An exception that occurs whenever a channel has no data. More...

#include <fw/Channel.h>

Public Member Functions
	Channel ()
	Create channel proxy that is not assigned to a channel. More...

	Channel (ConcreteChannel< T > *channel, ChannelAccessFlags accessFlags)
	Is used by Framework to create a channel proxy object. More...

void	reset ()
	Reset the proxy object so that it becomes invalid. More...

bool	isValid () const
	Returns true if the proxy object is valid. More...

void	validate () const
	Checks if the channel is valid otherwise throws an exception. More...

Channel Information.
The following methods allow to obtain information on the channel (name, type, etc).
const std::string &	getID () const
	Return the channel ID, its name. More...

int	getTypeId () const
	Returns the type id of the channel. More...

bool	isTyped () const
	Returns true, if the channel is typed and false, if it is untyped. More...

Typename	getTypename () const
	Return the typename of the channel. More...

void	setTypename (const Typename &type)
	Set the typename of this channel. More...

TypeMetaPtr	getTypeMeta () const
	Return the type meta information for this channel. More...

void	setTypeMeta (TypeMetaPtr meta)
	Set the type meta information for this channel. More...

Content information.
The following methods provide information on the channels content.
bool	isEmpty () const
	Returns if the channel is empty (no data has been published) More...

bool	hasSubscriber () const
	Returns true, if this channel has at least one subscriber. More...

bool	hasPublisher () const
	Returns true, if this channel has at least one publisher. More...

bool	hasSoloSlot () const
	Returns true, if this channel has one solo slot only. More...

std::size_t	getMaxSlots () const
	Returns the upper limit of slots that are allowed for this channel. More...

std::size_t	getMinSlots () const
	Returns the number slots that are guaranteed to be kept in the channel buffer. More...

Duration	getStorageDuration () const
	Returns the timeframe that specifies how long a slot is guaranteed to be kept in the channel buffer. More...

bool	isAutoIncreasingStorageDuration () const
	Returns whether the channel buffer is automatically increasing the storage duration. More...

std::size_t	getNrOfSlots () const
	Returns how many slots (i.e. More...

Accessing the channels data.
The Channel provides different methods for reading and writing data in different flavors.
ChannelRead< T >	waitForData (const Duration &timeout=Duration::infinity()) const
	Waits until data in this channel becomes available. More...

bool	waitForPublisher (const Duration &timeout=Duration::infinity()) const
	Waits until this channel has at least one publisher. More...

ChannelRead< T >	read ()
	Obtains read access to the latest data element of this channel. More...

ChannelRead< T >	read (const Time &timestamp, SlotQueryMode mode=NEAREST_SLOT, const Duration &tolerance=Duration::infinity())
	Obtains read access to the element at the specified timestamp. More...

ChannelRead< T >	read (uint32 sequenceID, const Duration &searchInterval=Duration::seconds(1))
	Obtains read access to the element with the specified sequenceID within the given search interval If no slot with the exact sequenceID exists within the search interval an XInvalidRead exception is thrown. More...

ChannelRead< T >	read (const Time &timestamp, const Duration &tolerance)
	Same as above, but always takes the nearest slot. More...

ChannelReadInterval< T >	readInterval (const Time &timestamp, std::size_t nrSlots, std::size_t olderSlots, std::size_t newerSlots, IntervalFillMode fillMode=PREFER_NEWER)
	Obtains read access to an interval of elements before and after the requested timestamp. More...

ChannelReadInterval< T >	readInterval (const Time &from, const Time &to=Time::eternity())
	Obtains read access to an interval of elements in a given time span. More...

ChannelWrite< T >	write ()
	Obtains exclusive write access to the next free data slot of this channel. More...

ChannelWrite< T >	write (bool copyLatestData)
	Same as write above with an additional parameter copyLatestData that allows you to specify whether the channel should copy the latest data available into the write slot. More...

Stamped< T >	get ()
	Returns the latest data from the channel by value. More...

Stamped< T >	get (const Time &timestamp, SlotQueryMode mode=NEAREST_SLOT, const Duration &tolerance=Duration::infinity())
	Returns the data at the given time by value. More...

