fix: uORB topics lost messages when publications overflow

msg/gps_inject_data.msg

@@ -3,4 +3,4 @@ uint8 len			# length of data
 uint8 flags         		# LSB: 1=fragmented
 uint8[182] data		# data to write to GPS device (RTCM message)
 
-uint8 ORB_QUEUE_LENGTH = 6
+uint8 ORB_QUEUE_LENGTH = 8

msg/mavlink_log.msg

@@ -3,4 +3,4 @@ uint64 timestamp		# time since system start (microseconds)
 char[127] text
 uint8 severity # log level (same as in the linux kernel, starting with 0)
 
-uint8 ORB_QUEUE_LENGTH = 5
+uint8 ORB_QUEUE_LENGTH = 4

msg/orb_test_medium.msg

@@ -4,4 +4,4 @@ int32 val
 
 uint8[64] junk
 
-# TOPICS orb_test_medium orb_test_medium_multi orb_test_medium_queue orb_test_medium_queue_poll
+# TOPICS orb_test_medium orb_test_medium_multi orb_test_medium_wrap_around orb_test_medium_queue orb_test_medium_queue_poll

msg/sensor_mag.msg

@@ -13,4 +13,4 @@ uint32 error_count
 
 bool is_external	# if true the mag is external (i.e. not built into the board)
 
-uint8 ORB_QUEUE_LENGTH = 3
+uint8 ORB_QUEUE_LENGTH = 4

msg/subsystem_info.msg

@@ -36,4 +36,4 @@ bool enabled
 bool ok
 uint64 subsystem_type
 
-uint8 ORB_QUEUE_LENGTH = 5
+uint8 ORB_QUEUE_LENGTH = 8

msg/transponder_report.msg

@@ -47,4 +47,4 @@ uint16 ADSB_EMITTER_TYPE_SERVICE_SURFACE=18
 uint16 ADSB_EMITTER_TYPE_POINT_OBSTACLE=19
 uint16 ADSB_EMITTER_TYPE_ENUM_END=20
 
-uint8 ORB_QUEUE_LENGTH = 10
+uint8 ORB_QUEUE_LENGTH = 8

msg/tune_control.msg

@@ -35,4 +35,4 @@ uint8 VOLUME_LEVEL_MIN = 0
 uint8 VOLUME_LEVEL_DEFAULT = 40
 uint8 VOLUME_LEVEL_MAX = 100
 
-uint8 ORB_QUEUE_LENGTH = 3
+uint8 ORB_QUEUE_LENGTH = 4

msg/uavcan_parameter_request.msg

@@ -20,4 +20,4 @@ uint8 param_type		# MAVLink parameter type
 int64 int_value			# current value if param_type is int-like
 float32 real_value		# current value if param_type is float-like
 
-uint8 ORB_QUEUE_LENGTH = 3
+uint8 ORB_QUEUE_LENGTH = 4

msg/ulog_stream.msg

@@ -16,4 +16,4 @@ uint16 msg_sequence		# allows determine drops
 uint8 flags			# see FLAGS_*
 uint8[249] data		# ulog data
 
-uint8 ORB_QUEUE_LENGTH = 14	# TODO: we might be able to reduce this if mavlink polled on the topic
+uint8 ORB_QUEUE_LENGTH = 16	# TODO: we might be able to reduce this if mavlink polled on the topic

msg/vehicle_command.msg

@@ -133,7 +133,7 @@ uint8 FAILURE_TYPE_SLOW = 5
 uint8 FAILURE_TYPE_DELAYED = 6
 uint8 FAILURE_TYPE_INTERMITTENT = 7
 
-uint8 ORB_QUEUE_LENGTH = 3
+uint8 ORB_QUEUE_LENGTH = 4
 
 float32 param1			# Parameter 1, as defined by MAVLink uint16 VEHICLE_CMD enum.
 float32 param2			# Parameter 2, as defined by MAVLink uint16 VEHICLE_CMD enum.

