diff --git a/libcxx/docs/ReleaseNotes.rst b/libcxx/docs/ReleaseNotes.rst
--- a/libcxx/docs/ReleaseNotes.rst
+++ b/libcxx/docs/ReleaseNotes.rst
@@ -59,7 +59,8 @@
   includes are removed based on the language version used. Incidental transitive
   inclusions of the following headers have been removed:
 
-  - C++2b: ``atomic``, ``bit``, ``cstring``, ``type_traits``
+  - C++2b: ``atomic``, ``bit``, ``cstdint``, ``cstdlib``, ``cstring``, ``initializer_list``, ``new``, ``stdexcept``,
+           ``type_traits``, ``typeinfo``
 
 - The headers ``<experimental/algorithm>`` and ``<experimental/functional>`` have been removed, since all the contents
   have been implemented in namespace ``std`` for at least two releases.
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -294,6 +294,7 @@
   __concepts/semiregular.h
   __concepts/swappable.h
   __concepts/totally_ordered.h
+  __condition_variable/condition_variable.h
   __config
   __coroutine/coroutine_handle.h
   __coroutine/coroutine_traits.h
@@ -474,7 +475,10 @@
   __memory_resource/pool_options.h
   __memory_resource/synchronized_pool_resource.h
   __memory_resource/unsynchronized_pool_resource.h
-  __mutex_base
+  __mutex/lock_guard.h
+  __mutex/mutex.h
+  __mutex/tag_types.h
+  __mutex/unique_lock.h
   __node_handle
   __numeric/accumulate.h
   __numeric/adjacent_difference.h
diff --git a/libcxx/include/__mutex_base b/libcxx/include/__condition_variable/condition_variable.h
rename from libcxx/include/__mutex_base
rename to libcxx/include/__condition_variable/condition_variable.h
--- a/libcxx/include/__mutex_base
+++ b/libcxx/include/__condition_variable/condition_variable.h
@@ -1,4 +1,3 @@
-// -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
@@ -7,20 +6,21 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP___MUTEX_BASE
-#define _LIBCPP___MUTEX_BASE
+#ifndef _LIBCPP___CONDITION_VARIABLE_CONDITION_VARIABLE_H
+#define _LIBCPP___CONDITION_VARIABLE_CONDITION_VARIABLE_H
 
-#include <__chrono/duration.h>
 #include <__chrono/steady_clock.h>
 #include <__chrono/system_clock.h>
 #include <__chrono/time_point.h>
 #include <__config>
+#include <__mutex/mutex.h>
+#include <__mutex/unique_lock.h>
 #include <__threading_support>
+#include <__type_traits/enable_if.h>
 #include <__type_traits/is_floating_point.h>
-#include <__type_traits/is_nothrow_default_constructible.h>
+#include <__utility/move.h>
 #include <ratio>
 #include <system_error>
-#include <time.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -29,242 +29,9 @@
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 
-
-_LIBCPP_BEGIN_NAMESPACE_STD
-
 #ifndef _LIBCPP_HAS_NO_THREADS
 
