class DownloaderController() {
    ...

    suspend fun download(downloadRequest: DownloadRequest.Download): Flow<DownloadResponse> =
        mutex.withLock {
            withContext(Dispatchers.IO) {
                if (channelMap.containsKey(downloadRequest.url)) {
                    return@withContext channelMap[downloadRequest.url]!!.asFlow()
                }

                val downloadChannel = ConflatedBroadcastChannel<DownloadResponse>()
                channelMap[downloadRequest.url] = downloadChannel
                jobMap[downloadRequest.url] = launch { startDownloadSendChannel(downloadRequest, downloadChannel) }
				//It does not return immediately. It returns when launch coroutine complete to collect all items from flow.
                return@withContext channelMap[downloadRequest.url]!!.asFlow()
            }
        }

     private suspend fun startDownloadSendChannel(downloadRequest: DownloadRequest.Download,channel: ConflatedBroadcastChannel<DownloadResponse>) {
        downloader.download(downloadRequest)
            .buffer()
            .flowOn(Dispatchers.IO)
            .collect { channel.send(it) }
    }
}


class ViewModel {
    
    ...

    viewModelScope.launch {
            downloaderController
                .download(requestList.first())
                .collect { 
					//Waits for downloaderController.download method and all of its child coroutines complete
					//Not start colllecting immediately.
				}
}