/**
 * A lightweight fair mutex. (Other libraries contain too many features and we want to keep size down).
 *
 * Characteristics:
 * - Non-reentrant.
 * - Fair.
 *   - This means multiple callers awaiting 'lock' will be granted the mutex in the order they requested it.
 *   - This is important, as in React, developers calling 'AuthManager.endAuthSession' in a 'useEffect' cleanup need it
 *     to take effect immediately, such that subsequent 'AuthManager.beginAuthSession' calls will always succeed.
 *   - When calling `safe` consecutively with no 'awaits' in-between, the current context will synchronously acquire
 *     the mutex every time.
 */
export declare class FairMutex {
    private locked;
    private readonly queue;
    safe<T>(callback: () => Promise<T>): Promise<T>;
    private lock;
    private unlock;
}