Adrian Vovk
7483708131
This utility lets us freeze units, and then automatically thaw them
when via a _cleanup_ handler. For example, you can now write something
like:
```
_cleanup_(unit_freezer_thaw) UnitFreezer freezer = UNIT_FREEZER_NULL;
r = unit_freezer_freeze("myunit.service", &freezer);
if (r < 0)
return r;
// Freeze is thawed once this scope ends
```
Aside from the basic _freeze and _thaw methods, there's also
_cancel and _restore. Cancel destroys the UnitFreezer without
thawing the unit. Restore creates a UnitFreezer without freezing it.
The idea of these two methods is that it allows the freeze/thaw to
be separated from each other (i.e. done in response to two separate
DBus method calls). For example:
```
_cleanup_(unit_freezer_thaw) UnitFreezer freezer = UNIT_FREEZER_NULL;
r = unit_freezer_freeze("myunit.service", &freezer);
if (r < 0)
return r;
// Freeze is thawed once this scope ends
r = do_something()
if (r < 0)
return r; // Freeze is thawed
unit_freezer_cancel(&freezer); // Thaw is canceled.
```
Then in another scope:
```
// Bring back a UnitFreezer object for the already-frozen service
_cleanup_(unit_freezer_thaw) UnitFreezer freezer = UNIT_FREEZER_NULL;
r = unit_freezer_restore("myunit.service", &freezer);
if (r < 0)
return r;
// Freeze is thawed once this scope ends
```
System and Service Manager
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