-class _LIBCPP_TYPE_VIS _LIBCPP_THREAD_SAFETY_ANNOTATION(capability("mutex")) mutex
-{
-    __libcpp_mutex_t __m_ = _LIBCPP_MUTEX_INITIALIZER;
-
-public:
-    _LIBCPP_INLINE_VISIBILITY
-    _LIBCPP_CONSTEXPR mutex() = default;
-
-    mutex(const mutex&) = delete;
-    mutex& operator=(const mutex&) = delete;
-
-#if defined(_LIBCPP_HAS_TRIVIAL_MUTEX_DESTRUCTION)
-    ~mutex() = default;
-#else
-    ~mutex() _NOEXCEPT;
-#endif
-
-    void lock() _LIBCPP_THREAD_SAFETY_ANNOTATION(acquire_capability());
-    bool try_lock() _NOEXCEPT _LIBCPP_THREAD_SAFETY_ANNOTATION(try_acquire_capability(true));
-    void unlock() _NOEXCEPT _LIBCPP_THREAD_SAFETY_ANNOTATION(release_capability());
-
-    typedef __libcpp_mutex_t* native_handle_type;
-    _LIBCPP_INLINE_VISIBILITY native_handle_type native_handle() {return &__m_;}
-};
-
-static_assert(is_nothrow_default_constructible<mutex>::value,
-              "the default constructor for std::mutex must be nothrow");
-
-struct _LIBCPP_TYPE_VIS defer_lock_t { explicit defer_lock_t() = default; };
-struct _LIBCPP_TYPE_VIS try_to_lock_t { explicit try_to_lock_t() = default; };
-struct _LIBCPP_TYPE_VIS adopt_lock_t { explicit adopt_lock_t() = default; };
-
-#if defined(_LIBCPP_CXX03_LANG) || defined(_LIBCPP_BUILDING_LIBRARY)
-
-extern _LIBCPP_EXPORTED_FROM_ABI const defer_lock_t  defer_lock;
-extern _LIBCPP_EXPORTED_FROM_ABI const try_to_lock_t try_to_lock;
-extern _LIBCPP_EXPORTED_FROM_ABI const adopt_lock_t  adopt_lock;
-
-#else
-
-/* inline */ constexpr defer_lock_t  defer_lock  = defer_lock_t();
-/* inline */ constexpr try_to_lock_t try_to_lock = try_to_lock_t();
-/* inline */ constexpr adopt_lock_t  adopt_lock  = adopt_lock_t();
-
-#endif
-
-template <class _Mutex>
-class _LIBCPP_TEMPLATE_VIS _LIBCPP_THREAD_SAFETY_ANNOTATION(scoped_lockable)
-lock_guard
-{
-public:
-    typedef _Mutex mutex_type;
-
-private:
-    mutex_type& __m_;
-public:
-
-    _LIBCPP_NODISCARD_EXT _LIBCPP_INLINE_VISIBILITY
-    explicit lock_guard(mutex_type& __m) _LIBCPP_THREAD_SAFETY_ANNOTATION(acquire_capability(__m))
-        : __m_(__m) {__m_.lock();}
-
-    _LIBCPP_NODISCARD_EXT _LIBCPP_INLINE_VISIBILITY
-    lock_guard(mutex_type& __m, adopt_lock_t) _LIBCPP_THREAD_SAFETY_ANNOTATION(requires_capability(__m))
-        : __m_(__m) {}
-    _LIBCPP_INLINE_VISIBILITY
-    ~lock_guard() _LIBCPP_THREAD_SAFETY_ANNOTATION(release_capability()) {__m_.unlock();}
-
-private:
-    lock_guard(lock_guard const&) = delete;
-    lock_guard& operator=(lock_guard const&) = delete;
-};
-_LIBCPP_CTAD_SUPPORTED_FOR_TYPE(lock_guard);
-
-template <class _Mutex>
-class _LIBCPP_TEMPLATE_VIS unique_lock
-{
-public:
-    typedef _Mutex mutex_type;
-
-private:
-    mutex_type* __m_;
-    bool __owns_;
-
-public:
-    _LIBCPP_INLINE_VISIBILITY
-    unique_lock() _NOEXCEPT : __m_(nullptr), __owns_(false) {}
-    _LIBCPP_INLINE_VISIBILITY
-    explicit unique_lock(mutex_type& __m)
-        : __m_(_VSTD::addressof(__m)), __owns_(true) {__m_->lock();}
-    _LIBCPP_INLINE_VISIBILITY
-    unique_lock(mutex_type& __m, defer_lock_t) _NOEXCEPT
-        : __m_(_VSTD::addressof(__m)), __owns_(false) {}
-    _LIBCPP_INLINE_VISIBILITY
-    unique_lock(mutex_type& __m, try_to_lock_t)
-        : __m_(_VSTD::addressof(__m)), __owns_(__m.try_lock()) {}
-    _LIBCPP_INLINE_VISIBILITY
-    unique_lock(mutex_type& __m, adopt_lock_t)
-        : __m_(_VSTD::addressof(__m)), __owns_(true) {}
-    template <class _Clock, class _Duration>
-    _LIBCPP_INLINE_VISIBILITY
-        unique_lock(mutex_type& __m, const chrono::time_point<_Clock, _Duration>& __t)
-            : __m_(_VSTD::addressof(__m)), __owns_(__m.try_lock_until(__t)) {}
-    template <class _Rep, class _Period>
-    _LIBCPP_INLINE_VISIBILITY
-        unique_lock(mutex_type& __m, const chrono::duration<_Rep, _Period>& __d)
-            : __m_(_VSTD::addressof(__m)), __owns_(__m.try_lock_for(__d)) {}
-    _LIBCPP_INLINE_VISIBILITY
-    ~unique_lock()
-    {
-        if (__owns_)
-            __m_->unlock();
-    }
-
-    unique_lock(unique_lock const&) = delete;
-    unique_lock& operator=(unique_lock const&) = delete;
-
-    _LIBCPP_INLINE_VISIBILITY
-    unique_lock(unique_lock&& __u) _NOEXCEPT
-        : __m_(__u.__m_), __owns_(__u.__owns_)
-        {__u.__m_ = nullptr; __u.__owns_ = false;}
-    _LIBCPP_INLINE_VISIBILITY
-    unique_lock& operator=(unique_lock&& __u) _NOEXCEPT
-        {
-            if (__owns_)
-                __m_->unlock();
-            __m_ = __u.__m_;
-            __owns_ = __u.__owns_;
-            __u.__m_ = nullptr;
-            __u.__owns_ = false;
-            return *this;
-        }
-
-    void lock();
-    bool try_lock();
-
-    template <class _Rep, class _Period>
-        bool try_lock_for(const chrono::duration<_Rep, _Period>& __d);
-    template <class _Clock, class _Duration>
-        bool try_lock_until(const chrono::time_point<_Clock, _Duration>& __t);
-
-    void unlock();
-
-    _LIBCPP_INLINE_VISIBILITY
-    void swap(unique_lock& __u) _NOEXCEPT
-    {
-        _VSTD::swap(__m_, __u.__m_);
-        _VSTD::swap(__owns_, __u.__owns_);
-    }
-    _LIBCPP_INLINE_VISIBILITY
-    mutex_type* release() _NOEXCEPT
-    {
-        mutex_type* __m = __m_;
-        __m_ = nullptr;
-        __owns_ = false;
-        return __m;
-    }
-
-    _LIBCPP_INLINE_VISIBILITY
-    bool owns_lock() const _NOEXCEPT {return __owns_;}
-    _LIBCPP_INLINE_VISIBILITY
-    explicit operator bool() const _NOEXCEPT {return __owns_;}
-    _LIBCPP_INLINE_VISIBILITY
-    mutex_type* mutex() const _NOEXCEPT {return __m_;}
-};
-_LIBCPP_CTAD_SUPPORTED_FOR_TYPE(unique_lock);
-
-template <class _Mutex>
-void
-unique_lock<_Mutex>::lock()
-{
-    if (__m_ == nullptr)
-        __throw_system_error(EPERM, "unique_lock::lock: references null mutex");
-    if (__owns_)
-        __throw_system_error(EDEADLK, "unique_lock::lock: already locked");
-    __m_->lock();
-    __owns_ = true;
-}
-
-template <class _Mutex>
-bool
-unique_lock<_Mutex>::try_lock()
-{
-    if (__m_ == nullptr)
-        __throw_system_error(EPERM, "unique_lock::try_lock: references null mutex");
-    if (__owns_)
-        __throw_system_error(EDEADLK, "unique_lock::try_lock: already locked");
-    __owns_ = __m_->try_lock();
-    return __owns_;
-}
-
-template <class _Mutex>
-template <class _Rep, class _Period>
-bool
-unique_lock<_Mutex>::try_lock_for(const chrono::duration<_Rep, _Period>& __d)
-{
-    if (__m_ == nullptr)
-        __throw_system_error(EPERM, "unique_lock::try_lock_for: references null mutex");
-    if (__owns_)
-        __throw_system_error(EDEADLK, "unique_lock::try_lock_for: already locked");
-    __owns_ = __m_->try_lock_for(__d);
-    return __owns_;
-}
-
-template <class _Mutex>
-template <class _Clock, class _Duration>
-bool
-unique_lock<_Mutex>::try_lock_until(const chrono::time_point<_Clock, _Duration>& __t)
-{
-    if (__m_ == nullptr)
-        __throw_system_error(EPERM, "unique_lock::try_lock_until: references null mutex");
-    if (__owns_)
-        __throw_system_error(EDEADLK, "unique_lock::try_lock_until: already locked");
-    __owns_ = __m_->try_lock_until(__t);
-    return __owns_;
-}
-
-template <class _Mutex>
-void
-unique_lock<_Mutex>::unlock()
-{
-    if (!__owns_)
-        __throw_system_error(EPERM, "unique_lock::unlock: not locked");
-    __m_->unlock();
-    __owns_ = false;
-}
-
-template <class _Mutex>
-inline _LIBCPP_INLINE_VISIBILITY
-void
-swap(unique_lock<_Mutex>& __x, unique_lock<_Mutex>& __y) _NOEXCEPT
-    {__x.swap(__y);}
+_LIBCPP_BEGIN_NAMESPACE_STD
 
