WaitAtBarrier

Blocks until the barrier releases for the requested generation or until timeout_seconds elapses. The outcome enum reports which happened: BARRIER_WAIT_OUTCOME_TRIPPED when all expected processes arrived and the barrier advanced a generation, or BARRIER_WAIT_OUTCOME_TIMED_OUT when timeout_seconds elapsed before the barrier tripped. Many peers can wait on the same generation at once; they are all released together when the last expected peer arrives.

WaitAtBarrier does not register an arrival — a peer that needs to both contribute and wait must call ArriveAtBarrier first.

Safe to retry — a timed-out caller can simply call again; late arrivals continue to accumulate in the background.

Request

• timeout_seconds tells the server how long to wait for all participants to arrive before giving up.
• The call blocks server-side, so set client/RPC timeouts comfortably above timeout_seconds.
• expected_generation is the cycle the caller is waiting on; specifying a stale generation returns immediately with the already-released state.

{
  "namespace_name": "pipelines",
  "barrier_name": "phase_1_complete",
  "expected_generation": 1,
  "timeout_seconds": 300
}

Response

• Returns NotFound if the namespace does not exist.
• Returns NotFound if the barrier does not exist.
• On TRIPPED, the next cycle’s generation is simply expected_generation + 1 — generations advance by exactly one per trip, so the caller computes it without a dedicated field. barrier.generation reports where the barrier actually is now (possibly further ahead if a later cohort has already tripped it again).

Released before timeout (the barrier has advanced to generation 2 and arrived_processes reset to 0):

{
  "barrier": {
    "name": "phase_1_complete",
    "expected_processes": 4,
    "arrived_processes": 0,
    "generation": 2
  },
  "outcome": "BARRIER_WAIT_OUTCOME_TRIPPED"
}

Timeout fired first (no trip, so the barrier is unchanged):

{
  "barrier": {
    "name": "phase_1_complete",
    "expected_processes": 4,
    "arrived_processes": 3,
    "generation": 1
  },
  "outcome": "BARRIER_WAIT_OUTCOME_TIMED_OUT"
}