SEI CERT Oracle Coding Standard for Java

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It is critical to ensure that threads are activated correctly. Thread activation can be misleading because sometimes the code appears to be performing the function correctly, whereas it may be operating in the presence of subtle concurrency issues.

It is usually a mistake to invoke the run() method on a Thread object. When invoked directly, the statements in the run() method execute, however, in the current thread instead of the newly created thread. Furthermore, if the Thread object is not constructed from a Runnable object but by instantiating a subclass of Thread that does not override the run() method, a call to the subclass's run() method invokes Thread.run() which does not perform any useful operations.

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It is recommended that if you have a Thread object that extends Runnable, and you wish to execute the object's run() method in the current thread, first cast the object to a Runnable and then invoke run().

Noncompliant Code Example

The run() method of interface Runnable must be invoked in its own thread, however, this noncompliant code example explicitly invokes it in the context of the current thread. 

class Foo implements Runnable {
  public void run() {
    // ...
  }
  
  public static void main(String[] args) {
    Foo f = new foo();
    new Thread(f).run();
  }
}

The start() method is not invoked on the new thread because of the incorrect assumption that run() activates the thread. Consequently, the statements in the run() method execute, however, in the same thread instead of the new one.

Compliant Solution

This compliant solution correctly uses the start() method to start a new thread which then executes the run() method.

class Foo implements Runnable {
  public void run() {
    // ...
  }
  
  public static void main(String[] args) {
    Foo f = new foo();
    new Thread(f).start();
  }
}

Exceptions

EX1: The Thread.run() method may be used when unit testing the functionality of the run() method of a class. Note that a class cannot be tested for multithreaded use by invoking Thread.run().

Risk Assessment

Failing to activate threads correctly can cause unexpected behavior.

Rule

Severity

Likelihood

Remediation Cost

Priority

Level

CON05- J

low

probable

medium

P4

L3

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

[[API 06]] Interface Runnable and class Thread

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