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POVectorizing operations in a contained class without breaking class structure
 

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    <p>My current project is split into multiple classes that correctly represent the way we think of the entities in the system. However, this is taking a performance price, so I'm trying to come up with a way of improving performance while maintaining the current class structure we have.</p> <p>I think an example will best illustrate the problem: Let's say I have an <code>Order</code> class that contains multiple <code>Item</code>s. A naive implementation for shipping an <code>Order</code> is shipping all of its <code>Item</code>s:</p> <pre><code>class Order { private List&lt;Item&gt; m_items; public void Ship() { foreach (Item item in m_items) { item.Ship(); } } } </code></pre> <p>Shipping an <code>Item</code> is a multi-stage process:</p> <pre><code>class Item { public void Ship() { var receipt = m_boat.ShipToDestination(this); ProcessReceipt(receipt); } } </code></pre> <p>As it turns out, shipping the <code>Item</code> on a <code>Boat</code> takes a long time. Luckily, the <code>Boat</code> can ship multiple <code>Item</code>s concurrently (<code>List&lt;Receipt&gt; Boat.ShipToDestination(List&lt;Item&gt; items)</code>). However, to use this method I will have to rewrite <code>Order.Ship()</code> as follows:</p> <pre><code>class Order { public void Ship() { var receipts = m_boat.ShipToDestination(m_items); foreach (Receipt receipt in receipts) { ProcessReceipt(receipt); } } } </code></pre> <p>This means that <code>ProcessReceipt</code> is now part of <code>Order</code> (rather than <code>Item</code>), and also that an <code>Item</code> no longer takes care of all of its shipping logistics.</p> <p>In my real code there are many methods with this problem, so using this solution effectively means that most of the <code>Item</code> logic will move into the <code>Order</code> class. However, this seems like the wrong place to have this logic - it really should be in <code>Item</code>.</p> <p>I considered using multiple threads (e.g. using a <code>Task</code> per <code>Item</code>) but this seems too wasteful, especially since an <code>Order</code> can have dozens of <code>Items</code>.</p> <p>Another approach I considered is creating a <code>QueuedBoat</code> with a <code>QueueForShipping(Item item)</code> method and a <code>ShipQueuedItems()</code> method. Now <code>Order</code> can call <code>ShipQueuedItems</code> while <code>Item</code> can call <code>QueueForShipping</code>. The problem with this approach is that in my real code, the <code>Receipt</code> is returned only after the <code>Item</code> was shipped, so the code would have to look like this:</p> <pre><code>class Order { private List&lt;Item&gt; m_items; public void Ship() { foreach (Item item in m_items) { item.Ship(); } m_queuedBoat.ShipQueuedItems(); foreach (Item item in m_items) { item.FinalizeShipping(); } } } class Item { public void Ship() { m_queuedBoat.QueueForShipping(this); } public void FinalizeShipping() { ProcessReceipt(m_queuedBoat.GetReceiptForItem(this)); } } </code></pre> <p>This feels like it's in the right direction (since <code>Order</code> knows how many <code>Item</code>s it has, it must be the component that knows when everything is on the <code>Boat</code>), but it broke <code>Ship</code> into two stages. In my real code I have multiple stages (each can be vectorized separately), so the method would be broken into 3-4 pieces, which is not a pretty sight.</p> <p>Can someone suggest a way of vectorizing <code>Item.Ship()</code> while keeping the business logic inside the <code>Item</code> class, or will I have to give up on the Order/Item separation in order to take advantage of vectorization?</p> <p><strong>Edit:</strong></p> <p>Another approach could be this:</p> <pre><code>class Order { private List&lt;Item&gt; m_items; public void Ship() { for (int i = 0; i &lt; m_items.Count; ++i) { bool isLast = (i == (m_items.Count - 1)); item.Ship(isLast); } } } class Item { public void Ship(bool isLast) { m_queuedBoat.QueueForShipping(this, FinalizeShipping); if (isLast) m_queuedBoat.ShipQueuedItems(); } private void FinalizeShipping(Receipt receipt) { ProcessReceipt(receipt); } } </code></pre> <p>Where the <code>QueuedBoat</code> class invokes a callback for each item with its <code>Receipt</code>.</p>
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    1. COIn C#5 it will be easier: one will be able to make `Ship` a `Task<Receipt>` and start it asynchronously with the new async/await technique.
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