Stamped< T >	get (const Time &timestamp, Duration tolerance)
	Same as above, but always takes the nearest slot. More...

template<typename Filter >
Stamped< T >	get (const Time &timestamp, Filter &&filter)
	Returns the data at the given time by value. More...

template<typename U = void>
void	post (const Stamped< T > &value)
	Writes the specified data into the channel. More...

template<typename U = void>
void	post (Stamped< T > &&value)
	Same as above, for rvalue reference (move semantics) More...

template<typename U >
std::enable_if<!std::is_base_of_v< StampedHeader, std::decay_t< U > > >::type	post (U &&value, const Time &timestamp=Time::now())
	Writes the specified data with the specified time stamp into the channel. More...

template<typename U = T>
std::enable_if<!std::is_void< U >::value >::type	post (const typename ParamHelper< T >::type &value, const Time &timestamp=Time::now())
	This allows post({}, Time()); to deduce we want to post an object of the channel's type. More...

template<typename U = T>
std::enable_if<!std::is_void< U >::value >::type	post (typename ParamHelper< T >::type &&value, const Time &timestamp=Time::now())
	Same as above, for rvalue reference (move semantics) More...

Detailed Description

template<typename T>
class mira::Channel< T >

An exception that occurs whenever a channel has no data.

A channel is a named data container that stores data of a certain type within a buffer.

forward decl for friend decl in Channel<T>

forward declaration

Each data element in the channel is called a slot. The channel manages the access to the data and ensures safe non-blocking access across different threads. Use read() and write() to obtain access to the channel data. Write access to the channel is non blocking. This means that data can be written to the channel while other threads still maintain read access to the data. For write access the channel returns the next free slot that is not locked by any pending write or read requests. Write and read access is allowed via ChannelRead and ChannelWrite objects only. They automatically take care that the data is unlocked at the right time and that the Channel is informed about changed data.

The signaling process is as follows:

some Writing to Channels finished the write process (went out of scope, called its finish method etc.).
the Channel calls ChannelSubscriber::signal() of all registered ChannelSubsribers to inform them that new data is available.
Each ChannelSubscriber calls SubscriberHandler::signal() of its associated SubscriberHandler.
The SubscriberHandler stores the ChannelSubscriber in an internal queue.
Within the SubscriberHandler thread the SubscriberHandler calls ChannelSubscriber::invoke() of the ChannelSubscriber.
the ChannelSubscriber finally calls the registered function that was assigned when it was constructed in Authority::subscribe()

This procedure ensures that type information won't get lost although the call. ChannelSubscriber are queued within the SubscriberHandler to decouple the threads.

Implementation notes:

must store shared pointer to BufferItem in mBuffer, since copying of ValueType can be expensive during a "push_back" and shared_mutex is not copyable.

This class is a proxy that allows restricted (based on access rights) access to ConcreteChannel to read or/and write data to channels.

Constructor & Destructor Documentation

◆ Channel() [1/2]

Channel ( )

inline

Create channel proxy that is not assigned to a channel.

◆ Channel() [2/2]

Channel	(	ConcreteChannel< T > *	channel,
		ChannelAccessFlags	accessFlags
	)

inline

Is used by Framework to create a channel proxy object.

Member Function Documentation

◆ reset()

void reset ( )

inline

Reset the proxy object so that it becomes invalid.

◆ isValid()

bool isValid ( ) const

inline

Returns true if the proxy object is valid.

Meaning if it points to a channel.

◆ validate()

void validate ( ) const

inline

Checks if the channel is valid otherwise throws an exception.

Exceptions

XAccessViolation If channel is not valid.

◆ getID()

const std::string& getID ( ) const

inline

Return the channel ID, its name.

◆ getTypeId()

int getTypeId ( ) const

inline

Returns the type id of the channel.

The type id is unique only within the same process. Use getTypename() to get a portable type information.

◆ isTyped()

bool isTyped ( ) const

inline

Returns true, if the channel is typed and false, if it is untyped.

◆ getTypename()

Typename getTypename ( ) const

inline

Return the typename of the channel.

Used to obtain type of the contained binary data of untyped channels.

◆ setTypename()

void setTypename ( const Typename & type )

inline

Set the typename of this channel.

Can be used when the channel is untyped to specify the type of contained binary data.

◆ getTypeMeta()

TypeMetaPtr getTypeMeta ( ) const

inline

Return the type meta information for this channel.

◆ setTypeMeta()

void setTypeMeta ( TypeMetaPtr meta )

inline

Set the type meta information for this channel.

