Feature: Profiling Hooks

[griffinmilsap]

Profiling Feature Overview

• Adds sliding-window profiling for publishers and channels to surface throughput, byte rate, and backpressure/processing latency without extra serialization hops.
• GraphServer can now fan out PROFILE requests over existing control links and aggregate JSON snapshots across all connected publishers/channels.

Key Details

• Telemetry primitives in src/ezmsg/core/profiling.py track rolling counts/bytes and buffer lease durations; Backpressure optionally emits timings per client.
• Publishers (src/ezmsg/core/pubclient.py) record msg/byte rates and backpressure lease timing; channels (src/ezmsg/core/messagechannel.py) capture per-subscriber processing time and last transport mode (local|shm|tcp), plus subscriber handles for readability.
• GraphServer (src/ezmsg/core/graphserver.py) understands new protocol commands PROFILE/PROFILE_DATA (src/ezmsg/core/netprotocol.py), gathers profiles, and exposes them via GraphService.profile(window_s).
• CLI support: python -m ezmsg.core profile --window 2.0 prints aggregated JSON, including per-publisher/channel stats.
• Subscribers may pass handle= when creating to label profiles; defaults to the topic/address.

Why It Matters

• Gives per-process, per-stream visibility into bottlenecks: time from backpressure lease→free (upper bound on publish rate) and per-subscriber processing latency inside ez.subscriber callbacks.
• Minimal overhead via small time windows (~2s default) and reuse of existing graph connections; no extra message serialization.

Usage Example

# Collect a 2s snapshot from a running graph
ezmsg profile --window 2.0

# Programmatic
from ezmsg.core.graphserver import GraphService
profile = await GraphService().profile(2.0)

Notable Outputs

• Publisher: total/window messages & bytes, message/byte rates, backpressure avg/max (ms), in-flight leases.
• Channel: per-subscriber avg/max processing (ms), samples, message rate, in-flight leases, transport mode, subscriber handle/id.