 //enum class cv_status
 _LIBCPP_DECLARE_STRONG_ENUM(cv_status)
@@ -516,10 +283,10 @@
     wait_for(__lk, __tp - _Clock::now());
 }
 
-#endif // !_LIBCPP_HAS_NO_THREADS
-
 _LIBCPP_END_NAMESPACE_STD
 
+#endif // _LIBCPP_HAS_NO_THREADS
+
 _LIBCPP_POP_MACROS
 
-#endif // _LIBCPP___MUTEX_BASE
+#endif // _LIBCPP___CONDITION_VARIABLE_CONDITION_VARIABLE_H
diff --git a/libcxx/include/__mutex/lock_guard.h b/libcxx/include/__mutex/lock_guard.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__mutex/lock_guard.h
@@ -0,0 +1,54 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___MUTEX_LOCK_GUARD_H
+#define _LIBCPP___MUTEX_LOCK_GUARD_H
+
+#include <__config>
+#include <__mutex/tag_types.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#ifndef _LIBCPP_HAS_NO_THREADS
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Mutex>
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_THREAD_SAFETY_ANNOTATION(scoped_lockable)
+lock_guard
+{
+public:
+    typedef _Mutex mutex_type;
+
+private:
+    mutex_type& __m_;
+public:
+
+    _LIBCPP_NODISCARD_EXT _LIBCPP_INLINE_VISIBILITY
+    explicit lock_guard(mutex_type& __m) _LIBCPP_THREAD_SAFETY_ANNOTATION(acquire_capability(__m))
+        : __m_(__m) {__m_.lock();}
+
+    _LIBCPP_NODISCARD_EXT _LIBCPP_INLINE_VISIBILITY
+    lock_guard(mutex_type& __m, adopt_lock_t) _LIBCPP_THREAD_SAFETY_ANNOTATION(requires_capability(__m))
+        : __m_(__m) {}
+    _LIBCPP_INLINE_VISIBILITY
+    ~lock_guard() _LIBCPP_THREAD_SAFETY_ANNOTATION(release_capability()) {__m_.unlock();}
+
+private:
+    lock_guard(lock_guard const&) = delete;
+    lock_guard& operator=(lock_guard const&) = delete;
+};
+_LIBCPP_CTAD_SUPPORTED_FOR_TYPE(lock_guard);
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_HAS_NO_THREADS
+
+#endif // _LIBCPP___MUTEX_LOCK_GUARD_H
diff --git a/libcxx/include/__mutex/mutex.h b/libcxx/include/__mutex/mutex.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__mutex/mutex.h
@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___MUTEX_MUTEX_H
+#define _LIBCPP___MUTEX_MUTEX_H
+
+#include <__config>
+#include <__threading_support>
+#include <__type_traits/is_nothrow_default_constructible.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#ifndef _LIBCPP_HAS_NO_THREADS
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+class _LIBCPP_TYPE_VIS _LIBCPP_THREAD_SAFETY_ANNOTATION(capability("mutex")) mutex
+{
+    __libcpp_mutex_t __m_ = _LIBCPP_MUTEX_INITIALIZER;
+
+public:
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR mutex() = default;
+
+    mutex(const mutex&) = delete;
+    mutex& operator=(const mutex&) = delete;
+
+#if defined(_LIBCPP_HAS_TRIVIAL_MUTEX_DESTRUCTION)
+    ~mutex() = default;
+#else
+    ~mutex() _NOEXCEPT;
+#endif
+
+    void lock() _LIBCPP_THREAD_SAFETY_ANNOTATION(acquire_capability());
+    bool try_lock() _NOEXCEPT _LIBCPP_THREAD_SAFETY_ANNOTATION(try_acquire_capability(true));
+    void unlock() _NOEXCEPT _LIBCPP_THREAD_SAFETY_ANNOTATION(release_capability());
+
+    typedef __libcpp_mutex_t* native_handle_type;
+    _LIBCPP_INLINE_VISIBILITY native_handle_type native_handle() {return &__m_;}
+};
+
+static_assert(is_nothrow_default_constructible<mutex>::value,
+              "the default constructor for std::mutex must be nothrow");
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_HAS_NO_THREADS
+
+#endif // _LIBCPP___MUTEX_MUTEX_H
diff --git a/libcxx/include/__mutex/tag_types.h b/libcxx/include/__mutex/tag_types.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__mutex/tag_types.h
@@ -0,0 +1,44 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___MUTEX_TAG_TYPES_H
+#define _LIBCPP___MUTEX_TAG_TYPES_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#ifndef _LIBCPP_HAS_NO_THREADS
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+struct _LIBCPP_TYPE_VIS defer_lock_t { explicit defer_lock_t() = default; };
+struct _LIBCPP_TYPE_VIS try_to_lock_t { explicit try_to_lock_t() = default; };
+struct _LIBCPP_TYPE_VIS adopt_lock_t { explicit adopt_lock_t() = default; };
+
+#if defined(_LIBCPP_CXX03_LANG) || defined(_LIBCPP_BUILDING_LIBRARY)
+
+extern _LIBCPP_EXPORTED_FROM_ABI const defer_lock_t  defer_lock;
+extern _LIBCPP_EXPORTED_FROM_ABI const try_to_lock_t try_to_lock;
+extern _LIBCPP_EXPORTED_FROM_ABI const adopt_lock_t  adopt_lock;
+
+#else
+
+/* inline */ constexpr defer_lock_t  defer_lock  = defer_lock_t();
+/* inline */ constexpr try_to_lock_t try_to_lock = try_to_lock_t();
+/* inline */ constexpr adopt_lock_t  adopt_lock  = adopt_lock_t();
+
+#endif
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_HAS_NO_THREADS
+
+#endif // _LIBCPP___MUTEX_TAG_TYPES_H
diff --git a/libcxx/include/__mutex/unique_lock.h b/libcxx/include/__mutex/unique_lock.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__mutex/unique_lock.h
@@ -0,0 +1,191 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___MUTEX_UNIQUE_LOCK_H
+#define _LIBCPP___MUTEX_UNIQUE_LOCK_H
+
+#include <__chrono/duration.h>
+#include <__chrono/time_point.h>
+#include <__config>
+#include <__memory/addressof.h>
+#include <__mutex/tag_types.h>
+#include <__utility/swap.h>
+#include <system_error>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#ifndef _LIBCPP_HAS_NO_THREADS
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Mutex>
