[libc++][PSTL] Add a simple std::thread backend

This is just to test that the PSTL works with parallelization. This is not supposed to be a production-ready backend.

Reviewed By: ldionne, #libc

Spies: EricWF, arichardson, libcxx-commits

Differential Revision: https://reviews.llvm.org/D150284

diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index 3c550d5..d3ed4a8 100644 (file)
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -287,6 +287,12 @@ option(LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY
     "Build libc++ with an externalized threading library.
      This option may only be set to ON when LIBCXX_ENABLE_THREADS=ON" OFF)
 
+if (LIBCXX_ENABLE_THREADS)
+  set(LIBCXX_PSTL_CPU_BACKEND "std_thread" CACHE STRING "Which PSTL CPU backend to use")
+else()
+  set(LIBCXX_PSTL_CPU_BACKEND "serial" CACHE STRING "Which PSTL CPU backend to use")
+endif()
+
 # Misc options ----------------------------------------------------------------
 # FIXME: Turn -pedantic back ON. It is currently off because it warns
 # about #include_next which is used everywhere.
@@ -796,6 +802,15 @@ else()
   config_define(0 _LIBCPP_ENABLE_ASSERTIONS_DEFAULT)
 endif()
 
+if (LIBCXX_PSTL_CPU_BACKEND STREQUAL "serial")
+  config_define(1 _LIBCPP_PSTL_CPU_BACKEND_SERIAL)
+elseif(LIBCXX_PSTL_CPU_BACKEND STREQUAL "std_thread")
+  config_define(1 _LIBCPP_PSTL_CPU_BACKEND_THREAD)
+else()
+  message(FATAL_ERROR "LIBCXX_PSTL_CPU_BACKEND is set to ${LIBCXX_PSTL_CPU_BACKEND}, which is not a valid backend.
+                       Valid backends are: serial, std_thread")
+endif()
+
 if (LIBCXX_ABI_DEFINES)
   set(abi_defines)
   foreach (abi_define ${LIBCXX_ABI_DEFINES})

diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index 4f37014..1939a55 100644 (file)
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -78,6 +78,7 @@ set(files
   __algorithm/pstl_backends/cpu_backends/find_if.h
   __algorithm/pstl_backends/cpu_backends/for_each.h
   __algorithm/pstl_backends/cpu_backends/serial.h
+  __algorithm/pstl_backends/cpu_backends/thread.h
   __algorithm/pstl_backends/cpu_backends/transform.h
   __algorithm/pstl_copy.h
   __algorithm/pstl_fill.h

diff --git a/libcxx/include/__algorithm/pstl_backend.h b/libcxx/include/__algorithm/pstl_backend.h
index 9ac8002..e80bae8 100644 (file)
--- a/libcxx/include/__algorithm/pstl_backend.h
+++ b/libcxx/include/__algorithm/pstl_backend.h
@@ -85,7 +85,7 @@ struct __select_backend<std::execution::unsequenced_policy> {
 };
 #  endif
 
-#  if defined(_PSTL_CPU_BACKEND_SERIAL)
+#  if defined(_LIBCPP_PSTL_CPU_BACKEND_SERIAL) || defined(_LIBCPP_PSTL_CPU_BACKEND_THREAD)
 template <>
 struct __select_backend<std::execution::parallel_policy> {
   using type = __cpu_backend_tag;

diff --git a/libcxx/include/__algorithm/pstl_backends/cpu_backends/backend.h b/libcxx/include/__algorithm/pstl_backends/cpu_backends/backend.h
index d6b03d2..e40d168 100644 (file)
--- a/libcxx/include/__algorithm/pstl_backends/cpu_backends/backend.h
+++ b/libcxx/include/__algorithm/pstl_backends/cpu_backends/backend.h
@@ -11,8 +11,10 @@
 
