Store and forward data. More...

#include <buffer.h>

Inheritance diagram for fkie_message_filters::Buffer< Inputs >:

[legend]

Classes
struct	Impl

class	RosCB

Public Member Functions
	Buffer (const ros::NodeHandle &nh, std::size_t max_queue_size) noexcept
	Constructor. More...

	Buffer (BufferPolicy policy=BufferPolicy::Discard, std::size_t max_queue_size=1, ros::CallbackQueueInterface *cbq=nullptr) noexcept
	Constructor. More...

bool	has_some () const noexcept
	Check if the buffer has pending data. More...

bool	process_one ()
	Wait for and process one data item. More...

template<class Rep , class Period >
bool	process_one (const std::chrono::duration< Rep, Period > &timeout)
	Wait for and process one data item. More...

void	reset () noexcept override
	Reset filter. More...

void	set_callback_queue (ros::CallbackQueueInterface *cbq) noexcept
	Process data with a ROS callback queue. More...

void	set_policy (BufferPolicy policy, std::size_t max_queue_size=0)
	Modify the buffer policy. More...

void	spin ()
	Process all data indefinitely. More...

void	spin_once ()
	Process pending data. More...

bool	wait () noexcept
	Wait for pending data. More...

template<class Rep , class Period >
bool	wait_for (const std::chrono::duration< Rep, Period > &timeout) noexcept
	Wait for pending data until timeout expires. More...

virtual	~Buffer ()

Public Member Functions inherited from fkie_message_filters::Sink< Inputs... >
Connection	connect_to_source (Source< Inputs... > &src) noexcept
	Connect this sink to a source. More...

void	disconnect_from_all_sources () noexcept
	Disconnect from all connected sources. More...

virtual	~Sink ()

Public Member Functions inherited from fkie_message_filters::FilterBase
virtual	~FilterBase ()

Public Member Functions inherited from fkie_message_filters::Source< IO< Inputs... > >
Connection	connect_to_sink (Sink< Outputs... > &dst) noexcept
	Connect this source to a sink. More...

void	disconnect_from_all_sinks () noexcept
	Disconnect from all connected sinks. More...

virtual	~Source ()

Protected Member Functions
virtual void	receive (const Inputs &... in) override
	Process incoming data. More...

Protected Member Functions inherited from fkie_message_filters::Source< IO< Inputs... > >
void	send (const Outputs &... out)
	Pass data to all connected sinks. More...

Private Types
using	QueueElement = std::tuple< Inputs... >

Private Member Functions
void	process_some (std::unique_lock< std::mutex > &)

void	send_queue_element (const QueueElement &e)

Private Attributes
ros::CallbackQueueInterface *	cbq_

std::shared_ptr< Impl >	impl_

Additional Inherited Members
Public Types inherited from fkie_message_filters::Sink< Inputs... >
using	Input = IO< Inputs... >
	Grouped input types. More...

Public Types inherited from fkie_message_filters::Source< IO< Inputs... > >
using	Output = IO< Outputs... >
	Grouped output types. More...

Static Public Attributes inherited from fkie_message_filters::Sink< Inputs... >
static constexpr std::size_t	NUM_INPUTS
	Number of input arguments. More...

Static Public Attributes inherited from fkie_message_filters::Source< IO< Inputs... > >
static constexpr std::size_t	NUM_OUTPUTS
	Number of output arguments. More...

Detailed Description

template<class... Inputs>
class fkie_message_filters::Buffer< Inputs >

Store and forward data.

The buffer acts as a decoupler in the filter pipeline. Data can be stored and processed at a later time. The pipeline is effectively split into independent upstream and downstream parts, and it becomes possible to run the downstream data processing asynchronously. For instance, you can run computationally expensive algorithms on ROS messages in a different thread without blocking the ROS subscriber callback queue.

The buffer can be used for at least three different use cases:

Use the buffer as a valve
You can toggle between the BufferPolicy::Discard and BufferPolicy::Passthru modes to selectively disable or enable data processing at specific times. This is the simplest use case without any asynchronous processing.
Run multiple ROS callback queues
If your ROS node runs multiple callback queues, you can use the buffer to bind processing to a particular queue:
namespace mf = fkie_message_filters;
ros::NodeHandle nh;
nh.setCallbackQueue(...);
// Version 1
mf::Buffer<M> buf1(nh, 10); // will use the callback queue of nh
// Version 2
mf::Buffer<M> buf2(mf::BufferPolicy::Queue, 10);
buf2.set_callback_queue(...); // will explicitly set the ROS callback queue
Run your own thread(s) for data processing
This is the most versatile option for advanced users. You can set up your worker threads as you desire and then call spin(), spin_once() or process_one() as you see fit.
namespace mf = fkie_message_filters;
mf::Subscriber<M> sub;
mf::Buffer<mf::Subscriber<M>::Output> buffer(mf::BufferPolicy::Queue, 10);
mf::SimpleUserFilter<mf::Subscriber<M>::Output> flt;
std::thread t([&buffer]{ buffer.spin(); });
flt.set_processing_function(...);
mf::chain(sub, buffer, flt);
ros::spin();

Definition at line 103 of file buffer.h.

