Class Environment

web/src/environment.ts:68–144

 * Environment to impelement most of the JS library functions.
 */
export class Environment implements LibraryProvider {
  logger: (msg: string) => void;
  imports: Record<string, any>;
  /**
   * Maintains a table of FTVMWasmPackedCFunc that the C part
   * can call via TVMWasmPackedCFunc.
   *
   * We maintain a separate table so that we can have un-limited amount
   * of functions that do not maps to the address space.
   */
  packedCFuncTable: Array<ctypes.FTVMFFIWasmSafeCallType | undefined> = [
    undefined,
  ];
  /**
   * Free table index that can be recycled.
   */
  packedCFuncTableFreeId: Array<number> = [];

  private libProvider?: LibraryProvider;

  constructor(
    importObject: Record<string, any> = {},
    logger: (msg: string) => void = console.log
  ) {
    this.logger = logger;
    this.libProvider = detectLibraryProvider(importObject);
    // get imports from the provider
    if (this.libProvider !== undefined) {
      this.imports = this.libProvider.imports;
    } else {
      this.imports = importObject;
    }
    // update with more functions
    this.imports.env = this.environment(this.imports.env);
  }

  /** Mark the start of the instance. */
  start(inst: WebAssembly.Instance): void {
    if (this.libProvider !== undefined) {
      this.libProvider.start(inst);
    }
  }

  private environment(initEnv: Record<string, any>): Record<string, any> {
    // default env can be overriden by libraries.
    const defaultEnv = {
      "__cxa_thread_atexit": (): void => {},
      "emscripten_notify_memory_growth": (index: number): void => {}
    };
    const wasmSafeCall: ctypes.FTVMFFIWasmSafeCallType = (
      self: Pointer,
      args: Pointer,
      num_args: number,
      result: Pointer
    ): number => {
      const cfunc = this.packedCFuncTable[self];
      assert(cfunc !== undefined);
      return cfunc(self, args, num_args, result);