3.4 KiB
ZeroMQ socket
Jungfraujoch process (jfjoch_broker) operates three ZeroMQ outputs.
All three can be operated/enabled independently.
These are:
- Image - all the images including metadata (PUSH socket)
- Preview - images with metadata at a reduced frame rate (PUB socket)
- Metadata - only metadata for all the images, bundled into packages (PUB socket)
Image stream
Images (with metadata) are serialized as CBOR image message. The stream will also include CBOR start message, calibration messages and end message with run metadata.
Image stream can be split into multiple sockets to increase performance, in this case images will be split according to file number to which the image belongs. All sockets will forward start and end messages. Only first socket will forward calibration messages and will be marked to write master file.
This is using PUSH ZeroMQ socket(s). It should be strictly avoided to have multiple receivers connected to one PUSH ZeroMQ socket. ZeroMQ will send the images in a round-robin basis to the receivers. In this case start and end messages will end up only with one receiver. Instead, Jungfraujoch feature of multiple sockets should be used.
Image stream can be replaced with direct HDF5 writer and CBOR dump image pushers, it can be disabled by select "None" image pusher for all the measurements.
If file_prefix is not provided for a data collection, images won't be sent to image stream (or its HDF5/CBOR replacements).
Behavior is as following:
- Start message is sent with timeout of 5s. If within the time the message cannot be put in the outgoing queue or there is no connected puller exception is thrown - stop data collection with error due to absence of a writer.
- Images are sent in non-blocking way and without timeout.
- End message is sent with timeout of 5s. No error is reported.
Preview stream
Jungfraujoch can also send images (with metadata) at a reduced frame rate for preview purpose. Images are serialized as CBOR image message. The stream will also include CBOR start message and end message with run metadata. Only start and image messages are sent.
This is using PUB socket with conflate option. I.e., only the last message is kept by ZeroMQ, so if receiver cannot cope with the messages, it will always receive the last generated message (no backlog). For this reason it is also recommended to use the same option on receiver side.
Given PUB socket properties, it is possible to connect multiple viewers to a single socket --- all the viewers should receive all the images sent.
Metadata stream
Jungfrajoch can also send pure metadata for the purpose of archiving such information. Metadata are serialized as CBOR metadata message. This is very similar as image message, but excludes the actual image array and spot positions. As metadata are relatively small, to avoid large number of messages, Jungfraujoch bundles metadata of many images in one message. Order of images within bundle, as well a size of the bundle, are not guaranteed The stream will also include CBOR start message and end message with run metadata.
This is using PUB socket with watermark, so there is some queuing of messages with ZeroMQ. Multiple receivers can be connected.