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FarhanAliRazaFarhanAliRaza
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Serialize production frontend work sharing one .web directory
Two exports (or an export and a prod/preview start) in the same project used to race on .web: the second replaced build/ and env.json while the first was still compiling or zipping, so one of them shipped the other's frontend. Hold an exclusive, reentrant file lock on .web/.reflex-build.lock from compilation through ZIP creation, release it before serving, and never create .web for a backend-only export that has nothing to protect. Split out of #7054 (lock only; the opt-in build cache that needs it follows separately). Claude-Session: https://claude.ai/code/session_018nWB9r2HcC5tkT72UxWgGj
1 parent 62a56ba commit b7d35ca

8 files changed

Lines changed: 663 additions & 59 deletions

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‎docs/hosting/self-hosting.md‎

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@@ -136,6 +136,16 @@ this, use the `--no-zip` parameter. This provides the frontend in the
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`.web/build/client/` directory and the backend can be found in the root directory of
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the project.
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139+
Production exports that share a `.web` directory wait for one another from
140+
compilation through ZIP creation, on macOS, Linux, and Windows. Backend-only
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exports also wait while archiving an existing `.web/backend` directory, but do
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not create `.web` when it is absent. Production and preview startup hold the
143+
same lock while compiling and building and release it before serving. The lock
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file `.web/.reflex-build.lock` stays in place between commands; do not remove it
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while a command is running. Initialization, development hot reload, and other
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tools writing to `.web` are outside this lock, so avoid running them during an
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export.
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139149
The export also writes a pre-compressed `.gz` copy of the compressible text
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assets (JS, CSS, HTML, JSON, SVG, and similar), so configure the static host
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to serve those directly where it supports it. Set the

‎news/+export-workspace-lock.bugfix.md‎

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@@ -0,0 +1 @@
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Production exports, `reflex run --env prod`, and preview startup that share a `.web` directory now wait for one another instead of overwriting each other's compiled frontend and archives. The lock file `.web/.reflex-build.lock` stays in place between commands.

‎reflex/reflex.py‎

Lines changed: 41 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -6,7 +6,7 @@
66
import signal
77
import sys
88
from collections.abc import Callable
9-
from contextlib import contextmanager
9+
from contextlib import contextmanager, nullcontext
1010
from importlib import import_module
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from importlib.util import find_spec
1212
from pathlib import Path
@@ -508,21 +508,33 @@ def _run_preview(running_mode: constants.RunningMode, port: int, host: str):
508508
"""
509509
import atexit
510510

511-
from reflex.utils import build, exec, processes, telemetry
511+
from reflex.utils import (
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build,
513+
build_lock,
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exec,
515+
prerequisites,
516+
processes,
517+
telemetry,
518+
)
512519

513520
config = get_config()
514521

515-
config._set_persistent(frontend_port=port, backend_port=port)
522+
with (
523+
build_lock.frontend_build_lock(prerequisites.get_web_dir())
524+
if running_mode.has_frontend()
525+
else nullcontext()
526+
):
527+
config._set_persistent(frontend_port=port, backend_port=port)
516528

517-
# Mount the compiled frontend into the dev backend so no Vite server is needed.
518-
environment.REFLEX_MOUNT_FRONTEND_COMPILED_APP.set(
519-
running_mode.has_frontend() and running_mode.has_backend()
520-
)
529+
# Mount the compiled frontend into the dev backend so no Vite server is needed.
530+
environment.REFLEX_MOUNT_FRONTEND_COMPILED_APP.set(
531+
running_mode.has_frontend() and running_mode.has_backend()
532+
)
521533

522-
if running_mode.has_frontend():
523-
# Compile the app and produce the initial frontend build.
524-
_compile_app()
525-
build.setup_frontend_prod(Path.cwd())
534+
if running_mode.has_frontend():
535+
# Compile the app and produce the initial frontend build.
536+
_compile_app()
537+
build.setup_frontend_prod(Path.cwd())
526538

527539
# Post a telemetry event.
528540
telemetry.send("run-preview")
@@ -547,16 +559,28 @@ def _run_preview(running_mode: constants.RunningMode, port: int, host: str):
547559
def _run_prod(running_mode: constants.RunningMode, port: int, host: str):
548560
import atexit
549561

550-
from reflex.utils import build, exec, processes, telemetry
562+
from reflex.utils import (
563+
build,
564+
build_lock,
565+
exec,
566+
prerequisites,
567+
processes,
568+
telemetry,
569+
)
551570

