[android] reduce JNI calls during layout measurement

[jonathanpeppers]

Context: https://github.com/unoplatform/performance/tree/master/src/dopes/DopeTestMaui

Building upon #7996, #8001, and #8033, I noticed while profiling the
sample app putting N Label on the screen:

783.92ms (6.2%) microsoft.maui!Microsoft.Maui.ViewHandlerExtensions.GetDesiredSizeFromHandler(Microsoft.Maui.IViewHandler,double,double)

So around %6 of the time spend just measuring.

Looking through the call stack, I can see 3 JNI calls happening:

932.51ms (7.4%)  mono.android!Android.Views.View.Measure(int,int)
115.53ms (0.91%) mono.android!Android.Views.View.get_MeasuredWidth()
 96.97ms (0.77%) mono.android!Android.Views.View.get_MeasuredHeight()

So, we could write a Java method that calls all three of these and
somehow returns the MeasuredWidth and MeasuredHeight. After a
little research, it seemed the best approach here was to "pack" two
integers into a long. If we tried to return some Java object
instead, then we'd have the same number of JNI calls to get the
integers out.

I found a couple links describing how to "pack" an int into a long:

• Java: https://stackoverflow.com/a/12772968
• C#: https://stackoverflow.com/a/827267

Which after some testing, arrives at:

public static long measureAndGetWidthAndHeight(View view, int widthMeasureSpec, int heightMeasureSpec) {
    view.measure(widthMeasureSpec, heightMeasureSpec);
    int width = view.getMeasuredWidth();
    int height = view.getMeasuredHeight();
    return ((long)width << 32) | (height & 0xffffffffL);
}

Unpacked in C# such as:

var packed = PlatformInterop.MeasureAndGetWidthAndHeight(platformView, widthSpec, heightSpec);
var measuredWidth = (int)(packed >> 32);
var measuredHeight = (int)(packed & 0xffffffffL);

Reducing 3 JNI calls in every View's layout to 1.

Results

A Release build on a Pixel 5 device, I was getting:

Before:  91.94 Dopes/s
After:  102.45 Dopes/s

After profiling again, it drops the % time spent in
GetDesiredSizeFromHandler:

528.96ms (4.5%) microsoft.maui!Microsoft.Maui.ViewHandlerExtensions.GetDesiredSizeFromHandler

So the added math is negligible compared to reduced JNI calls.

[jsuarezruiz]

/azp run

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Azure Pipelines successfully started running 2 pipeline(s).

[mattleibow]

FYI @hartez

[hartez]

Love it!