...
| Wiki Markup |
|---|
A programmer may sometimes wish to enumerate all the threads in a group as a precursor to other operations. This is accomplished by using the {{activeCount()}} method that ""Returns an estimate of the number of active threads in this thread group. "" \[[API 06|AA. Java References#API 06]\]. Notice that there is no absolute word on whether it returns the exact count or not; the definition of _active_ also has a different connotation here. A thread that is constructed and not started is still counted by the {{activeCount()}} method as _active_. |
...
| Code Block | ||
|---|---|---|
| ||
class NetworkHandler implements Runnable {
private static ThreadGroup tg = new ThreadGroup("Chief""Chief");
public void run() {
try {
method1();
method2();
Thread.sleep(500);
} catch(InterruptedException e) {
// Forward to handler
}
}
public static void method1() throws InterruptedException {
Thread t1 = new Thread(tg, new HandleRequest(), "t1""t1");
Thread t2 = new Thread(tg, new HandleRequest(), "t2""t2");
t1.start();
t2.start();
}
public static void method2() {
Thread t3 = new Thread(tg, new HandleRequest(), "t3""t3");
Thread t4 = new Thread(tg, new HandleRequest(), "t4""t4");
t3.start();
t4.start();
}
public static void main(String[] args) throws InterruptedException {
Thread t = new Thread(tg, new NetworkHandler(), "t""t");
t.start();
System.out.println(""Active Threads in Thread Group at point (1):"" +
t.getThreadGroup().getName() + " "" " + Thread.activeCount());
Thread ta[] = new Thread[Thread.activeCount()];
for(int i = 0; i << 500000; i++) { } // Delay to demonstrate TOCTOU condition
System.out.println(""Active Threads in Thread Group at point (2):"" +
t.getThreadGroup().getName() + " "" " + Thread.activeCount());
int n = Thread.enumerate(ta);
System.out.println(""Enumerating..."");
for(int i = 0; i << n; i++) {
System.out.println(""Thread "" + i + "" = "" + ta[i].getName());
}
}
}
class HandleRequest implements Runnable {
public void run() {
System.out.println(""Active Threads in Thread Group (Handler thread invoked this): "" +
Thread.currentThread().getThreadGroup().getName() + " "" " + Thread.activeCount());
}
}
|
...
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
| Wiki Markup |
|---|
\[[API 06|AA. Java References#API 06]\] Methods {{activeCount}} and {{enumerate}}, Classes ThreadGroup and Thread
\[[JavaThreads 04|AA. Java References#JavaThreads 04]\] 13.1 ThreadGroups
\[[Bloch 01|AA. Java References#Bloch 01]\] Item 53: Avoid thread groups
\[[Goetz 06|AA. Java References#Goetz 06]\] 7.3.1. Uncaught Exception Handlers
\[[SDN 06|AA. Java References#SDN 06]\] Bug ID: 4089701 and 4229558 |
...
CON00-J. Do not invoke a superclass method or constructor from a synchronized region in the subclass 11. Concurrency (CON) CON02-J. Facilitate thread reuse by using Thread Pools