[libc++] Handle threads-related .cpp files like we do all other source files (#71100)

Source files in libc++ are added to the CMake targets only if they are
required by the configuration. We do this pretty consistently for all
configurations like no-filesystem, no-random-device, etc. but we didn't
do it for no-threads. This patch makes this consistent for no-threads,
which is helpful in reducing the amount of work required to port libc++
to some platforms without threads.

Indeed, with the previous approach, several threads-related source files
would end up including headers that might fail to compile properly on
some platforms. This issue is sidestepped entirely by making the
approach for no-threads consistent with the other configurations.

Author: ldionne

libcxx/src/CMakeLists.txt

@@ -4,21 +4,17 @@ set(LIBCXX_LIB_CMAKEFILES_DIR "${CMAKE_CURRENT_BINARY_DIR}${CMAKE_FILES_DIRECTOR
 set(LIBCXX_SOURCES
   algorithm.cpp
   any.cpp
-  atomic.cpp
-  barrier.cpp
   bind.cpp
+  call_once.cpp
   charconv.cpp
   chrono.cpp
-  condition_variable.cpp
-  condition_variable_destructor.cpp
   error_category.cpp
   exception.cpp
   filesystem/filesystem_clock.cpp
   filesystem/filesystem_error.cpp
   filesystem/path_parser.h
   filesystem/path.cpp
   functional.cpp
-  future.cpp
   hash.cpp
   include/apple_availability.h
   include/atomic_support.h
@@ -37,8 +33,6 @@ set(LIBCXX_SOURCES
   legacy_pointer_safety.cpp
   memory.cpp
   memory_resource.cpp
-  mutex.cpp
-  mutex_destructor.cpp
   new_handler.cpp
   new_helpers.cpp
   optional.cpp
@@ -47,7 +41,6 @@ set(LIBCXX_SOURCES
   ryu/d2fixed.cpp
   ryu/d2s.cpp
   ryu/f2s.cpp
-  shared_mutex.cpp
   stdexcept.cpp
   string.cpp
   support/runtime/exception_fallback.ipp
@@ -62,14 +55,27 @@ set(LIBCXX_SOURCES
   support/runtime/stdexcept_default.ipp
   support/runtime/stdexcept_vcruntime.ipp
   system_error.cpp
-  thread.cpp
   typeinfo.cpp
   valarray.cpp
   variant.cpp
   vector.cpp
   verbose_abort.cpp
   )
 
+if (LIBCXX_ENABLE_THREADS)
+  list(APPEND LIBCXX_SOURCES
+    atomic.cpp
+    barrier.cpp
+    condition_variable_destructor.cpp
+    condition_variable.cpp
+    future.cpp
+    mutex_destructor.cpp
+    mutex.cpp
+    shared_mutex.cpp
+    thread.cpp
+    )
+endif()
+
 if (LIBCXX_ENABLE_RANDOM_DEVICE)
   list(APPEND LIBCXX_SOURCES
     random.cpp

libcxx/src/atomic.cpp

@@ -6,9 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <__config>
-#ifndef _LIBCPP_HAS_NO_THREADS
-
 #include <__thread/timed_backoff_policy.h>
 #include <atomic>
 #include <climits>
@@ -219,5 +216,3 @@ void __libcpp_atomic_wait(__cxx_atomic_contention_t const volatile* __location,
 }
 
 _LIBCPP_END_NAMESPACE_STD
-
-#endif //_LIBCPP_HAS_NO_THREADS

libcxx/src/barrier.cpp

@@ -6,10 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <__config>
-
-#ifndef _LIBCPP_HAS_NO_THREADS
-
 #include <barrier>
 #include <thread>
 
@@ -93,5 +89,3 @@ void __destroy_barrier_algorithm_base(__barrier_algorithm_base* __barrier)
 #endif // !defined(_LIBCPP_HAS_NO_TREE_BARRIER)
 
