ChannelKind enum

Which bounded channel backs a pull handle — and therefore what happens when it fills up.

One enum for one axis, across every carrier that has a channel mode: Session.declarePullSubscriber and Session.declarePullLivelinessSubscriber (samples), Session.pullGet, Querier.pullGet and Session.pullLivelinessGet (replies), and Session.declarePullQueryable (queries). The kind means the same thing on all six.

Canon ships two, and the difference is the whole point of the choice: one drops data to keep the producer running, the other stalls the producer to keep every sample. There is no third option and no "unbounded" option — a bounded channel is what a pull surface is.

⚠️ value is our shim's dispatch code, not a canon wire value. Canon has no channel-kind enum at all: it ships two separately-named constructor pairs (z_ring_channel_sample_new, z_fifo_channel_sample_new) over two distinct handler types, and the kind is chosen by which symbol you call. Dart cannot select a C symbol at run time across the FFI seam, so the kind crosses as an int and the shim dispatches on it. That makes these numbers an internal contract between our two layers, which is exactly why they are written out explicitly instead of being taken from declaration order.

This enum is send-only: canon exposes no accessor that returns a channel kind, so there is deliberately no fromWire decoder — one could never be driven by a real value, and an untestable decoder is worse than none.

Inheritance
Available extensions

Values

ring → const ChannelKind

Bounded and lossy: when the buffer is full the oldest entry is dropped to make room.

The producer is never blocked, so a slow consumer costs data rather than throughput. This is the shipped default and the kind canon's own z_pull.c example uses.

On disconnect a ring discards whatever it still holds: once the producer dies, an unread buffered sample is gone rather than drainable.

const ChannelKind(0)
fifo → const ChannelKind

Bounded and lossless: when the buffer is full the producer blocks until the consumer takes something out.

Nothing is dropped, so a slow consumer costs throughput rather than data.

On disconnect a fifo drains: calls keep delivering the samples it still holds and only report disconnected once it is empty. That is the opposite of ring, it is canon's own behaviour measured at 1.8.0, and it is rendered here unsmoothed rather than papered over.

⚠️ Never publish into a full fifo from the session that owns the subscriber. Same-session delivery pushes into the channel on the publisher's own thread, so a single thread acting as both producer and only consumer blocks inside the put permanently — measured at canon (zenoh-c 1.8.0: the third put into a capacity-2 same-session fifo never returned), and unrecoverable from Dart because the call is a synchronous FFI call. This is canon's backpressure doing exactly its job on the only thread available; no API design can remove it. Use a second session for the publisher, or the ring kind.

⚠️ At capacity 0 a fifo is a rendezvous, not a one-slot buffer — full when empty — so PullSubscriber.recv() cannot be used there (its readiness signal and the blocked delivery wait on each other). PullSubscriber.tryRecv() works normally at capacity 0, because a synchronous poll is itself the concurrent consumer the rendezvous needs. Measured at zenoh-c 1.8.0; canon documents nothing about capacity.

const ChannelKind(1)

Properties

hashCode → int
The hash code for this object.
no setterinherited
index → int
A numeric identifier for the enumerated value.
no setterinherited
name → String

Available on Enum, provided by the EnumName extension

The name of the enum value.
no setter
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited
value → int
The shim's dispatch code. Explicit; never derived from declaration order.
final

Methods

noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
toString() → String
A string representation of this object.
inherited

Operators

operator ==(Object other) → bool
The equality operator.
inherited

Constants

values → const List<ChannelKind>
A constant List of the values in this enum, in order of their declaration.