CWE

Double-Checked Locking

ID: 609		Date: (C)2012-05-14   (M)2022-10-10
Type: weakness		Status: DRAFT
Abstraction Type: Base

Description

The program uses double-checked locking to access a resource without the overhead of explicit synchronization, but the locking is insufficient.

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 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.

Applicable Platforms
Language: Java

Time Of Introduction

• Implementation

Common Consequences

Scope	Technical Impact	Notes
Integrity Other	Modify application data Alter execution logic

Detection Methods
None

Potential Mitigations

Phase	Strategy	Description	Effectiveness	Notes
Implementation		While double-checked locking can be achieved in some languages, it is inherently flawed in Java before 1.5, and cannot be achieved without compromising platform independence. Before Java 1.5, only use of the synchronized keyword is known to work. Beginning in Java 1.5, use of the "volatile" keyword allows double-checked locking to work successfully, although there is some debate as to whether it achieves sufficient performance gains. See references.

Relationships

Related CWE	Type	View	Chain
CWE-609 ChildOf CWE-894	Category	CWE-888

Demonstrative Examples   (Details)

1. It may seem that the following bit of code achieves thread safety while avoiding unnecessary synchronization... (Demonstrative Example Id DX-70)

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings

Taxynomy	Id	Name	Fit
CERT Java Secure Coding	LCK10-J	Do not use incorrect forms of the double-checked locking idiom

References:

1. David Bacon et al .The "Double-Checked Locking is Broken" Declaration.
2. Jeremy Manson and Brian Goetz .JSR 133 (Java Memory Model) FAQ.
3. Mark Dowd John McDonald Justin Schuh .The Art of Software Security Assessment 1st Edition. Addison Wesley. Section:'Chapter 13, "Threading Vulnerabilities", Page 815.'. Published on 2006.