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Core Glossary¶
What this chapter defines — concise definitions of the key terms shared throughout the Core specification. The exact contract for each term is owned by its corresponding spec document; other documents link here when they first use a term.
Context¶
zlink's top-level container for I/O threads and sockets. The exact contract is owned by Context.
I/O thread¶
A background thread that Context creates and manages. It performs the actual network send and receive operations.
socket¶
An endpoint that exchanges messages. It must belong to a Context. The contract is owned by Socket Common.
HWM¶
High-Water Mark. A value that limits the bytes retained in a queue to apply backpressure.
backpressure¶
The behavior that limits further submissions by a sender when downstream cannot keep up with the processing rate.
Auto HWM budget¶
The total number of bytes that Core calculates from memory input and uses as the basis for allocating HWM among application queues. The contract is owned by Auto HWM.
directional queue¶
A physical queue that holds messages for one application direction. It is counted only once even when both endpoints observe the same direction.
generation¶
A version number that distinguishes a recreated queue in the same direction, or a recreated transport pair, from its predecessor. It increases on every reconnect, and REPLY and FLOWSTATE frames of an earlier generation are discarded in the new one.
effective cap¶
The upper bound applied to the Auto HWM budget. It is the greater of the profile's fixed cap and "number of active directional queues × the profile's data-queue minimum".
water-filling¶
A distribution method that allocates the remaining budget evenly among queues that have not yet reached their caps, like filling them with water.
completion progress lane¶
A separate physical connection that ROUTER-ROUTER uses to break a bidirectional request wait cycle. It
carries terminal replies, error replies, and receive-flow control and is excluded from HWM admission and
Application budget calculation. DEALER-ROUTER has no such lane; replies use its single Application
connection. This physical connection is distinct from the socket-local completion queue consumed by
zlink_completion_recv().