Release History

Unreleased

Features

The threading client—and, thereby, the pyepics-compatible shim—have greater feature parity with epics-base.

  • In previous releases, the client resent any unanswered SearchRequests at a fast regular rate forever. Now, it backs off from that initial rate and rests at a slow interval to avoid creating too much wasteful network traffic. There is a new method, cancel(), for manually canceling some requests altogether if a response is never excepected (e.g. a typo). There is also a new method for manually resending all unanswered search requests, search_now(), primarily for debugging. All unanswered search requests are automatically resent when the user searches for a new PV or when a new server appears on the network (see next point).
  • The client monitors server beacons to notice changes in the CA servers on the network. When a new server appears, all standing unanswered search requests are given a fresh start and immediately resent. If a server does not send a beacon within the expected interval and has also not sent any TCP packets related to user activity during that interval, the client silently initiates an Echo. If the server still does not respond, it is deemed unresponsive. The client logs a warning and disconnects all circuits from that server so that their PVs can begin attempting to reconnect to a responsive server.

v0.2.3 (2018-01-02)

Usability Improvements

  • A new function set_handler() provides a convenient way to make common customizations to caproto’s default logging handler, such as writing to a file instead of the stdout.
  • In the threading client, store the current access rights level on the PV object as pv.access_rights. It was previously only accessible when it changed, via a callback, and had to be stashed/tracked by user code.
  • Display the version of caproto in the output of --help/-h in the commandline utilities. Add a new commandline argument --version/-V that outputs the version and exits.
  • In the threading client, DEBUG-log all read/write requests and read/write/event responses. (When these log messages were first introduced in v0.2.1, batched requests and their responses were not logged, and write responses were not logged when notify=True but wait=False.)

Bug Fixes

  • Fix critical bug in synchronous client that broke monitoring of multiple PVs.
  • Fix default (“AUTO”) broadcast address list (should always be 255.255.255.255). Removed internal utility function broadcast_address_list_from_interfaces().
  • In pyepics-compatible client, set default mask to SubscriptionType.DBE_VALUE | SubscriptionType.DBE_ALARM, consistent with pyepics.
  • Prevent subscriptions for being processed for all channels that share an alarm if the alarm state has not actually changed.

Updated Pyepics Compatibility

  • Added new method PV.get_with_metadata, which was added in pyepics 3.3.1.

Deprecations

  • The color_logs() convenience function has been deprecated in favor of set_handler().

Internal Changes

  • Enable -vvv (“very verbose”) option when running example IOCs in test suite.

v0.2.2 (2018-11-15)

The release improves the performance of the threading client and adds support for value-based alarms.

Improved Alarm Support

  • Value-based alarms are supported by all servers.
  • LOLO, LO, HI, and HIHI alarm status fields of mocked records are respected.
  • Channel limit metadata (upper_alarm_limit, upper_warning_limit, etc.) is now integrated with alarms.

Bug Fixes and Performance Improvements

  • The socket settings SO_KEEPALIVE and TCP_NODELAY are used in the threading client TCP sockets, making it consistent with epics-base and removing a 40ms overhead that can occur when sending small packets.
  • Some unnecessary locking was removed from the threading client, resolving a deadlock observed in ophyd and improving performance.
  • The spoof_beamline IOC is aware of more components of Area Detector and defaults to float-type channels instead of integer-type.
  • A rare but possible race condition that caused a subscription to be activated twice (thus getting two responses for each update) has been resolved.
  • The ChannelData objects are serializable with pickle.
  • A bug in length-checking that affected zero-length data has been fixed.

The detail and consistency of the exceptions raised by the clients has also been improved.

v0.2.1 (2018-10-29)

This release tunes server performance under high load and fixes several subtle bugs in the server identified via acctst, the server acceptance test that ships with epics-base.

Bug Fixes

  • When a new Subscription is added, send the most recent value immediately but only to the new Subscription. Previous releases sent redundant messages to all Subscriptions that had similar parameters.
  • Reduce the maximum size of a datagram of search requests to match the typical Maximum Transmission Unit seen in the wild.
  • Fix a bug in the pyepics-compatibility layer that caused the connection callbacks never to be called when underlying caproto.threading.client.PV’s were reused.
  • Fix a typo in the PV names in the spoof_beamline IOC.
  • Never send an EventAddResponse after a matching EventCancelResponse has been sent.
  • Always send a response to a failed write, and include the correct error code.
  • If a circuit has an oversized backlog of received commands to process, log a WARNING before disconnecting.