◆ isEmpty()

bool isEmpty ( ) const

inline

Returns if the channel is empty (no data has been published)

◆ hasSubscriber()

bool hasSubscriber ( ) const

inline

Returns true, if this channel has at least one subscriber.

◆ hasPublisher()

bool hasPublisher ( ) const

inline

Returns true, if this channel has at least one publisher.

◆ hasSoloSlot()

bool hasSoloSlot ( ) const

inline

Returns true, if this channel has one solo slot only.

◆ getMaxSlots()

std::size_t getMaxSlots ( ) const

inline

Returns the upper limit of slots that are allowed for this channel.

◆ getMinSlots()

std::size_t getMinSlots ( ) const

inline

Returns the number slots that are guaranteed to be kept in the channel buffer.

◆ getStorageDuration()

Duration getStorageDuration ( ) const

inline

Returns the timeframe that specifies how long a slot is guaranteed to be kept in the channel buffer.

◆ isAutoIncreasingStorageDuration()

bool isAutoIncreasingStorageDuration ( ) const

inline

Returns whether the channel buffer is automatically increasing the storage duration.

◆ getNrOfSlots()

std::size_t getNrOfSlots ( ) const

inline

Returns how many slots (i.e.

data objects) are currently stored in the channel buffer.

◆ waitForData()

ChannelRead<T> waitForData ( const Duration & timeout = Duration::infinity() ) const

inline

Waits until data in this channel becomes available.

If a timeout is specified, the method times out if no data becomes available after the given time.

Exceptions

XAccessViolation if channel has no read access rights

Parameters

[in] timeout Wait for this duration or forever if Duration::infinity() (default)

Returns: A valid ChannelRead, if data became available, or an invalid ChannelRead, if the method timed out or the thread was interrupted.

◆ waitForPublisher()

bool waitForPublisher ( const Duration & timeout = Duration::infinity() ) const

inline

Waits until this channel has at least one publisher.

If a timeout is specified, the method times out if no publisher becomes available after the given time.

Exceptions

XAccessViolation if channel has no read access rights

Parameters

[in] timeout Wait for this duration or forever if Duration::infinity() (default)

Returns: Returns true, if the wait was successfully and a publisher is available. If the wait timed out, false is returned.

◆ read() [1/4]

ChannelRead<T> read ( )

inline

Obtains read access to the latest data element of this channel.

Exceptions

XAccessViolation	if channel has no read access rights
XInvalidRead	when there is no data in the channel

Returns: ChannelRead object that has already locked the data. One can unlock the data manually or it is unlocked automatically when the ChannelRead object goes out of scope.

◆ read() [2/4]

ChannelRead<T> read	(	const Time &	timestamp,
		SlotQueryMode	mode = `NEAREST_SLOT`,
		const Duration &	tolerance = `Duration::infinity()`
	)

inline

Obtains read access to the element at the specified timestamp.

If no slot with the exact timestamp exists (most of the time there will be no such slot) a slot will be chosen according to the query mode (see SlotQueryMode).

Internally calls ConcreteChannel::read().

Parameters

[in]	timestamp	Timestamp of the desired slot.
[in]	mode	Specifies whether the nearest, newer or older slot to the given timestamp should be used (default: nearest slot)
[in]	tolerance	The max. allowed difference between the given timestamp and the best slot that was found (default: infinity)

Exceptions

XAccessViolation	if channel has no read access rights
XInvalidRead	when there is no data in the channel

Returns: ChannelRead object that has already locked the data. One can unlock the data manually or it is unlocked automatically when the ChannelRead object goes out of scope.

◆ read() [3/4]

ChannelRead<T> read	(	uint32	sequenceID,
		const Duration &	searchInterval = `Duration::seconds(1)`
	)

inline

Obtains read access to the element with the specified sequenceID within the given search interval If no slot with the exact sequenceID exists within the search interval an XInvalidRead exception is thrown.

Internally uses readInterval(newestSlotTime - searchInterval, newestSlotTime)

Parameters

[in]	sequenceID	The sequenceID of the desired slot.
[in]	searchInterval	The interval which is searched for the sequenceID (default: 1 second)

Exceptions

XAccessViolation	if channel has no read access rights
XInvalidRead	when there is no such sequenceID within the search interval the channel

Returns: ChannelRead object that has already locked the data. One can unlock the data manually or it is unlocked automatically when the ChannelRead object goes out of scope.