Member Typedef Documentation

◆ QueueElement

template<class... Inputs>

using fkie_message_filters::Buffer< Inputs >::QueueElement = std::tuple<Inputs...>

private

Definition at line 249 of file buffer.h.

Constructor & Destructor Documentation

◆ Buffer() [1/2]

template<class... Inputs>

fkie_message_filters::Buffer< Inputs >::Buffer	(	const ros::NodeHandle &	nh,
		std::size_t	max_queue_size
	)

noexcept

Constructor.

Constructs a buffer with BufferPolicy::Queue policy and data processing via ROS callbacks.

nh ROS node handle whose callback queue is used for data processing
max_queue_size the maximum number of queued data items

Definition at line 113 of file buffer_impl.h.

◆ Buffer() [2/2]

template<class... Inputs>

fkie_message_filters::Buffer< Inputs >::Buffer	(	BufferPolicy	policy = `BufferPolicy::Discard`,
		std::size_t	max_queue_size = `1`,
		ros::CallbackQueueInterface *	cbq = `nullptr`
	)

noexcept

Constructor.

policy the buffer policy
max_queue_size for the BufferPolicy::Queue policy, the maximum number of queued data items.
cbq ROS callback queue that is used to process queued data

See also: set_policy(), set_callback_queue()

Definition at line 106 of file buffer_impl.h.

◆ ~Buffer()

template<class... Inputs>

fkie_message_filters::Buffer< Inputs >::~Buffer ( )

virtual

Definition at line 120 of file buffer_impl.h.

Member Function Documentation

◆ has_some()

template<class... Inputs>

bool fkie_message_filters::Buffer< Inputs >::has_some ( ) const

noexcept

Check if the buffer has pending data.

Return values

true	if the current policy is BufferPolicy::Queue and a subsequent call to process_one() or spin_once() will process data.
false	otherwise

Definition at line 191 of file buffer_impl.h.

◆ process_one() [1/2]

template<class... Inputs>

bool fkie_message_filters::Buffer< Inputs >::process_one ( )

Wait for and process one data item.

Return values

true	data has been processed successfully
false	either the current buffer policy is not BufferPolicy::Queue, or the policy has been changed to something other than BufferPolicy::Queue while the function was waiting, or the ROS node has been shut down.

Definition at line 213 of file buffer_impl.h.

◆ process_one() [2/2]

template<class... Inputs>

template<class Rep , class Period >

bool fkie_message_filters::Buffer< Inputs >::process_one ( const std::chrono::duration< Rep, Period > & timeout )

Wait for and process one data item.

timeout maximum duration to wait for new data if none is available

Return values

true	data has been processed successfully
false	either the current buffer policy is not BufferPolicy::Queue, or the policy has been changed to something other than BufferPolicy::Queue while the function was waiting, or time timeout expired, or the ROS node has been shut down.

Definition at line 229 of file buffer_impl.h.

◆ process_some()

template<class... Inputs>

void fkie_message_filters::Buffer< Inputs >::process_some ( std::unique_lock< std::mutex > & lock )

private

Definition at line 176 of file buffer_impl.h.

◆ receive()

template<class... Inputs>

void fkie_message_filters::Buffer< Inputs >::receive ( const Inputs &... in )

overrideprotectedvirtual

Process incoming data.

Derived classes need to override this method to handle all data that is to be consumed by the sink.

Implements fkie_message_filters::Sink< Inputs... >.

Definition at line 244 of file buffer_impl.h.

◆ reset()

template<class... Inputs>

void fkie_message_filters::Buffer< Inputs >::reset ( )

overridevirtualnoexcept

Reset filter.

If the buffer policy is BufferPolicy::Queue, this will clear the internal queue and discard all pending data. Otherwise, this function has no effect.

Reimplemented from fkie_message_filters::FilterBase.

Definition at line 167 of file buffer_impl.h.

◆ send_queue_element()

template<class... Inputs>

void fkie_message_filters::Buffer< Inputs >::send_queue_element ( const QueueElement & e )

private

Definition at line 279 of file buffer_impl.h.

