Which of the following is responsible for managing the locking of the state file?

The component responsible for managing the locking of the state file in Terraform is the backend. The backend is the mechanism that determines how Terraform stores state and can also dictate whether state locking is enabled. This functionality is critical for preventing conflicting changes and ensuring the integrity of the state when multiple users or processes are interacting with the infrastructure.

When using a remote backend, such as AWS S3 with DynamoDB for state locking or Terraform Cloud, this management of state locking is implicitly handled by the backend. It ensures that when one operation is in progress, other operations that would alter the state cannot proceed, thus securing the state file from simultaneous writes and potential corruption.

The provider, Terraform CLI, and workspace, while integral parts of the Terraform ecosystem, do not directly manage state file locking. The provider interacts with the resources, the CLI is the command-line interface used to run Terraform commands, and the workspace serves to manage different sets of Terraform states but does not handle the locking mechanism itself. Therefore, the backend is the correct choice when discussing state file locking management.