Support for CDN resource of pthread worker

[DylanShang]

Hi, developers

When I host a multi-threaded package on platforms like jsDelivr with proper cross-origin isolation settings, I encounter an error such as:

Uncaught SecurityError: Failed to construct 'Worker': Script at 'https://cdn.jsdelivr.net/npm/xxx' cannot be accessed from origin 'http://127.0.0.1:8080'.

This issue arises because workers cannot be created across different origins. According to the discussion in this Webpack issue and the solution proposed in this comment, we can use fetch to bypass this limitation.

A potential solution is modify the allocateUnusedWorker function from

  allocateUnusedWorker() {
    var worker;
    var workerOptions = {
      "type": "module","name": "em-pthread"
    };
    worker = new Worker(new URL("your js file", import.meta.url), workerOptions);
    PThread.unusedWorkers.push(worker);
  }

to

allocateUnusedWorker() {
    var workerOptions = {
        type: "module",
        name: "em-pthread"
    };

    try {
        // Use XMLHttpRequest for a synchronous request
        var xhr = new XMLHttpRequest();
        xhr.open("GET", new URL('your js file', import.meta.url), false); // false means synchronous request
        xhr.send(null);

        // Check if the request was successful
        if (xhr.status === 200) {
            const scriptText = xhr.responseText; // Get the response text
            
            // Create a Blob URL
            const workerUrl = URL.createObjectURL(new Blob([scriptText], {
                type: 'application/javascript'
            }));

            // Create a Worker and add it to the unused Workers list
            PThread.unusedWorkers.push(new Worker(workerUrl, workerOptions));
        } else {
            console.error('Failed to fetch the script:', xhr.status);
        }
    } catch (error) {
        console.error("Error occurred while allocating worker:", error);
    }
}

[msqr1]

#21937 (comment) is a workaround, I think. This may be a duplicate of #21937

[DylanShang]

close it as the duplicate issue