+class _LIBCPP_TEMPLATE_VIS unique_lock
+{
+public:
+    typedef _Mutex mutex_type;
+
+private:
+    mutex_type* __m_;
+    bool __owns_;
+
+public:
+    _LIBCPP_INLINE_VISIBILITY
+    unique_lock() _NOEXCEPT : __m_(nullptr), __owns_(false) {}
+    _LIBCPP_INLINE_VISIBILITY
+    explicit unique_lock(mutex_type& __m)
+        : __m_(_VSTD::addressof(__m)), __owns_(true) {__m_->lock();}
+    _LIBCPP_INLINE_VISIBILITY
+    unique_lock(mutex_type& __m, defer_lock_t) _NOEXCEPT
+        : __m_(_VSTD::addressof(__m)), __owns_(false) {}
+    _LIBCPP_INLINE_VISIBILITY
+    unique_lock(mutex_type& __m, try_to_lock_t)
+        : __m_(_VSTD::addressof(__m)), __owns_(__m.try_lock()) {}
+    _LIBCPP_INLINE_VISIBILITY
+    unique_lock(mutex_type& __m, adopt_lock_t)
+        : __m_(_VSTD::addressof(__m)), __owns_(true) {}
+    template <class _Clock, class _Duration>
+    _LIBCPP_INLINE_VISIBILITY
+        unique_lock(mutex_type& __m, const chrono::time_point<_Clock, _Duration>& __t)
+            : __m_(_VSTD::addressof(__m)), __owns_(__m.try_lock_until(__t)) {}
+    template <class _Rep, class _Period>
+    _LIBCPP_INLINE_VISIBILITY
+        unique_lock(mutex_type& __m, const chrono::duration<_Rep, _Period>& __d)
+            : __m_(_VSTD::addressof(__m)), __owns_(__m.try_lock_for(__d)) {}
+    _LIBCPP_INLINE_VISIBILITY
+    ~unique_lock()
+    {
+        if (__owns_)
+            __m_->unlock();
+    }
+
+    unique_lock(unique_lock const&) = delete;
+    unique_lock& operator=(unique_lock const&) = delete;
+
+    _LIBCPP_INLINE_VISIBILITY
+    unique_lock(unique_lock&& __u) _NOEXCEPT
+        : __m_(__u.__m_), __owns_(__u.__owns_)
+        {__u.__m_ = nullptr; __u.__owns_ = false;}
+    _LIBCPP_INLINE_VISIBILITY
+    unique_lock& operator=(unique_lock&& __u) _NOEXCEPT
+        {
+            if (__owns_)
+                __m_->unlock();
+            __m_ = __u.__m_;
+            __owns_ = __u.__owns_;
+            __u.__m_ = nullptr;
+            __u.__owns_ = false;
+            return *this;
+        }
+
+    void lock();
+    bool try_lock();
+
+    template <class _Rep, class _Period>
+        bool try_lock_for(const chrono::duration<_Rep, _Period>& __d);
+    template <class _Clock, class _Duration>
+        bool try_lock_until(const chrono::time_point<_Clock, _Duration>& __t);
+
+    void unlock();
+
+    _LIBCPP_INLINE_VISIBILITY
+    void swap(unique_lock& __u) _NOEXCEPT
+    {
+        _VSTD::swap(__m_, __u.__m_);
+        _VSTD::swap(__owns_, __u.__owns_);
+    }
+    _LIBCPP_INLINE_VISIBILITY
+    mutex_type* release() _NOEXCEPT
+    {
+        mutex_type* __m = __m_;
+        __m_ = nullptr;
+        __owns_ = false;
+        return __m;
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    bool owns_lock() const _NOEXCEPT {return __owns_;}
+    _LIBCPP_INLINE_VISIBILITY
+    explicit operator bool() const _NOEXCEPT {return __owns_;}
+    _LIBCPP_INLINE_VISIBILITY
+    mutex_type* mutex() const _NOEXCEPT {return __m_;}
+};
+_LIBCPP_CTAD_SUPPORTED_FOR_TYPE(unique_lock);
+
+template <class _Mutex>
+void
+unique_lock<_Mutex>::lock()
+{
+    if (__m_ == nullptr)
+        __throw_system_error(EPERM, "unique_lock::lock: references null mutex");
+    if (__owns_)
+        __throw_system_error(EDEADLK, "unique_lock::lock: already locked");
+    __m_->lock();
+    __owns_ = true;
+}
+
+template <class _Mutex>
+bool
+unique_lock<_Mutex>::try_lock()
+{
+    if (__m_ == nullptr)
+        __throw_system_error(EPERM, "unique_lock::try_lock: references null mutex");
+    if (__owns_)
+        __throw_system_error(EDEADLK, "unique_lock::try_lock: already locked");
+    __owns_ = __m_->try_lock();
+    return __owns_;
+}
+
+template <class _Mutex>
+template <class _Rep, class _Period>
+bool
+unique_lock<_Mutex>::try_lock_for(const chrono::duration<_Rep, _Period>& __d)
+{
+    if (__m_ == nullptr)
+        __throw_system_error(EPERM, "unique_lock::try_lock_for: references null mutex");
+    if (__owns_)
+        __throw_system_error(EDEADLK, "unique_lock::try_lock_for: already locked");
+    __owns_ = __m_->try_lock_for(__d);
+    return __owns_;
+}
+
+template <class _Mutex>
+template <class _Clock, class _Duration>
+bool
+unique_lock<_Mutex>::try_lock_until(const chrono::time_point<_Clock, _Duration>& __t)
+{
+    if (__m_ == nullptr)
+        __throw_system_error(EPERM, "unique_lock::try_lock_until: references null mutex");
+    if (__owns_)
+        __throw_system_error(EDEADLK, "unique_lock::try_lock_until: already locked");
+    __owns_ = __m_->try_lock_until(__t);
+    return __owns_;
+}
+
+template <class _Mutex>
+void
+unique_lock<_Mutex>::unlock()
+{
+    if (!__owns_)
+        __throw_system_error(EPERM, "unique_lock::unlock: not locked");
+    __m_->unlock();
+    __owns_ = false;
+}
+
+template <class _Mutex>
+inline _LIBCPP_INLINE_VISIBILITY
+void
+swap(unique_lock<_Mutex>& __x, unique_lock<_Mutex>& __y) _NOEXCEPT
+    {__x.swap(__y);}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_HAS_NO_THREADS
+
+#endif // _LIBCPP___MUTEX_UNIQUE_LOCK_H
diff --git a/libcxx/include/condition_variable b/libcxx/include/condition_variable
--- a/libcxx/include/condition_variable
+++ b/libcxx/include/condition_variable
@@ -107,10 +107,18 @@
 */
 
