Exoplayer的缓存二下载服务DownloadService

Exoplayer的缓存 – 二下载服务 DownloadService

文章目录

DownloadService
- send 指令
- onStartCommand 解析Intent
DownloadManager
- DownloadManager 初始化
- addDownload 的实现
- **InternalHandler** 的**handleMessage** 方法
Download
- addDownload
- syncTasks
DownloadManager.Task
- syncQueuedDownload
- Task.run
ProgressiveDownloader
- ProgressiveDownloader 初始化CacheWriter
- download cache
CacheWrite
DownloadIndex

DownloadService

send 指令

DownloadService 是一个android 标准的service, DownloadService 封装了下载的多个指令, 由一系列静态函数组成：

sendAddDownload
sendRemoveDownload
sendRemoveAllDownloads
sendRemoveAllDownloads
sendResumeDownloads
sendPauseDownloads

DownloadService 在发送这些指令时，先把这些指令参数构建一个Intent，然后通过startService 的方法发送Intent 到 Service.

/*** Starts the service if not started already and adds a new download.** @param context A {@link Context}.* @param clazz The concrete download service to be started.* @param downloadRequest The request to be executed.* @param foreground Whether the service is started in the foreground.*/
public static void sendAddDownload(Context context,Class<? extends DownloadService> clazz,DownloadRequest downloadRequest,boolean foreground) {Intent intent = buildAddDownloadIntent(context, clazz, downloadRequest, foreground);startService(context, intent, foreground);
}

在Service 的 onStartCommand(@Nullable Intent intent, int flags, int startId) 中解析Intent, 并从Intent 中获取下载的参数，传递到 DownloadManager

onStartCommand 解析Intent

public int onStartCommand(@Nullable Intent intent, int flags, int startId) {if (intent != null) {intentAction = intent.getAction();contentId = intent.getStringExtra(KEY_CONTENT_ID);...}DownloadManager downloadManager =Assertions.checkNotNull(downloadManagerHelper).downloadManager;switch (intentAction) {...case ACTION_ADD_DOWNLOAD:@NullableDownloadRequest downloadRequest =Assertions.checkNotNull(intent).getParcelableExtra(KEY_DOWNLOAD_REQUEST);if (downloadRequest == null) {Log.e(TAG, "Ignored ADD_DOWNLOAD: Missing " + KEY_DOWNLOAD_REQUEST + " extra");} else {...downloadManager.addDownload(downloadRequest, stopReason);}break;...default:Log.e(TAG, "Ignored unrecognized action: " + intentAction);break;}return START_STICKY;
}

DownloadManager

DownloadManager 实现真正的下载管理工作。

DownloadManager 初始化的时候传入两个参数

WritableDownloadIndex downloadIndex 保存下载信息的数据库 Exoplayer 默认实现 DefaultDownloadIndex(databaseProvider)
DownloaderFactory downloaderFactory 生成下载器的工厂 Exoplayer 默认实现 DefaultDownloaderFactory(new DownloaderConstructorHelper(cache, upstreamFactory)));

DownloadManager 构造函数初始化的时候初始化了两个变量 internalThread 和 internalHandler

用于内部的消息转发

DownloadManager 初始化

public DownloadManager(Context context, WritableDownloadIndex downloadIndex, DownloaderFactory downloaderFactory) {this.context = context.getApplicationContext();this.downloadIndex = downloadIndex;HandlerThread internalThread = new HandlerThread("ExoPlayer:DownloadManager");internalThread.start();internalHandler =new InternalHandler(internalThread,downloadIndex,downloaderFactory,mainHandler,maxParallelDownloads,minRetryCount,downloadsPaused);internalHandler.obtainMessage(MSG_INITIALIZE, notMetRequirements, /* unused */ 0).sendToTarget();
}

addDownload 的实现

addDownload 内部通过internalHandler 发送消息到internalThread 线程进行消息处理

/*** Adds a download defined by the given request.** @param request The download request.*/
public void addDownload(DownloadRequest request) {addDownload(request, STOP_REASON_NONE);
}public void addDownload(DownloadRequest request, int stopReason) {pendingMessages++;internalHandler.obtainMessage(MSG_ADD_DOWNLOAD, stopReason, /* unused */ 0, request).sendToTarget();
}

