Simplified uvicorn running in multiprocess mode, avoiding a crash on Windows when it couldn't setup threads (running from a worker thread).

template/scripts/devserver.py

@@ -4,13 +4,11 @@
 
 import argparse
 import asyncio
-import contextlib
 import os
 import sys
+from contextlib import suppress
 from pathlib import Path
 
-from fastapi_vue import server
-
 # Import util.py from scripts/fastapi-vue (not a package, so we adjust sys.path)
 sys.path.insert(0, str(Path(__file__).with_name("fastapi-vue")))
 from devutil import (  # type: ignore
@@ -34,7 +32,7 @@ async def run_devserver(frontend: str, backend: str) -> None:
         raise SystemExit(1)
 
     viteurl, npm_install, vite = setup_vite(frontend, DEFAULT_VITE_PORT)
-    backurl, module, backend_config = setup_fastapi(
+    backurl, uvicorn = setup_fastapi(
         backend, "MODULE_NAME.APP_MODULE:APP_VAR", DEFAULT_DEV_PORT
     )
 
@@ -45,15 +43,8 @@ async def run_devserver(frontend: str, backend: str) -> None:
     async with ProcessGroup() as pg:
         npm_i = await pg.spawn(*npm_install, cwd=front)
         await check_ports_free(viteurl, backurl)
-
-        # Run backend in a thread (server.run is blocking)
-        loop = asyncio.get_event_loop()
-        loop.run_in_executor(None, lambda: server.run(module, **backend_config))
-
-        # Wait for both install and backend to be ready
+        await pg.spawn(*uvicorn)
         await pg.wait(npm_i, ready(backurl, path="/api/health?from=devserver.py"))
-
-        # Start Vite dev server (ProcessGroup waits for any exit, then terminates others)
         await pg.spawn(*vite, cwd=front)
 
 
@@ -75,7 +66,7 @@ def main():
         help=f"FastAPI backend endpoint (default: localhost:{DEFAULT_DEV_PORT})",
     )
     args = parser.parse_args()
-    with contextlib.suppress(KeyboardInterrupt):
+    with suppress(KeyboardInterrupt):
         asyncio.run(run_devserver(args.frontend, args.backend))
 
 
@@ -84,7 +75,8 @@ HELP_EPILOG = """
   scripts/devserver.py 3000                  # Vite on localhost:3000
   scripts/devserver.py :3000 --backend 8000  # *:3000, localhost:8000
 
-  JS_RUNTIME environment variable can be used to select the JS runtime
+  JS_RUNTIME environment variable can be used to select the JS runtime:
+  npm, deno, bun, or full path to the runtime executable (node maps to npm).
 """
 
 

template/scripts/fastapi-vue/devutil.py

@@ -2,6 +2,7 @@
 
 import asyncio
 import subprocess
+import sys
 from collections.abc import Coroutine
 from contextlib import suppress
 from pathlib import Path
@@ -159,10 +160,10 @@ def setup_vite(
 
 def setup_fastapi(
     endpoint: str, module: str, default_port: int = 8000
-) -> tuple[str, str, dict]:
-    """Parse backend endpoint and build server.run() config.
+) -> tuple[str, list[str]]:
+    """Parse backend endpoint and build uvicorn command.
 
-    Returns (url, module, config_dict).
+    Returns (url, uvicorn_cmd).
     Raises SystemExit(1) on invalid config.
     """
     endpoints = parse_endpoint(endpoint, default_port)
@@ -173,11 +174,17 @@ def setup_fastapi(
 
     host = endpoints[0]["host"]
     port = endpoints[0]["port"]
+    reload_dir = module.split(".")[0]  # Don't reload on frontend changes
 
-    config = {
-        "listen": f"{host}:{port}",
-        "reload": True,
-        "reload_dirs": [module.split(".")[0]],  # Don't reload on frontend changes
-        "forwarded_allow_ips": "*",
-    }
-    return f"http://{host}:{port}", module, config
+    cmd = [
+        sys.executable,
+        "-m",
+        "uvicorn",
+        module,
+        f"--host={host}",
+        f"--port={port}",
+        "--reload",
+        f"--reload-dir={reload_dir}",
+        "--forwarded-allow-ips=*",
+    ]
+    return f"http://{host}:{port}", cmd