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鏈接:https://mp.weixin.qq.com/s/cPLkefpEb3w12-uoiqzTig
作者:連凌能
Android上圖片加載的解決方案有多種,但是官方認(rèn)可的是Glide。Glide提供簡(jiǎn)潔易用的api,整個(gè)框架也方便擴(kuò)展,比如可以替換網(wǎng)絡(luò)請(qǐng)求庫(kù),同時(shí)也提供了完備的緩存機(jī)制,應(yīng)用層不需要自己去管理圖片的緩存與獲取,框架會(huì)分成內(nèi)存緩存,文件緩存和遠(yuǎn)程緩存。本文不會(huì)從簡(jiǎn)單的使用著手,會(huì)把重點(diǎn)放在緩存機(jī)制的分析上。
開(kāi)始之前,關(guān)于Glide緩存請(qǐng)先思考幾個(gè)問(wèn)題:
Glide有幾級(jí)緩存?
Glide內(nèi)存緩存之間是什么關(guān)系?
Glide本地文件IO和網(wǎng)絡(luò)請(qǐng)求是一個(gè)線程嗎?如果不是,怎么實(shí)現(xiàn)線程切換?
加載開(kāi)始入口從Engine.load()開(kāi)始,先看下對(duì)這個(gè)方法的注釋,
會(huì)先檢查(Active Resources),如果有就直接返回,Active Resources沒(méi)有被引用的資源會(huì)放入Memory Cache,如果Active Resources沒(méi)有,會(huì)往下走。
檢查Memory Cache中是否有需要的資源,如果有就返回,Memory Cache中沒(méi)有就繼續(xù)往下走。
* Starts a load for the given arguments.
*
* <p>Must be called on the main thread.
*
* <p>The flow for any request is as follows:
* <ul>
* <li>Check the current set of actively used resources, return the active resource if
* present, and move any newly inactive resources into the memory cache.</li>
* <li>Check the memory cache and provide the cached resource if present.</li>
* <li>Check the current set of in progress loads and add the cb to the in progress load if
* one is present.</li>
* <li>Start a new load.</li>
* </ul>
ok, find the source code.
public <R> LoadStatus load(
GlideContext glideContext,
Object model,
Key signature,
int width,
int height,
Class<?> resourceClass,
Class<R> transcodeClass,
Priority priority,
DiskCacheStrategy diskCacheStrategy,
Map<Class<?>, Transformation<?>> transformations,
boolean isTransformationRequired,
boolean isScaleOnlyOrNoTransform,
Options options,
boolean isMemoryCacheable,
boolean useUnlimitedSourceExecutorPool,
boolean useAnimationPool,
boolean onlyRetrieveFromCache,
ResourceCallback cb) {
Util.assertMainThread();
long startTime = VERBOSE_IS_LOGGABLE ? LogTime.getLogTime() : 0;
EngineKey key = keyFactory.buildKey(model, signature, width, height, transformations,
resourceClass, transcodeClass, options);
// focus 1
EngineResource<?> active = loadFromActiveResources(key, isMemoryCacheable);
if (active != null) {
cb.onResourceReady(active, DataSource.MEMORY_CACHE);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Loaded resource from active resources", startTime, key);
}
return null;
}
// focus 2
EngineResource<?> cached = loadFromCache(key, isMemoryCacheable);
if (cached != null) {
cb.onResourceReady(cached, DataSource.MEMORY_CACHE);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Loaded resource from cache", startTime, key);
}
return null;
}
// focus 3
EngineJob<?> current = jobs.get(key, onlyRetrieveFromCache);
if (current != null) {
current.addCallback(cb);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Added to existing load", startTime, key);
}
return new LoadStatus(cb, current);
}
EngineJob<R> engineJob =
engineJobFactory.build(
key,
isMemoryCacheable,
useUnlimitedSourceExecutorPool,
useAnimationPool,
onlyRetrieveFromCache);
DecodeJob<R> decodeJob =
decodeJobFactory.build(
glideContext,
model,
key,
signature,
width,
height,
resourceClass,
transcodeClass,
priority,
diskCacheStrategy,
transformations,
isTransformationRequired,
isScaleOnlyOrNoTransform,
onlyRetrieveFromCache,
options,
engineJob);
jobs.put(key, engineJob);
engineJob.addCallback(cb);
// focus 4
engineJob.start(decodeJob);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Started new load", startTime, key);
}
return new LoadStatus(cb, engineJob);
}
先看到 focus 1,這一步會(huì)從 ActiveResources 中加載資源,首先判斷是否使用內(nèi)存緩存,否的話返回null;否則到 ActiveResources 中取數(shù)據(jù):
// Engine.java
@Nullable
private EngineResource<?> loadFromActiveResources(Key key, boolean isMemoryCacheable) {
if (!isMemoryCacheable) {
return null;
}
EngineResource<?> active = activeResources.get(key);
if (active != null) {
active.acquire();
}
return active;
}
接下來(lái)看下ActiveResources, 其實(shí)是用過(guò)弱引用保存使用過(guò)的資源。
final class ActiveResources {
...
