Fix an issue where multiple identical figures would result in a race condition to write to the same output file (#53)

Author: LaurentRDC

.github/workflows/ci.yml

@@ -187,6 +187,12 @@ jobs:
           exit 1
         fi
         pandoc-plot clean tests/issue46.md
+        
+        pandoc --filter pandoc-plot -i tests/issue53.md -t native
+        if [ $(ls "plots" | wc -l) != 2 ]; then
+          exit 1
+        fi
+        pandoc-plot clean tests/issue53.md
     
     - name: Build documentation
       run: source tools/mkmanual.sh

src/Text/Pandoc/Filter/Plot/Monad.hs

@@ -126,7 +126,10 @@ data RuntimeEnv = RuntimeEnv
   { envFormat :: Maybe Format, -- pandoc output format
     envConfig :: Configuration,
     envLogger :: Logger,
-    envCWD :: FilePath
+    envCWD :: FilePath,
+    -- The following lock prevents from writing to the same file multiple times.
+    -- This is a rather crude fix for issue #53.
+    envIOLock :: MVar ()
   }
 
 -- | Get access to configuration within the @PlotM@ monad.
@@ -137,12 +140,13 @@ asksConfig f = asks (f . envConfig)
 runPlotM :: Maybe Format -> Configuration -> PlotM a -> IO a
 runPlotM fmt conf v = do
   cwd <- getCurrentDirectory
+  sem <- newMVar ()
   st <-
     PlotState <$> newMVar mempty
   let verbosity = logVerbosity conf
       sink = logSink conf
   withLogger verbosity sink $
-    \logger -> runReaderT (evalStateT v st) (RuntimeEnv fmt conf logger cwd)
+    \logger -> runReaderT (evalStateT v st) (RuntimeEnv fmt conf logger cwd sem)
 
 -- | maps a function, performing at most @N@ actions concurrently.
 mapConcurrentlyN :: Traversable t => Int -> (a -> PlotM b) -> t a -> PlotM (t b)

src/Text/Pandoc/Filter/Plot/Renderers.hs

@@ -149,7 +149,7 @@ availableToolkitsM = asNonStrictAndSilent $ do
         else return Nothing
     return $ catMaybes mtks
   where
-    asNonStrictAndSilent = local (\(RuntimeEnv f c l d) -> RuntimeEnv f (c{strictMode = False}) (l{lVerbosity = Silent}) d)
+    asNonStrictAndSilent = local (\(RuntimeEnv f c l d s) -> RuntimeEnv f (c{strictMode = False}) (l{lVerbosity = Silent}) d s)
 
     -- | Check that the supplied command results in
     -- an exit code of 0 (i.e. no errors)

src/Text/Pandoc/Filter/Plot/Scripting.hs

@@ -20,6 +20,7 @@ module Text.Pandoc.Filter.Plot.Scripting
   )
 where
 
+import Control.Concurrent.MVar (withMVar)
 import Data.Default (def)
 import Data.Functor.Identity (Identity (..))
 import Data.Hashable (hash)
@@ -114,7 +115,11 @@ runTempScript spec@FigureSpec {..} = do
 
       let scriptWithCapture = rendererCapture renderer_ spec target
 
-      liftIO $ T.writeFile scriptPath scriptWithCapture
+      -- Note the use of a lock. This is a crude solution for issue #53, where
+      -- multiple identical figures can cause a race condition to write to the 
+      -- same output file.
+      sem <- asks envIOLock
+      liftIO $ withMVar sem $ \_ -> T.writeFile scriptPath scriptWithCapture
       let outputSpec =
             OutputSpec
               { oFigureSpec = spec,
@@ -200,7 +205,12 @@ writeSource spec = do
             -- Note that making the document self-contained is absolutely required so that the CSS for
             -- syntax highlighting is included directly in the document.
             t = either (const mempty) id $ runPure (writeHtml5String opts doc >>= makeSelfContained)
-        liftIO $ T.writeFile scp t
+        
+        -- Note the use of a lock. This is a crude solution for issue #53, where
+        -- multiple identical figures can cause a race condition to write to the 
+        -- same output file.
+        sem <- asks envIOLock
+        liftIO $ withMVar sem $ \_ -> T.writeFile scp t
 
   either (err . pack) renderSource $ runIdentity $ compileTemplate mempty sourceTemplate
 

tests/issue53.md

@@ -0,0 +1,42 @@
+
+
+```{.python .matplotlib}
+import matplotlib.pyplot as plt
+plt.plot([1,2,3,4,5])
+```
+
+
+```{.python .matplotlib}
+import matplotlib.pyplot as plt
+plt.plot([1,2,3,4,5])
+```
+
+
+```{.python .matplotlib}
+import matplotlib.pyplot as plt
+plt.plot([1,2,3,4,5])
+```
+
+
+```{.python .matplotlib}
+import matplotlib.pyplot as plt
+plt.plot([1,2,3,4,5])
+```
+
+
+```{.python .matplotlib}
+import matplotlib.pyplot as plt
+plt.plot([1,2,3,4,5])
+```
+
+
+```{.python .matplotlib}
+import matplotlib.pyplot as plt
+plt.plot([1,2,3,4,5])
+```
+
+
+```{.python .matplotlib}
+import matplotlib.pyplot as plt
+plt.plot([1,2,3,4,5])
+```