6 replies to this topic

[gregwarner]

I have a question regarding the threads which Executor uses to run its Runnables. In the Javadoc for Executor, it says this:

Quote

void execute(Runnable command)

Executes the given command at some time in the future. The command may execute in a new thread, in a pooled thread, or in the calling thread, at the discretion of the Executor implementation.

My question is in regards to the bold green and red text above. What does it mean, "at the discretion of the Executor implementation?"

Basically, I want to ensure that my Executor does not execute my Runnable in the calling thread. The reason being is that the calling thread should not be tied up with lengthy tasks, as it needs to be free in the background to read and write data on a Socket. That's the whole point behind my using an Executor, so I can dump lengthy tasks into it whenever I want and forget about them (from the calling thread's point of view, that is). How can I be sure that the Executor won't use the calling thread?

I'm using a cached thread pool created by Executors.newCachedThreadPool() if that's relevant.

[lethalwire]

The newCachedThreadPool() method returns a ThreadPoolExecutor object.
The execute() method of the ThreadPoolExecutor object states that:

Quote

Executes the given task sometime in the future. The task may execute in a new thread or in an existing pooled thread. If the task cannot be submitted for execution, either because this executor has been shutdown or because its capacity has been reached, the task is handled by the current RejectedExecutionHandler.

So to me, it would seem that this implementation of Executor does NOT try running the command in the calling thread.

[gregwarner]

Thanks for clearing that up for me.

[lethalwire]

I'm not saying it's 100% correct, but that's how I would interpret the documentation! lol :)

[gregwarner]

Sounds correct to me. I had no idea newCachedThreadPool() returns a ThreadPoolExecutor object. I only looked at the method summary list on the Executors javadoc page instead of the detailed method description.

[wim DC]

For those kind of details I prefer looking at the source itself, who knows they dare changing something from version 6.0.x to 6.0.y, or you look at the wrong javadoc version. (cause google mostly gives 1.4.2 -.- )

public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
    }

(that's 6.0.26)

[lethalwire]

wim DC said:

For those kind of details I prefer looking at the source itself, who knows they dare changing something from version 6.0.x to 6.0.y, or you look at the wrong javadoc version. (cause google mostly gives 1.4.2 -.- )

public static ExecutorService newCachedThreadPool() {

        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,

                                      60L, TimeUnit.SECONDS,

                                      new SynchronousQueue<Runnable>());

    }

(that's 6.0.26)

I believe it's the same in jdk 1.7.0

Like DC says, I also look in the src code for details like this.