perf(8502): 并行生图(6并发)+超时重试；视频URL直连预览/下载；路径隔离

modules/limits.py

@@ -0,0 +1,49 @@
+"""
+Process-wide concurrency limits for Streamlit single-process deployment.
+
+These limits reduce tail latency and avoid a single user saturating network/CPU
+and impacting other concurrent sessions.
+"""
+
+from __future__ import annotations
+
+import os
+import threading
+from contextlib import contextmanager
+from typing import Iterator
+
+
+def _env_int(name: str, default: int) -> int:
+    try:
+        return max(1, int(os.getenv(name, str(default))))
+    except Exception:
+        return default
+
+
+MAX_CONCURRENT_IMAGE = _env_int("MAX_CONCURRENT_IMAGE", 6)
+MAX_CONCURRENT_VIDEO = _env_int("MAX_CONCURRENT_VIDEO", 1)
+
+_image_sem = threading.BoundedSemaphore(MAX_CONCURRENT_IMAGE)
+_video_sem = threading.BoundedSemaphore(MAX_CONCURRENT_VIDEO)
+
+
+@contextmanager
+def acquire_image(blocking: bool = True) -> Iterator[bool]:
+    ok = _image_sem.acquire(blocking=blocking)
+    try:
+        yield ok
+    finally:
+        if ok:
+            _image_sem.release()
+
+
+@contextmanager
+def acquire_video(blocking: bool = True) -> Iterator[bool]:
+    ok = _video_sem.acquire(blocking=blocking)
+    try:
+        yield ok
+    finally:
+        if ok:
+            _video_sem.release()
+
+