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The {{java.util.Collections}} interface's documentation \[[API 06|AA. Java References#API 06]\] warns about the consequences of synchronizing on any view over a collection object, rather than synchronizing on the collection object itself. |
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It
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is
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imperative
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that
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the
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user
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manually
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synchronize
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on
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the
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returned
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map
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when
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iterating
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over
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any
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of
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its
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collection
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views...
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Failure
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to
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follow
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this
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advice
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may
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result
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in
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non-deterministic
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behavior.
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Synchronize on the original Collection object when using synchronization wrappers. This synchronization is necessary to enforce atomicity (CON07-J.
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...
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).
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This
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also
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applies
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to
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java.util.Map
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objects,
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even
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though
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Maps
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are
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technically
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not
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Collections.
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Noncompliant Code Example (collection
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view)
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This noncompliant code example incorrectly synchronizes on the {{set}} view of the synchronized map ({{map}}) instead of the collection object \[[Tutorials 08|AA. Java References#Tutorials 08]\]. |
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} // map has package-private accessibility final Map<Integer, String> map = Collections.synchronizedMap(new HashMap<Integer, String>()); private final Set<Integer> set = map.keySet(); public void doSomething() { synchronized(set) { // Incorrectly synchronizes on set for (Integer k : set) { // ... } } } {code} h2. Compliant Solution |
Compliant Solution (collection
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lock
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object)
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This
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compliant
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solution
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synchronizes
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on
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the
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original
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Collection
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object
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map
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instead
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of
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the
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Collection
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view
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set.
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}}. {code:bgColor=#ccccff} // map has package-private accessibility final Map<Integer, String> map = Collections.synchronizedMap(new HashMap<Integer, String>()); private final Set<Integer> set = map.keySet(); public void doSomething() { synchronized(map) { // Synchronize on map, not set for (Integer k : set) { // ... } } } {code} h2. Risk Assessment Synchronizing on a collection view instead of the collection object may cause non-deterministic behavior. || Rule || Severity || Likelihood || Remediation Cost || Priority || Level || | CON40-J | medium | probable | medium | {color:#cc9900}{*}P8{*}{color} | {color:#cc9900}{*}L2{*}{color} | h3. Related Vulnerabilities Search for vulnerabilities resulting from the violation of this rule on the [CERT website|https://www.kb.cert.org/vulnotes/bymetric?searchview&query=FIELD+KEYWORDS+contains+CON36-J]. h2. References |
Risk Assessment
Synchronizing on a collection view instead of the collection object may cause non-deterministic behavior.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
CON40-J | medium | probable | medium | P8 | L2 |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
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\[[API 06|AA. Java References#API 06]\] Class Collections
\[[Tutorials 08|AA. Java References#Tutorials 08]\] [Wrapper Implementations|http://java.sun.com/docs/books/tutorial/collections/implementations/wrapper.html] |
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Issue
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Tracking
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||Completed||Priority||Locked||CreatedDate||CompletedDate||Assignee||Name||
|F|M|F|1269452979738| |dmohindr|The title could do away with "still"|
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VOID CON00-J. Synchronize access to shared mutable variables 11. Concurrency (CON) CON03-J. Do not use background threads during class initialization