private final Handler mainHandler = new Handler(Looper.getMainLooper(), new Callback() {
@Override
public boolean handleMessage(Message msg) {
if (msg.what == MSG_CLEAN_REF) {
cleanupActiveReference((ResourceWeakReference) msg.obj);
return true;
}
return false;
}
});
@VisibleForTesting
final Map<Key, ResourceWeakReference> activeEngineResources = new HashMap<>();
...
}
成功取到數(shù)據(jù)后回調(diào)類(lèi)型也是內(nèi)存緩存:
EngineResource<?> cached = loadFromCache(key, isMemoryCacheable);
if (cached != null) {
cb.onResourceReady(cached, DataSource.MEMORY_CACHE);
return null;
}
接著回到Engine.load()中繼續(xù)看到focus 2,如果在cache中找到就是remove掉,然后返回EngineResource,其中需要EngineResource進(jìn)行acquire一下,這個(gè)后面再看,然后會(huì)把資源移到ActiveResources中,也就是上面提到的緩存:
// Engine.java
private final MemoryCache cache;
private EngineResource<?> loadFromCache(Key key, boolean isMemoryCacheable) {
if (!isMemoryCacheable) {
return null;
}
EngineResource<?> cached = getEngineResourceFromCache(key);
if (cached != null) {
cached.acquire();
activeResources.activate(key, cached);
}
return cached;
}
private EngineResource<?> getEngineResourceFromCache(Key key) {
Resource<?> cached = cache.remove(key);
final EngineResource<?> result;
if (cached == null) {
result = null;
} else if (cached instanceof EngineResource) {
// Save an object allocation if we've cached an EngineResource (the typical case).
result = (EngineResource<?>) cached;
} else {
result = new EngineResource<>(cached, true /*isMemoryCacheable*/, true /*isRecyclable*/);
}
return result;
}
其中cache是MemoryCache接口的實(shí)現(xiàn),如果沒(méi)設(shè)置,默認(rèn)在build的時(shí)候是LruResourceCache, 也就是熟悉的LRU Cache:
// GlideBuilder.java
if (memoryCache == null) {
memoryCache = new LruResourceCache(memorySizeCalculator.getMemoryCacheSize());
}
再看下EngineResource,主要是對(duì)資源增加了引用計(jì)數(shù)的功能:
// EngineResource.java
private final boolean isCacheable;
private final boolean isRecyclable;
private ResourceListener listener;
private Key key;
private int acquired;
private boolean isRecycled;
private final Resource<Z> resource;
interface ResourceListener {
void onResourceReleased(Key key, EngineResource<?> resource);
}
EngineResource(Resource<Z> toWrap, boolean isCacheable, boolean isRecyclable) {
resource = Preconditions.checkNotNull(toWrap);
this.isCacheable = isCacheable;
this.isRecyclable = isRecyclable;
}
void setResourceListener(Key key, ResourceListener listener) {
this.key = key;
this.listener = listener;
}
Resource<Z> getResource() {
return resource;
}
boolean isCacheable() {
return isCacheable;
}
@NonNull
@Override
public Class<Z> getResourceClass() {
return resource.getResourceClass();
}
@NonNull
@Override
public Z get() {
return resource.get();
}
@Override
public int getSize() {
return resource.getSize();
}
@Override
public void recycle() {
if (acquired > 0) {
throw new IllegalStateException("Cannot recycle a resource while it is still acquired");
}
if (isRecycled) {
throw new IllegalStateException("Cannot recycle a resource that has already been recycled");
}
isRecycled = true;
if (isRecyclable) {
resource.recycle();
}
}
void acquire() {
if (isRecycled) {
throw new IllegalStateException("Cannot acquire a recycled resource");