 #include <__assert> // all public C++ headers provide the assertion handler
+#include <__chrono/duration.h>
+#include <__chrono/steady_clock.h>
+#include <__chrono/time_point.h>
+#include <__condition_variable/condition_variable.h>
 #include <__config>
 #include <__memory/shared_ptr.h>
 #include <__memory/unique_ptr.h>
-#include <__mutex_base>
+#include <__mutex/lock_guard.h>
+#include <__mutex/mutex.h>
+#include <__mutex/tag_types.h>
+#include <__mutex/unique_lock.h>
+#include <__utility/move.h>
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -271,7 +279,14 @@
 #if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
 #  include <atomic>
 #  include <concepts>
+#  include <cstdint>
+#  include <cstdlib>
+#  include <cstring>
+#  include <initializer_list>
+#  include <new>
+#  include <stdexcept>
 #  include <type_traits>
+#  include <typeinfo>
 #endif
 
 #endif // _LIBCPP_CONDITION_VARIABLE
diff --git a/libcxx/include/libcxx.imp b/libcxx/include/libcxx.imp
--- a/libcxx/include/libcxx.imp
+++ b/libcxx/include/libcxx.imp
@@ -22,6 +22,7 @@
   { include: [ "@<__chrono/.*>", "private", "<chrono>", "public" ] },
   { include: [ "@<__compare/.*>", "private", "<compare>", "public" ] },
   { include: [ "@<__concepts/.*>", "private", "<concepts>", "public" ] },
+  { include: [ "@<__condition_variable/.*>", "private", "<condition_variable>", "public" ] },
   { include: [ "@<__coroutine/.*>", "private", "<coroutine>", "public" ] },
   { include: [ "@<__debug_utils/.*>", "private", "<debug_utils>", "public" ] },
   { include: [ "@<__exception/.*>", "private", "<exception>", "public" ] },
@@ -34,6 +35,7 @@
   { include: [ "@<__iterator/.*>", "private", "<iterator>", "public" ] },
   { include: [ "@<__memory/.*>", "private", "<memory>", "public" ] },
   { include: [ "@<__memory_resource/.*>", "private", "<memory_resource>", "public" ] },
+  { include: [ "@<__mutex/.*>", "private", "<mutex>", "public" ] },
   { include: [ "@<__numeric/.*>", "private", "<numeric>", "public" ] },
   { include: [ "@<__random/.*>", "private", "<random>", "public" ] },
   { include: [ "@<__ranges/.*>", "private", "<ranges>", "public" ] },
diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in
--- a/libcxx/include/module.modulemap.in
+++ b/libcxx/include/module.modulemap.in
@@ -813,6 +813,10 @@
   module condition_variable {
     header "condition_variable"
     export *
+
+    module __condition_variable {
+      module condition_variable { private header "__condition_variable/condition_variable.h" }
+    }
   }
   module coroutine {
     header "coroutine"
@@ -1174,6 +1178,13 @@
     @requires_LIBCXX_ENABLE_THREADS@
     header "mutex"
     export *
+
+    module __mutex {
+      module lock_guard  { private header "__mutex/lock_guard.h" }
+      module mutex       { private header "__mutex/mutex.h" }
+      module tag_types   { private header "__mutex/tag_types.h" }
+      module unique_lock { private header "__mutex/unique_lock.h" }
+    }
   }
   module new {
     header "new"
@@ -1695,7 +1706,6 @@
     private header "__locale" export *
   }
   module __mbstate_t         { private header "__mbstate_t.h"       export * }
-  module __mutex_base        { private header "__mutex_base"        export * }
   module __node_handle       { private header "__node_handle"       export * }
   module __split_buffer      { private header "__split_buffer"      export * }
   module __std_stream        {
diff --git a/libcxx/include/mutex b/libcxx/include/mutex
--- a/libcxx/include/mutex
+++ b/libcxx/include/mutex
@@ -187,9 +187,15 @@
 */
 
