[libcxx-commits] [PATCH] D91992: [libc++] Add an extension to allow constructing std::thread from native handles

[Louis Dionne via Phabricator via libcxx-commits]

ldionne created this revision.
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On some systems, creating threads with the standard std::thread constructor
is not convenient, or downright impossible. For example, some systems require
passing a stack size when creating a thread, but the std::thread constructor
does not allow for that.

This patch adds a non-standard extension to std::thread that makes it
constructible from the native_handle_type. This allows creating a thread
using the underlying system's machinery (e.g. in a factory function),
while retaining the rest of the std::thread API.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D91992

Files:
  libcxx/include/thread
  libcxx/test/libcxx/thread/thread.threads/thread.thread.class/thread.thread.constr/ctor.native_handle.pass.cpp


Index: libcxx/test/libcxx/thread/thread.threads/thread.thread.class/thread.thread.constr/ctor.native_handle.pass.cpp
===================================================================
--- /dev/null
+++ libcxx/test/libcxx/thread/thread.threads/thread.thread.class/thread.thread.constr/ctor.native_handle.pass.cpp
@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: libcpp-has-no-threads
+
+// <thread>
+
+// This test tests the constructor from a native handle provided as an
+// extension to std::thread.
+
+// class thread
+
+// thread::thread(native_handle_type);
+
+#include <thread>
+#include <cassert>
+#include <cstddef>
+
+#include "test_macros.h"
+
+bool ran = false;
+void* f(void*) { ran = true; return NULL; }
+
+int main(int, char**) {
+    pthread_t native;
+    pthread_create(&native, NULL, f, NULL);
+    std::thread t(native);
+    assert(t.native_handle() == native);
+    t.join();
+    assert(ran);
+
+    return 0;
+}
Index: libcxx/include/thread
===================================================================
--- libcxx/include/thread
+++ libcxx/include/thread
@@ -229,7 +229,8 @@
     template <class _Fp, class ..._Args,
               class = typename enable_if
               <
-                   !is_same<typename __uncvref<_Fp>::type, thread>::value
+                   !is_same<typename __uncvref<_Fp>::type, thread>::value &&
+                   !is_same<typename __uncvref<_Fp>::type, native_handle_type>::value
               >::type
              >
         _LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS
@@ -239,6 +240,12 @@
     _LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS
     explicit thread(_Fp __f);
 #endif
+
+    _LIBCPP_INLINE_VISIBILITY
+    explicit thread(native_handle_type __handle)
+        : __t_(__handle)
+    { }
+
     ~thread();
 
     _LIBCPP_INLINE_VISIBILITY


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