High CPU in java.util.regex.Matcher

Environment

• JBoss Enterprise Application Platform (EAP)

Issue

• High CPU is seen in threads making calls to java.util.regex.Matcher:

"http-0.0.0.0-8080-1" daemon prio=10 tid=0x00000000499c9000 nid=0x1672 runnable [0x000000006880a000]
   java.lang.Thread.State: RUNNABLE
        ...
	at java.util.regex.Pattern$Curly.match0(Pattern.java:3782)
	at java.util.regex.Pattern$Curly.match(Pattern.java:3744)
	at java.util.regex.Pattern$Ques.match(Pattern.java:3691)
	at java.util.regex.Pattern$GroupHead.match(Pattern.java:4168)
	at java.util.regex.Pattern$Loop.match(Pattern.java:4295)
	at java.util.regex.Pattern$GroupTail.match(Pattern.java:4227)
	at java.util.regex.Pattern$Curly.match0(Pattern.java:3782)
	at java.util.regex.Pattern$Curly.match(Pattern.java:3744)
	at java.util.regex.Pattern$Ques.match(Pattern.java:3691)
	at java.util.regex.Pattern$GroupHead.match(Pattern.java:4168)
	at java.util.regex.Pattern$Loop.matchInit(Pattern.java:4314)
	at java.util.regex.Pattern$Prolog.match(Pattern.java:4251)
	at java.util.regex.Pattern$Curly.match0(Pattern.java:3782)
	at java.util.regex.Pattern$Curly.match(Pattern.java:3744)
	at java.util.regex.Pattern$Begin.match(Pattern.java:3120)
	at java.util.regex.Matcher.match(Matcher.java:1127)
	at java.util.regex.Matcher.matches(Matcher.java:502)

Resolution

• java.util.regex.Matcher is not a thread safe object so ensure each thread uses its own instance of the Matcher
• If sharing a single Matcher across multiple threads, ensure access to it is synchronized and call Matcher.reset() in between uses
• Improve efficiency of the regex patterns used

Root Cause

• Concurrent access to a single instance of java.util.regex.Matcher
• Weighty, inefficient regex patterns used

Diagnostic Steps

• Troubleshoot with CPU data and other diagnostic steps as described in Java application high CPU
• If unsure of the regex involved in these high CPU calls, capture a heap dump as well. Then after identifying the high CPU thread, inspect the underlying Pattern and Matchers in use by this thread in the heap dump to identify any problematic regex.

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