Version 14 (modified by dons, 6 years ago) (diff)



EventLog is a fast, extensible event logging framework in the GHC run-time system (RTS) to support profiling of GHC run-time events. The GHC User's Guide describes how to enable event logging, after the program is linked with eventlog.

An example:

$ ghc -O -eventlog -rtsopts A.hs --make
$ ./A +RTS -l

.. produces A.eventlog ...

$ $ show-ghc-events A.eventlog 
Event Types:
   0: Create thread (size 4)
   1: Run thread (size 4)
   2: Stop thread (size 6)
   3: Thread runnable (size 4)
   4: Migrate thread (size 6)

Log events in binary format to the file program.eventlog, where flags is a sequence of zero or more characters indicating which kinds of events to log. Currently there is only one type supported: -ls, for scheduler events.

The format of the log file is described by the header EventLogFormat.h that comes with GHC, and it can be parsed in Haskell using the ghc-events library. To dump the contents of a .eventlog file as text, use the tool show-ghc-events that comes with the ghc-events package.


  • EventLog framework is located in ghc_root/rts/eventlog/
  • A ghc-events library to parse EventLog files for any visualizer, which relies upon the Data.Binary library.
  • Visualizer: ThreadScope

Code repository



  • Satnam Singh
  • Simon Marlow
  • Donnie Jones <donnie@…>