}
if (!Looper.getMainLooper().equals(Looper.myLooper())) {
throw new IllegalThreadStateException("Must call acquire on the main thread");
}
++acquired;
}
void release() {
if (acquired <= 0) {
throw new IllegalStateException("Cannot release a recycled or not yet acquired resource");
}
if (!Looper.getMainLooper().equals(Looper.myLooper())) {
throw new IllegalThreadStateException("Must call release on the main thread");
}
if (--acquired == 0) {
listener.onResourceReleased(key, this);
}
}
在release后會(huì)判斷引用計(jì)數(shù)是否為0,如果是0就會(huì)回調(diào)onResourceReleased,在這里就是Engine,然后會(huì)把資源從ActiveResources中移除,資源默認(rèn)是可緩存的,因此會(huì)把資源放到LruCache中。
// Engine.java
@Override
public void onResourceReleased(Key cacheKey, EngineResource<?> resource) {
Util.assertMainThread();
activeResources.deactivate(cacheKey);
if (resource.isCacheable()) {
cache.put(cacheKey, resource);
} else {
resourceRecycler.recycle(resource);
}
}
// ActiveResources.java
void activate(Key key, EngineResource<?> resource) {
ResourceWeakReference toPut =
new ResourceWeakReference(
key,
resource,
getReferenceQueue(),
isActiveResourceRetentionAllowed);
ResourceWeakReference removed = activeEngineResources.put(key, toPut);
if (removed != null) {
removed.reset();
}
}
void deactivate(Key key) {
ResourceWeakReference removed = activeEngineResources.remove(key);
if (removed != null) {
removed.reset();
}
}
如果是回收呢,看看上面的EngineResource,如果引用計(jì)數(shù)為0并且還沒(méi)與回收,就會(huì)調(diào)用真正的Resource.recycle(),看其中的一個(gè)BitmapResource是怎么回收的,就是放到Bitmap池中,也是用的LRU Cache,這個(gè)和今天的主題不相關(guān),就不繼續(xù)往下拓展。
// BitmapResource.java
@Override
public void recycle() {
bitmapPool.put(bitmap);
}
思路再拉到Engine.load()的流程中,接下來(lái)該看focus 3,這里再貼一下代碼,如果job已經(jīng)在運(yùn)行了,那么直接添加一個(gè)回調(diào)后返回LoadStatus,這個(gè)可以允許用戶取消任務(wù):
// Engine.java
EngineJob<?> current = jobs.get(key, onlyRetrieveFromCache);
if (current != null) {
current.addCallback(cb);
if (VERBOSE_IS_LOGGABLE) {
logWithTimeAndKey("Added to existing load", startTime, key);
}
return new LoadStatus(cb, current);
}
// LoadStatus
public static class LoadStatus {
private final EngineJob<?> engineJob;
private final ResourceCallback cb;
LoadStatus(ResourceCallback cb, EngineJob<?> engineJob) {
this.cb = cb;
this.engineJob = engineJob;
}
public void cancel() {
engineJob.removeCallback(cb);
}
}
接著往下看到focus 4, 到這里就需要?jiǎng)?chuàng)建后臺(tái)任務(wù)去拉取磁盤(pán)文件或者發(fā)起網(wǎng)絡(luò)請(qǐng)求。
// Engine.java
EngineJob<R> engineJob =
engineJobFactory.build(
key,
isMemoryCacheable,
useUnlimitedSourceExecutorPool,
useAnimationPool,
onlyRetrieveFromCache);
DecodeJob<R> decodeJob =
decodeJobFactory.build(
glideContext,
model,
key,
signature,
width,
height,
resourceClass,
transcodeClass,
priority,
diskCacheStrategy,
transformations,
isTransformationRequired,
isScaleOnlyOrNoTransform,
onlyRetrieveFromCache,
options,
engineJob);
jobs.put(key, engineJob);
engineJob.addCallback(cb);
engineJob.start(decodeJob);
return new LoadStatus(cb, engineJob);
先構(gòu)造兩個(gè)job,一個(gè)是EngineJob,另外一個(gè)DecodeJob,其中DecodeJob會(huì)根據(jù)需要解碼的資源來(lái)源分成下面幾個(gè)階段:
// DecodeJob.java
/**
* Where we're trying to decode data from.