msg/vehicle_command_ack.msg

@@ -13,7 +13,7 @@ uint16 ARM_AUTH_DENIED_REASON_TIMEOUT = 3
 uint16 ARM_AUTH_DENIED_REASON_AIRSPACE_IN_USE = 4
 uint16 ARM_AUTH_DENIED_REASON_BAD_WEATHER = 5
 
-uint8 ORB_QUEUE_LENGTH = 3
+uint8 ORB_QUEUE_LENGTH = 4
 
 uint16 command
 uint8 result

src/modules/uORB/Subscription.cpp

@@ -65,10 +65,7 @@ bool Subscription::subscribe()
 				_node = node;
 				_node->add_internal_subscriber();
 
-				const unsigned curr_gen = _node->published_message_count();
-
-				// If there were any previous publications allow the subscriber to read them
-				_last_generation = curr_gen - math::min((unsigned)_node->get_queue_size(), curr_gen);
+				_last_generation = _node->get_initial_generation();
 
 				return true;
 			}

src/modules/uORB/Subscription.hpp

@@ -137,7 +137,7 @@ public:
 	/**
 	 * Check if there is a new update.
 	 */
-	bool updated() { return advertised() && (_node->published_message_count() != _last_generation); }
+	bool updated() { return advertised() && _node->updates_available(_last_generation); }
 
 	/**
 	 * Update the struct

src/modules/uORB/SubscriptionCallback.hpp

@@ -160,7 +160,7 @@ public:
 	{
 		// schedule immediately if updated (queue depth or subscription interval)
 		if ((_required_updates == 0)
-		    || (_subscription.get_node()->published_message_count() >= (_subscription.get_last_generation() + _required_updates))) {
+		    || (_subscription.get_node()->updates_available(_subscription.get_last_generation()) >= _required_updates)) {
 			if (updated()) {
 				_work_item->ScheduleNow();
 			}

src/modules/uORB/uORBDeviceMaster.cpp

@@ -268,7 +268,8 @@ int uORB::DeviceMaster::addNewDeviceNodes(DeviceNodeStatisticsData **first_node,
 			max_topic_name_length = name_length;
 		}
 
-		last_node->last_pub_msg_count = last_node->node->published_message_count();
+		// Pass in 0 to get the index of the latest published data
+		last_node->last_pub_msg_count = last_node->node->updates_available(0);
 	}
 
 	return 0;
@@ -374,9 +375,9 @@ void uORB::DeviceMaster::showTop(char **topic_filter, int num_filters)
 			cur_node = first_node;
 
 			while (cur_node) {
-				unsigned int num_msgs = cur_node->node->published_message_count();
-				cur_node->pub_msg_delta = roundf((num_msgs - cur_node->last_pub_msg_count) / dt);
-				cur_node->last_pub_msg_count = num_msgs;
+				unsigned int num_msgs = cur_node->node->updates_available(cur_node->last_pub_msg_count);
+				cur_node->pub_msg_delta = roundf(num_msgs / dt);
+				cur_node->last_pub_msg_count += num_msgs;
 				cur_node = cur_node->next;
 			}
 

src/modules/uORB/uORBDeviceNode.cpp

@@ -44,12 +44,48 @@
 
 static uORB::SubscriptionInterval *filp_to_subscription(cdev::file_t *filp) { return static_cast<uORB::SubscriptionInterval *>(filp->f_priv); }
 
+// Determine the data range
+static inline bool is_in_range(unsigned left, unsigned value, unsigned right)
+{
+	if (right > left) {
+		return (left <= value) && (value <= right);
+
+	} else {  // Maybe the data overflowed and a wraparound occurred
+		return (left <= value) || (value <= right);
+	}
+}
+
+// round up to nearest power of two
+// Such as 0 => 1, 1 => 1, 2 => 2 ,3 => 4, 10 => 16, 60 => 64, 65...255 => 128
+// Note: When the input value > 128, the output is always 128
+static inline uint8_t round_pow_of_two_8(uint8_t n)
+{
+	if (n == 0) {
+		return 1;
+	}
+
+	// Avoid is already a power of 2
+	uint8_t value = n - 1;
+
+	// Fill 1
+	value |= value >> 1U;
+	value |= value >> 2U;
+	value |= value >> 4U;
+
+	// Unable to round-up, take the value of round-down
+	if (value == UINT8_MAX) {
+		value >>= 1U;
+	}
+
+	return value + 1;
+}
+
 uORB::DeviceNode::DeviceNode(const struct orb_metadata *meta, const uint8_t instance, const char *path,
 			     uint8_t queue_size) :
 	CDev(path),
 	_meta(meta),
 	_instance(instance),
-	_queue_size(queue_size)
+	_queue_size(round_pow_of_two_8(queue_size))
 {
 }
 
