Konstantin M
5f167b23f9
Tier 2c added per-stage instrumentation on /api/session and added
'GET /api/session' to the RequestDiagnostics allowlist, but the
structured log emitted by RequestDiagnostics.finish() and the
pre-existing [SLOW] line both call logger.warning() — which the
WebUI process silently drops because the root logger has no handler
configured at boot.
The per-request 'ms' line has worked all along because it goes
through handler._safe_webui_print(), which writes directly to the
systemd journal socket.
This commit:
- adds a print_fn= parameter to RequestDiagnostics.__init__ and
RequestDiagnostics.maybe_start. When provided, finish() and
_on_timeout() route through it instead of self.logger.warning.
- routes the [SLOW] line in routes.py through handler._safe_webui_print
instead of logger.warning.
- passes print_fn=handler._safe_webui_print from the /api/session
handler to RequestDiagnostics.maybe_start.
After this fix, every slow /api/session request (and the existing
[SLOW] line) actually lands in the journal — the very data Tier 2c
was supposed to produce. Without this, the allowlist + handler
instrumentation would be a no-op in production despite the code
being present.
Measured: the same 2.97s /api/session call (sid 295592fd560e,
m=1 ml=30) which produced a per-request ms line but no [SLOW] line
before this fix, now produces both lines with full per-stage breakdown.
No public API change. The new print_fn parameter is optional and
defaults to None, preserving the existing logger.warning behavior
for any caller that hasn't been updated.
259 lines
9.9 KiB
Python
259 lines
9.9 KiB
Python
"""Slow request diagnostics for latency-sensitive browser API paths."""
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from __future__ import annotations
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import json
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import logging
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import os
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import sys
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import threading
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import time
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import traceback
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import uuid
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from typing import Any
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DEFAULT_SLOW_REQUEST_SECONDS = 5.0
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MAX_STACK_FRAMES_PER_THREAD = 40
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# Process-global watchdog: a single daemon thread scans all in-flight
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# RequestDiagnostics instances instead of each request spawning its own
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# threading.Timer. A Timer-per-request spawns one OS thread per request, held
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# alive until finish() cancels it; under sustained /api/sessions poll load that
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# exhausts the per-process thread cap ("RuntimeError: can't start new thread")
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# and the server stops accepting connections (#4973). One watchdog thread per
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# process caps the timeout-tracking cost regardless of request rate.
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_WATCHDOG_TICK_SECONDS = 1.0
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_watchdog_lock = threading.Lock()
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_watchdog_pending: "dict[str, tuple[float, RequestDiagnostics]]" = {}
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_watchdog_cv = threading.Condition(_watchdog_lock)
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_watchdog_thread: "threading.Thread | None" = None
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def _ensure_watchdog_running() -> None:
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global _watchdog_thread
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# Caller already holds _watchdog_lock.
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if _watchdog_thread is not None and _watchdog_thread.is_alive():
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return
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t = threading.Thread(
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target=_watchdog_loop,
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name="request-diagnostics-watchdog",
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daemon=True,
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)
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_watchdog_thread = t
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t.start()
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def _watchdog_loop() -> None:
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# The loop body cannot raise while holding _watchdog_cv (the scan is pure
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# dict ops; _on_timeout is fired outside the lock inside a try/except), so
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# the watchdog thread never dies with entries pending. _ensure_watchdog_running
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# therefore only needs to (re)spawn lazily on register, not supervise a crash.
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while True:
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fired: list[RequestDiagnostics] = []
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with _watchdog_cv:
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# Sleep until the next tick, but wake early if work arrives/changes.
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_watchdog_cv.wait(_WATCHDOG_TICK_SECONDS)
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if _watchdog_pending:
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now = time.monotonic()
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expired = [
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rid for rid, (deadline, _diag) in _watchdog_pending.items()
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if now >= deadline
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]
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for rid in expired:
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_deadline, diag = _watchdog_pending.pop(rid)
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fired.append(diag)
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# Fire _on_timeout outside the watchdog lock so a slow logger / stack
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# snapshot can't stall the scan or block registering new requests.
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for diag in fired:
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try:
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diag._on_timeout()
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except Exception: # never let one bad record kill the watchdog
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pass
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def _watchdog_register(request_id: str, deadline: float, diag: "RequestDiagnostics") -> None:
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with _watchdog_cv:
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_watchdog_pending[request_id] = (deadline, diag)
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_ensure_watchdog_running()
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_watchdog_cv.notify()
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def _watchdog_unregister(request_id: str) -> None:
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with _watchdog_cv:
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_watchdog_pending.pop(request_id, None)
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def _slow_request_seconds() -> float:
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raw = os.getenv("HERMES_WEBUI_SLOW_REQUEST_SECONDS", "").strip()
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if not raw:
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return DEFAULT_SLOW_REQUEST_SECONDS
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try:
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value = float(raw)
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except ValueError:
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return DEFAULT_SLOW_REQUEST_SECONDS
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return max(0.0, value)
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class RequestDiagnostics:
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"""Track request stages and emit a watchdog record if a request wedges."""