*/
private enum Stage {
/** The initial stage. */
INITIALIZE,
/** Decode from a cached resource. */
RESOURCE_CACHE,
/** Decode from cached source data. */
DATA_CACHE,
/** Decode from retrieved source. */
SOURCE,
/** Encoding transformed resources after a successful load. */
ENCODE,
/** No more viable stages. */
FINISHED,
}
在構(gòu)造DecodeJob時(shí)會(huì)把狀態(tài)置為INITIALIZE。
構(gòu)造完兩個(gè) Job 后會(huì)調(diào)用 EngineJob.start(DecodeJob),首先會(huì)調(diào)用getNextStage來(lái)確定下一個(gè)階段,這里面跟DiskCacheStrategy這個(gè)傳入的磁盤(pán)緩存策略有關(guān)。
磁盤(pán)策略有下面幾種:
**ALL:?**緩存原始數(shù)據(jù)和轉(zhuǎn)換后的數(shù)據(jù)
**NONE:?**不緩存
**DATA:?**原始數(shù)據(jù),未經(jīng)過(guò)解碼或者轉(zhuǎn)換
**RESOURCE:?**緩存經(jīng)過(guò)解碼的數(shù)據(jù)
默認(rèn)的AUTOMATIC方式是允許解碼緩存的RESOURCE:
public static final DiskCacheStrategy AUTOMATIC = new DiskCacheStrategy() {
@Override
public boolean isDataCacheable(DataSource dataSource) {
return dataSource == DataSource.REMOTE;
}
@Override
public boolean isResourceCacheable(boolean isFromAlternateCacheKey, DataSource dataSource,
EncodeStrategy encodeStrategy) {
return ((isFromAlternateCacheKey && dataSource == DataSource.DATA_DISK_CACHE)
|| dataSource == DataSource.LOCAL)
&& encodeStrategy == EncodeStrategy.TRANSFORMED;
}
@Override
public boolean decodeCachedResource() {
return true;
}
@Override
public boolean decodeCachedData() {
return true;
}
};
所以在 getNextStage 會(huì)先返回Stage.RESOURCE_CACHE,然后在start中會(huì)返回diskCacheExecutor,然后開(kāi)始執(zhí)行DecodeJob:
// EngineJob.java
public void start(DecodeJob<R> decodeJob) {
this.decodeJob = decodeJob;
GlideExecutor executor = decodeJob.willDecodeFromCache()
? diskCacheExecutor
: getActiveSourceExecutor();
executor.execute(decodeJob);
}
// DecodeJob.java
boolean willDecodeFromCache() {
Stage firstStage = getNextStage(Stage.INITIALIZE);
return firstStage == Stage.RESOURCE_CACHE || firstStage == Stage.DATA_CACHE;
}
private Stage getNextStage(Stage current) {
switch (current) {
case INITIALIZE:
return diskCacheStrategy.decodeCachedResource()
? Stage.RESOURCE_CACHE : getNextStage(Stage.RESOURCE_CACHE);
case RESOURCE_CACHE:
return diskCacheStrategy.decodeCachedData()
? Stage.DATA_CACHE : getNextStage(Stage.DATA_CACHE);
case DATA_CACHE:
// Skip loading from source if the user opted to only retrieve the resource from cache.
