shared_ptr: Make shared_ptr work with foreign_ptr

The foreign_ptr wrapper needs 'element_type' to be present in
shared_ptr to be able to access the data.

Fixes the following compilation failure when trying to use shared_ptr
with foreign_ptr:

  In file included from tests/foreign_ptr_test.cc:24:0:
  ./core/distributed.hh: In instantiation of ‘class foreign_ptr<shared_ptr<basic_sstring<char, unsigned int, 15u> > >’:
  tests/foreign_ptr_test.cc:28:54:   required from here
  ./core/distributed.hh:272:56: error: no type named ‘element_type’ in ‘class shared_ptr<basic_sstring<char, unsigned int, 15u> >’
       using element_type = typename PtrType::element_type;

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

configure.py

@@ -127,6 +127,7 @@ def debug_flag(compiler):
     'tests/timertest',
     'tests/tcp_test',
     'tests/futures_test',
+    'tests/foreign_ptr_test',
     'tests/smp_test',
     'tests/udp_server',
     'tests/udp_client',
@@ -282,6 +283,7 @@ def have_xen():
     'tests/tcp_test': ['tests/tcp_test.cc'] + core + libnet,
     'tests/timertest': ['tests/timertest.cc'] + core,
     'tests/futures_test': ['tests/futures_test.cc'] + core + boost_test_lib,
+    'tests/foreign_ptr_test': ['tests/foreign_ptr_test.cc'] + core + boost_test_lib,
     'tests/smp_test': ['tests/smp_test.cc'] + core,
     'tests/udp_server': ['tests/udp_server.cc'] + core + libnet,
     'tests/udp_client': ['tests/udp_client.cc'] + core + libnet,

core/shared_ptr.hh

@@ -312,6 +312,8 @@ private:
         }
     }
 public:
+    using element_type = T;
+
     shared_ptr() noexcept = default;
     shared_ptr(std::nullptr_t) noexcept : shared_ptr() {}
     shared_ptr(const shared_ptr& x) noexcept

tests/foreign_ptr_test.cc

@@ -0,0 +1,35 @@
+/*
+ * This file is open source software, licensed to you under the terms
+ * of the Apache License, Version 2.0 (the "License").  See the NOTICE file
+ * distributed with this work for additional information regarding copyright
+ * ownership.  You may not use this file except in compliance with the License.
+ *
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+/*
+ * Copyright (C) 2015 Cloudius Systems, Ltd.
+ */
+
+#include "tests/test-utils.hh"
+
+#include "core/distributed.hh"
+#include "core/shared_ptr.hh"
+
+BOOST_AUTO_TEST_CASE(make_foreign_ptr_from_lw_shared_ptr) {
+    auto p = make_foreign(make_lw_shared<sstring>("foo"));
+    BOOST_REQUIRE(p->size() == 3);
+}
+
+BOOST_AUTO_TEST_CASE(make_foreign_ptr_from_shared_ptr) {
+    auto p = make_foreign(make_shared<sstring>("foo"));
+    BOOST_REQUIRE(p->size() == 3);
+}