AckCmdReader

class lsst.ts.salobj.topics.AckCmdReader(salinfo, queue_len=100)

Bases: lsst.ts.salobj.topics.ReadTopic

Read the ackcmd command acknowledgement topic.

Parameters:

salinfo : SalInfo

SAL component information

queue_len : int

Number of elements that can be queued for get_oldest.

Notes

The same ackcmd topic is used for all command topics from a given SAL component.

Attributes Summary

DataType	The class of data for this topic.
allow_multiple_callbacks	Can callbacks can run simultaneously?
callback	Callback function, or None if there is not one.
has_callback	Return True if there is a callback function.
has_data	Has any data been seen for this topic?
max_history
metadata	Get topic metadata as a TopicMetadata, if available, else None.

Methods Summary

aget([timeout])	Get the current value, if any, else wait for the next value.
close()	Shut down and release resources.
flush()	Flush the queue of unread data.
get([flush])	Get the most recently seen value, or None if no data ever seen.
get_oldest()	Pop and return the oldest value from the queue, or None if the queue is empty.
next(*, flush[, timeout])	Wait for a value, possibly returning the oldest queued value.

Attributes Documentation

DataType

The class of data for this topic.

allow_multiple_callbacks

Can callbacks can run simultaneously?

Notes

Ignored for synchronous callbacks because those block while running. In particular, if the callback is synchronous but launches one or more background jobs then the number of those jobs cannot be limited by this class.

callback

Callback function, or None if there is not one.

The callback function is called when new data is received; it receives one argument: the data.

Raises:

TypeError

When setting a new callback if the callback is not None and is not callable.

Notes

The callback function can be synchronous or asynchronous (e.g. defined with async def).

Setting a callback flushes the queue, and it will remain empty as long as there is a callback.

get_oldest and next are prohibited if there is a callback function. Technically they could both work, but get_oldest would always return None and next would miss data if it arrived while waiting for something else. It seemed safer to just raise an exception.

has_callback

Return True if there is a callback function.

has_data

Has any data been seen for this topic?

max_history

metadata

Get topic metadata as a TopicMetadata, if available, else None.

Methods Documentation

aget(timeout=None)

Get the current value, if any, else wait for the next value.

Parameters:

timeout : float (optional)

Time limit, in seconds. If None then no time limit.

Returns:

data : DataType

The current or next value.

Raises:

RuntimeError

If a callback function is present.

Notes

Do not modify the returned data. To make a copy that you can modify use copy.copy(value).

close()

Shut down and release resources.

Intended to be called by SalInfo.close(), since that tracks all topics.

flush()

Flush the queue of unread data.

Raises:

RuntimeError

If a callback function is present.

get(flush=True)

Get the most recently seen value, or None if no data ever seen.

Parameters:

flush : bool (optional)

Flush the queue? Defaults to True for backwards compatibility. This only affects the next value returned by next and is ignored if there is a callback function.

Returns:

data : self.DataType or None

Return self.data if data has been read, else None.

get_oldest()

Pop and return the oldest value from the queue, or None if the queue is empty.

Returns:

data : self.DataType or None

The oldest value found on the queue, if any, else None.

Raises:

RuntimeError

If a callback function is present.

Notes

Use with caution when mixing with next, since that also consumes data from the queue.

next(*, flush, timeout=None)

Wait for a value, possibly returning the oldest queued value.

Parameters:

flush : bool

If True then flush the queue before starting a read. If False then pop and return the oldest value from the queue, if any, else wait for new data.

timeout : float (optional)

Time limit, in seconds. If None then no time limit.

Returns:

data : DataType

The data.

Raises:

RuntimeError

If a callback function is present.

Notes

Do not modify the returned data. To make a copy that you can modify use copy.copy(value).