How Does the Promise Disposer Pattern Prevent Resource Leaks in Asynchronous Operations?

Understanding the Promise Disposer Pattern

In the given code, the function getDb() returns a promise representing a database connection. Promises are commonly used to handle asynchronous operations, but they can lead to resource leaks if the resources they acquire are not properly released.

The Disposer Pattern

The promise disposer pattern addresses this issue by associating a scope with a resource. When the scope ends, the resource is automatically released. In other programming languages, this pattern is known as "try-with-resource" or "RAII."

Applying the Pattern

In our case, we create a function withDb() that accepts a callback to perform work on the database connection. Within the callback, we can execute queries or perform other operations. The withDb() function ensures that the connection is released when the callback completes.

Code Example

The following code demonstrates the disposer pattern applied to our original example:

function withDb(work) {
  var db;
  return myDbDriver.getConnection().then(function(connection) {
    db = connection; // Keep reference to release later
    return work(db); // Perform work on database
  }).finally(function() {
    if (db) db.release(); // Release the connection
  });
}

withDb(function(conn) {
  return conn.query("SELECT name FROM users");
}).then(function(users) {
  // Connection released here
});

By using the disposer pattern, we ensure that the database connection is always released, regardless of whether the callback executes successfully or encounters an error. This helps prevent resource leaks and ensures proper resource management.

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