uORB: introduce SubscriptionBlocking

- uORB::SubscriptionBlocking is a specialized uORB::Subscription that allows you to do a blocking read
 - this is intended to be an easy to use, hard to misuse replacement for the typical orb fd + poll pattern we've relied on historically

src/modules/uORB/SubscriptionBlocking.hpp

@@ -0,0 +1,152 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2019 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.
+ *
+ ****************************************************************************/
+
+#pragma once
+
+#include "SubscriptionCallback.hpp"
+
+#include <containers/LockGuard.hpp>
+#include <px4_time.h>
+
+namespace uORB
+{
+
+// Subscription with callback that schedules a WorkItem
+template<typename T>
+class SubscriptionBlocking : public SubscriptionCallback
+{
+public:
+	/**
+	 * Constructor
+	 *
+	 * @param meta The uORB metadata (usually from the ORB_ID() macro) for the topic.
+	 * @param interval_us The requested maximum update interval in microseconds.
+	 * @param instance The instance for multi sub.
+	 */
+	SubscriptionBlocking(const orb_metadata *meta, uint32_t interval_us = 0, uint8_t instance = 0) :
+		SubscriptionCallback(meta, interval_us, instance)
+	{
+		// pthread_mutexattr_init
+		pthread_mutexattr_t attr;
+		int ret_attr_init = pthread_mutexattr_init(&attr);
+
+		if (ret_attr_init != 0) {
+			PX4_ERR("pthread_mutexattr_init failed, status=%d", ret_attr_init);
+		}
+
+		// pthread_mutexattr_settype
+		int ret_mutexattr_settype = pthread_mutexattr_settype(&attr, PTHREAD_PRIO_NONE);
+
+		if (ret_mutexattr_settype != 0) {
+			PX4_ERR("pthread_mutexattr_settype failed, status=%d", ret_mutexattr_settype);
+		}
+
+		// pthread_mutex_init
+		int ret_mutex_init = pthread_mutex_init(&_mutex, &attr);
+
+		if (ret_mutex_init != 0) {
+			PX4_ERR("pthread_mutex_init failed, status=%d", ret_mutex_init);
+		}
+	}
+
+	virtual ~SubscriptionBlocking()
+	{
+		pthread_mutex_destroy(&_mutex);
+		pthread_cond_destroy(&_cv);
+	}
+
+	void call() override
+	{
+		// signal immediately if no interval, otherwise only if interval has elapsed
+		if ((_interval_us == 0) || (hrt_elapsed_time(&_last_update) >= _interval_us)) {
+			pthread_cond_signal(&_cv);
+		}
+	}
+
+	/**
+	 * Copy the struct if updated.
+	 * @param data The data reference where the struct will be copied.
+	 * @param timeout_us The requested timeout in microseconds, or 0 to wait indefinitely.
+	 *
+	 * @return true only if topic was updated and copied successfully.
+	 */
+	bool updateBlocking(T &data, uint32_t timeout_us = 0)
+	{
+		if (!_registered) {
+			registerCallback();
+		}
+
+		if (updated()) {
+			// copy immediately if updated
+			return copy(&data);
+
+		} else {
+			// otherwise wait
+
+			LockGuard lg{_mutex};
+
+			if (timeout_us == 0) {
+				// wait with no timeout
+				if (pthread_cond_wait(&_cv, &_mutex) == 0) {
+					return update(&data);
+				}
+
+			} else {
+				// otherwise wait with timeout based on interval
+
+				// Calculate an absolute time in the future
+				struct timespec ts;
+				px4_clock_gettime(CLOCK_REALTIME, &ts);
+				uint64_t nsecs = ts.tv_nsec + (timeout_us * 1000);
+				static constexpr unsigned billion = (1000 * 1000 * 1000);
+				ts.tv_sec += nsecs / billion;
+				nsecs -= (nsecs / billion) * billion;
+				ts.tv_nsec = nsecs;
+
+				if (px4_pthread_cond_timedwait(&_cv, &_mutex, &ts) == 0) {
+					return update(&data);
+				}
+			}
+		}
+
+		return false;
+	}
+
+private:
+
+	pthread_mutex_t _mutex = PTHREAD_MUTEX_INITIALIZER;
+	pthread_cond_t	_cv = PTHREAD_COND_INITIALIZER;
+
+};
+
+} // namespace uORB

src/modules/uORB/SubscriptionCallback.hpp

@@ -53,11 +53,11 @@ public:
 	 * Constructor
 	 *
 	 * @param meta The uORB metadata (usually from the ORB_ID() macro) for the topic.
-	 * @param interval_ms The requested maximum update interval in milliseconds.
+	 * @param interval_us The requested maximum update interval in microseconds.
 	 * @param instance The instance for multi sub.
 	 */
-	SubscriptionCallback(const orb_metadata *meta, uint8_t interval_ms = 0, uint8_t instance = 0) :
-		SubscriptionInterval(meta, interval_ms, instance)
+	SubscriptionCallback(const orb_metadata *meta, uint32_t interval_us = 0, uint8_t instance = 0) :
+		SubscriptionInterval(meta, interval_us, instance)
 	{
 	}
 
@@ -68,11 +68,9 @@ public:
 
 	bool registerCallback()
 	{
-		bool ret = false;
-
 		if (_subscription.get_node() && _subscription.get_node()->register_callback(this)) {
 			// registered
-			ret = true;
+			_registered = true;
 
 		} else {
 			// force topic creation by subscribing with old API
@@ -81,15 +79,14 @@ public:
 			// try to register callback again
 			if (_subscription.subscribe()) {
 				if (_subscription.get_node() && _subscription.get_node()->register_callback(this)) {
-					ret = true;
+					_registered = true;
 				}
 			}
 
 			orb_unsubscribe(fd);
 		}
 
-
-		return ret;
+		return _registered;
 	}
 
 	void unregisterCallback()
@@ -97,10 +94,16 @@ public:
 		if (_subscription.get_node()) {
 			_subscription.get_node()->unregister_callback(this);
 		}
+
+		_registered = false;
 	}
 
 	virtual void call() = 0;
 
+protected:
+
+	bool _registered{false};
+
 };
 
 // Subscription with callback that schedules a WorkItem