src/vs/workbench/services/tunnel/browser/tunnelService.ts/TunnelService/retainOrCreateTunnel
class TunnelService:	protected retainOrCreateTunnel(_addressProvider: IAddressProvider, remoteHost: string, remotePort: number, localPort: number | undefined, elevateIfNeeded: boolean, privacy: string, protocol?: string): Promise<RemoteTunnel | undefined> | undefined {
		const existing = this.getTunnelFromMap(remoteHost, remotePort);
		if (existing) {
			++existing.refcount;
			return existing.value;
		}

		if (this._tunnelProvider) {
			return this.createWithProvider(this._tunnelProvider, remoteHost, remotePort, localPort, elevateIfNeeded, privacy, protocol);
		}
		return undefined;
	}