/**
 * Copyright 2019, OpenCensus Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import * as webTypes from '@opencensus/web-types';
import { NoopExporter } from '../../exporters/noop_exporter';
import { Tracer } from './tracer';
export declare const NOOP_EXPORTER: NoopExporter;
/** Main interface for tracing. */
export declare class Tracing implements webTypes.Tracing {
    /** Object responsible for managing a trace. */
    readonly tracer: Tracer;
    /** Service to send collected traces to. */
    exporter: NoopExporter;
    /** Whether tracing is active - always true for opencensus-web. */
    active: boolean;
    /** Singleton instance */
    private static singletonInstance;
    /** Gets the tracing instance. */
    static readonly instance: Tracing;
    /** Sets tracer and exporter config. */
    start(config?: webTypes.Config): webTypes.Tracing;
    /** Stops tracer - this is a no-op for opencensus-web. */
    stop(): void;
    /**
     * Registers an exporter to send the collected traces to.
     * @param exporter The exporter to send the traces to.
     * @return The tracing object.
     */
    registerExporter(exporter: webTypes.Exporter): webTypes.Tracing;
    /**
     * Sets the exporter back to the no-op exporter.
     * @return The tracing object.
     */
    unregisterExporter(exporter: webTypes.Exporter): webTypes.Tracing;
}