feat(oci): support custom Compose workers and migration jobs

oci/remote/oci_instances.py

@@ -15,6 +15,7 @@ import re
 import subprocess
 import sys
 import tempfile
+import time
 import uuid
 
 from oci_installation_state import command, image_from_archive, private_directory, sha
@@ -42,8 +43,22 @@ def location(root, vmid):
     return path / 'oci-compose.json'
 
 
+def _acquire_lock(fd, timeout):
+    """Wait only for acquisition; a failure inside the operation is never replayed."""
+    deadline = time.monotonic() + max(0, float(timeout))
+    while True:
+        try:
+            fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
+            return
+        except BlockingIOError:
+            remaining = deadline - time.monotonic()
+            if remaining <= 0:
+                raise
+            time.sleep(min(0.2, remaining))
+
+
 @contextmanager
-def locked(root):
+def locked(root, timeout=0):
     private_directory(root)
     path = root / '.lock'
     if path.is_symlink():
@@ -53,12 +68,12 @@ def locked(root):
         fd = int(inherited)
         if os.fstat(fd).st_ino != path.stat().st_ino or os.fstat(fd).st_dev != path.stat().st_dev:
             raise ValueError(translate('Wrong inherited registry lock'))
-        fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
+        _acquire_lock(fd, timeout)
         yield
     else:
         with path.open('a') as lock:
             os.chmod(path, 0o600)
-            fcntl.flock(lock, fcntl.LOCK_EX | fcntl.LOCK_NB)
+            _acquire_lock(lock, timeout)
             yield