propellor-2.16.0: property-based host configuration management in haskell

Safe HaskellNone



Propellor properties can be made to run concurrently, using this module. This can speed up propellor, at the expense of using more CPUs and other resources.

It's up to you to make sure that properties that you make run concurrently don't implicitly depend on one-another. The worst that can happen though, is that propellor fails to ensure some of the properties, and tells you what went wrong.

Another potential problem is that output of concurrent properties could interleave into a scrambled mess. This is mostly prevented; all messages output by propellor are concurrency safe, including errorMessage, infoMessage, etc. However, if you write a property that directly uses print or putStrLn, you can still experience this problem.

Similarly, when properties run external commands, the command's output can be a problem for concurrency. No need to worry; createProcess is concurrent output safe (it actually uses createProcessConcurrent), and everything else in propellor that runs external commands is built on top of that. Of course, if you import System.Process and use it in a property, you can bypass that and shoot yourself in the foot.

Finally, anything that directly accesses the tty can bypass these protections. That's sometimes done for eg, password prompts. A well-written property should avoid running interactive commands anyway.



concurrently :: (IsProp p1, IsProp p2, Combines p1 p2, IsProp (CombinedType p1 p2)) => p1 -> p2 -> CombinedType p1 p2 Source

Ensures two properties concurrently.

	& foo `concurrently` bar

To ensure three properties concurrently, just use this combinator twice:

	& foo `concurrently` bar `concurrently` baz

concurrentList :: IO Int -> Desc -> PropList -> Property HasInfo Source

Ensures all the properties in the list, with a specified amount of concurrency.

 concurrentList (pure 2) "demo" $ props
	& foo
	& bar
	& baz

The above example will run foo and bar concurrently, and once either of those 2 properties finishes, will start running baz.

props :: PropList Source

Starts accumulating a list of properties.

propertyList "foo" $ props
	& someproperty
	! oldproperty
	& otherproperty

getNumProcessors :: IO Int

Returns the number of CPUs that the machine has


concurrentSatisfy :: Propellor Result -> Propellor Result -> Propellor Result Source

Running Propellor actions concurrently.