参考自: PX4/Pixhawk—uORB深入理解和应用. 修改部分内容和格式
完整的API文档可见：src/modules/uORB/uORBManager.hpp.
/**
* This is implemented as a singleton. This class manages creating the
* uORB nodes for each uORB topics and also implements the behavor of the
* uORB Api's.
*/
class uORB::Manager
#ifdef ORB_COMMUNICATOR
: public uORBCommunicator::IChannelRxHandler
#endif /* ORB_COMMUNICATOR */
{
public:
...
// ==== uORB interface methods ====
/**
* Advertise as the publisher of a topic.
*
* This performs the initial advertisement of a topic; it creates the topic
* node in /obj if required and publishes the initial data.
*
* Any number of advertisers may publish to a topic; publications are atomic
* but co-ordination between publishers is not provided by the ORB.
*
* Internally this will call orb_advertise_multi with an instance of 0 and
* default priority.
*
* @param meta The uORB metadata (usually from the ORB_ID() macro)
* for the topic.
* @param data A pointer to the initial data to be published.
* For topics updated by interrupt handlers, the advertisement
* must be performed from non-interrupt context.
* @param queue_size Maximum number of buffered elements. If this is 1, no queuing is
* used.
* @return nullptr on error, otherwise returns an object pointer
* that can be used to publish to the topic.
* If the topic in question is not known (due to an
* ORB_DEFINE with no corresponding ORB_DECLARE)
* this function will return nullptr and set errno to ENOENT.
*/
orb_advert_t orb_advertise(const struct orb_metadata *meta, const void *data, unsigned int queue_size = 1)
{
return orb_advertise_multi(meta, data, nullptr, ORB_PRIO_DEFAULT, queue_size);
}
/**
* Advertise as the publisher of a topic.
*
* This performs the initial advertisement of a topic; it creates the topic
* node in /obj if required and publishes the initial data.
*
* Any number of advertisers may publish to a topic; publications are atomic
* but co-ordination between publishers is not provided by the ORB.
*
* The multi can be used to create multiple independent instances of the same topic
* (each instance has its own buffer).
* This is useful for multiple publishers who publish the same topic. The subscriber
* then subscribes to all instances and chooses which source he wants to use.
*
* @param meta The uORB metadata (usually from the ORB_ID() macro)
* for the topic.
* @param data A pointer to the initial data to be published.
* For topics updated by interrupt handlers, the advertisement
* must be performed from non-interrupt context.
* @param instance Pointer to an integer which will yield the instance ID (0-based)
* of the publication. This is an output parameter and will be set to the newly
* created instance, ie. 0 for the first advertiser, 1 for the next and so on.
* @param priority The priority of the instance. If a subscriber subscribes multiple
* instances, the priority allows the subscriber to prioritize the best
* data source as long as its available. The subscriber is responsible to check
* and handle different priorities (@see orb_priority()).
* @param queue_size Maximum number of buffered elements. If this is 1, no queuing is
* used.
* @return PX4_ERROR on error, otherwise returns a handle
* that can be used to publish to the topic.
* If the topic in question is not known (due to an
* ORB_DEFINE with no corresponding ORB_DECLARE)
* this function will return -1 and set errno to ENOENT.
*/
orb_advert_t orb_advertise_multi(const struct orb_metadata *meta, const void *data, int *instance,
int priority, unsigned int queue_size = 1);
/**
* Unadvertise a topic.
*
* @param handle handle returned by orb_advertise or orb_advertise_multi.
* @return 0 on success
*/
int orb_unadvertise(orb_advert_t handle);
/** 2
* Publish new data to a topic.
*
* The data is atomically published to the topic and any waiting subscribers
* will be notified. Subscribers that are not waiting can check the topic
* for updates using orb_check and/or orb_stat.
* 即使订阅的主题没有被公告，但是也能订阅成功；但是在这种情况下，却得不到数据，直到主题被公告
* @param meta The uORB metadata (usually from the ORB_ID() macro) for the topic.
* @param handle The handle returned from orb_advertise.
* @param data A pointer to the data to be published.
