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public final class Client {
  private  lock. This can result in thread starvation and deadlock. According to the Java API \[[API 06|AA. Java References#API 06]\], class {{ReentrantLock}} documentation:

{quote}
A {{ReentrantLock}} is owned by the thread last successfully locking, but not yet unlocking it. A thread invoking {{lock}} will return, successfully acquiring the lock, when the lock is not owned by another thread.
{quote}

This means that an unreleased lock in any thread will stop other threads from acquiring the same lock. 


h2. Noncompliant Code Example (checked exception)

This noncompliant code example protects a resource by using a {{ReentrantLock}} but fails to release the lock on an exceptional condition. Control flow transfers to the {{catch}} block and the call to {{unlock()}} does not execute.

{code:bgColor=#FFcccc}
public void doSomething(File file) {
  final Lock lock = new ReentrantLock();

  public  tryvoid doSomething(File file) {
    InputStream in = lock.lock();
null;
    try {
     InputStream in = new FileInputStream( filefile);
      lock.lock();

      // DoPerform somethingoperations withon the open file.

      lock.unlock();
    } catch (FileNotFoundException fnfx) {
      // Handle the exception
    }
}
{code}

Note that the lock is not released even when the {{doSomething()}} method returns. 


h2. Compliant Solution

This compliant solution uses a {{try}}-{{finally}} block immediately after acquiring the lock. This ensures that the lock is appropriately released even in the event of an exceptional condition. Also, the lock is acquired outside the try block, which guarantees that the lock is held when the finally block executes.

{code:bgColor=#ccccff}
public void doSomething(File file) {
  finally {
      if (in != null) {
        try {
          in.close();
        } catch (IOException x) {
          // Handle exception
        }  
      }
    }
  }
}

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

  lock.lock() public void doSomething(File file) {
    InputStream in = null;
    try {
    InputStream  in = new FileInputStream( filefile);
      lock.lock();
      // DoPerform somethingoperations withon the open file.
    } catch (FileNotFoundException fnf) {
      // HandleForward theto exceptionhandler
    } finally {
      lock.unlock();
  }
}
{code}


h2. Noncompliant Code Example (unchecked exception)

This noncompliant code example uses a {{ReentrantLock}} to protect a {{java.util.Date}} instance, which is not thread-safe by design. It also needs to catch {{Throwable}} to be compliant with [EXC06-J. Do not allow exceptions to transmit sensitive information]. 

{mc} Do not declare lock as private as it need package-wide accessibility for illustrative purposes {mc}

{code:bgColor=#FFcccc}
final class     if (in != null) {
        try {
          in.close();
        } catch (IOException e) {
          // Forward to handler
        }
      }
    }
  }
}

public final class ClientDateHandler {
  private final DateLock datelock = new DateReentrantLock();

  public void doSomething(File file) {
  final  LockInputStream lockin = new ReentrantLock()null;

  public void doSomethingSafely(String str) {lock.lock();
    try {
      in = doSomethingnew FileInputStream(strfile);
      // Perform operations on the open file
    } catch (ThrowableFileNotFoundException tfnf) {
      // Forward to handler
    }
 finally }

  public void doSomething(String str) {
{
      lock.lockunlock();

    String dateString =if date.toString();
    if (str.equals(dateString)(in != null) {
       // ...
 try {
      }
    lockin.unlockclose();
  }
}
{code}

However, because the {{doSomething()}} method does not} checkcatch (IOException e) {
          // Forward to handler
        }
      }
    }
  }
}

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

public final class ReentrantLockAction {
  private staticwhether {{str}} is {{null}}, a runtime exception in this component may prevent the lock from being released.


h2. Compliant Solution

This compliant solution adds a {{finally}} block and moves the {{unlock()}} call into it. 

{code:bgColor=#ccccff}
final class DateHandler {
  private final Date date = new Date();
  final Lock lock = new ReentrantLock();

  public static void doSomethingSafely(String strdoSomething(File file, LockAction action)  {
    InputStream in = null;
    lock.lock();
    try {
      in = new FileInputStream(file);
  doSomething(str    action.doSomethingWithFile(in);
    } catch (ThrowableFileNotFoundException tfnf) {
      // Forward to handler
    } finally {
    }  lock.unlock();

   public   voidif doSomething(String strin != null) {
    try {
   try {
  lock.lock();
      String dateString = datein.toStringclose();
       if } catch (str.equals(dateString)IOException e) {
          // ...
Forward to handler
    }
    } finally {
      lock.unlock();}
    }
  }
}
{code}

Consequently, the lock is released successfully even in the event of a runtime exception. 


h2. Exceptions

*EX1* : Intrinsic locks of class objects are associated with the use of the {{synchronized}} keyword, and are automatically released on exceptional conditions such as abnormal thread termination.


h2. Risk Assessment

Failing to release a lock on an exceptional condition may lead to thread starvation and deadlock.

|| Rule || Severity || Likelihood || Remediation Cost || Priority || Level ||
| CON15- J | low | likely | low | {color:#cc9900}{*}P9{*}{color} | {color:#cc9900}{*}L2{*}{color} |



h3. Automated Detection

TODO


h3. Related Vulnerabilities

[GERONIMO-2234|http://issues.apache.org/jira/browse/GERONIMO-2234]

h2. References

\[[API 06|AA. Java References#API 06]\] Class {{ReentrantLock}}

----
[!The CERT Sun Microsystems Secure Coding Standard for Java^button_arrow_left.png!|VOID CON14-J. Ensure atomicity of 64-bit operations]      [!The CERT Sun Microsystems Secure Coding Standard for Java^button_arrow_up.png!|11. Concurrency (CON)]      [!The CERT Sun Microsystems Secure Coding Standard for Java^button_arrow_right.png!|CON16-J. Do not expect sleep(), yield() and getState() methods to have any synchronization semantics]


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
      }
    });
  }
}

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();
  }
}

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();
    }
  }
}