ArriveAtBarrier

Records a peer’s arrival at the barrier for a specific generation. Returns immediately (non-blocking) with the current state and all_arrived indicating whether the barrier has released for this generation. If the peer needs to block until the rendezvous completes, follow this with a WaitAtBarrier call.

The call is idempotent per (generation, process_id) — a retry by the same peer in the same generation is a no-op.

Request

• process_id is a free-form string identifying the peer.
• expected_generation must match the barrier’s current generation; arriving for a past or future generation is rejected.
• metadata is an optional, opaque map of string key/value pairs attached to this participant — see Metadata.

{
  "namespace_name": "pipelines",
  "barrier_name": "phase_1_complete",
  "process_id": "shard-0",
  "expected_generation": 1,
  "metadata": {
    "host": "node-1"
  }
}

Response

• Returns NotFound if the namespace does not exist.
• Returns NotFound if the barrier does not exist.
• Returns InvalidRequest if the call would push ArrivedProcesses above ExpectedProcesses.
• Returns InvalidArgument if the generation is older than the current barrier generation.
• When this arrival completes the rendezvous (all_arrived: true), the barrier has already advanced: generation is incremented and arrived_processes resets to 0.

Not yet released:

{
  "barrier": {
    "name": "phase_1_complete",
    "expected_processes": 4,
    "arrived_processes": 1,
    "generation": 1
  },
  "all_arrived": false
}

This caller’s arrival completed the rendezvous (the barrier has advanced to generation 2):

{
  "barrier": {
    "name": "phase_1_complete",
    "expected_processes": 4,
    "arrived_processes": 0,
    "generation": 2
  },
  "all_arrived": true
}