java.util.ConcurrentModificationException when running AssetCompile in parallel

[musketyr]

If there are multiple assetCompile tasks running in parallel then they may fail with a following error. I assume the issue is that the resolvers are hold in the static field.

Caused by: java.util.ConcurrentModificationException: (No message provided)	
at asset.pipeline.AssetHelper.fileForUri(AssetHelper.groovy:50)	
at asset.pipeline.AssetHelper.fileForUri(AssetHelper.groovy)	
at asset.pipeline.AssetHelper$fileForUri$8.call(Unknown Source)	
at asset.pipeline.processors.AbstractUrlRewritingProcessor.replacementUrl(AbstractUrlRewritingProcessor.groovy:74)	
at asset.pipeline.processors.HtmlProcessor$_process_closure1.doCall(HtmlProcessor.groovy:64)	
at asset.pipeline.processors.HtmlProcessor.process(HtmlProcessor.groovy:51)	
at asset.pipeline.Processor$process.call(Unknown Source)	
at asset.pipeline.Processor$process.call(Unknown Source)	
at asset.pipeline.AbstractAssetFile.processedStream(AbstractAssetFile.groovy:171)	
at asset.pipeline.AbstractAssetFile.processedStream(AbstractAssetFile.groovy)	
at asset.pipeline.DirectiveProcessor.fileContents(DirectiveProcessor.groovy:305)	
at asset.pipeline.DirectiveProcessor$fileContents$1.callCurrent(Unknown Source)	
at asset.pipeline.DirectiveProcessor$fileContents$1.callCurrent(Unknown Source)	
at asset.pipeline.DirectiveProcessor.loadContentsForTree(DirectiveProcessor.groovy:127)	
at asset.pipeline.DirectiveProcessor.compile(DirectiveProcessor.groovy:65)	
at asset.pipeline.DirectiveProcessor$compile$0.call(Unknown Source)	
at asset.pipeline.DirectiveProcessor$compile$0.call(Unknown Source)	
at asset.pipeline.AssetCompiler$_compile_closure4.doCall(AssetCompiler.groovy:160)