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If the JVM is operating on a platform that uses a file system that operates over the network, then file I/O might also suffer the same performance hits as networked I/O. If such a platform is in use, then file I/O to files over the network should also not be performed while locks are held.

Noncompliant Code Example

This noncompliant code example shows the method sendPage() that sends a Page object from a server to a client. The method is synchronized so that the array pageBuff is accessed safely, when multiple threads request concurrent access.

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Calling writeObject() within the synchronized sendPage() method can result in delays and deadlock-like conditions in high latency networks or when network connections are inherently lossy.

Compliant Solution

This compliant solution entails separating the actions into a sequence of steps:

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public boolean sendPage(Socket socket, String pageName) { // No synchronization
  Page targetPage = getPage(pageName); 

  if(targetPage == null)
    return FAILURE;

  return deliverPage(socket, targetPage);
}

private synchronized Page getPage(String pageName) { // Requires synchronization
  Page targetPage = null;

  for(Page p : pageBuff) {
    if(p.getName().equals(pageName)) {
      targetPage = p;
    }
  }
  return targetPage;
}

public boolean deliverPage(Socket socket, Page page){
  try{
    // Get the output stream to write the Page to
    ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());

    // Send the Page to the client
    out.writeObject(page);

  } catch(IOException io){
    // If recovery is not possible return FAILURE
    return FAILURE;    
  } finally {
    out.flush();
    out.close();
  }  
  return SUCCESS;
}

Risk Assessment

If a lock is held by a block that contains network transactional logic, temporary or permanent deadlocks may result.

Related Vulnerabilities

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

References

\[[Grosso 01|AA. Java References#Grosso 01]\] [Chapter 10: Serialization|http://oreilly.com/catalog/javarmi/chapter/ch10.html]
\[[JLS 05|AA. Java References#JLS 05]\] [Chapter 17, Threads and Locks|http://java.sun.com/docs/books/jls/third_edition/html/memory.html]
\[[Rotem 08|AA. Java References#Rotem 08]\] [Falacies of Distributed Computing Explained|http://www.rgoarchitects.com/Files/fallacies.pdf]

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