@@ -130,24 +166,23 @@ uORB::DeviceNode::copy(void *dst, unsigned &generation)
 			ATOMIC_ENTER;
 			const unsigned current_generation = _generation.load();
 
-			if (current_generation > generation + _queue_size) {
-				// Reader is too far behind: some messages are lost
-				generation = current_generation - _queue_size;
-			}
-
-			if ((current_generation == generation) && (generation > 0)) {
+			if (current_generation == generation) {
 				/* The subscriber already read the latest message, but nothing new was published yet.
 				* Return the previous message
 				*/
 				--generation;
 			}
 
+			// Compatible with normal and overflow conditions
+			if (!is_in_range(current_generation - _queue_size, generation, current_generation - 1)) {
+				// Reader is too far behind: some messages are lost
+				generation = current_generation - _queue_size;
+			}
+
 			memcpy(dst, _data + (_meta->o_size * (generation % _queue_size)), _meta->o_size);
 			ATOMIC_LEAVE;
 
-			if (generation < current_generation) {
-				++generation;
-			}
+			++generation;
 
 			return true;
 		}
@@ -223,6 +258,9 @@ uORB::DeviceNode::write(cdev::file_t *filp, const char *buffer, size_t buflen)
 		item->call();
 	}
 
+	/* Mark at least one data has been published */
+	_data_valid = true;
+
 	ATOMIC_LEAVE;
 
 	/* notify any poll waiters */
@@ -502,10 +540,22 @@ int uORB::DeviceNode::update_queue_size(unsigned int queue_size)
 		return PX4_ERROR;
 	}
 
-	_queue_size = queue_size;
+	_queue_size = round_pow_of_two_8(queue_size);
 	return PX4_OK;
 }
 
+unsigned uORB::DeviceNode::get_initial_generation()
+{
+	ATOMIC_ENTER;
+
+	// If there any previous publications allow the subscriber to read them
+	unsigned generation = _generation.load() - (_data_valid ? 1 : 0);
+
+	ATOMIC_LEAVE;
+
+	return generation;
+}
+
 bool
 uORB::DeviceNode::register_callback(uORB::SubscriptionCallback *callback_sub)
 {

src/modules/uORB/uORBDeviceNode.hpp

@@ -50,6 +50,11 @@ class Manager;
 class SubscriptionCallback;
 }
 
+namespace uORBTest
+{
+class UnitTest;
+}
+
 /**
  * Per-object device instance.
  */
@@ -188,7 +193,18 @@ public:
 
 	int8_t subscriber_count() const { return _subscriber_count; }
 
-	unsigned published_message_count() const { return _generation.load(); }
+	/**
+	 * Returns the number of updated data relative to the parameter 'generation'
+	 * We can get the correct value regardless of wrap-around or not.
+	 * @param generation The generation of subscriber
+	 */
+	unsigned updates_available(unsigned generation) const { return _generation.load() - generation; }
+
+	/**
+	 * Return the initial generation to the subscriber
+	 * @return The initial generation.
+	 */
+	unsigned get_initial_generation();
 
 	const orb_metadata *get_meta() const { return _meta; }
 
@@ -224,10 +240,12 @@ protected:
 	void poll_notify_one(px4_pollfd_struct_t *fds, px4_pollevent_t events) override;
 
 private:
+	friend uORBTest::UnitTest;
 
