Bug 58179 - Atomicity violation
Atomicity violation
Product: Tomcat 7
Classification: Unclassified
Component: Catalina
PC Linux
: P2 normal (vote)
: ---
Assigned To: Tomcat Developers Mailing List
Depends on:
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Reported: 2015-07-24 14:54 UTC by Bai Guangdong
Modified: 2015-07-27 10:25 UTC (History)
0 users


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Description Bai Guangdong 2015-07-24 14:54:37 UTC
My name is Bai Guangdong, a research fellow from National University of Singapore. I find an atomicity violation similar to bug 53498. 

The problem occurs in the same file java/org/apache/catalina/core/ApplicationContext.java. Look at the code snippet below. 

L791         oldValue = attributes.get(name);
L792         if (oldValue != null)
L793             replaced = true;
L794         attributes.put(name, value);
...          ... 
L801         if (replaced)
L802             event =
L803                 new ServletContextAttributeEvent(context.getServletContext(),
L804                                                  name, oldValue);
L805         else
L806             event =
L807                 new ServletContextAttributeEvent(context.getServletContext(),
L808                                                  name, value);
...          ... 
L816                 if (replaced) {
L817                     context.fireContainerEvent
L818                         ("beforeContextAttributeReplaced", listener);
L819                     listener.attributeReplaced(event);
L820                     context.fireContainerEvent("afterContextAttributeReplaced",
L821                                                listener);
L822                 } else {
L823                     context.fireContainerEvent("beforeContextAttributeAdded",
L824                                                listener);
L825                     listener.attributeAdded(event);
L826                     context.fireContainerEvent("afterContextAttributeAdded",
L827                                                listener);

Suppose two threads T1 and T2 executes this code snippet with the same key ("name"). Initially, "attributes" is empty. T1 executes line 791 and "oldValue" in T1 becomes null. Before T1 executes line 794, T2 executes 791 and "oldValue" in T2 becomes null as well. Then T1 executes line 794, and later T2 replaces T1's "value" at line 794. Afterwards, both T1 and T2 fire the "beforeContextAttributeAdded" event at line 823. However, in the above situation, "replaced" in T2 should be true and "beforeContextAttributeReplaced" should be fired at line 817.
Comment 1 Mark Thomas 2015-07-27 10:25:45 UTC
Thanks for the report.

Fixed in trunk, 8.0.x (for 8.0.25) and 7.0.x (for 7.0.64).