return onlyRetrieveFromCache ? Stage.FINISHED : Stage.SOURCE;
case SOURCE:
case FINISHED:
return Stage.FINISHED;
default:
throw new IllegalArgumentException("Unrecognized stage: " + current);
}
}
DecodeJob會(huì)回調(diào)run()開(kāi)始執(zhí)行, run()中調(diào)用runWrapped執(zhí)行工作,這里runReason還是RunReason.INITIALIZE ,根據(jù)前面的分析指導(dǎo)這里會(huì)獲得一個(gè)ResourceCacheGenerator,然后調(diào)用runGenerators:
// DecodeJob.java
private void runWrapped() {
switch (runReason) {
case INITIALIZE:
stage = getNextStage(Stage.INITIALIZE);
currentGenerator = getNextGenerator();
runGenerators();
break;
case SWITCH_TO_SOURCE_SERVICE:
runGenerators();
break;
case DECODE_DATA:
decodeFromRetrievedData();
break;
default:
throw new IllegalStateException("Unrecognized run reason: " + runReason);
}
}
private DataFetcherGenerator getNextGenerator() {
switch (stage) {
case RESOURCE_CACHE:
return new ResourceCacheGenerator(decodeHelper, this);
case DATA_CACHE:
return new DataCacheGenerator(decodeHelper, this);
case SOURCE:
return new SourceGenerator(decodeHelper, this);
case FINISHED:
return null;
default:
throw new IllegalStateException("Unrecognized stage: " + stage);
}
}
在 runGenerators 中,會(huì)調(diào)用 startNext,目前currentGenerator是ResourceCacheGenerator, 那么就是調(diào)用它的startNext方法:
// DecodeJob.java
private void runGenerators() {
currentThread = Thread.currentThread();
startFetchTime = LogTime.getLogTime();
boolean isStarted = false;
while (!isCancelled && currentGenerator != null
&& !(isStarted = currentGenerator.startNext())) {
stage = getNextStage(stage);
currentGenerator = getNextGenerator();
if (stage == Stage.SOURCE) {
reschedule();
return;
}
}
// We've run out of stages and generators, give up.
if ((stage == Stage.FINISHED || isCancelled) && !isStarted) {
notifyFailed();
}
}
看下ResourceCacheGenerator.startNext(), 這里面就是重點(diǎn)邏輯了,首先從Registry中獲取支持資源類(lèi)型的ModelLoader(其中ModelLoader是在構(gòu)造Glide的時(shí)候傳進(jìn)去), 然后從ModelLoader中構(gòu)造LoadData,接著就能拿到DataFetcher,(關(guān)于ModelLoader/LoadData/DataFetcher之間的關(guān)系不在本次范圍內(nèi),后面有機(jī)會(huì)再另寫(xiě))通過(guò)它的loadData方法加載數(shù)據(jù):
@Override
public boolean startNext() {
List<Key> sourceIds = helper.getCacheKeys();
if (sourceIds.isEmpty()) {
return false;
}
List<Class<?>> resourceClasses = helper.getRegisteredResourceClasses();
if (resourceClasses.isEmpty()) {
if (File.class.equals(helper.getTranscodeClass())) {
return false;
}
}
