Holding locks while performing time-consuming or blocking operations can severely degrade system performance and can result in starvation. Furthermore, deadlock can result if interdependent threads block indefinitely. Blocking operations include network, file, and console I/O (for example, Console.readLine()) and object serialization. Deferring a thread indefinitely also constitutes a blocking operation. Consequently, programs must not perform blocking operations while holding a lock.
When the JVM interacts with a file system that operates over an unreliable network, file I/O might incur a large performance penalty. In such cases, avoid file I/O over the network while holding a lock. File operations (such as logging) that could block waiting for the output stream lock or for I/O to complete could be performed in a dedicated thread to speed up task processing. Logging requests can be added to a queue, assuming that the queue's put() operation incurs little overhead as compared to file I/O [Goetz 2006].
Noncompliant Code Example (Deferring a Thread)
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According to the Java API class Object documentation [API 2006]
Note that the
waitmethod, as it places the current thread into the wait set for this object, unlocks only this object; any other objects on which the current thread may be synchronized remain locked while the thread waits. This method should only be called by a thread that is the owner of this object's monitor.
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Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
LCK09-J | low | probable | high | P2 | L3 |
Related Guidelines
Bibliography
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