From 6e8c2b8df3898d0f50463f3151831f5d7c9306a2 Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom@tomsmeding.com>
Date: Sun, 2 Aug 2026 20:19:10 +0100
Subject: Index logs in parallel

---
 src/Index.hs    |  3 ++-
 src/Parallel.hs | 30 ++++++++++++++++++++++++++++++
 tirclogv.cabal  |  3 ++-
 3 files changed, 34 insertions(+), 2 deletions(-)
 create mode 100644 src/Parallel.hs

diff --git a/src/Index.hs b/src/Index.hs
index 81eb5f2..ee3cdaf 100644
--- a/src/Index.hs
+++ b/src/Index.hs
@@ -56,6 +56,7 @@ import Cache
 import Config (Channel(..), prettyChannel)
 import ImmutGrowVector qualified as IGV
 import Mmap
+import Parallel
 import Util
 import ZNC.Parser
 
@@ -151,7 +152,7 @@ initIndex basedir toimport = do
       let nw = T.unpack nwT
           ch = T.unpack chT
       files <- listDirectory (basedir </> nw </> ch)
-      days <- fmap sort . forM (sort files) $ \fn -> do
+      days <- fmap sort . parallelForM (sort files) $ \fn -> do
         -- atomicPrintS $ " -> " ++ fn
         let path = basedir </> nw </> ch </> fn
             date = case parseFileName fn of
diff --git a/src/Parallel.hs b/src/Parallel.hs
new file mode 100644
index 0000000..cc6eb22
--- /dev/null
+++ b/src/Parallel.hs
@@ -0,0 +1,30 @@
+module Parallel where
+
+import Control.Concurrent
+import Control.Monad (replicateM_)
+import Data.IORef
+
+
+-- | Does not return results in-order.
+parallelForM :: [a] -> (a -> IO b) -> IO [b]
+parallelForM inputList action = do
+  nthread <- getNumCapabilities
+
+  listref <- newIORef inputList
+  outref <- newIORef []
+  donechan <- newChan
+  replicateM_ nthread $ forkIO $
+    let loop = do
+          mitem <- atomicModifyIORef' listref (\case l@[] -> (l, Nothing)
+                                                     item : l -> (l, Just item))
+          case mitem of
+            Just item -> do
+              res <- action item
+              atomicModifyIORef' outref (\l -> (res : l, ()))
+              loop
+            Nothing -> do
+              writeChan donechan ()
+    in loop
+
+  replicateM_ nthread $ readChan donechan
+  reverse <$> readIORef outref
diff --git a/tirclogv.cabal b/tirclogv.cabal
index 2cb0831..26c676e 100644
--- a/tirclogv.cabal
+++ b/tirclogv.cabal
@@ -31,6 +31,7 @@ executable tirclogv
     Mmap
     Pages
     Pages.TH
+    Parallel
     Util
     -- ZNC.Slow
     ZNC.Parser
@@ -63,7 +64,7 @@ executable tirclogv
   -- necessary so profiling works:
   other-extensions:
     TemplateHaskell
-  ghc-options: -threaded
+  ghc-options: -threaded -rtsopts
 
 library escapexml
   import: common
-- 
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