FlightTasks: add SubscriptionArray class that contains all subscriptions

This is to avoid dynamic (re-)allocations on task switching, due to
orb_{un,}subscribe calls.

src/lib/FlightTasks/SubscriptionArray.cpp

@@ -0,0 +1,78 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2017 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+#include "SubscriptionArray.hpp"
+
+#include <string.h>
+
+SubscriptionArray::~SubscriptionArray()
+{
+	cleanup();
+}
+
+void SubscriptionArray::cleanup()
+{
+	for (int i = 0; i < _subscriptions_count; ++i) {
+		delete _subscriptions[i];
+	}
+
+	delete[] _subscriptions;
+	_subscriptions = nullptr;
+}
+
+bool SubscriptionArray::resizeSubscriptions()
+{
+	const int new_size = _subscriptions_size == 0 ? 4 : _subscriptions_size * 2;
+	uORB::SubscriptionNode **new_array = new uORB::SubscriptionNode*[new_size];
+
+	if (!new_array) {
+		return false;
+	}
+
+	if (_subscriptions) {
+		memcpy(new_array, _subscriptions, sizeof(uORB::SubscriptionNode *)*_subscriptions_count);
+		delete[] _subscriptions;
+	}
+
+	_subscriptions = new_array;
+	_subscriptions_size = new_size;
+
+	return true;
+}
+
+void SubscriptionArray::update()
+{
+	for (int i = 0; i < _subscriptions_count; ++i) {
+		_subscriptions[i]->update();
+	}
+}