...
| Code Block | ||
|---|---|---|
| ||
class BadStop implements Runnable {
public void run() {
try {
Thread.currentThread().sleep(1000);
}catch(InterruptedException ie) { System.out.println("Performing cleanup"); } // not executed
finally { System.out.println("Closing resources"); } // not executed
System.out.println("Done!");
}
}
class Controller {
public static void main(String[] args) {
Thread t = new Thread(new BadStop());
t.start();
t.interrupt(); // artificially induce an InterruptedException
t.stop(); // force thread cancellation
}
}
|
Compliant Solution (1)
This compliant example uses a boolean flag called done to indicate whether the thread should be stopped after any necessary cleanup code has finished executing. An accessor method shutdown() is used to set the flag to true upon which the thread will start the cancellation process. The done flag has also been set immediately following the execution of the initial finally block statements so that the system does not continue to relinquish the resources that it has already released, in the event of done staying false.
| Code Block | ||
|---|---|---|
| ||
class ControlledStop implements Runnable{
protected volatile boolean done = false;
public void run() {
while(!done) {
try {
Thread.currentThread().sleep(1000);
}catch(InterruptedException ie) { System.out.println("Performing cleanup"); }
finally {
System.out.println("Closing resources");
done = true;
}
}
System.out.println("Done!");
}
protected void shutdown(){
done = true;
}
}
class Controller {
public static void main(String[] args) throws InterruptedException {
ControlledStop c = new ControlledStop();
Thread t = new Thread(c);
t.start();
t.interrupt(); // artificially induce an InterruptedException
Thread.sleep(1000); // wait for some time to allow the exception to be caught (demonstration only)
c.shutdown();
}
}
|
Compliant Solution (2)
Remove the default java.lang.RuntimePermission "stopThread" from the policy file used by the security manager to deny the Thread.stop invoking code, the required privileges.
Noncompliant Code Example
...
| Code Block | ||
|---|---|---|
| ||
class StopSocket extends Thread {
protected Socket s;
protected volatile boolean done = false;
public void run() {
while(!done) {
try {
s = new Socket("somehost",25);
BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream()));
String s = null;
while((s = br.readLine()) != null) {
// blocks until end of stream (null)
}
System.out.println("Blocked, will not get executed until some data is received. " + s);
}catch (IOException ie) { System.out.println("Performing cleanup"); }
finally {
System.out.println("Closing resources");
done = true;
}
}
}
public void shutdown() throws IOException {
done = true;
}
}
class Controller {
public static void main(String[] args) throws InterruptedException, IOException {
StopSocket ss = new StopSocket();
Thread t = new Thread(ss);
t.start();
Thread.sleep(1000);
ss.shutdown();
}
}
|
Compliant Solution
The compliant solution simply closes the socket connection, both using the shutdown method as well as in the finally block. Thus, the thread is bound to stop due to a socketException. Note that there is no way to keep the connection alive if the thread is to be cleanly halted immediately.
...