Hacklang async code example?

Question

How modify the following code to get article data and top articles asynchronously in hack ?

class ArticleController
{
    public function viewAction()
    {
        // how get
        $article = $this->getArticleData();
        $topArticles = $this->getTopArticles();
    }

    private function getArticleData() : array
    {
        // return article data from db
    }

    private function getTopArticles() : array
    {
        // return top articles from db
    }
}

Answer 1

HHVM 3.6 and newer

async functions info

The two HHVM PHP language keywords that enable async functions are async and await. async declares a function as asynchronous. await suspends the execution of an async function until the result of the asynchronous operation represented by await is available. The return value of a function that await can be used upon is an object that implements Awaitable<T>.

You have an example in the documentation (1). There is a discussion about asynchronous functions in the language specification as well (2).

It actually took me some time to realize how to use and call the asynchronous functions, so I think you will find some more info useful.

We have these two functions: foo() and bar().

async function foo(): Awaitable<void> {
  print "executed from foo";
}
async function bar(int $n): Awaitable<int> {
  print "executed from bar";
  return $n+1;
}

Let's experiment some ways to call these two functions:

foo();                  // will print "executed from foo"
bar(15);                // will print "executed from bar"
$no1 = bar(15);         // will print "executed from bar"
print $no1;             // will output error, because $number is not currently an `int`; it is a `WaitHandle`
$no2 = bar(15)->join(); // will print "executed from bar"
print $no2;             // will print 16

AsyncMysqlClient tips

The connection to a MySQL database is made with AsyncMysqlClient::connect asynchronous function which returns an ExternalThreadEventWaitHandle to an AsyncMysqlConnection.

You can perform query or queryf on an AsyncMysqlConnection. Note: the data you send to a queryf is properly escaped by the function.

A query you perform on an AsyncMysqlConnection returns either an AsyncMysqlQueryResult (when the query performs ok) or AsyncMysqlQueryErrorResult (if the query goes wrong; then you can treat errors with the mysql_error(), mysql_errno() and failureType() members of this class). Both AsyncMysqlQueryResult and AsyncMysqlQueryErrorResult extend AsyncMysqlResult abstract class.

---

Below is a probable implementation of your class:

class ArticleController {
  private AsyncMysqlConnection $connection;
  public async function viewAction(int $articleId): Awaitable<void> {
    $this->connection = await AsyncMysqlClient::connect( /* connection data */ );
    $article = await $this->getArticleData($articleId);
  }
  public async function getArticleData(int $id): Awaitable<?Vector> {
    $articleDataQuery = await $this->connection->queryf("SELECT * FROM articles WHERE id %=d", $id);
    if($articleDataQuery instanceof AsyncMysqlQueryErrorResult) {
      throw new Exception("Error on getting data: ".$articleDataQuery->mysql_error());
    }

    // Considering that $id represents a unique id in your database, then
    // you are going to get only one row from your database query
    // so you return the first (and only) row in the query result
    if($articleDataQuery->numRows() == 1) {
      return $articleDataQuery->mapRowsTyped()[0];
    }
    return null;
  }
} 

P.S. I hope it is not too late for this answer and I hope it helps you. If you consider this useful, please, accept it.