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https://issues.apache.org/jira/browse/TIKA-4393?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17935136#comment-17935136
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Tim Allison commented on TIKA-4393:
-----------------------------------
Thank you for opening this issue. I haven't worked much in this area of the
codebase. On a quick review, it looks like even with a synchronized method, the
underlying map's contents would not be threadsafe -- AbstractConverter
maintains and modifies instance data. For example, in MSOfficeXMLConverter, the
call to {{process(...)}} calls {{super.setMetadata(metadata)}}.
It looks like we need to create new converters for each call to convert or use
threadlocal, which I really want to avoid.
We should add multithreaded tests on the same document type to confirm my above
suspicions from the code review.
WDYT?
> Thread-safety issue in TikaToXMP.getConverterMap()
> --------------------------------------------------
>
> Key: TIKA-4393
> URL: https://issues.apache.org/jira/browse/TIKA-4393
> Project: Tika
> Issue Type: Bug
> Components: tika-app
> Affects Versions: 2.9.3, 3.1.0
> Environment: java 8, fedora 3.9, tika 2.9.3
> Reporter: Ghiles OUAREZKI
> Priority: Minor
>
> h2. Description:
> We execute TikaToXmp conversion in a multithreaded environment where we call
> multiple conversion at the same time. According to new parser contribution
> guide, there is nothing about thread-safety. During our test, a thread-safety
> issue has been found in the getConverterMap() method of the TikaToXMP class
> in the tika-xmp module.
>
> We are currently using the 2.9.3 version. We checked in the latest version
> and we think the behavior is the same.
> h2. Problem:
> The method manipulates the static class variable converterMap, but it is not
> thread-safe. Since there is no synchronization mechanism, multiple threads
> can enter getConverterMap() at the same time and create different instances
> of converterMap, leading to potential race conditions.
> Current code:
> {code:java}
> private static Map<MediaType, Class<? extends ITikaToXMPConverter>>
> converterMap;
> private static Map<MediaType, Class<? extends ITikaToXMPConverter>>
> getConverterMap() {
> if (converterMap == null) {
> converterMap = new HashMap<>();
> initialize();
> }
> return converterMap;
> }
> {code}
> If multiple threads call getConverterMap() simultaneously when converterMap
> is still null, they might create multiple instances of converterMap, which
> can lead to unexpected behavior.
> h2.
> Potential solution:
> To ensure thread safety, we offer a simple patch : to synchronize
> getConverterMap() so that only one thread can initialize converterMap at a
> time. The fix consists of adding the *synchronized* keyword to the method:
> {code:java}
> private static synchronized Map<MediaType, Class<? extends
> ITikaToXMPConverter>> getConverterMap() {
> if (converterMap == null) {
> converterMap = new HashMap<>();
> initialize();
> }
> return converterMap;
> }{code}
>
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