 	const orb_metadata *_meta; /**< object metadata information */
 
-	uint8_t     *_data{nullptr};   /**< allocated object buffer */
+	uint8_t *_data{nullptr};   /**< allocated object buffer */
+	bool _data_valid{false}; /**< At least one valid data */
 	px4::atomic<unsigned>  _generation{0};  /**< object generation count */
 	List<uORB::SubscriptionCallback *>	_callbacks;
 

src/modules/uORB/uORB_tests/uORBTest_UnitTest.cpp

@@ -202,6 +202,12 @@ int uORBTest::UnitTest::test()
 		return ret;
 	}
 
+	ret = test_wrap_around();
+
+	if (ret != OK) {
+		return ret;
+	}
+
 	ret = test_queue();
 
 	if (ret != OK) {
@@ -582,6 +588,162 @@ int uORBTest::UnitTest::test_multi_reversed()
 	return test_note("PASS multi-topic reversed");
 }
 
+int uORBTest::UnitTest::test_wrap_around()
+{
+	test_note("Testing orb wrap-around");
+
+	orb_test_medium_s t{};
+	orb_test_medium_s u{};
+	orb_advert_t ptopic{nullptr};
+	bool updated{false};
+
+	// Advertise but not publish topics, only generate device_node, which is convenient for modifying DeviceNode::_generation
+	const int queue_size = 16;
+	ptopic = orb_advertise_queue(ORB_ID(orb_test_medium_wrap_around), nullptr, queue_size);
+
+	if (ptopic == nullptr) {
+		return test_fail("advertise failed: %d", errno);
+	}
+
+	auto node = uORB::Manager::get_instance()->get_device_master()->getDeviceNode(ORB_ID(orb_test_medium_wrap_around), 0);
+
+	if (node == nullptr) {
+		return test_fail("get device node failed.");
+	}
+
+	// Set generation
+	{
+		// Set generation to the location where wrap-around is about to be: (0 - queue_size / 2) => (UINT_MAX - queue_size / 2 + 1)
+		set_generation(*node, unsigned(-(queue_size / 2)));
+
+		if (node->updates_available(0) != unsigned(-(queue_size / 2))) {
+			return test_fail("set generation failed.");
+		}
+	}
+
+	t.val = 0;
+	orb_publish(ORB_ID(orb_test_medium_wrap_around), ptopic, &t);
+
+	int sfd = orb_subscribe(ORB_ID(orb_test_medium_wrap_around));
+
+	if (sfd < 0) {
+		return test_fail("subscribe failed: %d", errno);
+	}
+
+	orb_check(sfd, &updated);
+
+	if (!updated) {
+		return test_fail("update flag not set");
+	}
+
+	if (PX4_OK != orb_copy(ORB_ID(orb_test_medium_wrap_around), sfd, &u)) {
+		return test_fail("copy(1) failed: %d", errno);
+	}
+
+	if (u.val != t.val) {
+		return test_fail("copy(1) mismatch: %d expected %d", u.val, t.val);
+	}
+
+	orb_check(sfd, &updated);
+
+	if (updated) {
+		return test_fail("spurious updated flag");
+	}
+
+#define CHECK_UPDATED(element) \
+	orb_check(sfd, &updated); \
+	if (!updated) { \
+		return test_fail("update flag not set, element %i", element); \
+	}
+#define CHECK_NOT_UPDATED(element) \
+	orb_check(sfd, &updated); \
+	if (updated) { \
+		return test_fail("update flag set, element %i", element); \
+	}
+#define CHECK_COPY(i_got, i_correct) \
+	orb_copy(ORB_ID(orb_test_medium_wrap_around), sfd, &u); \
+	if (i_got != i_correct) { \
+		return test_fail("got wrong element from the queue (got %i, should be %i)", i_got, i_correct); \
+	}
+
+	//no messages in the queue anymore
+
+	test_note("  Testing to write some elements...");
+
+	for (int i = 0; i < queue_size - 2; ++i) {
+		t.val = i;
+		orb_publish(ORB_ID(orb_test_medium_wrap_around), ptopic, &t);
+	}
+
+	for (int i = 0; i < queue_size - 2; ++i) {
+		CHECK_UPDATED(i);
+		CHECK_COPY(u.val, i);
+	}
+
+	CHECK_NOT_UPDATED(queue_size);
+
+#define SET_GENERTATION() \
+	set_generation(*node, unsigned(-(queue_size / 2))); \
+	if (node->updates_available(0) != unsigned(-(queue_size / 2))) { \
+		return test_fail("set generation failed."); \
+	} \
+	for (int i = 0; i < queue_size; i++) { \
+		if (PX4_OK != orb_copy(ORB_ID(orb_test_medium_wrap_around), sfd, &u)) { \
+			break; \
+		} \
+	}
+
+	test_note("  Testing overflow...");
+	int overflow_by = 3;
+
+	SET_GENERTATION();
+
+	for (int i = 0; i < queue_size + overflow_by; ++i) {
+		t.val = i;
+		orb_publish(ORB_ID(orb_test_medium_wrap_around), ptopic, &t);
+	}
+
+	for (int i = 0; i < queue_size; ++i) {
+		CHECK_UPDATED(i);
+		CHECK_COPY(u.val, i + overflow_by);
+	}
+
+	CHECK_NOT_UPDATED(queue_size);
+
+	test_note("  Testing underflow...");
+
+	SET_GENERTATION();
+
+	t.val = queue_size;
+	orb_publish(ORB_ID(orb_test_medium_wrap_around), ptopic, &t);
+
+	CHECK_UPDATED(-1);
+	CHECK_COPY(u.val, t.val);
+
+	for (int i = 0; i < queue_size; ++i) {
+		CHECK_NOT_UPDATED(i);
+		CHECK_COPY(u.val, t.val);
+	}
+
+#undef SET_GENERTATION
+
+	t.val = 943;
+	orb_publish(ORB_ID(orb_test_medium_wrap_around), ptopic, &t);
+	CHECK_UPDATED(-1);
+	test_note("before copy");
+	CHECK_COPY(u.val, t.val);
+
+#undef CHECK_COPY
+#undef CHECK_UPDATED
+#undef CHECK_NOT_UPDATED
+
+	test_note("before unadvertise");
+	orb_unadvertise(ptopic);
+	orb_unsubscribe(sfd);
+
+	return test_note("PASS orb queuing");
+}
+
 int uORBTest::UnitTest::test_queue()
 {
 	test_note("Testing orb queuing");
@@ -597,7 +759,7 @@ int uORBTest::UnitTest::test_queue()
 		return test_fail("subscribe failed: %d", errno);
 	}
 