while (modelLoaders == null || !hasNextModelLoader()) {
resourceClassIndex++;
if (resourceClassIndex >= resourceClasses.size()) {
sourceIdIndex++;
if (sourceIdIndex >= sourceIds.size()) {
return false;
}
resourceClassIndex = 0;
}
Key sourceId = sourceIds.get(sourceIdIndex);
Class<?> resourceClass = resourceClasses.get(resourceClassIndex);
Transformation<?> transformation = helper.getTransformation(resourceClass);
currentKey =
new ResourceCacheKey(// NOPMD AvoidInstantiatingObjectsInLoops
helper.getArrayPool(),
sourceId,
helper.getSignature(),
helper.getWidth(),
helper.getHeight(),
transformation,
resourceClass,
helper.getOptions());
cacheFile = helper.getDiskCache().get(currentKey);
if (cacheFile != null) {
sourceKey = sourceId;
modelLoaders = helper.getModelLoaders(cacheFile);
modelLoaderIndex = 0;
}
}
loadData = null;
boolean started = false;
while (!started && hasNextModelLoader()) {
ModelLoader<File, ?> modelLoader = modelLoaders.get(modelLoaderIndex++);
loadData = modelLoader.buildLoadData(cacheFile,
helper.getWidth(), helper.getHeight(), helper.getOptions());
if (loadData != null && helper.hasLoadPath(loadData.fetcher.getDataClass())) {
started = true;
loadData.fetcher.loadData(helper.getPriority(), this);
}
}
return started;
}
如果在Resource中找不到需要的資源,那么startNext就會(huì)返回false,在runGenerators中就會(huì)進(jìn)入循環(huán)體內(nèi):
接著會(huì)重復(fù)上面執(zhí)行g(shù)etNextStage,由于現(xiàn)在Stage已經(jīng)是RESOURCE_CACHE,所以接下來(lái)會(huì)返回DataCacheGenerator,執(zhí)行邏輯和上面的ResourceCacheGenerator是一樣的,如果還是沒(méi)有找到需要的,進(jìn)入循環(huán)體內(nèi)。
此時(shí)getNextStage會(huì)根據(jù)用于是否設(shè)置只從磁盤(pán)中獲取資源,如果是就會(huì)通知失敗,回調(diào)onLoadFailed;如果不是就設(shè)置當(dāng)前Stage為Stage.SOURCE,接著往下走。
狀態(tài)就會(huì)進(jìn)入循環(huán)內(nèi)部的if條件邏輯里面,調(diào)用reschedule。
在reschedule把runReason設(shè)置成SWITCH_TO_SOURCE_SERVICE,然后通過(guò)callback回調(diào)。
DecodeJob中的callback是EngineJob傳遞過(guò)來(lái)的,所以現(xiàn)在返回到EngineJob。
在Stage.SOURCE階段,通過(guò)getNextGenerator返回的是SourceGenerator,所以目前的currentGenerator就是它。
流程還是一樣的,SourceGenerator還是調(diào)用startNext方法,獲取到對(duì)應(yīng)的DataFetcher,這里其實(shí)是HttpUrlFetcher,發(fā)起網(wǎng)絡(luò)請(qǐng)求。
// DecodeJob.java
private void runGenerators() {
...
while (!isCancelled && currentGenerator != null
&& !(isStarted = currentGenerator.startNext())) {
stage = getNextStage(stage);
currentGenerator = getNextGenerator();
if (stage == Stage.SOURCE) {
reschedule();
return;
}
}
...
