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Reliance on {{ConcurrentModificationException}} is insufficient to stop side effects resulting from modifying an underlying Collection while simultaneously iterating over the collection. The fail-fast behavior may occur only after processing an arbitrary number of elements. In _Java Concurrency In Practice_ \[[Goetz 2006|AA. Bibliography#Goetz 06]\], GöetzGoetz et al. note "\[Fail-fast iterators\] are implemented by associating a modification count with the collection: if the modification count changes during iteration, {{hasNext}} or {{next}} throws {{ConcurrentModificationException}}. However, this check is done without synchronization, so there is a risk of seeing a stale value of the modification count and therefore that the iterator does not realize a modification has been made. This was a deliberate design tradeoff to reduce the performance impact of the concurrent modification detection code." |
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This noncompliant code example (based on a SDN 2008 bug report 6687277) uses the Collection's remove() method to remove an element from an ArrayList while iterating over the ArrayList. The resulting behavior is unspecified.
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<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="6ae2a01139fa4f25-21e99475-41404223-a2708899-f85d84088a7f4210c3637313"><ac:plain-text-body><![CDATA[ | [[SDN 2008 | AA. Bibliography#SDN 08]] | [Sun Bug database, Bug ID:6687277 | http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6687277] | ]]></ac:plain-text-body></ac:structured-macro> |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="748107a2d05bf48d-a8d97faa-4cf24c8a-9ba28a40-975bff485f4a47638233f6b8"><ac:plain-text-body><![CDATA[ | [[Goetz 2006 | AA. Bibliography#Goetz 06]] | 5.1.2. Iterators and Concurrentmodificationexception | ]]></ac:plain-text-body></ac:structured-macro> |
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