _Rel_time, _Predicate _Pred) {
-        return wait_until(_Lck, _STD move(_Stoken), chrono::steady_clock::now() + _Rel_time, _STD move(_Pred));
+        return wait_until(_Lck, _STD move(_Stoken), _To_absolute_time(_Rel_time), _STD move(_Pred));
     }
 #endif // _HAS_CXX20
 

diff --git a/stl/inc/mutex b/stl/inc/mutex
@@ -628,7 +628,7 @@ public:
     template <class _Rep, class _Period, class _Predicate>
     bool wait_for(unique_lock<mutex>& _Lck, const chrono::duration<_Rep, _Period>& _Rel_time, _Predicate _Pred) {
         // wait for signal with timeout and check predicate
-        return _Wait_until1(_Lck, chrono::steady_clock::now() + _Rel_time, _Pred);
+        return _Wait_until1(_Lck, _To_absolute_time(_Rel_time), _Pred);
     }
 
     template <class _Clock, class _Duration>
@@ -776,7 +776,7 @@ public:
 
     template <class _Rep, class _Period>
     _NODISCARD bool try_lock_for(const chrono::duration<_Rep, _Period>& _Rel_time) { // try to lock for duration
-        return try_lock_until(chrono::steady_clock::now() + _Rel_time);
+        return try_lock_until(_To_absolute_time(_Rel_time));
     }
 
     template <class _Time>
@@ -875,7 +875,7 @@ public:
 
     template <class _Rep, class _Period>
     _NODISCARD bool try_lock_for(const chrono::duration<_Rep, _Period>& _Rel_time) { // try to lock for duration
-        return try_lock_until(chrono::steady_clock::now() + _Rel_time);
+        return try_lock_until(_To_absolute_time(_Rel_time));
     }
 
     template <class _Time>

diff --git a/stl/inc/shared_mutex b/stl/inc/shared_mutex
@@ -110,7 +110,7 @@ public:
 
     template <class _Rep, class _Period>
     _NODISCARD bool try_lock_for(const chrono::duration<_Rep, _Period>& _Rel_time) { // try to lock for duration
-        return try_lock_until(chrono::steady_clock::now() + _Rel_time);
+        return try_lock_until(_To_absolute_time(_Rel_time));
     }
 
     template <class _Clock, class _Duration>
@@ -168,7 +168,7 @@ public:
     template <class _Rep, class _Period>
     _NODISCARD bool try_lock_shared_for(
         const chrono::duration<_Rep, _Period>& _Rel_time) { // try to lock non-exclusive for relative time
-        return try_lock_shared_until(_Rel_time + chrono::steady_clock::now());
+        return try_lock_shared_until(_To_absolute_time(_Rel_time));
     }
 
     template <class _Time>

diff --git a/stl/inc/thread b/stl/inc/thread
@@ -156,6 +156,22 @@ private:
     _Thrd_t _Thr;
 };
 
+template <class _Rep, class _Period>
+_NODISCARD auto _To_absolute_time(const chrono::duration<_Rep, _Period>& _Rel_time) noexcept {
+    constexpr auto _Zero                 = chrono::duration<_Rep, _Period>::zero();
+    const auto _Now                      = chrono::steady_clock::now();
+    decltype(_Now + _Rel_time) _Abs_time = _Now; // return common type
+    if (_Rel_time > _Zero) {
+        constexpr auto _Forever = (chrono::steady_clock::time_point::max)();
+        if (_Abs_time < _Forever - _Rel_time) {
+            _Abs_time += _Rel_time;
+        } else {
+            _Abs_time = _Forever;
+        }
+    }
+    return _Abs_time;
+}
+
 namespace this_thread {
     _NODISCARD thread::id get_id() noexcept;
 
@@ -183,7 +199,7 @@ namespace this_thread {
 
     template <class _Rep, class _Period>
     void sleep_for(const chrono::duration<_Rep, _Period>& _Rel_time) {
-        sleep_until(chrono::steady_clock::now() + _Rel_time);
+        sleep_until(_To_absolute_time(_Rel_time));
     }
 } // namespace this_thread
 

diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
@@ -18,7 +18,7 @@ add_subdirectory(tr1)
 # chance to add to the config map and test directory global properties.
 add_subdirectory(utils/stl-lit)
 
-find_package(Python "3.8" REQUIRED COMPONENTS Interpreter)
+find_package(Python "3.9" REQUIRED COMPONENTS Interpreter)
 
 if(NOT DEFINED LIT_FLAGS)
     list(APPEND LIT_FLAGS "-o" "${CMAKE_CURRENT_BINARY_DIR}/test_results.json")

diff --git a/tests/std/tests/P0660R10_jthread_and_cv_any/test.cpp b/tests/std/tests/P0660R10_jthread_and_cv_any/test.cpp
@@ -180,7 +180,7 @@ int main() {
         jthread worker([&](stop_token token) {
             unique_lock lck{m};
             assert(cv.wait(lck, move(token), [] { return true; }) == true);
-            assert(cv.wait(lck, move(token), [&] { return b; }) == true);
+            assert(cv.wait(lck, move(token), [&] { return b; }) == true); // Intentionally uses moved-from token
         });
 
         {
@@ -198,7 +198,8 @@ int main() {
         jthread worker([&](stop_token token) {
             unique_lock lck{m};
             assert(cv.wait_until(lck, move(token), infinity, [] { return true; }) == true);
-            assert(cv.wait_until(lck, move(token), infinity, [&] { return b; }) == true);
+            assert(cv.wait_until(lck, move(token), infinity, [&] { return b; })
+                   == true); // Intentionally uses moved-from token
         });
 
         {
@@ -216,7 +217,8 @@ int main() {
         jthread worker([&](stop_token token) {
             unique_lock lck{m};
             assert(cv.wait_for(lck, move(token), forever, [] { return true; }) == true);
-            assert(cv.wait_for(lck, move(token), forever, [&] { return b; }) == true);
+            assert(cv.wait_for(lck, move(token), forever, [&] { return b; })
+                   == true); // Intentionally uses moved-from token
         });
 
         {