* @return OK on success, PX4_ERROR otherwise with errno set accordingly.
*/
int orb_publish(const struct orb_metadata *meta, orb_advert_t handle, const void *data);
/**
* Subscribe to a topic.
*
* The returned value is a file descriptor that can be passed to poll()
* in order to wait for updates to a topic, as well as topic_read,
* orb_check and orb_stat.
*
* If there were any publications of the topic prior to the subscription,
* an orb_check right after orb_subscribe will return true.
*
* Subscription will succeed even if the topic has not been advertised;
* in this case the topic will have a timestamp of zero, it will never
* signal a poll() event, checking will always return false and it cannot
* be copied. When the topic is subsequently advertised, poll, check,
* stat and copy calls will react to the initial publication that is
* performed as part of the advertisement.
*
* Subscription will fail if the topic is not known to the system, i.e.
* there is nothing in the system that has declared the topic and thus it
* can never be published.
*
* Internally this will call orb_subscribe_multi with instance 0.
*
* @param meta The uORB metadata (usually from the ORB_ID() macro)
* for the topic.
* @return PX4_ERROR on error, otherwise returns a handle
* that can be used to read and update the topic.
*/
int orb_subscribe(const struct orb_metadata *meta);
/**
* Subscribe to a multi-instance of a topic.
*
* The returned value is a file descriptor that can be passed to poll()
* in order to wait for updates to a topic, as well as topic_read,
* orb_check and orb_stat.
*
* If there were any publications of the topic prior to the subscription,
* an orb_check right after orb_subscribe_multi will return true.
*
* Subscription will succeed even if the topic has not been advertised;
* in this case the topic will have a timestamp of zero, it will never
* signal a poll() event, checking will always return false and it cannot
* be copied. When the topic is subsequently advertised, poll, check,
* stat and copy calls will react to the initial publication that is
* performed as part of the advertisement.
*
* Subscription will fail if the topic is not known to the system, i.e.
* there is nothing in the system that has declared the topic and thus it
* can never be published.
*
* If a publisher publishes multiple instances the subscriber should
* subscribe to each instance with orb_subscribe_multi
* (@see orb_advertise_multi()).
*
* @param meta The uORB metadata (usually from the ORB_ID() macro)
* for the topic.
* @param instance The instance of the topic. Instance 0 matches the
* topic of the orb_subscribe() call, higher indices
* are for topics created with orb_advertise_multi().
* @return PX4_ERROR on error, otherwise returns a handle
* that can be used to read and update the topic.
* If the topic in question is not known (due to an
* ORB_DEFINE_OPTIONAL with no corresponding ORB_DECLARE)
* this function will return -1 and set errno to ENOENT.
*/
int orb_subscribe_multi(const struct orb_metadata *meta, unsigned instance);
/**
* Unsubscribe from a topic.
*
* @param handle A handle returned from orb_subscribe.
* @return OK on success, PX4_ERROR otherwise with errno set accordingly.
*/
int orb_unsubscribe(int handle);
/****
* Fetch data from a topic.
*
* This is the only operation that will reset the internal marker that
* indicates that a topic has been updated for a subscriber. Once poll
* or check return indicating that an updaet is available, this call
* must be used to update the subscription.
*
* @param meta The uORB metadata (usually from the ORB_ID() macro)
* for the topic.
* @param handle A handle returned from orb_subscribe.
* @param buffer Pointer to the buffer receiving the data, or NULL
* if the caller wants to clear the updated flag without
* using the data.
* @return OK on success, PX4_ERROR otherwise with errno set accordingly.
*/
int orb_copy(const struct orb_metadata *meta, int handle, void *buffer);
/**
* Check whether a topic has been published to since the last orb_copy.
*
* This check can be used to determine whether to copy the topic when
* not using poll(), or to avoid the overhead of calling poll() when the
* topic is likely to have updated.
*
* Updates are tracked on a per-handle basis; this call will continue to
* return true until orb_copy is called using the same handle. This interface
* should be preferred over calling orb_stat due to the race window between
* stat and copy that can lead to missed updates.
