40ecf58d4b
This does not change the overall license of the git-annex program, which was already AGPL due to a number of sources files being AGPL already. Legally speaking, I'm adding a new license under which these files are now available; I already released their current contents under the GPL license. Now they're dual licensed GPL and AGPL. However, I intend for all my future changes to these files to only be released under the AGPL license, and I won't be tracking the dual licensing status, so I'm simply changing the license statement to say it's AGPL. (In some cases, others wrote parts of the code of a file and released it under the GPL; but in all cases I have contributed a significant portion of the code in each file and it's that code that is getting the AGPL license; the GPL license of other contributors allows combining with AGPL code.)
47 lines
1.4 KiB
Haskell
47 lines
1.4 KiB
Haskell
{- dynamic configuration
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-
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- Copyright 2017 Joey Hess <id@joeyh.name>
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-
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- Licensed under the GNU AGPL version 3 or higher.
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-}
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module Config.DynamicConfig where
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import Common
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import Control.Concurrent.STM
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-- | A configuration value that may only be known after performing an IO
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-- action. The IO action will only be run the first time the configuration
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-- is accessed; its result is then cached.
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data DynamicConfig a = DynamicConfig (IO a, TMVar a) | StaticConfig a
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mkDynamicConfig :: CommandRunner a -> Maybe String -> a -> STM (DynamicConfig a)
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mkDynamicConfig _ Nothing static = return $ StaticConfig static
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mkDynamicConfig cmdrunner (Just cmd) _ = do
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tmvar <- newEmptyTMVar
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return $ DynamicConfig (cmdrunner cmd, tmvar)
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getDynamicConfig :: DynamicConfig a -> IO a
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getDynamicConfig (StaticConfig v) = return v
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getDynamicConfig (DynamicConfig (a, tmvar)) =
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go =<< atomically (tryReadTMVar tmvar)
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where
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go Nothing = do
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v <- a
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atomically $ do
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_ <- tryTakeTMVar tmvar
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putTMVar tmvar v
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return v
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go (Just v) = return v
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type CommandRunner a = String -> IO a
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successfullCommandRunner :: CommandRunner Bool
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successfullCommandRunner cmd = boolSystem "sh" [Param "-c", Param cmd]
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unsuccessfullCommandRunner :: CommandRunner Bool
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unsuccessfullCommandRunner cmd = not <$> successfullCommandRunner cmd
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readCommandRunner :: Read a => CommandRunner (Maybe a)
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readCommandRunner cmd = readish <$> readProcess "sh" ["-c", cmd]
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