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Programs must ensure that threads that hold locks on other objects release those locks appropriately before entering the wait state. Additional guidance on waiting and notification is available in THI03-J. Always invoke wait() and await() methods inside a loop and THI02-J. Notify all waiting threads rather than a single thread.

Noncompliant Code Example (Network I/O)

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

  if (targetPage == null){
    return false;
  }
  return deliverPage(socket, targetPage);
}

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

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

// Return false if an error occurs, true if successful
public boolean deliverPage(Socket socket, Page page) {
  ObjectOutputStream out = null;
  boolean result = true;
  try {
    // Get the output stream to write the Page to
    out = new ObjectOutputStream(socket.getOutputStream());

    // Send the page to the client
    out.writeObject(page);out.flush();
  } catch (IOException io) {
    result = false;
  } finally {
    if (out != null) {
      try {
        out.close();
      } catch (IOException e) {
        result = false;
      }
    }
  }
  return result;
}

Exceptions

LCK09-J-EX0: Classes that provide an appropriate termination mechanism to callers are permitted to violate this rule (see THI04-J. Ensure that threads performing blocking operations can be terminated).

LCK09-J-EX1: Methods that require multiple locks may hold several locks while waiting for the remaining locks to become available. This constitutes a valid exception, although the programmer must follow other applicable rules, especially LCK07-J. Avoid deadlock by requesting and releasing locks in the same order to avoid deadlock .

Automated Detection

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

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CCE_LK_LOCKED_BLOCKING_CALLS

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Risk Assessment

Blocking or lengthy operations performed within synchronized regions could result in a deadlocked or unresponsive system.

Automated Detection

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

Related Guidelines

Bibliography

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