Tag Archives: Threads

Listing all Threads in an Application


Java allows multi threading. A good technique to make Applications run faster and can handle more tasks at the same time. In some cases you want to keep track on the number of active threads. The example below shows how to get an overview of all active threads.

// Find the root thread group
ThreadGroup root = Thread.currentThread().getThreadGroup().getParent();
while (root.getParent() != null) {
    root = root.getParent();

// Visit each thread group
visit(root, 0);

// This method recursively visits all thread groups under `group'.
public static void visit(ThreadGroup group, int level) {
    // Get threads in `group'
    int numThreads = group.activeCount();
    Thread[] threads = new Thread[numThreads*2];
    numThreads = group.enumerate(threads, false);

    // Enumerate each thread in `group'
    for (int i=0; i<numThreads; i++) {
        // Get thread
        Thread thread = threads[i];

    // Get thread subgroups of `group'
    int numGroups = group.activeGroupCount();
    ThreadGroup[] groups = new ThreadGroup[numGroups*2];
    numGroups = group.enumerate(groups, false);

    // Recursively visit each subgroup
    for (int i=0; i<numGroups; i++) {
        visit(groups[i], level+1);