◆ set_callback_queue()

template<class... Inputs>

void fkie_message_filters::Buffer< Inputs >::set_callback_queue ( ros::CallbackQueueInterface * cbq )

noexcept

Process data with a ROS callback queue.

Instead of running your own processing threads, you can use the ROS callback system to schedule data processing whenever new data arrives.

cbq the ROS callback queue or nullptr to disable ROS callbacks.

namespace mf = fkie_message_filters;
mf::Buffer<...> buf;
buf.set_callback_queue(ros::getGlobalCallbackQueue());
ros::spin();

Definition at line 153 of file buffer_impl.h.

◆ set_policy()

template<class... Inputs>

void fkie_message_filters::Buffer< Inputs >::set_policy	(	BufferPolicy	policy,
		std::size_t	max_queue_size = `0`
	)

Modify the buffer policy.

If the new buffer policy is not BufferPolicy::Queue, any pending call to wait(), process_one(), or spin() will return. If the buffer policy is changed to BufferPolicy::Passthru, all pending data is processed immediately before the function returns. If the buffer policy is changed to BufferPolicy::Discard, all pending data is discarded immediately.

policy the buffer policy
max_queue_size for the BufferPolicy::Queue policy, the maximum number of queued data items. If zero, the previously set queue size remains unchanged.

Warning: If you change the policy from BufferPolicy::Queue to BufferPolicy::Passthru and there is still a pending call to process_one(), spin_once(), or spin() in a different thread, some data might be processed in parallel or out of order when the queue is flushed.

Definition at line 126 of file buffer_impl.h.

◆ spin()

template<class... Inputs>

void fkie_message_filters::Buffer< Inputs >::spin ( )

Process all data indefinitely.

Blocks and processes all incoming data until the buffer policy is changed to something other than BufferPolicy::Queue or the ROS node is shut down.

You can call the function from multiple threads at once, and the workload will be shared among all participating threads.

See also: set_policy()

Definition at line 265 of file buffer_impl.h.

◆ spin_once()

template<class... Inputs>

void fkie_message_filters::Buffer< Inputs >::spin_once ( )

Process pending data.

Does nothing if the buffer policy is not BufferPolicy::Queue. The method is guaranteed to return as it will only process data which is pending at invocation time. This also means that there may be new data pending already when this method returns.

Definition at line 160 of file buffer_impl.h.

◆ wait()

template<class... Inputs>

bool fkie_message_filters::Buffer< Inputs >::wait ( )

noexcept

Wait for pending data.

Return values

true	there is data available for consumption by spin_once()
false	either the current buffer policy is not BufferPolicy::Queue, or the policy has been changed to something other than BufferPolicy::Queue while the function was waiting, or the ROS node has been shut down.

Definition at line 198 of file buffer_impl.h.

◆ wait_for()

template<class... Inputs>

template<class Rep , class Period >

bool fkie_message_filters::Buffer< Inputs >::wait_for ( const std::chrono::duration< Rep, Period > & timeout )

noexcept

Wait for pending data until timeout expires.

timeout maximum duration to wait for new data if none is available

Return values

true	there is data available for consumption by spin_once()
false	either the current buffer policy is not BufferPolicy::Queue, or the policy has been changed to something other than BufferPolicy::Queue while the function was waiting, or the timeout expired, or the ROS node has been shut down.

Definition at line 206 of file buffer_impl.h.

Member Data Documentation

◆ cbq_

template<class... Inputs>

ros::CallbackQueueInterface* fkie_message_filters::Buffer< Inputs >::cbq_

private

Definition at line 253 of file buffer.h.

◆ impl_

template<class... Inputs>

std::shared_ptr<Impl> fkie_message_filters::Buffer< Inputs >::impl_

private

Definition at line 252 of file buffer.h.

The documentation for this class was generated from the following files:

Classes

Public Member Functions

Protected Member Functions

Private Types

Private Member Functions

Private Attributes

Additional Inherited Members

Detailed Description

template<class... Inputs> class fkie_message_filters::Buffer< Inputs >

Member Typedef Documentation

◆ QueueElement

Constructor & Destructor Documentation

◆ Buffer() [1/2]

◆ Buffer() [2/2]

◆ ~Buffer()

Member Function Documentation

◆ has_some()

◆ process_one() [1/2]

◆ process_one() [2/2]

◆ process_some()

◆ receive()

◆ reset()

◆ send_queue_element()

◆ set_callback_queue()

◆ set_policy()

◆ spin()

◆ spin_once()

◆ wait()

◆ wait_for()

Member Data Documentation

◆ cbq_

◆ impl_

template<class... Inputs>
class fkie_message_filters::Buffer< Inputs >