DateTime.Parse is slow

[nmoore-genetec]

• Dart 3.6.0 (stable) (Thu Dec 5 07:46:24 2024 -0800) on "windows_x64"
• on windows / "Windows 10 Enterprise" 10.0 (Build 22631)
• locale is en-CA

Hi there,

The following little code block:

var stringToParse = "2026-01-02"; var watch = Stopwatch()..start(); for(int i=0;i<1_000_000;i++){ DateTime.parse(stringToParse); }

Takes a whopping 15-16 seconds to complete. My machine is an i7 dev workstation. It's running on a background isolate, if that matters.

Let me know if i'm comparing apples to oranges here, but that same piece of code in C# takes 200ms. Anything I can do to parse a large number of DateTime values, in a reasonable amount of time ?

[julemand101]

@nmoore-genetec Can you perhaps make a complete standalone Dart program example which reproduces this issue? I have a hard time to reproduce this with your example (or small adjustments of it including using isolates).

On both Dart 3.6 and Dart 3.7 with JIT and AOT, I can run the parsing in 2-3 seconds on my old i5-2410M CPU.

[lrhn]

These inputs are parsed as local-time DateTimes, so there is some time-zone calculation on top of the parsing.
The performance of that can differ between operating systems, since it includes asking the operating system for time zone information a number of times. (More if close to a time zone change.)

Seems Windows is slow. I get ~17 seconds JIT, ~14 seconds compile exe.
In comparison, compile js run with node takes ~1 sec.

The VM does have an issue.

If you change the input string to "2026-01-02T00:00:00Z", the VM's time drops to ~0.8 seconds, so it's almost certainly the time-zone code that takes all the time.

(So, that's the workaround: Make it an UTC date.)

And the VM might want to see what V8 does to make it so fast.

[julemand101]

Ah I tested on Linux with a danish locale for the record.

[nmoore-genetec]

Thanks a ton for looking into this! Workaround will be fine for now, and we're keen to test the fix whenever it becomes available.