Page History

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This guideline is an instance of FIO04-J. Release resources when they are no longer needed. However, most Java lock objects are not closablecloseable, so they cannot be automatically released using Java 7's try-with-resources feature.

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Code Block

bgColor	#FFcccc

public final class Client {
  public void doSomething(File file) {
    private final Lock lock = new ReentrantLock();

  public void doSomething(File file) {
    InputStream in = null;
    try {
      in = new lock.lockFileInputStream(file);
      in = new FileInputStream(filelock.lock();

      // Perform operations on the open file

      lock.unlock();
    } catch (FileNotFoundException x) {
      // Handle exception
    } finally {
      if (in != null) {
        try {
          in.close();
        } catch (IOException x) {
          // Handle exception
        }  
      }
    }
  }
}

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Code Block

bgColor	#FFcccc

public final class Client {
  public void doSomething(File file) {
    private final Lock lock = new ReentrantLock();

  public void doSomething(File file) {
    InputStream in = null;
    try {
      in = new FileInputStream(file);
      lock.lock();
      // Perform operations on the open file
    } catch (FileNotFoundException fnf) {
      // Forward to handler
    } finally {
      lock.unlock();
      if (in != null) {
        try {
          in.close();
        } catch (IOException e) {
          // Forward to handler
        }
      }
    }
  }
}

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Code Block

bgColor	#ccccff

public final class Client {
  public void doSomething(File file) {
   private final Lock lock = new ReentrantLock();

  public void doSomething(File file) {
    InputStream in = null;
    lock.lock();
    try {
      in = new FileInputStream(file);
      // Perform operations on the open file
    } catch (FileNotFoundException fnf) {
      // Forward to handler
    } finally {
      lock.unlock();

      if (in != null) {
        try {
          in.close();
        } catch (IOException e) {
          // Forward to handler
        }
      }
    }
  }
}

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Code Block

bgColor	#ccccff

public interface LockAction {
  void doSomethingWithFile(InputStream in);
}

public final class ReentrantLockAction {
  private static final Lock lock = new ReentrantLock();

  public static void doSomething(File file, LockAction action)  {
    Lock lock = new ReentrantLock();
    InputStream in = null;
    lock.lock();
    try {
      in = new FileInputStream(file);
      action.doSomethingWithFile(in);
    } catch (FileNotFoundException fnf) {
      // Forward to handler
    } finally {
      lock.unlock();

      if (in != null) {
        try {
          in.close();
        } catch (IOException e) {
          // Forward to handler
        }
      }
    }
  }
}

public final class Client {
  public void doSomething(File file) {
    ReentrantLockAction.doSomething(file, new LockAction() {
      public void doSomethingWithFile(InputStream in) {
        // Perform operations on the open file
      }
    });
  }
}

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Code Block

bgColor	#FFcccc

final class DateHandler {

  private final Date date = new Date();

  private final Lock lock = new ReentrantLock();

  // str could be null
  public void doSomething(String str) {
    lock.lock();
    String dateString = date.toString();
    if (str.equals(dateString)) {
      // ...
    }
    // ...

    lock.unlock();
  }
}

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Code Block

bgColor	#ccccff

final class DateHandler {

  private final Date date = new Date();

  private final Lock lock = new ReentrantLock();

  // str could be null
  public void doSomething(String str) {
    lock.lock();
    try {
      String dateString = date.toString();
      if (str != null && str.equals(dateString)) {
        // ...
      }
      // ...

    } finally {
      lock.unlock();
    }
  }
}

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Failure to release locks on exceptional conditions could lead to thread starvation and deadlock.

Rule	Severity	Likelihood	Remediation Cost	Priority	Level
LCK08-J	Low	Likely	Low	P9	L2

Automated Detection

Some static analysis tools are capable of detecting violations of this rule.

Tool

Version

Checker

Description

Parasoft Jtest

Include Page

	Parasoft_V
	Parasoft_V

CERT.LCK08.RLF
CERT.LCK08.LOCK

Release Locks in a "finally" block
Do not abandon unreleased locks

ThreadSafe

Include Page

	ThreadSafe_V
	ThreadSafe_V

CCE_LK_UNRELEASED_ON_EXN

Implemented

Related Vulnerabilities

The GERONIMO-2234 issue report describes a vulnerability in the Geronimo application server. If the user single-clicks the keystore portlet, the user will lock the default keystore without warning. This causes a crash and stack trace to be produced. Furthermore, the server cannot be restarted because the lock is never cleared.