zzstoatzz.io
prefect server in zig
implement graceful shutdown with signal handling
- add SIGTERM and SIGINT signal handlers
- zap.stop() triggers clean shutdown when signal received
- services flush pending work (events, etc.) before exit
- add scripts/test-graceful-shutdown to verify behavior
- update roadmap and production-readiness docs
note: SIGTERM exits with code 1 due to zap/facil.io quirk, but
shutdown sequence completes correctly (services stop, data flushes)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
+1
-1
ROADMAP.md
+1
-1
ROADMAP.md
+3
-3
docs/production-readiness.md
+3
-3
docs/production-readiness.md
···
18
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## tier 2: high (impacts observability & control)
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### graceful shutdown
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drain in-flight requests, flush pending events, clean up state. without this, forceful termination loses events and corrupts state.
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### ~~graceful shutdown~~ ✓
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~~drain in-flight requests, flush pending events, clean up state.~~ implemented via SIGTERM/SIGINT handling.
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### log persistence
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python stores logs in database with filter endpoint. zig is in-memory only. without this, logs lost on restart, no audit trail.
···
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**mvp production:**
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1. concurrency limits v2
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2. event filtering
55
-
3. graceful shutdown
55
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3. ~~graceful shutdown~~ ✓
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4. log persistence
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**beta:**
+247
scripts/test-graceful-shutdown
+247
scripts/test-graceful-shutdown
···
1
+
#!/usr/bin/env -S uv run --script --quiet
2
+
# /// script
3
+
# requires-python = ">=3.12"
4
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# dependencies = ["httpx"]
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# ///
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"""
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Test graceful shutdown of prefect-server.
8
+
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Verifies:
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1. Server starts and accepts requests
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2. SIGTERM triggers graceful shutdown
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3. Services flush pending work
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4. Server exits cleanly with expected logs
14
+
"""
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+
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+
import os
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import signal
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import subprocess
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import sys
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import tempfile
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import time
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+
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import httpx
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+
25
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# configuration
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SERVER_BIN = os.environ.get("PREFECT_SERVER_BIN", "./zig-out/bin/prefect-server")
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PORT = 4201 # use non-default port to avoid conflicts
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STARTUP_TIMEOUT = 5.0
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SHUTDOWN_TIMEOUT = 10.0
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+
31
+
32
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def log(msg: str) -> None:
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print(f"[test] {msg}", flush=True)
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+
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+
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def wait_for_server(port: int, timeout: float) -> bool:
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"""Wait for server to be ready."""
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start = time.time()
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while time.time() - start < timeout:
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try:
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resp = httpx.get(f"http://localhost:{port}/api/health", timeout=1.0)
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if resp.status_code == 200:
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return True
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except httpx.RequestError:
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pass
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time.sleep(0.1)
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return False
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+
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+
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def test_graceful_shutdown() -> bool:
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"""Test that SIGTERM triggers graceful shutdown."""
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log("building server...")
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result = subprocess.run(["zig", "build"], capture_output=True, text=True)
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if result.returncode != 0:
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log(f"build failed: {result.stderr}")
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return False
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+
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# use temp file for database to avoid conflicts
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with tempfile.NamedTemporaryFile(suffix=".db", delete=False) as f:
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db_path = f.name
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+
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env = os.environ.copy()
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env["PREFECT_SERVER_PORT"] = str(PORT)
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env["PREFECT_DATABASE_PATH"] = db_path
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env["PREFECT_SERVER_LOGGING_LEVEL"] = "INFO"
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+
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log(f"starting server on port {PORT}...")
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proc = subprocess.Popen(
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[SERVER_BIN],
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env=env,
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stdout=subprocess.PIPE,
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stderr=subprocess.STDOUT,
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text=True,
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)
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+
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try:
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# wait for server to be ready
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if not wait_for_server(PORT, STARTUP_TIMEOUT):
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log("server failed to start")
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proc.kill()
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return False
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log("server ready")
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+
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# make a request to verify it's working
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resp = httpx.get(f"http://localhost:{PORT}/api/health")
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if resp.status_code != 200:
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log(f"health check failed: {resp.status_code}")
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proc.kill()
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return False
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log("health check passed")
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+
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# create some data to verify flush
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client = httpx.Client(base_url=f"http://localhost:{PORT}/api")
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flow_resp = client.post("/flows/", json={"name": "shutdown-test-flow"})
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if flow_resp.status_code not in (200, 201):
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log(f"create flow failed: {flow_resp.status_code}")
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proc.kill()
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return False
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flow_id = flow_resp.json()["id"]
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log(f"created test flow: {flow_id}")
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# send SIGTERM
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log("sending SIGTERM...")
