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

Noncompliant Code Example

when it is actually being executed by the wrong thread.
Invoking the Thread.start() method instructs the Java runtime to start executing the thread's run() method using the started thread. Invoking a Thread object's run() method directly is incorrect. When a Thread object's run() method is invoked directly, the statements in the run() method are executed by the current thread rather than by the newly created thread. Furthermore, if the Thread object was constructed by instantiating a subclass of Thread that fails to override the run() method rather than constructed from a Runnable object, any calls to the subclass's run() method would invoke Thread.run(), which does nothing. Consequently, programs must not directly invoke a Thread object's run() method.

Noncompliant Code Example

This noncompliant code example explicitly invokes run() 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. :

public final class Foo implements Runnable {
  @Override public void run() {
    // ...
  }
  
  public static void main(String[] args) {
    Foo ffoo = new fooFoo();
    new Thread(ffoo).run();
  }
}

The start() method is not invoked on the new thread newly created thread is never started because of the incorrect assumption that run() activates starts the new thread. Consequently, the statements in the run() method execute, however, in the same thread instead of the new oneare 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 runtime to start a new thread which then executes the run() method.:

public final class Foo implements Runnable {
  @Override public void run() {
    // ...
  }
  
  public static void main(String[] args) {
    Foo ffoo = new fooFoo();
    new Thread(ffoo).start();
  }
}

Risk Assessment

Exceptions

THI00-J-EX0: The run() method may be directly invoked during unit testing. Note that this method cannot be used to test a class for multithreaded use.

Given a Thread object that was constructed with a runnable argument, when invoking the Thread.run() method, the Thread object may be cast to Runnable to eliminate analyzer diagnostics:

public void sampleRunTest() {

  Thread thread = new Thread(new Runnable() {
      @Override public void run() {
        // ...
      }
    });
  
  ((Runnable) thread).run();  // THI00-J-EX0: Does not start a new thread

}

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.

THI00-J-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

Failure to start Failing to activate threads correctly can cause unexpected behavior.

Automated Detection

...

TODO

Related Vulnerabilities

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

References

\[[API 06|AA. Java References#API 06]\] Interface {{Runnable}} and class {{Thread}}

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

Tool	Version	Checker	Description
CodeSonar	Include Page CodeSonar_V CodeSonar_V	JAVA.CONCURRENCY.LOCK.SCTB	Synchronous Call to Thread Body (Java)
Coverity	7.5	DC.THREADING.thread_run	Implemented
Parasoft Jtest	Include Page Parasoft_V Parasoft_V	CERT.THI00.IRUN	Do not call the 'run()' method directly on classes extending 'java.lang.Thread' or implementing 'java.lang.Runnable'
PVS-Studio	Include Page PVS-Studio_V PVS-Studio_V	V6064
SonarQube	Include Page SonarQube_V SonarQube_V	S1217	Thread.run() should not be called directly

Related Guidelines

Android Implementation Details

Android provides a couple of solutions for threading. The Android Developers Blog's article "Painless Threading" discusses those solutions.

Bibliography

...

Image Added Image Added Image AddedCON04-J. Use the private lock object idiom instead of the object's intrinsic lock      11. Concurrency (CON)      CON06-J. Do not defer a thread that is holding a lock