fix: lock the pack directory while splitting

scripts/split_pack.py

@@ -21,6 +21,8 @@ import sys
 import zipfile
 from pathlib import Path
 
+from artifacts import ArtifactLockBusy, artifact_lock
+
 # "Each file included in a release must be under 2 GiB."
 ASSET_LIMIT = 2 * 1024**3
 
@@ -222,12 +224,17 @@ def main() -> int:
         help="a part stays under this many bytes (K, M, G suffixes; default 2G)",
     )
     args = parser.parse_args()
+    # The packs are rewritten in place by generate_pack under this lock: a
+    # build running beside the split mixes its bytes into the pack being
+    # read, or writes a pack that the split then deletes.
+    directory = args.target if args.target.is_dir() else args.target.parent
     try:
-        if args.target.is_dir():
-            published = split_directory(args.target, args.max_size)
-        else:
-            published = split_pack(args.target, args.max_size)
-    except (OSError, ValueError, zipfile.BadZipFile) as exc:
+        with artifact_lock(str(directory)):
+            if args.target.is_dir():
+                published = split_directory(args.target, args.max_size)
+            else:
+                published = split_pack(args.target, args.max_size)
+    except (ArtifactLockBusy, OSError, ValueError, zipfile.BadZipFile) as exc:
         print(f"Error: {exc}", file=sys.stderr)
         return 1
     for path in published:

tests/test_split_pack.py

@@ -135,6 +135,32 @@ class PartsAreArchives(SplitFixture):
         self.assertTrue(modes["bin/engine"] & stat.S_IXUSR)
 
 
+class SplitHoldsTheDirectory(SplitFixture):
+    """split_pack read and deleted packs in a directory a build was writing:
+    the build could truncate the pack under the split, or the split delete
+    the pack the build had just written."""
+
+    def test_a_held_directory_is_left_alone(self):
+        import subprocess
+
+        from artifacts import artifact_lock
+
+        for target in (self.dist, self.pack):
+            with self.subTest(target=target.name), artifact_lock(str(self.dist)):
+                proc = subprocess.run(
+                    [sys.executable, "scripts/split_pack.py", str(target),
+                     "--max-size", str(LIMIT)],
+                    cwd=str(REPO_ROOT), capture_output=True, text=True,
+                    timeout=60, check=False,
+                )
+                self.assertEqual(proc.returncode, 1, proc.stdout + proc.stderr)
+                self.assertIn("in use by another run", proc.stderr)
+                self.assertTrue(self.pack.exists())
+                self.assertEqual(
+                    sorted(p.name for p in self.dist.glob("*.zip")), [self.pack.name]
+                )
+
+
 class PartsAreNotTakenForPacks(SplitFixture):
     def test_a_part_is_recognised_by_its_name(self):
         self.assertTrue(split_pack.is_part("RetroArch_BIOS_Pack.part1of2.zip"))