How Does the Promise Disposer Pattern Prevent Resource Leaks?

The Promise Disposer Pattern: Resolving Resource Leaks

Context:
The problem at hand involves a potential resource leak in the code responsible for retrieving users from a database. The asynchronous nature of the code makes it difficult to ensure that the database connection is released promptly.

Defining the Promise Disposer Pattern:
The promise disposer pattern is a technique used to associate a resource with a specific scope of code. This technique guarantees that the resource is released as soon as the code execution completes, preventing resource leaks.

Applying the Pattern to the Code:
In the provided code snippet, the getDb() function establishes a database connection. To address the resource leak issue, the code can be refactored using the disposer pattern:

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

Using the disposer pattern, the code can be modified as follows:

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

Benefits of the Disposer Pattern:
By employing the promise disposer pattern:

• Resources are released promptly, preventing leaks.
• Code maintenance is simplified as the resource management is isolated within the disposer scope.
• The pattern is reusable across various scenarios, including AJAX request handling and resource ownership management.

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