[Webkit-unassigned] [Bug 237144] New: SharedArrayBuffer posted to AudioWorkletProcessor is not actually shared with the main thread

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=237144

            Bug ID: 237144
           Summary: SharedArrayBuffer posted to AudioWorkletProcessor is
                    not actually shared with the main thread
           Product: WebKit
           Version: Safari 15
          Hardware: Mac (Intel)
                OS: macOS 12
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Web Audio
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: tasnimrock2k6 at gmail.com
                CC: cdumez at apple.com

Created attachment 453112

  --> https://bugs.webkit.org/attachment.cgi?id=453112&action=review

Screenshot of steps in safari

When SharedArrayBuffer is posted to AudioWorkletProcessor from main thread, changing value of an element from main thread should be reflected within AudioWorkletProcessor (which is running in its own Web Audio render thread). This doesn't seem to be happening in Safari but works perfectly fine in Chrome. Moreover, when SharedArrayBuffer is posted to a Worker, the changed value is noticed in Safari and chrome (both).

Minimal steps to reproduce:

In the same directory, need 3 files: safari.html, white-noise-processor.js & server.py (this one is for overriding response headers to enable cross origin isolation). The first two can be found here: https://jsfiddle.net/vzh29gk1/2/ . Copy them in a directory and create server.py there like below:

#!/usr/bin/env python
try:
    from http import server # Python 3
except ImportError:
    import SimpleHTTPServer as server # Python 2

class MyHTTPRequestHandler(server.SimpleHTTPRequestHandler):
    def end_headers(self):
        self.send_my_headers()

        server.SimpleHTTPRequestHandler.end_headers(self)

    def send_my_headers(self):
        self.send_header("Access-Control-Allow-Origin", "*")
        self.send_header("Cross-Origin-Opener-Policy", "same-origin")
        self.send_header("Cross-Origin-Embedder-Policy", "require-corp")

if __name__ == '__main__':
    server.test(HandlerClass=MyHTTPRequestHandler)

On terminal, in the same directory which has all 3 above files, type: 'python3 -m server' and then open URL: localhost:8000/safari.html on browser. Keep the Developer Console tab. Now, click anywhere in the screen. This should be enough to kick-off the worklet processor. In the console tab, try tweaking the value of an element of SharedArrayBuffer and notice that its still not changed within AudioWorkletProcessor. Have attached the image on how the steps look like in safari.

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