angel-0.2: Angel/Main.hs

module Main where 

import Control.Concurrent (threadDelay, forkIO, forkOS)
import Control.Concurrent
import Control.Concurrent.STM
import Control.Concurrent.STM.TVar (readTVar, writeTVar)
import Control.Concurrent.STM.TChan (newTChan)
import Control.Monad (unless, when, forever)
import System.Environment (getArgs)
import System.Posix.Signals
import System.IO (hSetBuffering, BufferMode(..), stdout, stderr)

import qualified Data.Map as M

import Angel.Log (logger)
import Angel.Config (monitorConfig)
import Angel.Data (GroupConfig(..))
import Angel.Job (pollStale)
import Angel.Files (startFileManager)

-- |Signal handler: when a HUP is trapped, write to the wakeSig Tvar
-- |to make the configuration monitor loop cycle/reload
handleHup :: TVar (Maybe Int) -> IO ()
handleHup wakeSig = atomically $ writeTVar wakeSig $ Just 1

main = do 
    hSetBuffering stdout LineBuffering
    hSetBuffering stderr LineBuffering
    let log = logger "main" 
    log "Angel started"
    args <- getArgs

    -- Exactly one argument required for the `angel` executable
    unless (length args == 1) $ error "exactly one argument required: config file"
    let configPath = head args
    log $ "Using config file: " ++ configPath

    -- Create the TVar that represents the "global state" of running applications
    -- and applications that _should_ be running
    fileReqChan <- atomically $ newTChan
    sharedGroupConfig <- newTVarIO $ GroupConfig M.empty M.empty fileReqChan

    -- The wake signal, set by the HUP handler to wake the monitor loop
    wakeSig <- newTVarIO Nothing
    installHandler sigHUP (Catch $ handleHup wakeSig) Nothing

    -- Fork off an ongoing state monitor to watch for inconsistent state
    forkIO $ pollStale sharedGroupConfig
    forkIO $ startFileManager fileReqChan

    -- Finally, run the config load/monitor thread
    runInUnboundThread $ forever $ monitorConfig configPath sharedGroupConfig wakeSig