How to join a fragment of code

Question

hi,
i've coded a solution for the following simple problem
1) code block A needs to pass some code (B) to a framework
1.5) the code in B needs to be executed by the framework, so you can't just execute it
2) the framework will schedule it in an asynchronous way unknown to you - you can't get a reference to the thread its executed in, (there isn't guaranteed to be a unique dedicated thread for the code fragment anyway)
3) you want to block code A until the job is done (you know this won't cause trouble..)
the approach i tried (and works) is below, but its not very concise.. does anyone know a simpler way?
void foo() throws InterrupedException {
   boolean[] flag = new boolean[1];
   SomeFramework fw = ...
   fw.start(new Runnable() {
      public void run() {
         // do a load of work
         synchronized(flag) {
            flag[0] = true;
            flag.notify();
   // manually join here
   synchronized(flag) {
      while(!flag[0]) {
         flag.wait();
}this was in Java 1.4 - is there a suitable class for simplifying this in 5.0? I've had a quick look at Semaphore and Condition, but neither seemed a good match (??)
thanks,
asjf

Answer 1

You could write your own Sentinel. For example this untested uncompiled class:
class Sentinel {
    boolean busy = true;
    void trigger() {
         synchronized(this) {
            busy = false;
            this.notify();
    void waitUntilTriggered() {
        synchronized(this) {
            while(busy) {
                this.wait();
}Or you can use a Semaphore as previously suggested.
-o-