 _LIBCPP_END_NAMESPACE_STD
-
-#endif //_LIBCPP_HAS_NO_THREADS

libcxx/src/call_once.cpp

@@ -0,0 +1,72 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include <__mutex/once_flag.h>
+#include <__utility/exception_guard.h>
+
+#ifndef _LIBCPP_HAS_NO_THREADS
+#  include <__threading_support>
+#endif
+
+#include "include/atomic_support.h"
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// If dispatch_once_f ever handles C++ exceptions, and if one can get to it
+// without illegal macros (unexpected macros not beginning with _UpperCase or
+// __lowercase), and if it stops spinning waiting threads, then call_once should
+// call into dispatch_once_f instead of here. Relevant radar this code needs to
+// keep in sync with:  7741191.
+
+#ifndef _LIBCPP_HAS_NO_THREADS
+static constinit __libcpp_mutex_t mut = _LIBCPP_MUTEX_INITIALIZER;
+static constinit __libcpp_condvar_t cv = _LIBCPP_CONDVAR_INITIALIZER;
+#endif
+
+void __call_once(volatile once_flag::_State_type& flag, void* arg,
+                 void (*func)(void*))
+{
+#if defined(_LIBCPP_HAS_NO_THREADS)
+
+    if (flag == once_flag::_Unset) {
+        auto guard = std::__make_exception_guard([&flag] { flag = once_flag::_Unset; });
+        flag = once_flag::_Pending;
+        func(arg);
+        flag = once_flag::_Complete;
+        guard.__complete();
+    }
+
+#else // !_LIBCPP_HAS_NO_THREADS
+
+    __libcpp_mutex_lock(&mut);
+    while (flag == once_flag::_Pending)
+        __libcpp_condvar_wait(&cv, &mut);
+    if (flag == once_flag::_Unset) {
+        auto guard = std::__make_exception_guard([&flag] {
+            __libcpp_mutex_lock(&mut);
+            __libcpp_relaxed_store(&flag, once_flag::_Unset);
+            __libcpp_mutex_unlock(&mut);
+            __libcpp_condvar_broadcast(&cv);
+        });
+
+        __libcpp_relaxed_store(&flag, once_flag::_Pending);
+        __libcpp_mutex_unlock(&mut);
+        func(arg);
+        __libcpp_mutex_lock(&mut);
+        __libcpp_atomic_store(&flag, once_flag::_Complete, _AO_Release);
+        __libcpp_mutex_unlock(&mut);
+        __libcpp_condvar_broadcast(&cv);
+        guard.__complete();
+    } else {
+        __libcpp_mutex_unlock(&mut);
+    }
+
+#endif // !_LIBCPP_HAS_NO_THREADS
+}
+
+_LIBCPP_END_NAMESPACE_STD

libcxx/src/condition_variable.cpp

@@ -6,10 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <__config>
-
-#ifndef _LIBCPP_HAS_NO_THREADS
-
 #include <condition_variable>
 #include <thread>
 
@@ -92,5 +88,3 @@ notify_all_at_thread_exit(condition_variable& cond, unique_lock<mutex> lk)
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
-
-#endif // !_LIBCPP_HAS_NO_THREADS

libcxx/src/condition_variable_destructor.cpp

@@ -14,10 +14,8 @@
 #include <__config>
 #include <__threading_support>
 
-#if !defined(_LIBCPP_HAS_NO_THREADS)
-# if _LIBCPP_ABI_VERSION == 1 || !defined(_LIBCPP_HAS_TRIVIAL_CONDVAR_DESTRUCTION)
-#   define NEEDS_CONDVAR_DESTRUCTOR
-# endif
+#if _LIBCPP_ABI_VERSION == 1 || !defined(_LIBCPP_HAS_TRIVIAL_CONDVAR_DESTRUCTION)
+#  define NEEDS_CONDVAR_DESTRUCTOR
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD

libcxx/src/future.cpp

@@ -6,10 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <__config>
-
-#ifndef _LIBCPP_HAS_NO_THREADS
-
 #include <future>
 #include <string>
 
@@ -268,5 +264,3 @@ shared_future<void>::operator=(const shared_future& __rhs)
 }
 
 _LIBCPP_END_NAMESPACE_STD
-
-#endif // !_LIBCPP_HAS_NO_THREADS

libcxx/src/mutex.cpp

@@ -14,19 +14,15 @@
 
 #include "include/atomic_support.h"
 
-#ifndef _LIBCPP_HAS_NO_THREADS
-#  if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
-#    pragma comment(lib, "pthread")
-#  endif
+#if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
+#  pragma comment(lib, "pthread")
 #endif
 
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#ifndef _LIBCPP_HAS_NO_THREADS
-
 // ~mutex is defined elsewhere
 
