Add multithreaded tests

test/spinlock_pool_mt_test.cpp

@@ -0,0 +1,41 @@
+// Copyright 2018, 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/smart_ptr/detail/spinlock_pool.hpp>
+#include <boost/smart_ptr/detail/lightweight_thread.hpp>
+#include <boost/bind/bind.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+static int count = 0;
+
+void f( int n )
+{
+    for( int i = 0; i < n; ++i )
+    {
+        boost::detail::spinlock_pool<0>::scoped_lock lock( &count );
+        ++count;
+    }
+}
+
+int main()
+{
+    int const N = 100000; // iterations
+    int const M = 8;      // threads
+
+    boost::detail::lw_thread_t th[ M ] = {};
+
+    for( int i = 0; i < M; ++i )
+    {
+        boost::detail::lw_thread_create( th[ i ], boost::bind( f, N ) );
+    }
+
+    for( int i = 0; i < M; ++i )
+    {
+        boost::detail::lw_thread_join( th[ i ] );
+    }
+
+    BOOST_TEST_EQ( count, N * M );
+
+    return boost::report_errors();
+}