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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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{quote} It is imperative that the user manually synchronize on the returned map when iterating over any of its collection views... Failure to follow this advice may result in non-deterministic behavior. |
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{quote} Synchronize on the original {{Collection}} object when using synchronization wrappers. This synchronization is necessary to enforce atomicity ([CON07-J. Do not assume that a grouping of calls to independently atomic methods is atomic]). |
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This also applies to {{java.util.Map}} objects, even though Maps are technically not Collections. h2. |
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Noncompliant Code Example (collection 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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{code | ||
:bgColor | =#FFcccc | } // 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} |
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h2. Compliant Solution (collection lock object) |
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This compliant solution synchronizes on the original {{Collection}} object {{map}} instead of the {{Collection}} view {{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) {
// ...
}
}
}
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Risk Assessment
Synchronizing on a collection view instead of the collection object may cause non-deterministic behavior.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
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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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{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 \[[API 06|AA. Java References#API 06]\] 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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h2. Issue Tracking {dynamictasklist:Review List} ---- [!The CERT Sun Microsystems Secure Coding Standard for Java^button_arrow_left.png!|VOID CON00-J. Synchronize access to shared mutable |
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variables] [!The CERT Sun Microsystems Secure Coding Standard for Java^button_arrow_up.png!|11. Concurrency (CON)] [!The CERT Sun Microsystems Secure Coding Standard for Java^button_arrow_right.png!|CON03-J. Do not use background threads during class initialization] |