◆ read() [4/4]

ChannelRead<T> read	(	const Time &	timestamp,
		const Duration &	tolerance
	)

inline

Same as above, but always takes the nearest slot.

Internally calls ConcreteChannel::read().

◆ readInterval() [1/2]

ChannelReadInterval<T> readInterval	(	const Time &	timestamp,
		std::size_t	nrSlots,
		std::size_t	olderSlots,
		std::size_t	newerSlots,
		IntervalFillMode	fillMode = `PREFER_NEWER`
	)

inline

Obtains read access to an interval of elements before and after the requested timestamp.

It is required that nrSlots >= olderSlots + newerSlots. The following the rules are applied:

The interval will contain nrSlots number of elements
The interval will contain olderSlots number of slots with a timestamp < requested timestamp (if they exist)
The interval will contain newerSlots number of slots with a timestamp >= requested timestamp (if they exist)
If the number of available older + newer slots is < nrSlots more slots are added according to the specified fillMode.
- If fillMode == PREFER_OLDER, first older slots are added to the interval as needed. If there are not enough older slots, newer slots are added to the interval as needed.
- If fillMode == PREFER_NEWER, first newer slots are added to the interval as needed. If there are not enough newer slots, older slots are added to the interval as needed.

Internally calls ConcreteChannel::readInterval().

Exceptions

XAccessViolation	if channel has no read access rights
XRuntime	when there are not enough slots available.

Returns: ChannelReadInterval object that has already locked all the data in the interval. One can unlock the data manually or it is unlocked automatically when the ChannelReadInterval object goes out of scope.

◆ readInterval() [2/2]

ChannelReadInterval<T> readInterval	(	const Time &	from,
		const Time &	to = `Time::eternity()`
	)

inline

Obtains read access to an interval of elements in a given time span.

The first element in the interval will be the first slot with a timestamp > from
The last element in the interval will be the last slot with a timestamp <= to So slot with timestamp = from is excluded and slot with timestamp = to is included in the interval.

Internally calls ConcreteChannel::readInterval().

Exceptions

XAccessViolation if channel has no read access rights

Returns: ChannelReadInterval object that has already locked all the data in the interval. One can unlock the data manually or it is unlocked automatically when the ChannelReadInterval object goes out of scope.

◆ write() [1/2]

ChannelWrite<T> write ( )

inline

Obtains exclusive write access to the next free data slot of this channel.

If no such slot exists the queue will grow until its maximum size. If all slots are locked and the queue has maximum size this method will block until a slot is released.

Internally calls ConcreteChannel::write().

Exceptions

XAccessViolation if channel has no write access rights

Returns: ChannelWrite object that has already locked the data. One can unlock the data manually or it is unlocked automatically when the ChannelWrite object goes out of scope. All subscribers will be notified.

◆ write() [2/2]

ChannelWrite<T> write ( bool copyLatestData )

inline

Same as write above with an additional parameter copyLatestData that allows you to specify whether the channel should copy the latest data available into the write slot.

This is suitable whenever the caller wants to modify the latest data partially since it allows to omit an additional read call. To use this feature the caller must obtain read access, i.e. it must be a subscriber of the channel.

Internally calls ConcreteChannel::write().

Exceptions

XAccessViolation if channel has no write access rights

Returns: ChannelWrite object that has already locked the data. One can unlock the data manually or it is unlocked automatically when the ChannelWrite object goes out of scope. All subscribers will be notified.

Attention: If copyLatestData = true, this copies from the existing slot by creating a temporary copy (using copy construction), then assigning it to the new write slot (by operator=). Do not use this feature with channel types that need explicit deep copying (e.g. Img<> and subclasses)! In that case, get the ChannelRead explicitly and properly (deep) copy from it. In general, the internal copying is just for convenience, not efficiency.

◆ get() [1/4]

Stamped<T> get ( )

inline

Returns the latest data from the channel by value.

This method is provided to allow easy read access to the channel, however internally it leads to unnecessary copying of data and should be used for lightweight objects only. For large objects like range scans or images use the read() method to obtain read access without any performance penalties.

Internally calls ConcreteChannel::read().

Exceptions

XAccessViolation if channel has no read access rights

Returns: Latest stamped data from the channel

◆ get() [2/4]

Stamped<T> get	(	const Time &	timestamp,
		SlotQueryMode	mode = `NEAREST_SLOT`,
		const Duration &	tolerance = `Duration::infinity()`
	)

inline

Returns the data at the given time by value.