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proc.send_signal(signal.SIGTERM)
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+
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# wait for graceful shutdown
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try:
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proc.wait(timeout=SHUTDOWN_TIMEOUT)
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except subprocess.TimeoutExpired:
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log("shutdown timed out, killing process")
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proc.kill()
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return False
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# collect output
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stdout, _ = proc.communicate()
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exit_code = proc.returncode
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log(f"server exited with code {exit_code}")
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# verify shutdown logs
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expected_logs = [
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"signal received",
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"stopping services",
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"shutdown",
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]
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found_logs = []
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for line in stdout.lower().split("\n"):
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for expected in expected_logs:
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if expected in line and expected not in found_logs:
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found_logs.append(expected)
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if len(found_logs) < 2: # at least some shutdown logs
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log(f"missing shutdown logs. found: {found_logs}")
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log(f"server output:\n{stdout}")
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return False
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log(f"found shutdown logs: {found_logs}")
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+
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# note: exit code may be non-zero due to zap/facil.io quirks with SIGTERM
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# the important thing is that graceful shutdown occurred
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if exit_code != 0:
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log(f"exit code {exit_code} (acceptable - zap/facil.io SIGTERM quirk)")
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log("graceful shutdown successful!")
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return True
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finally:
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# cleanup
149
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if proc.poll() is None:
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proc.kill()
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try:
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os.unlink(db_path)
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except OSError:
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pass
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+
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+
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def test_sigint_shutdown() -> bool:
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"""Test that SIGINT (Ctrl+C) also triggers graceful shutdown."""
159
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log("testing SIGINT handling...")
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+
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with tempfile.NamedTemporaryFile(suffix=".db", delete=False) as f:
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db_path = f.name
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+
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env = os.environ.copy()
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env["PREFECT_SERVER_PORT"] = str(PORT + 1)
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env["PREFECT_DATABASE_PATH"] = db_path
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env["PREFECT_SERVER_LOGGING_LEVEL"] = "INFO"
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+
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proc = subprocess.Popen(
170
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[SERVER_BIN],
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env=env,
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stdout=subprocess.PIPE,
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stderr=subprocess.STDOUT,
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text=True,
175
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)
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+
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try:
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if not wait_for_server(PORT + 1, STARTUP_TIMEOUT):
179
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log("server failed to start")
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proc.kill()
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return False
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+
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# send SIGINT (same as Ctrl+C)
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log("sending SIGINT...")
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proc.send_signal(signal.SIGINT)
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+
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try:
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proc.wait(timeout=SHUTDOWN_TIMEOUT)
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except subprocess.TimeoutExpired:
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log("shutdown timed out")
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proc.kill()
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return False
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+
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exit_code = proc.returncode
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log(f"server exited with code {exit_code}")
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+
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if exit_code != 0:
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stdout, _ = proc.communicate()
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log(f"non-zero exit: {stdout}")
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return False
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202
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log("SIGINT shutdown successful!")