}
@Override
public void reschedule() {
runReason = RunReason.SWITCH_TO_SOURCE_SERVICE;
callback.reschedule(this);
}
// EngineJob.java
@Override
public void reschedule(DecodeJob<?> job) {
getActiveSourceExecutor().execute(job);
}
先緩一緩,本文其實(shí)到了上面已經(jīng)可以結(jié)束了,Glide涉及到的五級(jí)緩存都已經(jīng)涉及到了,是真的就可以結(jié)束了嗎?不是的,網(wǎng)絡(luò)請(qǐng)求回來(lái)和緩存還有關(guān)系嗎?接著看到HttpUrlFetcher,下載成功后回調(diào)onDataReady,其中callback是SourceGenerator:
// HttpUrlFetcher.java
@Override
public void loadData(@NonNull Priority priority,
@NonNull DataCallback<? super InputStream> callback) {
long startTime = LogTime.getLogTime();
try {
InputStream result = loadDataWithRedirects(glideUrl.toURL(), 0, null, glideUrl.getHeaders());
callback.onDataReady(result);
} catch (IOException e) {
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(TAG, "Failed to load data for url", e);
}
callback.onLoadFailed(e);
} finally {
if (Log.isLoggable(TAG, Log.VERBOSE)) {
Log.v(TAG, "Finished http url fetcher fetch in " + LogTime.getElapsedMillis(startTime));
}
}
}
// EngineJob.java
@Override
public void reschedule(DecodeJob<?> job) {
getActiveSourceExecutor().execute(job);
}
正常情況會(huì)進(jìn)入if判斷邏輯里面,賦值dataToCache,然后回調(diào)cb.reschedule,而cb就是DecodeJob構(gòu)造SourceGenerator的時(shí)候傳入,cb是DecodeJob。
// SourceGenerator.java
@Override
public void onDataReady(Object data) {
DiskCacheStrategy diskCacheStrategy = helper.getDiskCacheStrategy();
if (data != null && diskCacheStrategy.isDataCacheable(loadData.fetcher.getDataSource())) {
dataToCache = data;
cb.reschedule();
} else {
cb.onDataFetcherReady(loadData.sourceKey, data, loadData.fetcher,
loadData.fetcher.getDataSource(), originalKey);
}
}
DecodeJob在reschedule回調(diào)EngineJob,最后還是回到SourceGenerator中的startNext()邏輯。
// DecodeJob.java
private DataFetcherGenerator getNextGenerator() {
switch (stage) {
case RESOURCE_CACHE:
return new ResourceCacheGenerator(decodeHelper, this);
case DATA_CACHE:
return new DataCacheGenerator(decodeHelper, this);
case SOURCE:
return new SourceGenerator(decodeHelper, this);
case FINISHED:
return null;
default:
throw new IllegalStateException("Unrecognized stage: " + stage);
}
}
@Override
public void reschedule() {
runReason = RunReason.SWITCH_TO_SOURCE_SERVICE;
callback.reschedule(this);
}
和第一次進(jìn)來(lái)的邏輯不一樣,現(xiàn)在dataToCache != null,進(jìn)入第一個(gè)if邏輯。
在邏輯里面調(diào)用cacheData,邏輯很明顯,保持?jǐn)?shù)據(jù)到本地,然后會(huì)構(gòu)造一個(gè)DataCacheGenerator。
而DataCacheGenerator前面已經(jīng)分析過(guò)了,就是用來(lái)加載本地原始數(shù)據(jù)的,這回會(huì)加載成功,返回true。
// SourceGenerator.java
@Override
public boolean startNext() {
if (dataToCache != null) {
Object data = dataToCache;
dataToCache = null;
cacheData(data);
}
if (sourceCacheGenerator != null && sourceCacheGenerator.startNext()) {
return true;
}
...
}
private void cacheData(Object dataToCache) {
long startTime = LogTime.getLogTime();
try {
Encoder<Object> encoder = helper.getSourceEncoder(dataToCache);
DataCacheWriter<Object> writer =
new DataCacheWriter<>(encoder, dataToCache, helper.getOptions());
originalKey = new DataCacheKey(loadData.sourceKey, helper.getSignature());
helper.getDiskCache().put(originalKey, writer);
} finally {
loadData.fetcher.cleanup();
}
sourceCacheGenerator =
new DataCacheGenerator(Collections.singletonList(loadData.sourceKey), helper, this);
}
接下來(lái)就是一系列的回調(diào)了:
DataCacheGenerator的startNext邏輯里面會(huì)給DataFetcher傳遞自身作為callback,在加載本地?cái)?shù)據(jù)成功后回調(diào)onDataReady。
// DataCacheGenerator
@Override
public boolean startNext() {
...
loadData = null;
boolean started = false;
while (!started && hasNextModelLoader()) {
...