This method is provided to allow easy read access to the channel, however internally it leads to unnecessary copying of data and should be used for lightweight objects only. For large objects like range scans or images use the read() method to obtain read access without any performance penalties.

Internally calls ConcreteChannel::read().

Exceptions

XAccessViolation if channel has no read access rights

Returns: Latest stamped data from the channel

◆ get() [3/4]

Stamped<T> get	(	const Time &	timestamp,
		Duration	tolerance
	)

inline

Same as above, but always takes the nearest slot.

Internally calls ConcreteChannel::read().

◆ get() [4/4]

Stamped<T> get	(	const Time &	timestamp,
		Filter &&	filter
	)

inline

Returns the data at the given time by value.

Moreover, this variant of the get method allows to specify a filter that is applied on the data, e.g. linear interpolation, etc.

The following example returns the value at timestamp t, where the value is linearly interpolated between two samples in the channel near the timestamp t:

myValue = myChannel.get(t, LinearInterpolator());

If you do not need filtering or interpolation you should use the get() method without a filter or the read() method for large objects to obtain direct read access without any performance penalties.

Exceptions

XAccessViolation if channel has no read access rights

Returns: Stamped interpolated data

◆ post() [1/5]

void post ( const Stamped< T > & value )

inline

Writes the specified data into the channel.

This method is provided to allow easy write access to the channel, however internally it leads to unnecessary copying of data and should be used for lightweight objects only. For large objects like range scans or images use the write() method to obtain write access without any performance penalties.

Exceptions

XAccessViolation if channel has no write access rights

◆ post() [2/5]

void post ( Stamped< T > && value )

inline

Same as above, for rvalue reference (move semantics)

◆ post() [3/5]

std::enable_if<!std::is_base_of_v<StampedHeader, std::decay_t<U> > >::type post	(	U &&	value,
		const Time &	timestamp = `Time::now()`
	)

inline

Writes the specified data with the specified time stamp into the channel.

This method is provided to allow easy write access to the channel, however internally it leads to unnecessary copying of data and should be used for lightweight objects only. For large objects like range scans or images use the write() method to obtain write access without any performance penalties.

Exceptions

XAccessViolation if channel has no write access rights

◆ post() [4/5]

std::enable_if<!std::is_void<U>::value>::type post	(	const typename ParamHelper< T >::type &	value,
		const Time &	timestamp = `Time::now()`
	)

inline

This allows post({}, Time()); to deduce we want to post an object of the channel's type.

It will also make post({}) ambiguous instead of confidently posting a defaulted Stamped().

The ParamHelper indirection is required in order to avoid declaring a void reference as parameter type (for T=void).

◆ post() [5/5]

std::enable_if<!std::is_void<U>::value>::type post	(	typename ParamHelper< T >::type &&	value,
		const Time &	timestamp = `Time::now()`
	)

inline

Same as above, for rvalue reference (move semantics)

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

framework/include/fw/Channel.h

Public Member Functions

Detailed Description

template<typename T> class mira::Channel< T >

Constructor & Destructor Documentation

◆ Channel() [1/2]

◆ Channel() [2/2]

Member Function Documentation

◆ reset()

◆ isValid()

◆ validate()

◆ getID()

◆ getTypeId()

◆ isTyped()

◆ getTypename()

◆ setTypename()

◆ getTypeMeta()

◆ setTypeMeta()

◆ isEmpty()

◆ hasSubscriber()

◆ hasPublisher()

◆ hasSoloSlot()

◆ getMaxSlots()

◆ getMinSlots()

◆ getStorageDuration()

◆ isAutoIncreasingStorageDuration()

◆ getNrOfSlots()

◆ waitForData()

◆ waitForPublisher()

◆ read() [1/4]

◆ read() [2/4]

◆ read() [3/4]

◆ read() [4/4]

◆ readInterval() [1/2]

◆ readInterval() [2/2]

◆ write() [1/2]

◆ write() [2/2]

◆ get() [1/4]

◆ get() [2/4]

◆ get() [3/4]

◆ get() [4/4]

◆ post() [1/5]

◆ post() [2/5]

◆ post() [3/5]

◆ post() [4/5]

◆ post() [5/5]

template<typename T>
class mira::Channel< T >