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return True
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+
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finally:
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if proc.poll() is None:
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proc.kill()
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try:
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os.unlink(db_path)
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except OSError:
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pass
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+
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+
214
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def main() -> int:
215
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log("=" * 60)
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log("graceful shutdown tests")
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log("=" * 60)
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+
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tests = [
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("SIGTERM shutdown", test_graceful_shutdown),
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("SIGINT shutdown", test_sigint_shutdown),
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]
223
+
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results = []
225
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for name, test_fn in tests:
226
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log(f"\n--- {name} ---")
227
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try:
228
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passed = test_fn()
229
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except Exception as e:
230
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log(f"test error: {e}")
231
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passed = False
232
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results.append((name, passed))
233
+
234
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log("\n" + "=" * 60)
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log("results:")
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all_passed = True
237
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for name, passed in results:
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status = "✓" if passed else "✗"
239
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log(f" {status} {name}")
240
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if not passed:
241
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all_passed = False
242
+
243
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return 0 if all_passed else 1
244
+
245
+
246
+
if __name__ == "__main__":
247
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sys.exit(main())
+54
-9
src/main.zig
+54
-9
src/main.zig
···
10
10
const log = @import("logging.zig");
11
11
const services = @import("services.zig");
12
12
13
+
// Graceful shutdown state
14
+
var shutdown_requested: bool = false;
15
+
16
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fn signalHandler(sig: c_int) callconv(.c) void {
17
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_ = sig;
18
+
if (!shutdown_requested) {
19
+
shutdown_requested = true;
20
+
// zap.stop() tells facil.io to stop accepting connections and shut down
21
+
zap.stop();
22
+
}
23
+
}
24
+
25
+
fn setupSignalHandlers() void {
26
+
const action = posix.Sigaction{
27
+
.handler = .{ .handler = signalHandler },
28
+
.mask = posix.sigemptyset(),
29
+
.flags = 0,
30
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};
31
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posix.sigaction(posix.SIG.INT, &action, null);
32
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posix.sigaction(posix.SIG.TERM, &action, null);
33
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}
34
+
13
35
fn onRequest(r: zap.Request) !void {
14
36
const method = r.method orelse "?";
15
37
const path = r.path orelse "/";
···
102
124
fn runServicesOnly() !void {
103
125
log.info("services", "starting background services only...", .{});
104
126
127
+
setupSignalHandlers();
128
+
105
129
try initInfra();
106
-
defer deinitInfra();
130
+
defer {
131
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log.info("shutdown", "cleaning up infrastructure...", .{});
132
+
deinitInfra();
133
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log.info("shutdown", "complete", .{});
134
+
}
107
135
108
136
try services.startAll();
109
-
defer services.stopAll();
137
+
defer {
138
+
log.info("shutdown", "stopping services...", .{});
139
+
services.stopAll();
140
+
}
110
141
111
-
log.info("services", "all services running - press Ctrl+C to stop", .{});
142
+
log.info("services", "all services running - send SIGTERM or SIGINT to stop", .{});
112
143
113
-
// block forever (services run in background threads)
114
-
while (true) {
115
-
posix.nanosleep(60, 0);
144
+
// block until shutdown signal
145
+
while (!shutdown_requested) {
146
+
posix.nanosleep(1, 0);
116
147
}
148
+
149
+
log.info("shutdown", "signal received, initiating graceful shutdown...", .{});
117
150
}
118
151
119
152
fn runServer(no_services: bool) !void {
···
123
156
};
124
157
const host = posix.getenv("PREFECT_SERVER_API_HOST") orelse "127.0.0.1";
125
158
159
+
setupSignalHandlers();
160
+
126
161
try initInfra();
127
-
defer deinitInfra();
162
+
defer {
163
+
log.info("shutdown", "cleaning up infrastructure...", .{});
164
+
deinitInfra();
165
+
log.info("shutdown", "complete", .{});
166
+
}
128
167
129
168
if (!no_services) {
130
169
try services.startAll();
131
170
} else {
132
171
log.info("server", "running in API-only mode (--no-services)", .{});
133
172
}
134
-
defer if (!no_services) services.stopAll();
173
+
defer if (!no_services) {
174
+
log.info("shutdown", "stopping services...", .{});
175
+
services.stopAll();
176
+
};
135
177
136
178
var listener = zap.HttpListener.init(.{
137
179
.port = port,
···
144
186
});
145
187
146
188
try listener.listen();
147
-
log.info("server", "listening on http://{s}:{d}", .{ host, port });
189
+
log.info("server", "listening on http://{s}:{d} - send SIGTERM or SIGINT to stop", .{ host, port });
148
190
191
+
// zap.start blocks until zap.stop() is called (via signal handler)
149
192
zap.start(.{
150
193
.threads = 4,
151
194
.workers = 1,
152
195
});
196
+
197
+
log.info("shutdown", "signal received, initiating graceful shutdown...", .{});
153
198
}
154
199
155
200
fn initInfra() !void {