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From aledsage <...@git.apache.org>
Subject [GitHub] brooklyn-server pull request #480: Config self reference fix
Date Tue, 28 Feb 2017 14:08:25 GMT
Github user aledsage commented on a diff in the pull request:

    https://github.com/apache/brooklyn-server/pull/480#discussion_r103446823
  
    --- Diff: core/src/main/java/org/apache/brooklyn/util/core/task/BasicExecutionContext.java
---
    @@ -96,7 +98,50 @@ public ExecutionManager getExecutionManager() {
         /** returns tasks started by this context (or tasks which have all the tags on this
object) */
         @Override
         public Set<Task<?>> getTasks() { return executionManager.getTasksWithAllTags(tags);
}
    -     
    +
    +    /** performs execution without spawning a new task thread, though it does temporarily
set a fake task for the purpose of getting context;
    +     * currently supports suppliers or callables  */
    +    @SuppressWarnings("unchecked")
    +    @Override
    +    public <T> Maybe<T> getImmediately(Object callableOrSupplier) {
    +        BasicTask<?> fakeTaskForContext;
    +        if (callableOrSupplier instanceof BasicTask) {
    +            fakeTaskForContext = (BasicTask<?>)callableOrSupplier;
    --- End diff --
    
    Under what code path do we get here? Looking at `ValueResolver.getMaybeInternal(...)`,
`allowImmediateExecution` will be false if the object is a task (rather than a `TaskFactory`
or `DeferredSupplier`). 
    
    For example, the test below fails (added to `ValueResolverTest`). It leaves a single instance
of the task executing.
    
    ```
        public void testTaskGetImmediatelyDoesNotBlock() {
            final AtomicInteger executingCount = new AtomicInteger();
            
            final Task<String> task = new BasicTask<>(new Callable<String>()
{
                public String call() {
                    executingCount.incrementAndGet();
                    try {
                        Time.sleep(Duration.ONE_MINUTE);
                        return "myval";
                    } finally {
                        executingCount.decrementAndGet();
                    }
                }});
            
            for (int i = 0; i < 3; i++) {
                Maybe<String> result = Tasks.resolving(task).as(String.class).context(app).immediately(true).getMaybe();
                Asserts.assertTrue(result.isAbsent(), "result="+result);
            }
    
            Asserts.assertFalse(task.isSubmitted());
            
            // The call below default times out after 30s while the task above is still running
            // Expect the task to not be left running.
            Asserts.succeedsEventually(new Runnable() {
                public void run() {
                    Asserts.assertEquals(executingCount.get(), 0);
                }
            });
        }
    ```
    
    I'm not convinced that we want to support setting a config key with a value of type `Task`
(long term). But I guess that will require more work, to change how `DependentConfiguration`
is implemented. So we do need to support it short-term :-(


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