Merge pull request #1470 from hercules-ci/locking-usability

Locking usability improvements

nixops/args.py

@@ -352,6 +352,12 @@
 subparser.add_argument(
     "args", metavar="SSH_ARGS", nargs=REMAINDER, help="SSH flags and/or command",
 )
+subparser.add_argument(
+    "--now",
+    dest="now",
+    action="store_true",
+    help="do not acquire a lock before fetching the state",
+)
 
 subparser = add_subparser(
     subparsers, "ssh-for-each", help="execute a command on each machine via SSH"
@@ -443,14 +449,12 @@
     "--freeze",
     dest="freeze_fs",
     action="store_true",
-    default=False,
     help="freeze filesystems for non-root filesystems that support this (e.g. xfs)",
 )
 subparser.add_argument(
     "--force",
     dest="force",
     action="store_true",
-    default=False,
     help="start new backup even if previous is still running",
 )
 subparser.add_argument(
@@ -478,17 +482,12 @@
     help="do not perform backup actions on the specified machines",
 )
 subparser.add_argument(
-    "--wait",
-    dest="wait",
-    action="store_true",
-    default=False,
-    help="wait until backup is finished",
+    "--wait", dest="wait", action="store_true", help="wait until backup is finished",
 )
 subparser.add_argument(
     "--latest",
     dest="latest",
     action="store_true",
-    default=False,
     help="show status of latest backup only",
 )
 
@@ -498,7 +497,6 @@
 subparser.add_argument(
     "--keep-physical",
     dest="keep_physical",
-    default=False,
     action="store_true",
     help="do not remove the physical backups, only remove backups from nixops state",
 )
@@ -518,7 +516,6 @@
 subparser.add_argument(
     "--keep-physical",
     dest="keep_physical",
-    default=False,
     action="store_true",
     help="do not remove the physical backups, only remove backups from nixops state",
 )

nixops/locks/__init__.py

@@ -2,10 +2,35 @@
 from typing_extensions import Protocol
 
 
+"""
+Interface to a lock driver.
+
+An implementation should inherit from LockDriver in order to for a plugin to be
+able to integrate it.
+"""
+
+
+# This separation was introduced to hide the LockOptions details from the
+# LockInterface type. It only matters for construction and clients don't have
+# to know about it.
+class LockInterface(Protocol):
+    # lock: acquire a lock.
+    # Note: no arguments will be passed over kwargs. Making it part of
+    # the type definition allows adding new arguments later.
+    def lock(self, description: str, exclusive: bool, **kwargs) -> None:
+        raise NotImplementedError
+
+    # unlock: release the lock.
+    # Note: no arguments will be passed over kwargs. Making it part of
+    # the type definition allows adding new arguments later.
+    def unlock(self, **kwargs) -> None:
+        raise NotImplementedError
+
+
 LockOptions = TypeVar("LockOptions")
 
 
-class LockDriver(Protocol[LockOptions]):
+class LockDriver(LockInterface, Protocol[LockOptions]):
     # Hack: Make T a mypy invariant. According to PEP-0544, a
     # Protocol[T] whose T is only used in function arguments and
     # returns is "de-facto covariant".
@@ -26,15 +51,3 @@ def options(**kwargs) -> LockOptions:
 
     def __init__(self, args: LockOptions) -> None:
         raise NotImplementedError
-
-    # lock: acquire a lock.
-    # Note: no arguments will be passed over kwargs. Making it part of
-    # the type definition allows adding new arguments later.
-    def lock(self, **kwargs) -> None:
-        raise NotImplementedError
-
-    # unlock: release the lock.
-    # Note: no arguments will be passed over kwargs. Making it part of
-    # the type definition allows adding new arguments later.
-    def unlock(self, **kwargs) -> None:
-        raise NotImplementedError

nixops/locks/noop.py

@@ -19,5 +19,5 @@ def __init__(self, args: NoopLockOptions) -> None:
     def unlock(self, **_kwargs) -> None:
         pass
 
-    def lock(self, **_kwargs) -> None:
+    def lock(self, description, exclusive, **_kwargs) -> None:
         pass