 void
@@ -189,60 +185,6 @@ recursive_timed_mutex::unlock() noexcept
     }
 }
 
-#endif // !_LIBCPP_HAS_NO_THREADS
-
-// If dispatch_once_f ever handles C++ exceptions, and if one can get to it
-// without illegal macros (unexpected macros not beginning with _UpperCase or
-// __lowercase), and if it stops spinning waiting threads, then call_once should
-// call into dispatch_once_f instead of here. Relevant radar this code needs to
-// keep in sync with:  7741191.
-
-#ifndef _LIBCPP_HAS_NO_THREADS
-static constinit __libcpp_mutex_t mut = _LIBCPP_MUTEX_INITIALIZER;
-static constinit __libcpp_condvar_t cv = _LIBCPP_CONDVAR_INITIALIZER;
-#endif
-
-void __call_once(volatile once_flag::_State_type& flag, void* arg,
-                 void (*func)(void*))
-{
-#if defined(_LIBCPP_HAS_NO_THREADS)
-
-    if (flag == once_flag::_Unset) {
-        auto guard = std::__make_exception_guard([&flag] { flag = once_flag::_Unset; });
-        flag = once_flag::_Pending;
-        func(arg);
-        flag = once_flag::_Complete;
-        guard.__complete();
-    }
-
-#else // !_LIBCPP_HAS_NO_THREADS
-
-    __libcpp_mutex_lock(&mut);
-    while (flag == once_flag::_Pending)
-        __libcpp_condvar_wait(&cv, &mut);
-    if (flag == once_flag::_Unset) {
-        auto guard = std::__make_exception_guard([&flag] {
-            __libcpp_mutex_lock(&mut);
-            __libcpp_relaxed_store(&flag, once_flag::_Unset);
-            __libcpp_mutex_unlock(&mut);
-            __libcpp_condvar_broadcast(&cv);
-        });
-
-        __libcpp_relaxed_store(&flag, once_flag::_Pending);
-        __libcpp_mutex_unlock(&mut);
-        func(arg);
-        __libcpp_mutex_lock(&mut);
-        __libcpp_atomic_store(&flag, once_flag::_Complete, _AO_Release);
-        __libcpp_mutex_unlock(&mut);
-        __libcpp_condvar_broadcast(&cv);
-        guard.__complete();
-    } else {
-        __libcpp_mutex_unlock(&mut);
-    }
-
-#endif // !_LIBCPP_HAS_NO_THREADS
-}
-
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS

libcxx/src/mutex_destructor.cpp

@@ -19,10 +19,8 @@
 #include <__config>
 #include <__threading_support>
 
-#if !defined(_LIBCPP_HAS_NO_THREADS)
-#  if _LIBCPP_ABI_VERSION == 1 || !defined(_LIBCPP_HAS_TRIVIAL_MUTEX_DESTRUCTION)
-#    define NEEDS_MUTEX_DESTRUCTOR
-#  endif
+#if _LIBCPP_ABI_VERSION == 1 || !defined(_LIBCPP_HAS_TRIVIAL_MUTEX_DESTRUCTION)
+#  define NEEDS_MUTEX_DESTRUCTOR
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
@@ -45,6 +43,6 @@ mutex::~mutex() noexcept
 {
     __libcpp_mutex_destroy(&__m_);
 }
+#endif // !NEEDS_MUTEX_DESTRUCTOR
 
-#endif // !_LIBCPP_HAS_NO_THREADS
 _LIBCPP_END_NAMESPACE_STD

libcxx/src/shared_mutex.cpp

@@ -6,15 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <__config>
-
-#ifndef _LIBCPP_HAS_NO_THREADS
-
-#  include <mutex>
-#  include <shared_mutex>
-#  if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
-#    pragma comment(lib, "pthread")
-#  endif
+#include <mutex>
+#include <shared_mutex>
+#if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
+#  pragma comment(lib, "pthread")
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -95,5 +91,3 @@ bool shared_timed_mutex::try_lock_shared() { return __base_.try_lock_shared(); }
 void shared_timed_mutex::unlock_shared() { return __base_.unlock_shared(); }
 
 _LIBCPP_END_NAMESPACE_STD
-
-#endif // !_LIBCPP_HAS_NO_THREADS

libcxx/src/thread.cpp

@@ -6,10 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <__config>
-
-#ifndef _LIBCPP_HAS_NO_THREADS
-
 #include <__thread/poll_with_backoff.h>
 #include <__thread/timed_backoff_policy.h>
 #include <exception>
@@ -215,5 +211,3 @@ __thread_struct::__make_ready_at_thread_exit(__assoc_sub_state* __s)
 }
 
 _LIBCPP_END_NAMESPACE_STD
-
-#endif // !_LIBCPP_HAS_NO_THREADS

libcxx/utils/data/ignore_format.txt

@@ -492,6 +492,7 @@ libcxx/src/any.cpp
 libcxx/src/atomic.cpp
 libcxx/src/barrier.cpp
 libcxx/src/bind.cpp
+libcxx/src/call_once.cpp
 libcxx/src/charconv.cpp
 libcxx/src/chrono.cpp
 libcxx/src/condition_variable.cpp