[Webkit-unassigned] [Bug 235448] New: file.stream() is slow and CPU-bound

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=235448

            Bug ID: 235448
           Summary: file.stream() is slow and CPU-bound
           Product: WebKit
           Version: Safari 15
          Hardware: Mac (Apple Silicon)
                OS: macOS 12
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: New Bugs
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: jacob at bandes-stor.ch

Created attachment 449672

  --> https://bugs.webkit.org/attachment.cgi?id=449672&action=review

Screen recording demonstrating the issue

Also filed as FB9854642

Reading a file with file.stream() is much slower than repeatedly calling file.slice().

1. Visit https://jsfiddle.net/0hnembvu/21/
2. Choose a large file (~200MB). Observe the progress bar updates smoothly, and the file can be read in ~200ms.
3. Reload the page.
4. Enable the "use ReadableStream API" checkbox.
5. Choose the same large file again. Observe the page becomes unresponsive while reading (the progress bar does not update smoothly) and the file takes much longer to read (~1500ms).

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