Scratch 3.0 takes 10 times longer to execute a simple loop

[Mr-Dave2]

Expected Behavior

The time to run a simple loop with a single block should be the same, perhaps less, when run under Scratch 3.0.

Actual Behavior

Depending on the browser that is used and use of the no-refresh option, the execution times, when run under Scratch 3.0 and using the same Browser and no-refresh option as Scratch 2.0, increased by a factor of 1.6 to 10.

Steps to Reproduce

See this test case: Scratch 2.0 link and Scratch 3.0 link.

The program executes a repeat block 500000 times with only a repeat(0) block inside. (Initially I tried to use just an empty repeat block but the times I got under Scratch 2 were many times greater than expected. This may due to the timing patches that were applied after the Flash security patch. Using the Repeat(0) block was my best guess of what to use for a ‘no op’ block.)

Operating System and Browser

Firefox 62.0.3 (64-bit)
Chrome Version 69.0.3497.100 (Official Build) (64-bit)
Edge: 42.17134.1.0
Flash player: 31.0.0.122
System: Dell Dual Core t4400 @2.2GHz 4GB, Win10
The results are a little disappointing and very much so if you are a Firefox or an Edge user.

[thisandagain]

/cc @mzgoddard @kchadha

[mzgoddard]

This might be improved by #1683.

[towerofnix]

Here are my results now (just Firefox):

Old (@Mr-Dave2's results):

2.0	3.0	3.0 vs 2.0
0.77	4.98	650%
0.23	2.31	1000%

New (my results):

2.0	3.0	3.0 vs 2.0
0.30	1.00	333%
0.13	0.65	500%

So yep, definitely significant improvement! It's about double the speed now (although it still doesn't match 2.0).