Simon M writes back in 2016 > Related to this, I think it's about time we made -threaded the default. We could add a -single-threaded option to get back the old behaviour. > > There is a small overhead to using -threaded, but -threaded is also required to make a lot of things work (e.g. waitForProcess in a multithreaded program, not to mention parallelism). All that needs doing is to add a flag `-single-threaded` to enable the old behaviour and a deprecation warning alerting uses that `-threaded` is the new default. https://mail.haskell.org/pipermail/ghc-devs/2016-October/013101.html <details><summary>Trac metadata</summary> | Trac field | Value | | ---------------------- | ------------ | | Version | 8.6.3 | | Type | Task | | TypeOfFailure | OtherFailure | | Priority | normal | | Resolution | Unresolved | | Component | Compiler | | Test case | | | Differential revisions | | | BlockedBy | | | Related | | | Blocking | | | CC | | | Operating system | | | Architecture | | </details> <!-- {"blocked_by":[],"summary":"Make -threaded the default","status":"New","operating_system":"","component":"Compiler","related":[],"milestone":"","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"8.6.3","keywords":["newcomer"],"differentials":[],"test_case":"","architecture":"","cc":[""],"type":"Task","description":"Simon M writes back in 2016\r\n\r\n> Related to this, I think it's about time we made -threaded the default. We could add a -single-threaded option to get back the old behaviour.\r\n>\r\n> There is a small overhead to using -threaded, but -threaded is also required to make a lot of things work (e.g. waitForProcess in a multithreaded program, not to mention parallelism).\r\n\r\nAll that needs doing is to add a flag `-single-threaded` to enable the old behaviour and a deprecation warning alerting uses that `-threaded` is the new default.\r\n\r\nhttps://mail.haskell.org/pipermail/ghc-devs/2016-October/013101.html","type_of_failure":"OtherFailure","blocking":[]} -->