 #include <__config>
 
-#if defined(_LIBCPP_HAS_NO_THREADS) || defined(_PSTL_CPU_BACKEND_SERIAL)
+#if defined(_LIBCPP_PSTL_CPU_BACKEND_SERIAL)
 #  include <__algorithm/pstl_backends/cpu_backends/serial.h>
+#elif defined(_LIBCPP_PSTL_CPU_BACKEND_THREAD)
+#  include <__algorithm/pstl_backends/cpu_backends/thread.h>
 #else
 #  error "Invalid CPU backend choice"
 #endif

diff --git a/libcxx/include/__algorithm/pstl_backends/cpu_backends/thread.h b/libcxx/include/__algorithm/pstl_backends/cpu_backends/thread.h
new file mode 100644 (file)
index 0000000..967ce8c
--- /dev/null
+++ b/libcxx/include/__algorithm/pstl_backends/cpu_backends/thread.h
@@ -0,0 +1,43 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_THREAD_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_THREAD_H
+
+#include <__assert>
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+// This backend implementation is for testing purposes only and not meant for production use. This will be replaced
+// by a proper implementation once the PSTL implementation is somewhat stable.
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace __par_backend {
+inline namespace __thread_cpu_backend {
+
+template <class _RandomAccessIterator, class _Fp>
+_LIBCPP_HIDE_FROM_ABI void __parallel_for(_RandomAccessIterator __first, _RandomAccessIterator __last, _Fp __f) {
+  __f(__first, __last);
+}
+
+_LIBCPP_HIDE_FROM_ABI inline void __cancel_execution() {}
+
+} // namespace __thread_cpu_backend
+} // namespace __par_backend
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_THREAD_H

diff --git a/libcxx/include/__config b/libcxx/include/__config
index 6890635..4a7ca97 100644 (file)
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -1280,7 +1280,6 @@ __sanitizer_verify_double_ended_contiguous_container(const void*, const void*, c
 
 // TODO: Make this a proper configuration option
 #define _PSTL_PAR_BACKEND_SERIAL
-#define _PSTL_CPU_BACKEND_SERIAL
 
 #define _PSTL_PRAGMA(x) _Pragma(#    x)
 

diff --git a/libcxx/include/__config_site.in b/libcxx/include/__config_site.in
index c0f719b..88f7383 100644 (file)
--- a/libcxx/include/__config_site.in
+++ b/libcxx/include/__config_site.in
@@ -32,6 +32,10 @@
 #cmakedefine01 _LIBCPP_ENABLE_ASSERTIONS_DEFAULT
 #cmakedefine _LIBCPP_ENABLE_DEBUG_MODE
 
+// PSTL backends
+#cmakedefine _LIBCPP_PSTL_CPU_BACKEND_SERIAL
+#cmakedefine _LIBCPP_PSTL_CPU_BACKEND_THREAD
+
 // __USE_MINGW_ANSI_STDIO gets redefined on MinGW
 #ifdef __clang__
 #  pragma clang diagnostic push

diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in
index 502c4f6..743fce2 100644 (file)
--- a/libcxx/include/module.modulemap.in
+++ b/libcxx/include/module.modulemap.in
@@ -341,6 +341,9 @@ module std [system] {
       module pstl_backends_cpu_backends_serial {
         private header "__algorithm/pstl_backends/cpu_backends/serial.h"
       }
+      module pstl_backends_cpu_backends_thread {
+        private header "__algorithm/pstl_backends/cpu_backends/thread.h"
+      }
       module pstl_backends_cpu_backends_transform {
         private header "__algorithm/pstl_backends/cpu_backends/transform.h"
       }

diff --git a/libcxx/test/libcxx/private_headers.verify.cpp b/libcxx/test/libcxx/private_headers.verify.cpp
index 3cafdeb..2c79212 100644 (file)
--- a/libcxx/test/libcxx/private_headers.verify.cpp
+++ b/libcxx/test/libcxx/private_headers.verify.cpp
@@ -121,6 +121,7 @@ END-SCRIPT
 #include <__algorithm/pstl_backends/cpu_backends/find_if.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/pstl_backends/cpu_backends/find_if.h'}}
 #include <__algorithm/pstl_backends/cpu_backends/for_each.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/pstl_backends/cpu_backends/for_each.h'}}
 #include <__algorithm/pstl_backends/cpu_backends/serial.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/pstl_backends/cpu_backends/serial.h'}}
+#include <__algorithm/pstl_backends/cpu_backends/thread.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/pstl_backends/cpu_backends/thread.h'}}
 #include <__algorithm/pstl_backends/cpu_backends/transform.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/pstl_backends/cpu_backends/transform.h'}}
 #include <__algorithm/push_heap.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/push_heap.h'}}
 #include <__algorithm/ranges_adjacent_find.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_adjacent_find.h'}}