How can PHP developers ensure that session_start() is only called when necessary to avoid unnecessary exposure of PHPSESSID?

To ensure that session_start() is only called when necessary and avoid unnecessary exposure of PHPSESSID, PHP developers can check if a session has already been started before calling session_start(). This can be done by checking if the session_id() is empty or not. If it is empty, then session_start() should be called to start a new session.

if (empty(session_id())) {
    session_start();
}