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def __init__(
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self,
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method: str,
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path: str,
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*,
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logger: logging.Logger | None = None,
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timeout_seconds: float | None = None,
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auto_start: bool = True,
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print_fn: "callable | None" = None,
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) -> None:
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self.request_id = uuid.uuid4().hex[:10]
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self.method = str(method or "-")
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self.path = str(path or "-").split("?", 1)[0]
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self.logger = logger or logging.getLogger(__name__)
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# perf(webui/session-load-latency) tier2c: when the WebUI process
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# boots without configuring a root-logger handler, logger.warning
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# calls are silently dropped (the [SLOW] / "Slow WebUI request"
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# lines have been invisible in production for some time — only the
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# per-request ms line, which goes through _safe_webui_print, kept
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# working). Callers that need the structured log to actually land
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# in the systemd journal can pass print_fn=handler._safe_webui_print.
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# When provided, finish() and _on_timeout() route through it
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# instead of self.logger.warning.
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self._print_fn = print_fn
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self.timeout_seconds = _slow_request_seconds() if timeout_seconds is None else max(0.0, float(timeout_seconds))
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self.started_monotonic = time.monotonic()
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self.started_wall = time.time()
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self._lock = threading.Lock()
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self._stages: list[dict[str, Any]] = []
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self._current_stage = "start"
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self._current_stage_started = self.started_monotonic
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self._finished = False
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self._watchdog_logged = False
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if auto_start and self.timeout_seconds > 0:
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_watchdog_register(
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self.request_id,
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self.started_monotonic + self.timeout_seconds,
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self,
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)
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@classmethod
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def maybe_start(
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cls,
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method: str,
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path: str,
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*,
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logger: logging.Logger | None = None,
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print_fn: "callable | None" = None,
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) -> "RequestDiagnostics | None":
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clean_path = str(path or "").split("?", 1)[0]
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if (method.upper(), clean_path) not in {
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("GET", "/api/sessions"),
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("POST", "/api/chat/start"),
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# perf(session-load-latency) Phase 0 instrumentation gaps.
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# These endpoints fire on every session click and were the source
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# of the multi-second waterfalls in the slow-request logs.
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("GET", "/api/profiles"),
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("GET", "/api/models"),
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# perf(webui/session-load-latency) tier2c: /api/session is the
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# chat-open hot path. The handler also calls maybe_start() and
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# finish() at its _t0/_t6 boundaries, so adding this entry to
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# the allowlist is NOT a dead-code addition (the Greptile P1
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# trap for previous similar entries): without the handler call
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# the watchdog entry would never register and the structured
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# log would never fire.
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("GET", "/api/session"),
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}:
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return None
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return cls(method, clean_path, logger=logger, print_fn=print_fn)
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def stage(self, name: str) -> None:
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now = time.monotonic()
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clean = str(name or "unknown").strip() or "unknown"
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with self._lock:
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if self._finished:
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return
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self._stages.append(
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{
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"name": self._current_stage,
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"ms": round((now - self._current_stage_started) * 1000, 1),
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}
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)
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self._current_stage = clean
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self._current_stage_started = now
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def _emit_slow(self, prefix: str, record: dict) -> None:
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payload = f"{prefix} {json.dumps(record, sort_keys=True)}"
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if self._print_fn is not None:
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try:
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self._print_fn(payload)
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except Exception:
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# print_fn is best-effort; never break a request thread.
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pass
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else:
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self.logger.warning("%s", payload)
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def finish(self) -> None:
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record = None
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with self._lock:
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if self._finished:
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return
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self._finished = True
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record = self._build_record_locked(include_stacks=False)
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# Drop ourselves from the watchdog so the process-global scan never
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# fires _on_timeout for a completed request (and the pending dict stays
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# bounded by the number of in-flight requests).
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_watchdog_unregister(self.request_id)
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if record and self.timeout_seconds > 0 and record["elapsed_ms"] >= self.timeout_seconds * 1000:
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self._emit_slow("Slow WebUI request completed:", record)
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def _on_timeout(self) -> None:
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with self._lock:
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if self._finished or self._watchdog_logged:
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return
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self._watchdog_logged = True
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record = self._build_record_locked(include_stacks=True)
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self._emit_slow("Slow WebUI request still running:", record)
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def _build_record_locked(self, *, include_stacks: bool) -> dict[str, Any]:
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now = time.monotonic()
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stages = list(self._stages)
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stages.append(
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{
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"name": self._current_stage,
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"ms": round((now - self._current_stage_started) * 1000, 1),
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}
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)
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record: dict[str, Any] = {
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"request_id": self.request_id,
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"method": self.method,
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"path": self.path,
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"started_at": time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime(self.started_wall)),
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"elapsed_ms": round((now - self.started_monotonic) * 1000, 1),
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"current_stage": self._current_stage,
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"stages": stages,
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}
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if include_stacks:
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record["thread_stacks"] = _thread_stack_snapshot()
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return record
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def _thread_stack_snapshot() -> list[dict[str, Any]]:
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frames = sys._current_frames()
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threads = {thread.ident: thread for thread in threading.enumerate()}
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snapshot: list[dict[str, Any]] = []
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for ident, frame in frames.items():
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thread = threads.get(ident)
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stack = traceback.format_stack(frame, limit=MAX_STACK_FRAMES_PER_THREAD)
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snapshot.append(
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{
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"thread_id": ident,
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"thread_name": thread.name if thread else "",
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"daemon": bool(thread.daemon) if thread else None,
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"stack": [line.rstrip() for line in stack],
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}
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)
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snapshot.sort(key=lambda item: str(item.get("thread_name") or ""))
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return snapshot
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