552571
config = get_config()
553572

554-
config._set_persistent(frontend_port=port, backend_port=port)
573+
with (
574+
build_lock.frontend_build_lock(prerequisites.get_web_dir())
575+
if running_mode.has_frontend()
576+
else nullcontext()
577+
):
578+
config._set_persistent(frontend_port=port, backend_port=port)
555579

556-
if running_mode.has_frontend():
557-
# Get the app module.
558-
_compile_app(avoid_dirty_check=False)
559-
build.setup_frontend_prod(Path.cwd())
580+
if running_mode.has_frontend():
581+
# Get the app module.
582+
_compile_app(avoid_dirty_check=False)
583+
build.setup_frontend_prod(Path.cwd())
560584

561585
_skip_compile()
562586

‎reflex/utils/build_lock.py‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,119 @@
1+
"""Serialize production frontend work that shares one ``.web`` directory."""
2+
3+
from __future__ import annotations
4+
5+
import errno
6+
import logging
7+
import os
8+
import stat
9+
import sys
10+
import threading
11+
import time
12+
from collections.abc import Iterator
13+
from contextlib import contextmanager
14+
from pathlib import Path
15+
16+
from reflex_base import constants
17+
18+
logger = logging.getLogger(__name__)
19+
20+
LOCK_FILE = ".reflex-build.lock"
21+
_lock_state = threading.local()
22+
_lock_descriptors: set[int] = set()
23+
24+
25+
def _reset_build_locks_after_fork() -> None:
26+
"""Close inherited descriptors without unlocking the parent's file descriptions."""
27+
for descriptor in _lock_descriptors:
28+
os.close(descriptor)
29+
_lock_descriptors.clear()
30+
_lock_state.paths = set()
31+
32+
33+
if not constants.IS_WINDOWS:
34+
os.register_at_fork(after_in_child=_reset_build_locks_after_fork)
35+
36+
37+
def _lock_descriptor(descriptor: int, *, unlock: bool = False) -> None:
38+
"""Acquire or release the platform's exclusive file lock.
39+
40+
Args:
41+
descriptor: Open lock-file descriptor, positioned at byte zero.
42+
unlock: Whether to release a previously acquired lock.
43+
44+
Raises:
45+
OSError: The lock operation fails for a reason other than contention.
46+
"""
47+
if sys.platform == "win32":
48+
import msvcrt
49+
50+
if unlock:
51+
msvcrt.locking(descriptor, msvcrt.LK_UNLCK, 1)
52+
return
53+
while True:
54+
try:
55+
msvcrt.locking(descriptor, msvcrt.LK_NBLCK, 1)
56+
except OSError as error: # noqa: PERF203 - retry a contended OS lock
57+
if error.errno != errno.EACCES:
58+
raise
59+
# Poll every 100 ms; builds can exceed LK_LOCK's ten-second limit.
60+
time.sleep(0.1)
61+
else:
62+
return
63+
else:
64+
import fcntl
65+
66+
fcntl.flock(descriptor, fcntl.LOCK_UN if unlock else fcntl.LOCK_EX)
67+
68+
69+
@contextmanager
70+
def frontend_build_lock(web_dir: Path) -> Iterator[None]:
71+
"""Serialize production workspace access, including builds with caching disabled.
72+
73+
Nested calls from the same thread reuse its lock. Other threads and processes
74+
open independent descriptors and wait on the same persistent lock file.
75+
76+
Args:
77+
web_dir: Shared frontend working directory.
78+
79+
Yields:
80+
Control while this thread owns the production workspace.
81+
82+
Raises:
83+
OSError: A regular lock file cannot be opened or locked safely.
84+
"""
85+
owner_pid = os.getpid()
86+
web_dir = web_dir.resolve()
87+
held: set[Path] = getattr(_lock_state, "paths", set())
88+
if web_dir in held:
89+
yield
90+
return
91+
web_dir.mkdir(parents=True, exist_ok=True)
92+
lock_path = web_dir / LOCK_FILE
93+
descriptor = os.open(
94+
lock_path, os.O_CREAT | os.O_RDWR | getattr(os, "O_NOFOLLOW", 0), 0o600
95+
)
96+
_lock_descriptors.add(descriptor)
97+
try:
98+
info = os.fstat(descriptor)
99+
path_info = lock_path.lstat()
100+
if (
101+
not stat.S_ISREG(info.st_mode)
102+
or not stat.S_ISREG(path_info.st_mode)
103+
or not os.path.samestat(info, path_info)
104+
):
105+
msg = "Production build lock must be a regular file"
106+
raise OSError(msg)
107+
_lock_descriptor(descriptor)
108+
held.add(web_dir)
109+
_lock_state.paths = held
110+
try:
111+
yield
112+
finally:
113+
if os.getpid() == owner_pid:
114+
held.remove(web_dir)
115+
_lock_descriptor(descriptor, unlock=True)
116+
finally:
117+
if os.getpid() == owner_pid:
118+
_lock_descriptors.discard(descriptor)
119+
os.close(descriptor)

