ghc-eventlog-loopback

This library provides a low overhead way to consume GHC's eventlog from inside the application that is emitting it.

Normally an eventlog is written to a file (controlled by the -ol RTS flag). This file must be stored and the processed.

eventlog-socket provides an alternative workflow where a user can create a persistent socket. Processing applications can then connect to this socket and see a valid stream of the eventlog.

Both of these options require managing either a file or a socket. This requires an extra operation overhead.

ghc-eventlog-loopback provides different trade-offs. It allows you to stream an application's eventlog into the application itself, so no extra external resource needs to be managed. It comes with the risk that eventlog processing can overwhelm an application. Users of the library should be careful to ensure that they can process the eventlog faster than it is output.

Example

To instrument your application you should do something like the following:

import Control.Monad
import GHC.RTS.Events.Loopback
import Control.Concurrent
process :: ByteString -> IO ()
...
main = do
 void . forkIO . forever $ readEventLogChunk >>= process
 start
 ...