CWE-543: Use of Singleton Pattern in a Non-thread-safe Manner
Use of Singleton Pattern in a Non-thread-safe Manner
Weakness ID: 543 (Weakness Variant)
Status: Incomplete
Description
Description Summary
The use of a singleton pattern may not be
thread-safe.
Time of Introduction
Implementation
Applicable Platforms
Languages
Java
Demonstrative Examples
Example 1
This method is part of a singleton pattern, yet the following
singleton() pattern is not thread-safe. It fails to ensure the creation of
only one object.
(Bad Code)
Java
private static NumberConverter singleton;
public static NumberConverter get_singleton() {
if (singleton == null) singleton = new
NumberConverter();
return singleton;
}
Consider the following course of events: Thread A enters the method,
finds singleton to be null, begins the NumberConverter constructor, and
then is swapped out of execution. Thread B enters the method and finds
that singleton remains null. This will happen if A was swapped out
during the middle of the constructor, for the object reference is not
set to point at the new object on the heap until the object is fully
initialized. Thread B continues and constructs another NumberConverter
object and returns it while exiting the method. Thread A continues,
finishes constructing its NumberConverter object, and returns its
version. It created and returned two different objects. Many programmers
turned to the double-check pattern to avoid the overhead of a
synchronized call, which is an extension of the one employed, until it
too was shown to be not thread-safe.
Potential Mitigations
Phase
Description
Use Thread-Specific Storage Pattern
In multithreading environments, storing user data in Servlet member
fields introduces a data access race condition. Do not use member fields
to store information in the Servlet.
Description
