[gcc r10-9559] libstdc++: Fix net::system_context stop condition

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:6531087573216bf2404fbf682eeae4a4866a18b7

commit r10-9559-g6531087573216bf2404fbf682eeae4a4866a18b7
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Aug 11 16:16:21 2020 +0100

    libstdc++: Fix net::system_context stop condition
    
    libstdc++-v3/ChangeLog:
    
            * include/experimental/executor (system_context::_M_run()):
            Fix predicate.
            (system_context::join()): Do not join unless joinable.
            * testsuite/experimental/net/system_context/1.cc: New test.
    
    (cherry picked from commit 61759518adc7679a6f46369543e30a761a16490a)

Diff:
---
 libstdc++-v3/include/experimental/executor         |  5 +--
 .../testsuite/experimental/net/system_context/1.cc | 42 ++++++++++++++++++++++
 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/experimental/executor b/libstdc++-v3/include/experimental/executor
index 1d5b5b3afb0..e79ac7df380 100644
--- a/libstdc++-v3/include/experimental/executor
+++ b/libstdc++-v3/include/experimental/executor
@@ -878,7 +878,8 @@ inline namespace v1
 
     void join()
     {
-      _M_thread.join();
+      if (_M_thread.joinable())
+	_M_thread.join();
     }
 
   private:
@@ -902,7 +903,7 @@ inline namespace v1
 	  {
 	    unique_lock<mutex> __lock(_M_mtx);
 	    _M_cv.wait(__lock,
-		       [this]{ return !_M_stopped && !_M_tasks.empty(); });
+		       [this]{ return _M_stopped || !_M_tasks.empty(); });
 	    if (_M_stopped)
 	      return;
 	    __f = std::move(_M_tasks.front());
diff --git a/libstdc++-v3/testsuite/experimental/net/system_context/1.cc b/libstdc++-v3/testsuite/experimental/net/system_context/1.cc
new file mode 100644
index 00000000000..bc2405d31d3
--- /dev/null
+++ b/libstdc++-v3/testsuite/experimental/net/system_context/1.cc
@@ -0,0 +1,42 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do run }
+// { dg-options "-pthread"  }
+// { dg-require-effective-target c++14 }
+// { dg-require-effective-target pthread }
+// { dg-require-gthreads "" }
+
+#include <experimental/executor>
+#include <testsuite_hooks.h>
+
+namespace net = std::experimental::net;
+
+void
+test01()
+{
+  net::system_context& c = net::system_executor{}.context();
+  net::post( [&c] { c.stop(); } );
+  c.join();
+  VERIFY( c.stopped() );
+}
+
+int
+main()
+{
+  test01();
+}