https://bz.apache.org/bugzilla/show_bug.cgi?id=57959
Bug ID: 57959
Summary: Deadlock in FileHandler.java when log is rotated
Product: Tomcat 7
Version: 7.0.62
Hardware: PC
OS: Linux
Status: NEW
Severity: major
Priority: P2
Component: Catalina
Assignee: [email protected]
Reporter: [email protected]
Tomcat 7 will deadlock when a log file is rotated. This issue has been fixed
in latest tomcat 6 and tomcat 8 but not in tomcat 7.
The issue is in following code
(apache-tomcat-7.0.62-src/java/org/apache/juli/FileHandler.java:188)
} finally {
writerLock.writeLock().unlock();
// Down grade to read-lock. This ensures the writer remains
valid
// until the log message is written
writerLock.readLock().lock();
}
}
Despite the comment the order is wrong, you have to acquire a read lock then
release write lock to make sure the race condition does not occur.
The correct way to do it is:
} finally {
writerLock.readLock().lock();
writerLock.writeLock().unlock();
}
}
In tomcat 6
(apache-tomcat-6.0.44-src/java/org/apache/juli/FileHandler.java:187) and tomcat
8 (apache-tomcat-8.0.22-src/java/org/apache/juli/FileHandler.java:186) the
order is correct.
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