55 lines
1.5 KiB
Haskell
55 lines
1.5 KiB
Haskell
{-# LANGUAGE BangPatterns #-}
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-- | This module defines a type for mutable, integer-valued gauges.
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-- Gauges are variable values and can be used to track e.g. the
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-- current number of concurrent connections. All operations on gauges
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-- are thread-safe.
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module System.Remote.Gauge
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(
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Gauge
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, inc
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, dec
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, add
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, subtract
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, set
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, modify
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) where
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import Data.IORef (atomicModifyIORef)
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import Prelude hiding (subtract)
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import System.Remote.Gauge.Internal
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-- | Increase the gauge by one.
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inc :: Gauge -> IO ()
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inc (C ref) = do
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!_ <- atomicModifyIORef ref $ \ n -> let n' = n + 1 in (n', n')
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return ()
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-- | Decrease the gauge by one.
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dec :: Gauge -> IO ()
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dec (C ref) = do
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!_ <- atomicModifyIORef ref $ \ n -> let n' = n - 1 in (n', n')
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return ()
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-- | Increase the gauge by the given amount.
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add :: Gauge -> Int -> IO ()
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add (C ref) i = do
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!_ <- atomicModifyIORef ref $ \ n -> let n' = n + i in (n', n')
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return ()
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-- | Decrease the gauge by the given amount.
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subtract :: Gauge -> Int -> IO ()
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subtract (C ref) i = do
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!_ <- atomicModifyIORef ref $ \ n -> let n' = n - i in (n', n')
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return ()
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-- | Set the gauge to the given value.
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set :: Gauge -> Int -> IO ()
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set (C ref) !i = atomicModifyIORef ref $ \ _ -> (i, ())
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-- | Set the gauge to the result of applying the given function to the
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-- value.
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modify :: (Int -> Int) -> Gauge -> IO ()
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modify f (C ref) = do
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!_ <- atomicModifyIORef ref $ \ i -> let i' = f i in (i', i')
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return ()
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