InternalHandler 的handleMessage 方法

public void handleMessage(Message message) {boolean processedExternalMessage = true;switch (message.what) {case MSG_INITIALIZE:int notMetRequirements = message.arg1;initialize(notMetRequirements);break;......case MSG_ADD_DOWNLOAD:DownloadRequest request = (DownloadRequest) message.obj;stopReason = message.arg1;addDownload(request, stopReason);break;

Download

Download 用于记录下载相关的信息。下载状态，时间，下载进度等。

public Download(DownloadRequest request,@State int state,long startTimeMs,long updateTimeMs,long contentLength,int stopReason,@FailureReason int failureReason,DownloadProgress progress) {this.request = request;this.state = state;this.startTimeMs = startTimeMs;this.updateTimeMs = updateTimeMs;this.contentLength = contentLength;this.stopReason = stopReason;this.failureReason = failureReason;this.progress = progress;
}

addDownload

最终在 private void addDownload(DownloadRequest request, int stopReason) 中把下载的DownloadRequest 转化为Download，通过putDownload 把Download 放入到下载队列中。在构建Download 首先检查下是否有正在下载的Download，如果有 mergeRequest 两个下载请求合并

private void addDownload(DownloadRequest request, int stopReason) {@Nullable Download download = getDownload(request.id, /* loadFromIndex= */ true);long nowMs = System.currentTimeMillis();if (download != null) {putDownload(mergeRequest(download, request, stopReason, nowMs));} else {putDownload(new Download(request,stopReason != STOP_REASON_NONE ? STATE_STOPPED : STATE_QUEUED,/* startTimeMs= */ nowMs,/* updateTimeMs= */ nowMs,/* contentLength= */ C.LENGTH_UNSET,stopReason,FAILURE_REASON_NONE));}syncTasks();
}

syncTasks

syncTasks 函数会根据当前下载队列的状态去同步下载任务

DownloadManager.Task

DownloadManager.Task Task 继承于Thread, 下载线程。

syncQueuedDownload

syncTasks 函数中根据下载状态调用到syncQueuedDownload 。

首先构建一个 downloaderFactory 创建一个Downloader，这里的Downloader 实例为ProgressiveDownloader,

然后构建一个Task ，然后Task 启动通过downloader 下载

private Task syncQueuedDownload(@Nullable Task activeTask, Download download) {Downloader downloader = downloaderFactory.createDownloader(download.request);activeTask =new Task(download.request,downloader,download.progress,/* isRemove= */ false,minRetryCount,/* internalHandler= */ this);activeTasks.put(download.request.id, activeTask);if (activeDownloadTaskCount++ == 0) {sendEmptyMessageDelayed(MSG_UPDATE_PROGRESS, UPDATE_PROGRESS_INTERVAL_MS);}activeTask.start();return activeTask;
}

Task.run

Task 的run 函数

@Override
public void run() {try {if (isRemove) {} else {while (!isCanceled) {try {downloader.download(/* progressListener= */ this);break;} catch (IOException e) {...}}}}} catch (InterruptedException e) {Thread.currentThread().interrupt();}@Nullable Handler internalHandler = this.internalHandler;if (internalHandler != null) {internalHandler.obtainMessage(MSG_TASK_STOPPED, this).sendToTarget();}
}

