Added extra header file needed to work around an issue(see issue #74) when reading samples in c++

And updated dds_read_instance_mask and dds_take_instance_mask to work with DDS_READ_WITHOUT_LOCK

Signed-off-by: Thijs Sassen <thijs.sassen@adlinktech.com>

src/core/ddsc/include/dds/ddsc/dds_internal_api.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright(c) 2006 to 2020 ADLINK Technology Limited and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0, or the Eclipse Distribution License
+ * v. 1.0 which is available at
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
+ */
+
+/** @file
+ * WARNING This file is only needed for the work around for https://github.com/eclipse-cyclonedds/cyclonedds/issues/74
+ * Do not include this file in an application! Once issue #74 is solved this header file should be removed.
+ */
+
+#ifndef DDS_INTERNAL_API_H
+#define DDS_INTERNAL_API_H
+
+#if defined (__cplusplus)
+extern "C" {
+#endif
+
+#define DDS_READ_WITHOUT_LOCK (0xFFFFFFED)
+/*
+ * @private
+ * dds_reader_lock_samples: Returns number of samples in read cache and locks the
+ * reader cache to make sure that the samples content doesn't change.
+ * Because the cache is locked, you should be able to read/take without having to
+ * lock first. This is done by passing the DDS_READ_WITHOUT_LOCK value to the
+ * read/take call as maxs. Then the read/take will not lock but still unlock.
+ *
+ * CycloneDDS doesn't support a read/take that just returns all
+ * available samples issue #74. As a work around to support LENGTH_UNLIMITED in C++.
+ * dds_reader_lock_samples() and DDS_READ_WITHOUT_LOCK are needed.
+ */
+DDS_EXPORT uint32_t
+dds_reader_lock_samples (dds_entity_t entity);
+
+#if defined (__cplusplus)
+}
+#endif
+#endif