 #include <__assert> // all public C++ headers provide the assertion handler
+#include <__chrono/time_point.h>
+#include <__chrono/steady_clock.h>
+#include <__condition_variable/condition_variable.h>
 #include <__config>
 #include <__memory/shared_ptr.h>
-#include <__mutex_base>
+#include <__mutex/lock_guard.h>
+#include <__mutex/mutex.h>
+#include <__mutex/tag_types.h>
+#include <__mutex/unique_lock.h>
 #include <__threading_support>
 #include <__utility/forward.h>
 #include <cstdint>
@@ -706,9 +712,15 @@
 #if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
 #  include <atomic>
 #  include <concepts>
+#  include <cstdlib>
+#  include <cstring>
 #  include <ctime>
 #  include <functional>
+#  include <initializer_list>
+#  include <new>
+#  include <stdexcept>
 #  include <type_traits>
+#  include <typeinfo>
 #endif
 
 #endif // _LIBCPP_MUTEX
diff --git a/libcxx/include/shared_mutex b/libcxx/include/shared_mutex
--- a/libcxx/include/shared_mutex
+++ b/libcxx/include/shared_mutex
@@ -124,7 +124,19 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__availability>
+#include <__chrono/duration.h>
+#include <__chrono/ostream.h>
+#include <__chrono/steady_clock.h>
+#include <__chrono/time_point.h>
+#include <__condition_variable/condition_variable.h>
 #include <__config>
+#include <__memory/addressof.h>
+#include <__mutex/mutex.h>
+#include <__mutex/tag_types.h>
+#include <__mutex/unique_lock.h>
+#include <__utility/swap.h>
+#include <cerrno>
+#include <system_error>
 #include <version>
 
 _LIBCPP_PUSH_MACROS
@@ -133,8 +145,6 @@
 
 #if _LIBCPP_STD_VER >= 14 || defined(_LIBCPP_BUILDING_LIBRARY)
 
-#include <__mutex_base>
-
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
diff --git a/libcxx/include/thread b/libcxx/include/thread
--- a/libcxx/include/thread
+++ b/libcxx/include/thread
@@ -84,10 +84,14 @@
 */
 
 #include <__assert> // all public C++ headers provide the assertion handler
+#include <__chrono/steady_clock.h>
+#include <__chrono/time_point.h>
+#include <__condition_variable/condition_variable.h>
 #include <__config>
 #include <__functional/hash.h>
 #include <__memory/unique_ptr.h>
-#include <__mutex_base>
+#include <__mutex/mutex.h>
+#include <__mutex/unique_lock.h>
 #include <__thread/poll_with_backoff.h>
 #include <__thread/timed_backoff_policy.h>
 #include <__threading_support>
@@ -414,7 +418,10 @@
 #endif
 
 #if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
+#  include <cstdint>
+#  include <cstring>
 #  include <functional>
+#  include <new>
 #endif
 
 #endif // _LIBCPP_THREAD
diff --git a/libcxx/src/shared_mutex.cpp b/libcxx/src/shared_mutex.cpp
--- a/libcxx/src/shared_mutex.cpp
+++ b/libcxx/src/shared_mutex.cpp
@@ -10,6 +10,7 @@
 
 #ifndef _LIBCPP_HAS_NO_THREADS
 
+#include <mutex>
 #include <shared_mutex>
 #if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
 #  pragma comment(lib, "pthread")
diff --git a/libcxx/test/libcxx/private_headers.verify.cpp b/libcxx/test/libcxx/private_headers.verify.cpp
--- a/libcxx/test/libcxx/private_headers.verify.cpp
+++ b/libcxx/test/libcxx/private_headers.verify.cpp
@@ -328,6 +328,7 @@
 #include <__concepts/semiregular.h> // expected-error@*:* {{use of private header from outside its module: '__concepts/semiregular.h'}}
 #include <__concepts/swappable.h> // expected-error@*:* {{use of private header from outside its module: '__concepts/swappable.h'}}
 #include <__concepts/totally_ordered.h> // expected-error@*:* {{use of private header from outside its module: '__concepts/totally_ordered.h'}}
+#include <__condition_variable/condition_variable.h> // expected-error@*:* {{use of private header from outside its module: '__condition_variable/condition_variable.h'}}
 #include <__coroutine/coroutine_handle.h> // expected-error@*:* {{use of private header from outside its module: '__coroutine/coroutine_handle.h'}}
 #include <__coroutine/coroutine_traits.h> // expected-error@*:* {{use of private header from outside its module: '__coroutine/coroutine_traits.h'}}
 #include <__coroutine/noop_coroutine_handle.h> // expected-error@*:* {{use of private header from outside its module: '__coroutine/noop_coroutine_handle.h'}}
@@ -505,7 +506,10 @@
 #include <__memory_resource/pool_options.h> // expected-error@*:* {{use of private header from outside its module: '__memory_resource/pool_options.h'}}
 #include <__memory_resource/synchronized_pool_resource.h> // expected-error@*:* {{use of private header from outside its module: '__memory_resource/synchronized_pool_resource.h'}}
 #include <__memory_resource/unsynchronized_pool_resource.h> // expected-error@*:* {{use of private header from outside its module: '__memory_resource/unsynchronized_pool_resource.h'}}
-#include <__mutex_base> // expected-error@*:* {{use of private header from outside its module: '__mutex_base'}}
+#include <__mutex/lock_guard.h> // expected-error@*:* {{use of private header from outside its module: '__mutex/lock_guard.h'}}
+#include <__mutex/mutex.h> // expected-error@*:* {{use of private header from outside its module: '__mutex/mutex.h'}}
+#include <__mutex/tag_types.h> // expected-error@*:* {{use of private header from outside its module: '__mutex/tag_types.h'}}
+#include <__mutex/unique_lock.h> // expected-error@*:* {{use of private header from outside its module: '__mutex/unique_lock.h'}}
 #include <__node_handle> // expected-error@*:* {{use of private header from outside its module: '__node_handle'}}
 #include <__numeric/accumulate.h> // expected-error@*:* {{use of private header from outside its module: '__numeric/accumulate.h'}}
 #include <__numeric/adjacent_difference.h> // expected-error@*:* {{use of private header from outside its module: '__numeric/adjacent_difference.h'}}
diff --git a/libcxx/test/libcxx/thread/thread.condition/thread.condition.condvar/native_handle.pass.cpp b/libcxx/test/libcxx/thread/thread.condition/thread.condition.condvar/native_handle.pass.cpp
--- a/libcxx/test/libcxx/thread/thread.condition/thread.condition.condvar/native_handle.pass.cpp
+++ b/libcxx/test/libcxx/thread/thread.condition/thread.condition.condvar/native_handle.pass.cpp
@@ -17,8 +17,10 @@
 // typedef pthread_cond_t* native_handle_type;
 // native_handle_type native_handle();
 