-	const int queue_size = 11;
+	const int queue_size = 16;
 	t.val = 0;
 	ptopic = orb_advertise_queue(ORB_ID(orb_test_medium_queue), &t, queue_size);
 

src/modules/uORB/uORB_tests/uORBTest_UnitTest.hpp

@@ -35,6 +35,9 @@
 #define _uORBTest_UnitTest_hpp_
 
 #include <uORB/uORB.h>
+#include <uORB/uORBDeviceMaster.hpp>
+#include <uORB/uORBDeviceNode.hpp>
+#include <uORB/uORBManager.hpp>
 #include <uORB/topics/orb_test.h>
 #include <uORB/topics/orb_test_medium.h>
 #include <uORB/topics/orb_test_large.h>
@@ -68,6 +71,12 @@ public:
 	// Disallow copy
 	UnitTest(const uORBTest::UnitTest & /*unused*/) = delete;
 
+	// Assist in testing the wrap-around situation
+	static void set_generation(uORB::DeviceNode &node, unsigned generation)
+	{
+		node._generation.store(generation);
+	}
+
 private:
 	UnitTest() : pubsubtest_passed(false), pubsubtest_print(false) {}
 
@@ -94,6 +103,8 @@ private:
 
 	int test_multi2();
 
+	int test_wrap_around();
+
 	/* queuing tests */
 	int test_queue();
 	static int pub_test_queue_entry(int argc, char *argv[]);