gh-145176 Move Emscripten files into Platforms/emscripten (#145806)

Moves Emscripten build files into Platforms/emscripten.

Platforms/emscripten/web_example/python.worker.mjs

@@ -0,0 +1,106 @@
+import createEmscriptenModule from "./python.mjs";
+
+class StdinBuffer {
+  constructor() {
+    this.sab = new SharedArrayBuffer(128 * Int32Array.BYTES_PER_ELEMENT);
+    this.buffer = new Int32Array(this.sab);
+    this.readIndex = 1;
+    this.numberOfCharacters = 0;
+    this.sentNull = true;
+  }
+
+  prompt() {
+    this.readIndex = 1;
+    Atomics.store(this.buffer, 0, -1);
+    postMessage({
+      type: "stdin",
+      buffer: this.sab,
+    });
+    Atomics.wait(this.buffer, 0, -1);
+    this.numberOfCharacters = this.buffer[0];
+  }
+
+  stdin = () => {
+    while (this.numberOfCharacters + 1 === this.readIndex) {
+      if (!this.sentNull) {
+        // Must return null once to indicate we're done for now.
+        this.sentNull = true;
+        return null;
+      }
+      this.sentNull = false;
+      // Prompt will reset this.readIndex to 1
+      this.prompt();
+    }
+    const char = this.buffer[this.readIndex];
+    this.readIndex += 1;
+    return char;
+  };
+}
+
+const stdout = (charCode) => {
+  if (charCode) {
+    postMessage({
+      type: "stdout",
+      stdout: charCode,
+    });
+  } else {
+    console.log(typeof charCode, charCode);
+  }
+};
+
+const stderr = (charCode) => {
+  if (charCode) {
+    postMessage({
+      type: "stderr",
+      stderr: charCode,
+    });
+  } else {
+    console.log(typeof charCode, charCode);
+  }
+};
+
+const stdinBuffer = new StdinBuffer();
+
+const emscriptenSettings = {
+  noInitialRun: true,
+  stdin: stdinBuffer.stdin,
+  stdout: stdout,
+  stderr: stderr,
+  onRuntimeInitialized: () => {
+    postMessage({ type: "ready", stdinBuffer: stdinBuffer.sab });
+  },
+  async preRun(Module) {
+    const versionInt = Module.HEAPU32[Module._Py_Version >>> 2];
+    const major = (versionInt >>> 24) & 0xff;
+    const minor = (versionInt >>> 16) & 0xff;
+    // Prevent complaints about not finding exec-prefix by making a lib-dynload directory
+    Module.FS.mkdirTree(`/lib/python${major}.${minor}/lib-dynload/`);
+    Module.addRunDependency("install-stdlib");
+    const resp = await fetch(`python${major}.${minor}.zip`);
+    const stdlibBuffer = await resp.arrayBuffer();
+    Module.FS.writeFile(
+      `/lib/python${major}${minor}.zip`,
+      new Uint8Array(stdlibBuffer),
+      { canOwn: true },
+    );
+    Module.removeRunDependency("install-stdlib");
+  },
+};
+
+const modulePromise = createEmscriptenModule(emscriptenSettings);
+
+onmessage = async (event) => {
+  if (event.data.type === "run") {
+    const Module = await modulePromise;
+    if (event.data.files) {
+      for (const [filename, contents] of Object.entries(event.data.files)) {
+        Module.FS.writeFile(filename, contents);
+      }
+    }
+    const ret = Module.callMain(event.data.args);
+    postMessage({
+      type: "finished",
+      returnCode: ret,
+    });
+  }
+};