-#include <condition_variable>
 #include <cassert>
+#include <condition_variable>
+#include <pthread.h>
+#include <type_traits>
 
 #include "test_macros.h"
 
diff --git a/libcxx/test/libcxx/transitive_includes/cxx2b.csv b/libcxx/test/libcxx/transitive_includes/cxx2b.csv
--- a/libcxx/test/libcxx/transitive_includes/cxx2b.csv
+++ b/libcxx/test/libcxx/transitive_includes/cxx2b.csv
@@ -110,11 +110,14 @@
 concepts cstddef
 concepts version
 condition_variable cstddef
-condition_variable cstdint
 condition_variable cstdlib
+<<<<<<< HEAD
 condition_variable cstring
 condition_variable ctime
 condition_variable initializer_list
+=======
+condition_variable ctime
+>>>>>>> f626323c3b1a ([libc++] Granularize __mutex_base)
 condition_variable iosfwd
 condition_variable limits
 condition_variable new
@@ -406,9 +409,13 @@
 mutex cstddef
 mutex cstdint
 mutex cstdlib
+<<<<<<< HEAD
 mutex cstring
 mutex ctime
 mutex initializer_list
+=======
+mutex ctime
+>>>>>>> f626323c3b1a ([libc++] Granularize __mutex_base)
 mutex iosfwd
 mutex limits
 mutex new
@@ -596,12 +603,9 @@
 system_error version
 thread compare
 thread cstddef
-thread cstdint
-thread cstring
 thread ctime
 thread iosfwd
 thread limits
-thread new
 thread ratio
 thread system_error
 thread tuple
diff --git a/libcxx/test/std/thread/futures/futures.shared_future/wait.pass.cpp b/libcxx/test/std/thread/futures/futures.shared_future/wait.pass.cpp
--- a/libcxx/test/std/thread/futures/futures.shared_future/wait.pass.cpp
+++ b/libcxx/test/std/thread/futures/futures.shared_future/wait.pass.cpp
@@ -18,6 +18,7 @@
 #include <cassert>
 #include <chrono>
 #include <future>
+#include <ratio>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/futures/futures.unique_future/wait.pass.cpp b/libcxx/test/std/thread/futures/futures.unique_future/wait.pass.cpp
--- a/libcxx/test/std/thread/futures/futures.unique_future/wait.pass.cpp
+++ b/libcxx/test/std/thread/futures/futures.unique_future/wait.pass.cpp
@@ -18,6 +18,7 @@
 #include <cassert>
 #include <chrono>
 #include <future>
+#include <ratio>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.cons/mutex.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.cons/mutex.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.cons/mutex.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.cons/mutex.pass.cpp
@@ -22,11 +22,12 @@
 // template<class _Mutex> shared_lock(shared_lock<_Mutex>)
 //     -> shared_lock<_Mutex>;  // C++17
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <shared_mutex>
 #include <thread>
 #include <vector>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.cons/mutex_try_to_lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.cons/mutex_try_to_lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.cons/mutex_try_to_lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.cons/mutex_try_to_lock.pass.cpp
@@ -19,11 +19,13 @@
 
 // shared_lock(mutex_type& m, try_to_lock_t);
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
+#include <mutex>
 #include <shared_mutex>
 #include <thread>
 #include <vector>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/lock.pass.cpp
@@ -19,11 +19,13 @@
 
 // void lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
+#include <mutex>
 #include <shared_mutex>
 #include <thread>
 #include <vector>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock.pass.cpp
@@ -17,9 +17,10 @@
 
 // bool try_lock();
 
-#include <shared_mutex>
 #include <cassert>
 #include <mutex>
+#include <shared_mutex>
+#include <system_error>
 
 #include "test_macros.h"
 
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock_for.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock_for.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock_for.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock_for.pass.cpp
@@ -16,10 +16,11 @@
 // template <class Rep, class Period>
 //   bool try_lock_for(const chrono::duration<Rep, Period>& rel_time);
 
-#include <shared_mutex>
 #include <cassert>
 #include <chrono>
 #include <mutex>
+#include <shared_mutex>
+#include <system_error>
 
 #include "test_macros.h"
 
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock_until.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock_until.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock_until.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock_until.pass.cpp
@@ -16,10 +16,11 @@
 // template <class Clock, class Duration>
 //   bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time);
 