ProgressiveDownloader

ProgressiveDownloader 初始化CacheWriter

ProgressiveDownloader的构造函数中通过MediaItem CacheDataSource.Factory 生成 dataSource

然后 new 出 CacheWriter

public ProgressiveDownloader(MediaItem mediaItem, CacheDataSource.Factory cacheDataSourceFactory, Executor executor) {dataSpec =new DataSpec.Builder().setUri(mediaItem.localConfiguration.uri).setKey(mediaItem.localConfiguration.customCacheKey).setFlags(DataSpec.FLAG_ALLOW_CACHE_FRAGMENTATION).build();dataSource = cacheDataSourceFactory.createDataSourceForDownloading();@SuppressWarnings("nullness:methodref.receiver.bound")CacheWriter.ProgressListener progressListener = this::onProgress;cacheWriter =new CacheWriter(dataSource, dataSpec, /* temporaryBuffer= */ null, progressListener);
}

download cache

在download 函数中 cacheWriter 构造出一个Runable, 然后post 到 executor 中执行

public void download(@Nullable ProgressListener progressListener)throws IOException, InterruptedException {this.progressListener = progressListener;downloadRunnable =new RunnableFutureTask<Void, IOException>() {@Overrideprotected Void doWork() throws IOException {cacheWriter.cache();return null;}@Overrideprotected void cancelWork() {cacheWriter.cancel();}};try {boolean finished = false;while (!finished && !isCanceled) {if (priorityTaskManager != null) {priorityTaskManager.proceed(C.PRIORITY_DOWNLOAD);}executor.execute(downloadRunnable);try {downloadRunnable.get();} }} finally {}
}

CacheWrite

CacheWrite 中首先从cache 中获取已下载的长度，

public void cache() throws IOException {bytesCached = cache.getCachedBytes(cacheKey, dataSpec.position, dataSpec.length);if (dataSpec.length != C.LENGTH_UNSET) {endPosition = dataSpec.position + dataSpec.length;} else {long contentLength = ContentMetadata.getContentLength(cache.getContentMetadata(cacheKey));endPosition = contentLength == C.LENGTH_UNSET ? C.POSITION_UNSET : contentLength;}while (endPosition == C.POSITION_UNSET || nextPosition < endPosition) {if (blockLength > 0) {} else {// There's a hole of length -blockLength.blockLength = -blockLength;long nextRequestLength = blockLength == Long.MAX_VALUE ? C.LENGTH_UNSET : blockLength;nextPosition += readBlockToCache(nextPosition, nextRequestLength);}}
}

readBlockToCache 函数中通过 dataSource 读取数据

private long readBlockToCache(long position, long length) throws IOException {boolean isLastBlock = position + length == endPosition || length == C.LENGTH_UNSET;long resolvedLength = C.LENGTH_UNSET;boolean isDataSourceOpen = false;if (length != C.LENGTH_UNSET) {// If the length is specified, try to open the data source with a bounded request to avoid// the underlying network stack requesting more data than required.DataSpec boundedDataSpec =dataSpec.buildUpon().setPosition(position).setLength(length).build();try {resolvedLength = dataSource.open(boundedDataSpec);} catch (IOException e) {}}int totalBytesRead = 0;try {int bytesRead = 0;while (bytesRead != C.RESULT_END_OF_INPUT) {throwIfCanceled();bytesRead = dataSource.read(temporaryBuffer, /* offset= */ 0, temporaryBuffer.length);if (bytesRead != C.RESULT_END_OF_INPUT) {onNewBytesCached(bytesRead);totalBytesRead += bytesRead;}}if (isLastBlock) {onRequestEndPosition(position + totalBytesRead);}} catch (IOException e) {DataSourceUtil.closeQuietly(dataSource);throw e;}return totalBytesRead;
}

DownloadIndex

DownloadIndex 用于保存Download 的状态。在DownloadManager 中同步

DownloadIndex 的实例类型为 DefaultDownloadIndex，底层的实现是 SQLiteDatabase。通过DownloaderManger 注入DatabaseProvider

exoplayer 提供了一个默认实现 StandaloneDatabaseProvider