First work on the functions that take the longest, and then look at commonly used methods to see if you can speed them up using these tips.
Xojo for loop code#
To make sure there isn’t a blank space in the UI while it is invisible, an identical blank Listbox can be put behind the Listbox in use, or a “please wait” image can be used instead, but you have to remember that the window may be resizable and the list may be resized too.Īnd don’t forget to use the Xojo Profiler to check your code performance when you see it needs some work. This is not necessary for most uses, but if you are populating a Listbox with a very large amount of data, this can bring a big performance improvement. Although it is not as fast as the single line of code to add the row, it is still much faster than adding a blank row and then populating each cell one by one.Īnother tip is to make a Listbox invisible while rows are being added, and visible again when it is ready. This makes the code easier to read and edit. Take the following example, which may look familiar: If we can reduce inefficiencies in loop code, we can make significant performance improvements. Loops are used to repeat blocks of code over and over again.
…you can store values in variables first: And if you don’t want long and hard to read lines of code like this… MyListbox.AddRow rs.Field(âvalue1â).StringValue, _ For a WebListbox on a WebPage it is a very noticeable difference. If your lists are long and have several columns you will see a difference. This works significantly faster and is less code to write. This is inefficient and can be improved by adding the entire row to the list in one go: MyListbox.Cell(MyListbox.LastIndex,3) = z MyListbox.Cell(MyListbox.LastIndex,2) = y MyListbox.Cell(MyListbox.LastIndex,1) = x MyListbox.Cell(MyListbox.LastIndex,0) = w I often see code like this to add rows to Listboxes: MyListbox.AddRow " " If you have a feature that processes a large volume of data, and various different methods get called from inside a loop, flattening the code would help improve performance. If the code within the CalculateTotals method were put directly into our loop instead, 5,000 calls to the method would be eliminated, so the loop code would run faster. In our tiny example above, the CalculateTotals method gets called 5,000 times. Xojo is great for building structured code using methods, but we can speed things up in a loop by reducing the number of calls to methods. If our Listbox had 5,000 rows, the loop would calculate this same value 5,000 times! We get improved performance by calculating it only once: Dim n As Integer = MyListbox.ListCount - 1 // or MyPopupMenu.ListCount-1 Here the For loop is calculating the value of (MyListbox.ListCount – 1) each time it goes around the loop. In this short and simple example, the value of the “i” variable is never used so it can be discarded, saving both iteration time and storage space.// Also works with MyPopupMenu.ListCount-1įor i As Integer = 0 to MyListbox.ListCount - 1 So to unroll the loop, the idea is that there are only two iterations of the loop which the compiler is able to determine.
For example, Xojo adds Yield function calls to enable cooperative threading and these function calls cannot be removed by the optimization process. This is essentially a Goto, for old-timers.īut the compiler may also insert stuff on your behalf. If the condition is false, then it branches to the beep. After the integer assignment, there is a branch back to the if. Looking at the above, the while gets converted to an if. This gets modeled as a control flow graph:Ī control flow graph is a directed graph. Here is a simple loop: Dim i As Integer = 0 Modern hardware hates branches because it makes other optimization more difficult, so unrolling a loop enables additional optimizations for both the compiler itself and the CPU. This will not necessarily unroll the entire loop so that you get code repeated 100s of times, but it may unroll it a bit so the code repeats a few times. It is essentially exactly what you are taught not to do when writing code. Loops are a key optimization point. Unrolling a loop means that you repeat the code content of the loop multiple times.
This is the seventh post in our Compiler series. In this post you’ll look at a specific optimization called “loop unrolling”. The last post covered optimization in general.
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