CLDR-17014 Make ExtraPaths.getInstance synchronized

[btangmu]

-ConcurrentModificationException was thrown when ExtraPaths.getInstance called computeIfAbsent during cldr-generate-json.sh

-Unable to repro the exception before making this change; anyway, this should prevent it

CLDR-17014

• This PR completes the ticket.

ALLOW_MANY_COMMITS=true

[btangmu]

FYI the stack trace was as follows, called from Ldml2JsonConverter.mapPathsToSections

📂#######################  main #######################
📍 main (step 1/9)	[000%]:	 ⚙️ Beginning parallel process of 1,067 files
[WARNING] 
com.google.common.util.concurrent.UncheckedExecutionException: com.google.common.util.concurrent.UncheckedExecutionException: Bad path: //ldml/numbers/otherNumberingSystems/traditional
    at jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0 (Native Method)
    at jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance (NativeConstructorAccessorImpl.java:62)
    at jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance (DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance (Constructor.java:490)
    at java.util.concurrent.ForkJoinTask.getThrowableException (ForkJoinTask.java:600)
    at java.util.concurrent.ForkJoinTask.reportException (ForkJoinTask.java:678)
    at java.util.concurrent.ForkJoinTask.invoke (ForkJoinTask.java:737)
    at java.util.stream.Nodes.collect (Nodes.java:336)
    at java.util.stream.ReferencePipeline.evaluateToNode (ReferencePipeline.java:109)
    at java.util.stream.AbstractPipeline.evaluate (AbstractPipeline.java:545)
    at java.util.stream.AbstractPipeline.evaluateToArrayNode (AbstractPipeline.java:260)
    at java.util.stream.ReferencePipeline.toArray (ReferencePipeline.java:517)
    at java.util.stream.ReferencePipeline.toArray (ReferencePipeline.java:523)
    at org.unicode.cldr.json.Ldml2JsonConverter.processDirectory (Ldml2JsonConverter.java:2288)
    at org.unicode.cldr.json.Ldml2JsonConverter.processType (Ldml2JsonConverter.java:337)
    at org.unicode.cldr.json.Ldml2JsonConverter.main (Ldml2JsonConverter.java:300)
    at org.codehaus.mojo.exec.ExecJavaMojo$1.run (ExecJavaMojo.java:254)
    at java.lang.Thread.run (Thread.java:829)
Caused by: com.google.common.util.concurrent.UncheckedExecutionException: Bad path: //ldml/numbers/otherNumberingSystems/traditional
    at org.unicode.cldr.util.CLDRFile.getStringValue (CLDRFile.java:612)
    at org.unicode.cldr.util.CLDRFile.getWinningValue (CLDRFile.java:2898)
    at org.unicode.cldr.json.Ldml2JsonConverter.mapPathsToSections (Ldml2JsonConverter.java:555)
    at org.unicode.cldr.json.Ldml2JsonConverter.lambda$processDirectory$20 (Ldml2JsonConverter.java:2258)
    at java.util.stream.ReferencePipeline$3$1.accept (ReferencePipeline.java:195)
    at java.util.HashMap$KeySpliterator.forEachRemaining (HashMap.java:1621)
    at java.util.stream.AbstractPipeline.copyInto (AbstractPipeline.java:484)
    at java.util.stream.AbstractPipeline.wrapAndCopyInto (AbstractPipeline.java:474)
    at java.util.stream.Nodes$CollectorTask.doLeaf (Nodes.java:2191)
    at java.util.stream.Nodes$CollectorTask.doLeaf (Nodes.java:2157)
    at java.util.stream.AbstractTask.compute (AbstractTask.java:327)
    at java.util.concurrent.CountedCompleter.exec (CountedCompleter.java:746)
    at java.util.concurrent.ForkJoinTask.doExec (ForkJoinTask.java:290)
    at java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec (ForkJoinPool.java:1020)
    at java.util.concurrent.ForkJoinPool.scan (ForkJoinPool.java:1656)
    at java.util.concurrent.ForkJoinPool.runWorker (ForkJoinPool.java:1594)
    at java.util.concurrent.ForkJoinWorkerThread.run (ForkJoinWorkerThread.java:183)
Caused by: java.util.ConcurrentModificationException
    at java.util.HashMap.computeIfAbsent (HashMap.java:1135)
    at org.unicode.cldr.util.ExtraPaths.getInstance (ExtraPaths.java:16)
    at org.unicode.cldr.util.CLDRFile.getRawExtraPathsPrivate (CLDRFile.java:3156)
    at org.unicode.cldr.util.CLDRFile.getRawExtraPaths (CLDRFile.java:3122)
    at org.unicode.cldr.util.CLDRFile.getFallbackPath (CLDRFile.java:731)
    at org.unicode.cldr.util.CLDRFile.getStringValue (CLDRFile.java:591)
    at org.unicode.cldr.util.CLDRFile.getWinningValue (CLDRFile.java:2898)
    at org.unicode.cldr.json.Ldml2JsonConverter.mapPathsToSections (Ldml2JsonConverter.java:555)
    at org.unicode.cldr.json.Ldml2JsonConverter.lambda$processDirectory$20 (Ldml2JsonConverter.java:2258)
    at java.util.stream.ReferencePipeline$3$1.accept (ReferencePipeline.java:195)
    at java.util.HashMap$KeySpliterator.forEachRemaining (HashMap.java:1621)
    at java.util.stream.AbstractPipeline.copyInto (AbstractPipeline.java:484)
    at java.util.stream.AbstractPipeline.wrapAndCopyInto (AbstractPipeline.java:474)
    at java.util.stream.Nodes$CollectorTask.doLeaf (Nodes.java:2191)
    at java.util.stream.Nodes$CollectorTask.doLeaf (Nodes.java:2157)
    at java.util.stream.AbstractTask.compute (AbstractTask.java:327)
    at java.util.concurrent.CountedCompleter.exec (CountedCompleter.java:746)
    at java.util.concurrent.ForkJoinTask.doExec (ForkJoinTask.java:290)
    at java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec (ForkJoinPool.java:1020)
    at java.util.concurrent.ForkJoinPool.scan (ForkJoinPool.java:1656)
    at java.util.concurrent.ForkJoinPool.runWorker (ForkJoinPool.java:1594)
    at java.util.concurrent.ForkJoinWorkerThread.run (ForkJoinWorkerThread.java:183)
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE

[btangmu]

Alternatively, maybe could use ConcurrentHashMap...

[btangmu]

Compare alternative #4321 which uses ConcurrentHashMap -- but fails

[macchiati]

This looks very strange. The extra paths that are added here are all static. That is, they do not depend on any locale data, just on stuff like StandardCodes, which don't vary by locale, and don't vary during any Survey Tool or ConsoleCheck run.

Since they can all be built statically, once, it should be just reformulated to be Bill Pugh Singleton, which is thread-safe and avoids the synchronization overhead. @srl295

[macchiati]

See ticket

[srl295]

First of all, the code change itself here makes sense - the collision was on the hash, and this synchronizes the hash. So merging this PR might make sense to remove the collision immediately..

However, I could only find one call site, in CLDRFile:

        ExtraPaths.getInstance(NameType.LANGUAGE).append(toAddTo);
        ExtraPaths.getInstance(NameType.SCRIPT).append(toAddTo);

So instead of making ExtraPaths synchronized, we could just remove ExtraPaths.getInstance() and have a public static ExtraPaths.append(toAddTo) - that's internally singleton initialized.