-#include <shared_mutex>
 #include <cassert>
 #include <chrono>
 #include <mutex>
+#include <shared_mutex>
+#include <system_error>
 
 #include "test_macros.h"
 
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.cons/mutex.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.cons/mutex.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.cons/mutex.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.cons/mutex.pass.cpp
@@ -18,10 +18,11 @@
 // template<class _Mutex> unique_lock(unique_lock<_Mutex>)
 //     -> unique_lock<_Mutex>;  // C++17
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.cons/mutex_try_to_lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.cons/mutex_try_to_lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.cons/mutex_try_to_lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.cons/mutex_try_to_lock.pass.cpp
@@ -15,10 +15,11 @@
 
 // unique_lock(mutex_type& m, try_to_lock_t);
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/lock.pass.cpp
@@ -15,10 +15,11 @@
 
 // void lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock.pass.cpp
@@ -16,8 +16,9 @@
 
 // bool try_lock();
 
-#include <mutex>
 #include <cassert>
+#include <mutex>
+#include <system_error>
 
 #include "test_macros.h"
 
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock_for.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock_for.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock_for.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock_for.pass.cpp
@@ -15,8 +15,9 @@
 // template <class Rep, class Period>
 //   bool try_lock_for(const chrono::duration<Rep, Period>& rel_time);
 
-#include <mutex>
 #include <cassert>
+#include <mutex>
+#include <system_error>
 
 #include "test_macros.h"
 
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock_until.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock_until.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock_until.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock_until.pass.cpp
@@ -15,8 +15,9 @@
 // template <class Clock, class Duration>
 //   bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time);
 
-#include <mutex>
 #include <cassert>
+#include <mutex>
+#include <system_error>
 
 #include "test_macros.h"
 
diff --git a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/unlock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/unlock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/unlock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/unlock.pass.cpp
@@ -14,8 +14,9 @@
 
 // void unlock();
 
-#include <mutex>
 #include <cassert>
+#include <mutex>
+#include <system_error>
 
 #include "test_macros.h"
 
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.class/lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.class/lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.class/lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.class/lock.pass.cpp
@@ -15,10 +15,11 @@
 
 // void lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.class/try_lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.class/try_lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.class/try_lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.class/try_lock.pass.cpp
@@ -15,10 +15,11 @@
 
 // bool try_lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.recursive/lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.recursive/lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.recursive/lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.recursive/lock.pass.cpp
@@ -15,10 +15,11 @@
 
 // void lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.recursive/try_lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.recursive/try_lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.recursive/try_lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.recursive/try_lock.pass.cpp
@@ -15,10 +15,11 @@
 
 // bool try_lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/lock.pass.cpp
@@ -20,10 +20,11 @@
 
 // void lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <shared_mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/lock_shared.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/lock_shared.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/lock_shared.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/lock_shared.pass.cpp
@@ -20,11 +20,12 @@
 
 // void lock_shared();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <shared_mutex>
 #include <thread>
 #include <vector>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/try_lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/try_lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/try_lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/try_lock.pass.cpp
@@ -20,10 +20,11 @@
 
 // bool try_lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <shared_mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/try_lock_shared.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/try_lock_shared.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/try_lock_shared.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.shared_mutex.requirements/thread.shared_mutex.class/try_lock_shared.pass.cpp
@@ -20,11 +20,12 @@
 
 // bool try_lock_shared();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <shared_mutex>
 #include <thread>
 #include <vector>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/lock.pass.cpp
@@ -20,12 +20,12 @@
 
 // void lock();
 
-#include <thread>
-
 #include <atomic>
-#include <cstdlib>
 #include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <shared_mutex>
+#include <thread>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/lock_shared.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/lock_shared.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/lock_shared.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/lock_shared.pass.cpp
@@ -20,12 +20,13 @@
 
 // void lock_shared();
 
-#include <thread>
 
 #include <atomic>
 #include <cassert>
+#include <chrono>
 #include <cstdlib>
 #include <shared_mutex>
+#include <thread>
 #include <vector>
 
 #include "make_test_thread.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock.pass.cpp
@@ -20,10 +20,11 @@
 
 // bool try_lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <shared_mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock_shared.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock_shared.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock_shared.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock_shared.pass.cpp
@@ -20,11 +20,12 @@
 
 // bool try_lock_shared();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <shared_mutex>
 #include <thread>
 #include <vector>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.class/lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.class/lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.class/lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.class/lock.pass.cpp
@@ -15,10 +15,11 @@
 
 // void lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.class/try_lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.class/try_lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.class/try_lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.class/try_lock.pass.cpp
@@ -15,10 +15,11 @@
 
 // bool try_lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.recursive/lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.recursive/lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.recursive/lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.recursive/lock.pass.cpp
@@ -15,10 +15,11 @@
 
 // void lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.recursive/try_lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.recursive/try_lock.pass.cpp
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.recursive/try_lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.recursive/try_lock.pass.cpp
@@ -15,10 +15,11 @@
 
 // bool try_lock();
 
+#include <cassert>
+#include <chrono>
+#include <cstdlib>
 #include <mutex>
 #include <thread>
-#include <cstdlib>
-#include <cassert>
 
 #include "make_test_thread.h"
 #include "test_macros.h"
diff --git a/libcxx/test/std/thread/thread.threads/thread.thread.this/sleep_until.pass.cpp b/libcxx/test/std/thread/thread.threads/thread.thread.this/sleep_until.pass.cpp
--- a/libcxx/test/std/thread/thread.threads/thread.thread.this/sleep_until.pass.cpp
+++ b/libcxx/test/std/thread/thread.threads/thread.thread.this/sleep_until.pass.cpp
@@ -13,9 +13,10 @@
 // template <class Clock, class Duration>
 //   void sleep_until(const chrono::time_point<Clock, Duration>& abs_time);
 
-#include <thread>
-#include <cstdlib>
 #include <cassert>
+#include <chrono>
+#include <cstdlib>
+#include <thread>
 
 #include "test_macros.h"