*
* @param handle A handle returned from orb_subscribe.
* @param updated Set to true if the topic has been updated since the
* last time it was copied using this handle.
* @return OK if the check was successful, PX4_ERROR otherwise with
* errno set accordingly.
*/
int orb_check(int handle, bool *updated);
/**
* Return the last time that the topic was updated. If a queue is used, it returns
* the timestamp of the latest element in the queue.
*
* @param handle A handle returned from orb_subscribe.
* @param time Returns the absolute time that the topic was updated, or zero if it has
* never been updated. Time is measured in microseconds.
* @return OK on success, PX4_ERROR otherwise with errno set accordingly.
*/
int orb_stat(int handle, uint64_t *time);
/**
* Check if a topic has already been created and published (advertised)
*
* @param meta ORB topic metadata.
* @param instance ORB instance
* @return OK if the topic exists, PX4_ERROR otherwise.
*/
int orb_exists(const struct orb_metadata *meta, int instance);
/**
* Return the priority of the topic
*
* @param handle A handle returned from orb_subscribe.
* @param priority Returns the priority of this topic. This is only relevant for
* topics which are published by multiple publishers (e.g. mag0, mag1, etc.)
* and allows a subscriber to pick the topic with the highest priority,
* independent of the startup order of the associated publishers.
* @return OK on success, PX4_ERROR otherwise with errno set accordingly.
*/
int orb_priority(int handle, int32_t *priority);
/**
* Set the minimum interval between which updates are seen for a subscription.
*
* If this interval is set, the subscriber will not see more than one update
* within the period.
*
* Specifically, the first time an update is reported to the subscriber a timer
* is started. The update will continue to be reported via poll and orb_check, but
* once fetched via orb_copy another update will not be reported until the timer
* expires.
*
* This feature can be used to pace a subscriber that is watching a topic that
* would otherwise update too quickly.
*
* @param handle A handle returned from orb_subscribe.
* @param interval An interval period in milliseconds.
* @return OK on success, PX4_ERROR otherwise with ERRNO set accordingly.
*/
int orb_set_interval(int handle, unsigned interval);
/**
* Get the minimum interval between which updates are seen for a subscription.
*
* @see orb_set_interval()
*
* @param handle A handle returned from orb_subscribe.
* @param interval The returned interval period in milliseconds.
* @return OK on success, PX4_ERROR otherwise with ERRNO set accordingly.
*/
int orb_get_interval(int handle, unsigned *interval);
#ifdef ORB_COMMUNICATOR
/**
* Method to set the uORBCommunicator::IChannel instance.
* @param comm_channel
* The IChannel instance to talk to remote proxies.
* @note:
* Currently this call only supports the use of one IChannel
* Future extensions may include more than one IChannel's.
*/
void set_uorb_communicator(uORBCommunicator::IChannel *comm_channel);
/**
* Gets the uORB Communicator instance.
*/
uORBCommunicator::IChannel *get_uorb_communicator();
/**
* Utility method to check if there is a remote subscriber present
* for a given topic
*/
bool is_remote_subscriber_present(const char *messageName);
#endif /* ORB_COMMUNICATOR */
private:
...
#endif /* ORB_USE_PUBLISHER_RULES */
};
#endif /* _uORBManager_hpp_ */
1 int poll(struct pollfd fds[], nfds_t nfds, int timeout)
/**
* @brief 监控文件描述符（多个）；
timemout=0,poll()函数立即返回而不阻塞；timeout=INFTIM(-1),poll()会一直阻塞下去，直到检测到return > 0；
* @param fds:struct pollfd结构类型的数组；
* @param nfds:用于标记数组fds中的结构体元素的总数量；
* @param timeout:是poll函数调用阻塞的时间，单位：毫秒；
* @retval: >0:数组fds中准备好读、写或出错状态的那些socket描述符的总数量；
0:poll()函数会阻塞timeout所指定的毫秒时间长度之后返回;
-1:poll函数调用失败；同时会自动设置全局变量errno；
*/
int poll(struct pollfd fds[], nfds_t nfds, int timeout){
}