‎reflex/utils/export.py‎

Lines changed: 42 additions & 39 deletions
Original file line numberDiff line numberDiff line change
@@ -3,15 +3,15 @@
33
import logging
44
import time
55
from collections.abc import Iterator
6-
from contextlib import contextmanager
6+
from contextlib import contextmanager, nullcontext
77
from pathlib import Path
88

99
from reflex_base import constants
1010
from reflex_base.config import get_config
1111
from reflex_base.environment import environment
1212
from reflex_base.utils import console
1313

14-
from reflex.utils import build, exec, prerequisites, telemetry
14+
from reflex.utils import build, build_lock, exec, prerequisites, telemetry
1515

1616
logger = logging.getLogger(__name__)
1717

@@ -49,23 +49,6 @@ def export(
4949
# Set the log level.
5050
console.set_log_level(loglevel)
5151

52-
# Set env mode in the environment
53-
environment.REFLEX_ENV_MODE.set(env)
54-
55-
# Override the config url values if provided.
56-
if api_url is not None:
57-
config._set_persistent(api_url=str(api_url))
58-
logger.debug(f"overriding API URL: {config.api_url}")
59-
if deploy_url is not None:
60-
config._set_persistent(deploy_url=str(deploy_url))
61-
logger.debug(f"overriding deploy URL: {config.deploy_url}")
62-
63-
# Show system info
64-
exec.output_system_info()
65-
66-
# Compile the app in production mode and export it.
67-
console.rule("[bold]Compiling production app and preparing for export.")
68-
6952
start = time.monotonic()
7053
phase_durations: dict[str, float] = {}
7154
status = "success"
@@ -80,26 +63,46 @@ def _time_phase(name: str) -> Iterator[None]:
8063
phase_durations[name] = time.monotonic() - t0
8164

8265
try:
83-
if frontend:
84-
with _time_phase("compile_duration"):
85-
# Ensure module can be imported and app.compile() is called.
86-
prerequisites.get_compiled_app(
87-
prerender_routes=prerender_routes, trigger="export"
88-
)
89-
with _time_phase("setup_duration"):
90-
# Set up .web directory and install frontend dependencies.
91-
build.setup_frontend(Path.cwd())
92-
with _time_phase("build_duration"):
93-
build.build()
94-
if zipping:
95-
with _time_phase("zip_duration"):
96-
build.zip_app(
97-
frontend=frontend,
98-
backend=backend,
99-
zip_dest_dir=zip_dest_dir,
100-
include_db_file=upload_db_file,
101-
backend_excluded_dirs=backend_excluded_dirs,
102-
)
66+
web_dir = prerequisites.get_web_dir()
67+
with (
68+
build_lock.frontend_build_lock(web_dir)
69+
if frontend or (backend and zipping and web_dir.is_dir())
70+
else nullcontext()
71+
):
72+
# Set env mode in the environment.
73+
environment.REFLEX_ENV_MODE.set(env)
74+
75+
# Override the config url values if provided.
76+
if api_url is not None:
77+
config._set_persistent(api_url=str(api_url))
78+
logger.debug(f"overriding API URL: {config.api_url}")
79+
if deploy_url is not None:
80+
config._set_persistent(deploy_url=str(deploy_url))
81+
logger.debug(f"overriding deploy URL: {config.deploy_url}")
82+
83+
exec.output_system_info()
84+
console.rule("[bold]Compiling production app and preparing for export.")
85+
86+
if frontend:
87+
with _time_phase("compile_duration"):
88+
# Ensure module can be imported and app.compile() is called.
89+
prerequisites.get_compiled_app(
90+
prerender_routes=prerender_routes, trigger="export"
91+
)
92+
with _time_phase("setup_duration"):
93+
# Set up .web directory and install frontend dependencies.
94+
build.setup_frontend(Path.cwd())
95+
with _time_phase("build_duration"):
96+
build.build()
97+
if zipping:
98+
with _time_phase("zip_duration"):
99+
build.zip_app(
100+
frontend=frontend,
101+
backend=backend,
102+
zip_dest_dir=zip_dest_dir,
103+
include_db_file=upload_db_file,
104+
backend_excluded_dirs=backend_excluded_dirs,
105+
)
103106
except Exception as exc:
104107
status = "failure"
105108
detail = type(exc).__name__

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