CWE-609: Double-Checked Locking
Description
The product uses double-checked locking to access a resource without the overhead of explicit synchronization, but the locking is insufficient.
Submission Date :
May 7, 2007, midnight
Modification Date :
2023-06-29 00:00:00+00:00
Organization :
MITRE
Extended Description
Double-checked locking refers to the situation where a programmer checks to see if a resource has been initialized, grabs a lock, checks again to see if the resource has been initialized, and then performs the initialization if it has not occurred yet. This should not be done, as it is not guaranteed to work in all languages and on all architectures. In summary, other threads may not be operating inside the synchronous block and are not guaranteed to see the operations execute in the same order as they would appear inside the synchronous block.
Example - 1
It may seem that the following bit of code achieves thread safety while avoiding unnecessary synchronization... The programmer wants to guarantee that only one Helper() object is ever allocated, but does not want to pay the cost of synchronization every time this code is called. Suppose that helper is not initialized. Then, thread A sees that helper==null and enters the synchronized block and begins to execute: If a second thread, thread B, takes over in the middle of this call and helper has not finished running the constructor, then thread B may make calls on helper while its fields hold incorrect values.helper = new Helper();if (helper == null) {}synchronized (this) {}
if (helper == null) {}return helper;helper = new Helper();
Related Weaknesses
This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined to give an overview of the different insight to similar items that may exist at higher and lower levels of abstraction.
Visit http://cwe.mitre.org/ for more details.