Server Performance Tuning

  • Increase the max backlog of subscription updates queued up to send (both updates per specific Subscription and total updates per circuit) by a factor of 10. Likewise for the max backlog of received commands queued up to process.
  • When under sustained high load of subscription updates to send, iteratively double the latency between packets up to at most 1 second to achieve higher overall throughput (more commands per packet, less overhead).
  • When a Read[Notify]Request arrives on the heels of a Write[Notify]Request, wait for up to 0.001 seconds for the write to process before reading the current value. If the write happens to complete in less than 0.001 seconds, the read will reflect the new value. This behavior is in the spirit of, but distinct from, EPICS’ “synchronous writes.” EPICS allows a device to block while writing if it promises to finish quickly (< 0.1 miliseconds). We take a different approach, making all writes asynchronous. This ensures that an accidentally-slow write cannot lock up the server. It adds latency to some reads, up to a hard maximum of 1 milisecond, giving the effect of synchronous write whenever the write finishes fast.

The release also includes one small new feature: in the threading client, DEBUG-level logging of channels/PVs caproto.ch now logs (non-batch) read/write requests and read/write/event responses. [Update: In v0.2.3, this feature was extended to include batched requests and their responses.] Related — there is expanded documentation on Loggers.

v0.2.0 (2018-10-17)

This release improves compliance with the protocol and server performance under high load.

Features

  • Under high load (with many subscription updates queued up to send) servers batch subscriptions into blocks, trading a little latency for efficiency. Under low load, servers prioritize low latency.
  • The servers’ medium-verbose setting (-v) displays current load and latency.
  • In the threading client, process user callbacks using one threadpool per circuit instead of one threadpool for the entire context. Make the size of the threadpool configurable via a new Context parameter, max_workers.
  • We now test the servers against a Python 3-compatible fork of Michael Davidsaver’s utility for testing Channel Access servers, catvs. This has generated several fixes improving protocol compliance, list a section below. There are a small number of known failures wherein the best/correct behavior is arguable; see caproto#327 on GitHub for discussion. There may be more progress on these in future releases of caproto.
  • Added pvproperty.scan. See the mini_beamline example IOC for a usage example.
  • Add a server-side data source for ChannelType.INT (a.k.a SHORT) data.
  • The default printed output of the caproto-monitor CLI utility now includes microseconds.
  • There are several new IOC examples.

Breaking Changes

  • The expected signature of the access_rights_callback passed to Context has been changed from f(access_rights) to f(pv, access_rights). This makes it consistent with the connection_callback.
  • If a beacon fails to send, do not kill the server; just log the failure, along with a suggestion on how to fix the environment to omit the failed address, and continue to run.
  • In the high-level server, implemented with pvproperty, PV values can be defined as scalars. The accessor pvproperty.value now returns a scalar instead of a length-1 list (API break), while write() accepts either list or scalar.

Bug Fixes

  • A critical bug CHAR-type payload serialization which made caproto clients unusable with CHAR-type channels has been fixed.
  • The asyncio server now executes its cleanup code when interrupted with SIGINT (Ctrl+C).
  • All three servers were relying on the operating system to clean up their sockets when the process exited. They now close their sockets explicitly when the server task exits. This fixes the runaway usage of file descriptors when the tests are run.

Improved Protocol Compliance

  • The servers send CreateChFailResponse when the client requests a channel name that does not exist on the server. They previously did not respond.
  • The servers reply to SearchRequest messages sent over TCP. (UDP is more common, but TCP is allowed.) They previously did not respond.
  • The EventCancelResponse message includes a data_count.
  • The servers respect the data_count requested by the client.
  • Servers enforce quota per subscription to avoid one prolific subscription (or slow client) from drowning out others.
  • Servers respect EventsOn and EventsOff requests.
  • Servers differentiate between current length and maximum length of an array, and they properly declare the maximum length in CreateChanResponse. They formerly declared the current length, which was not correct.
  • The caproto-put commandline utility now supports -a for arrays.

v0.1.2 (2018-08-31)

This is a bug-fix release fixing some critical bugs. We recommend that all users ugprade.

  • Fix critical typo in threading client’s search functionality that could cause it to conflate addresses from different search responses and then attempt to connect to the wrong server.
  • Fix handshake with servers and clients speaking Version 11 (or older) of the protocol.

v0.1.1 (2018-06-17)

This is a bug-fix release following closely on the initial release. We recommend that all users update.

  • Fix straightforward but important bug in the synchronous client that broke monitoring of multiple channels concurrently.
  • In servers, abide by the spec’s recommendation that beacons should be issued quickly at startup before backing off to a slower, steady rate.
  • Fix a bug that broke the array (“arr”) channel filter if numpy was not installed.
  • Add a new section to the documentation detailing caproto’s compliance with the Channel Access protocol and the feature parity of caproto’s clients and servers with respect to the reference implementations in epics-base.

v0.1.0 (2018-06-14)

This initial release contains some fairly stable components and some very experimental ones.

  • The core protocol code, the synchronous client, the threading client, and the pyepics-compatible client are fairly stable.
  • The high-level interface to IOCs has no known issues but could in a future release of caproto, as we gain experience from its use.
  • The three server implementations are thoroughly tested, but their low level API is likely to change in a future release.
  • The asynchronous client implementations (trio client and curio client) are highly experimental. They lack feature-parity with the other clients and have some known bugs. They may be heavily revised or removed in a future release of caproto.