Swift 调度组是否阻止iOS中的主线程

我正在调用一些代码来查询和更新CallKit调用扩展，偶尔我会看到挂起，调用超时.我想我应该把它从主线程上移开，这样它就不会阻塞UI，但实际上情况并非如此吗？

用户界面被阻塞了，我不知道是下面这段代码，还是别的什么.

以下是查询函数:

    private func queryCallExtensionStatusWithDispatchGroup() {
        let dg = DispatchGroup()
        dg.enter()
        self.doQueryCallExtensionStatusWithDispatchGroup(dispatchGroup: dg)
        Logger.trace(TAG + "queryCallExtensionStatusWithDispatchGroup() WAITING .... ")
        let dispatchTimeoutResult = dg.wait(timeout:  DispatchTime.now() + DispatchTimeInterval.seconds(30))
        if dispatchTimeoutResult == .timedOut {
            Logger.info(TAG + "queryCallExtensionStatusWithDispatchGroup() TIMED OUT")
        } else {
            Logger.trace(TAG + "queryCallExtensionStatusWithDispatchGroup() LEFT")
        }
    }


private func doQueryCallExtensionStatusWithDispatchGroup(dispatchGroup:DispatchGroup)  {
<snip>
    dispatchGroup.leave() 
}

以及它的调用:

private let callExtensionQueue = DispatchQueue(label: "com.appname.serialQueue")

...
callExtensionQueue.async {
    self!.queryCallExtensionStatusWithDispatchGroup()
}