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From: geomacy <git@git.apache.org>
To: dev@brooklyn.apache.org
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References: <git-pr-443-brooklyn-server@git.apache.org>
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Subject: [GitHub] brooklyn-server pull request #443: Adds maxConcurrentChildCommands paramter ...
Content-Type: text/plain
Message-Id: <20161118172504.5EFC6E0FC4@git1-us-west.apache.org>
Date: Fri, 18 Nov 2016 17:25:04 +0000 (UTC)
archived-at: Fri, 18 Nov 2016 17:25:07 -0000

Github user geomacy commented on a diff in the pull request:

    https://github.com/apache/brooklyn-server/pull/443#discussion_r88699540
  
    --- Diff: core/src/main/java/org/apache/brooklyn/entity/group/DynamicClusterImpl.java ---
    @@ -1040,14 +1077,80 @@ protected void discardNode(Entity entity) {
     
         protected void stopAndRemoveNode(Entity member) {
             removeMember(member);
    -
             try {
                 if (member instanceof Startable) {
    -                Task<?> task = member.invoke(Startable.STOP, Collections.<String,Object>emptyMap());
    +                Task<?> task = newThrottledEffectorTask(member, Startable.STOP, Collections.<String, Object>emptyMap());
                     task.getUnchecked();
                 }
             } finally {
                 Entities.unmanage(member);
             }
         }
    +
    +    protected <T> Task<?> newThrottledEffectorTask(Entity target, Effector<T> effector, Map<?, ?> arguments) {
    +        return newThrottledEffectorTask(target, effector, arguments, false);
    +    }
    +
    +    protected <T> Task<?> newThrottledEffectorTask(Entity target, Effector<T> effector, Map<?, ?> arguments, boolean isPrivileged) {
    +        final Semaphore permit = childTaskSemaphore;
    +        final Task<?> toSubmit;
    +        final Task<T> effectorTask = Effectors.invocation(target, effector, arguments).asTask();
    +        if (permit != null) {
    +            // Acquire the permit now for the privileged task and just queue the effector invocation.
    +            // If it's unprivileged then queue a task to obtain a permit first.
    +            final String description = "Waiting for permit to run " + effector.getName() + " on " + target;
    +            final Runnable obtain = new ObtainPermit(permit, description);
    +            if (isPrivileged) {
    +                obtain.run();
    +                toSubmit = effectorTask;
    +            } else {
    +                // acquire semaphore here if privileged?
    +                Task<?> obtainMutex = Tasks.builder()
    --- End diff --
    
    Is it worth moving this and `ObtainPermit` into `Tasks.java`, so that this call would become something like 
    ```
                    Task<?> obtainMutex = Tasks.builder()
                            .description(description)
                            .throttleOn(permit)
                            .build();
    ```



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