if (loadData != null && helper.hasLoadPath(loadData.fetcher.getDataClass())) {
started = true;
loadData.fetcher.loadData(helper.getPriority(), this);
}
}
return started;
}
@Override
public void onDataReady(Object data) {
cb.onDataFetcherReady(sourceKey, data, loadData.fetcher, DataSource.DATA_DISK_CACHE, sourceKey);
}
而cb現(xiàn)在是SourceGenerator傳遞過(guò)來(lái),SourceGenerator再回調(diào)它自己的cb,是DecodeJob在構(gòu)造它的時(shí)候傳過(guò)來(lái)。
// SourceGenerator.java
@Override
public void onDataFetcherReady(Key sourceKey, Object data, DataFetcher<?> fetcher,
DataSource dataSource, Key attemptedKey) {
cb.onDataFetcherReady(sourceKey, data, fetcher, loadData.fetcher.getDataSource(), sourceKey);
}
// DecodeJob.java
@Override
public void onDataFetcherReady(Key sourceKey, Object data, DataFetcher<?> fetcher,
DataSource dataSource, Key attemptedKey) {
this.currentSourceKey = sourceKey;
this.currentData = data;
this.currentFetcher = fetcher;
this.currentDataSource = dataSource;
this.currentAttemptingKey = attemptedKey;
if (Thread.currentThread() != currentThread) {
runReason = RunReason.DECODE_DATA;
callback.reschedule(this);
} else {
try {
decodeFromRetrievedData();
} finally {
GlideTrace.endSection();
}
}
}
在上面SourceGenerator把DecodeJob切換到ActiveSourceExecutor線程中執(zhí)行,還記得一開(kāi)始DecodeJob是在哪啟動(dòng)的嗎?在EngineJob中啟動(dòng),然后是把DecodeJob放到diskCacheExecutor中執(zhí)行。
// EngineJob.java
public void start(DecodeJob<R> decodeJob) {
this.decodeJob = decodeJob;
GlideExecutor executor = decodeJob.willDecodeFromCache()
? diskCacheExecutor
: getActiveSourceExecutor();
executor.execute(decodeJob);
}
所以上面在DecodeJob的onDataFetcherReady會(huì)走到第一個(gè)if邏輯里面,然后賦值runReason = RunReason.DECODE_DATA,再一次回調(diào)Engine.reschedule,將工作線程切換到ActiveSourceExecutor。
// Engine.java
@Override
public void reschedule(DecodeJob<?> job) {
// Even if the job is cancelled here, it still needs to be scheduled so that it can clean itself
// up.
getActiveSourceExecutor().execute(job);
}
//
然后還是走到DecodeJob, 現(xiàn)在會(huì)進(jìn)入DECODE_DATA分支,在這里面會(huì)調(diào)用ResourceDecoder把數(shù)據(jù)解碼:
private void runWrapped() {
switch (runReason) {
case INITIALIZE:
stage = getNextStage(Stage.INITIALIZE);
currentGenerator = getNextGenerator();
runGenerators();
break;
case SWITCH_TO_SOURCE_SERVICE:
runGenerators();
break;
case DECODE_DATA:
decodeFromRetrievedData();
break;
default:
throw new IllegalStateException("Unrecognized run reason: " + runReason);
}
}
解碼成功后調(diào)用notifyComplete(result, dataSource);
private void notifyComplete(Resource<R> resource, DataSource dataSource) {
setNotifiedOrThrow();
callback.onResourceReady(resource, dataSource);
}
現(xiàn)在回答一下開(kāi)頭的幾個(gè)問(wèn)題。
活動(dòng)資源 (Active Resources)
內(nèi)存緩存 (Memory Cache)
資源類(lèi)型(Resource Disk Cache)
原始數(shù)據(jù) (Data Disk Cache)
專門(mén)畫(huà)了一幅圖表明這個(gè)關(guān)系,言簡(jiǎn)意賅。
明顯不是,本地IO通過(guò)diskCacheExecutor,而網(wǎng)絡(luò)IO通過(guò)ActiveSourceExecutor
不是直接返回給用戶,會(huì)在SourceGenerator中構(gòu)造一個(gè)DataCacheGenerator來(lái)取數(shù)據(jù)。
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