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Consequently, programs must not directly invoke a Thread object's run() method.

Noncompliant Code Example

This noncompliant code example explicitly invokes run() in the context of the current thread.

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The newly created thread is never started because of the incorrect assumption that run() starts the new thread. Consequently, the statements in the run() method are executed by the current thread rather than by the new thread.

Compliant Solution

This compliant solution correctly uses the start() method to tell the Java runtimes to start a new thread.

public final class Foo implements Runnable {
  @Override public void run() {
    // ...
  }

  public static void main(String[] args) {
    Foo foo = new Foo();
    new Thread(foo).start();
  }
}

Exceptions

THI02THI00-EX0: The run() method may be invoked when unit testing functionality. Note that this method cannot be used to test a class for multithreaded use.

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Casting a thread to Runnable before calling the run() method documents that the explicit call to Thread.run() is intentional. Adding an explanatory comment alongside the invocation is highly recommended.

THI02THI00-EX1: Runtime system code involved in starting new threads is permitted to invoke a Thread object's run() method directly; this is an obvious necessity for a working Java runtime system. Note that the likelihood that this exception applies to user-written code is vanishingly small.

Risk Assessment

Failing to start threads correctly can cause unexpected behavior.

Automated Detection

Automated detection of direct invocations of Thread object's run() methods appears to be straightforward. Sound automated determination of which specific invocations are permitted may be infeasible. Heuristic approaches may be useful.

Related Guidelines

Bibliography

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