Revise ResourceManager mutexing implementation with a decorator pattern

[jlrobins]

Revise work done in #646 to use a decorator pattern instead. Decorator should take a parameter -- the key for which mutex to use.

And then write a new prove-race-proof test for at least one of the methods.

Sample method decorator:

function mutexWrapper(key: string) {
  // target is the class, propertyKey is the method name, descriptor is the method descriptor
  return function (target: any, propertyKey: string, descriptor: PropertyDescriptor) {
    const originalMethod = descriptor.value;

    descriptor.value = async function (...args: any[]) {
      console.log("mutexWrapper() start", { methodName: propertyKey, key});
      const result = await originalMethod(args);
      console.log("mutexWrapper() end", { methodName: propertyKey, key});
      return result;
    };

    return descriptor;
  };
}

class ResourceManager {
  constructor() {}
 
  @mutexWrapper("FOO")
  async readAndWrite() {
    console.log("readAndWrite()");
  }

  @mutexWrapper("BAR")
  async readAndDelete() {
    console.log("readAndDelete()");
  }
}

async function main() {
  const resourceManager = new ResourceManager();
  await resourceManager.readAndWrite();
  await resourceManager.readAndDelete();
}

main()

Output:

mutexWrapper() start { methodName: 'readAndWrite', key: 'FOO' }
readAndWrite()
mutexWrapper() end { methodName: 'readAndWrite', key: 'FOO' }
mutexWrapper() start { methodName: 'readAndDelete', key: 'BAR' }
readAndDelete()
mutexWrapper() end { methodName: 'readAndDelete', key: 'BAR' }

Note

This does require adding "experimentalDecorators": true into the tsconfig.json under compilerOptions, otherwise we'll see errors like:

Unable to resolve signature of method decorator when called as an expression.
  The runtime will invoke the decorator with 2 arguments, but the decorator expects 3.ts(1241)