fix(ai): drop per-frame pymatting in animated background removal (#684)

The frame loop spent 2-19s per frame in CPU pymatting while the CUDA session sat idle; a 30-frame GIF took 353s on a 4070. Animations skip alpha matting now (stills keep it), the session device is logged, and the CUDA-to-CPU session fallback says why. Same fixture finishes in 46s with every frame on the GPU. Fixes #668.
2026-08-03 07:46:42 +02:00 · 2026-07-30 10:05:09 +08:00
parent 470a0a4acb
commit 4d07014e76
2 changed files with 97 additions and 8 deletions
@@ -0,0 +1,77 @@
+"""The animated-removal session helper must not downgrade to CPU silently.
+
+The 2.2.0 fleet QA (#668) burned hours on an unexplainable six-minute GIF job
+because nothing in the logs said which device the frame loop used, and the
+CUDA-to-CPU retry in _create_session swallowed the reason entirely.
+"""
+
+import importlib.util
+import os
+import sys
+import types
+
+
+def load_gif_module(fake_new_session):
+    """Load gif_remove_bg with fakes for its function-local imports."""
+    rembg = types.ModuleType("rembg")
+    rembg.new_session = fake_new_session
+    rembg.remove = lambda *a, **k: b""
+    sessions = types.ModuleType("rembg.sessions")
+    sessions.sessions_class = []
+    rembg.sessions = sessions
+
+    remove_bg = types.ModuleType("remove_bg")
+    remove_bg._register_matting_session = lambda _c: None
+    remove_bg._register_hr_matting_session = lambda _c: None
+    remove_bg.ALLOWED_MODELS = {"u2net"}
+
+    sys.modules["rembg"] = rembg
+    sys.modules["rembg.sessions"] = sessions
+    sys.modules["remove_bg"] = remove_bg
+
+    script_path = os.path.join(os.path.dirname(__file__), "..", "gif_remove_bg.py")
+    spec = importlib.util.spec_from_file_location("gif_remove_bg_under_test", script_path)
+    module = importlib.util.module_from_spec(spec)
+    assert spec.loader is not None
+    spec.loader.exec_module(module)
+    return module
+
+
+def teardown_function(_fn):
+    for name in ("rembg", "rembg.sessions", "remove_bg"):
+        sys.modules.pop(name, None)
+
+
+def test_cuda_session_failure_falls_back_to_cpu_and_says_so(capsys):
+    calls = []
+
+    def new_session(model, providers=None):
+        calls.append(providers)
+        if "CUDAExecutionProvider" in providers:
+            raise RuntimeError("CUDA failure for the test")
+        return "cpu-session"
+
+    mod = load_gif_module(new_session)
+    session, device = mod._create_session(
+        "u2net", ["CUDAExecutionProvider", "CPUExecutionProvider"], "cuda"
+    )
+
+    assert session == "cpu-session"
+    assert device == "cpu"
+    assert calls == [
+        ["CUDAExecutionProvider", "CPUExecutionProvider"],
+        ["CPUExecutionProvider"],
+    ]
+    err = capsys.readouterr().err
+    assert "falling back to CPU" in err
+    assert "CUDA failure for the test" in err
+
+
+def test_successful_cuda_session_keeps_device_and_stays_quiet(capsys):
+    mod = load_gif_module(lambda model, providers=None: "gpu-session")
+    session, device = mod._create_session(
+        "u2net", ["CUDAExecutionProvider", "CPUExecutionProvider"], "cuda"
+    )
+    assert session == "gpu-session"
+    assert device == "cuda"
+    assert "falling back" not in capsys.readouterr().err