feat: Evict instead delete on prefetch (#6404)

This change gives better performance when playing low latency streams
shaka-project · Apr 5, 2024 · 0fc5814 · 0fc5814
1 parent 83d3f51
commit 0fc5814
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Showing 4 changed files with 8 additions and 38 deletions.
diff --git a/lib/media/segment_prefetch.js b/lib/media/segment_prefetch.js
@@ -25,9 +25,8 @@ shaka.media.SegmentPrefetch = class {
    * @param {number} prefetchLimit
    * @param {shaka.extern.Stream} stream
    * @param {shaka.media.SegmentPrefetch.FetchDispatcher} fetchDispatcher
-   * @param {boolean} deleteOnGet
    */
-  constructor(prefetchLimit, stream, fetchDispatcher, deleteOnGet = true) {
+  constructor(prefetchLimit, stream, fetchDispatcher) {
     /** @private {number} */
     this.prefetchLimit_ = prefetchLimit;
 
@@ -40,9 +39,6 @@ shaka.media.SegmentPrefetch = class {
     /** @private {shaka.media.SegmentPrefetch.FetchDispatcher} */
     this.fetchDispatcher_ = fetchDispatcher;
 
-    /** @private {boolean} */
-    this.deleteOnGet_ = deleteOnGet;
-
     /**
      * @private {!Map.<
      *        !(shaka.media.SegmentReference),
@@ -185,9 +181,6 @@ shaka.media.SegmentPrefetch = class {
       if (streamDataCallback) {
         segmentPrefetchOperation.setStreamDataCallback(streamDataCallback);
       }
-      if (this.deleteOnGet_) {
-        prefetchMap.delete(reference);
-      }
       if (reference instanceof shaka.media.SegmentReference) {
         shaka.log.debug(
             logPrefix,
@@ -242,14 +235,17 @@ shaka.media.SegmentPrefetch = class {
 
   /**
    * @param {number} time
+   * @param {boolean=} clearInitSegments
    */
-  evict(time) {
+  evict(time, clearInitSegments = false) {
     for (const ref of this.segmentPrefetchMap_.keys()) {
       if (time > ref.endTime) {
         this.abortPrefetchedSegment_(ref);
       }
     }
-    this.clearInitSegments_();
+    if (clearInitSegments) {
+      this.clearInitSegments_();
+    }
   }
 
   /**
@@ -296,24 +292,12 @@ shaka.media.SegmentPrefetch = class {
     this.clearInitSegments_();
   }
 
-  /**
-   * Update deleteOnGet.
-   * @param {boolean} newDeleteOnGet
-   * @public
-   */
-  deleteOnGet(newDeleteOnGet) {
-    this.deleteOnGet_ = newDeleteOnGet;
-  }
-
   /**
    * Called by Streaming Engine when switching variant.
    * @param {shaka.extern.Stream} stream
    * @public
    */
   switchStream(stream) {
-    goog.asserts.assert(this.deleteOnGet_,
-        'switchStream should only be used if deleteOnGet is true');
-
     if (stream && stream !== this.stream_) {
       this.clearAll();
       this.stream_ = stream;

diff --git a/lib/media/streaming_engine.js b/lib/media/streaming_engine.js
@@ -1030,10 +1030,6 @@ shaka.media.StreamingEngine = class {
                 (lang) => LanguageUtils.areLanguageCompatible(
                     variant.audio.language, lang))
         ) {
-          // if we're here, we are switching back to single stream prefetch,
-          // so we want to switch back to delete on get, even if the prefetch
-          // may end up getting deleted below.
-          prefetch.deleteOnGet(true);
           const type = /** @type {!shaka.util.ManifestParserUtils.ContentType}*/
             (variant.audio.type);
           const mediaState = this.mediaStates_.get(type);
@@ -1064,7 +1060,6 @@ shaka.media.StreamingEngine = class {
       // use the helper to create a segment prefetch to ensure that existing
       // objects are reused.
       const segmentPrefetch = this.createSegmentPrefetch_(variant.audio);
-      segmentPrefetch.deleteOnGet(false);
 
       // if a segment prefetch wasn't created, skip the rest
       if (!segmentPrefetch) {
@@ -1245,7 +1240,7 @@ shaka.media.StreamingEngine = class {
       // evict all prefetched segments that are before the presentationTime
       for (const stream of this.audioPrefetchMap_.keys()) {
         const prefetch = this.audioPrefetchMap_.get(stream);
-        prefetch.evict(presentationTime);
+        prefetch.evict(presentationTime, /* clearInitSegments= */ true);
         prefetch.prefetchSegmentsByTime(presentationTime);
       }
     }
@@ -1355,6 +1350,7 @@ shaka.media.StreamingEngine = class {
 
     if (mediaState.segmentPrefetch && mediaState.segmentIterator &&
         !this.audioPrefetchMap_.has(mediaState.stream)) {
+      mediaState.segmentPrefetch.evict(presentationTime);
       mediaState.segmentPrefetch.prefetchSegmentsByTime(reference.startTime);
     }
 

diff --git a/test/media/segment_prefetch_unit.js b/test/media/segment_prefetch_unit.js
@@ -160,7 +160,6 @@ describe('SegmentPrefetch', () => {
 
   describe('evict', () => {
     it('does not evict a segment that straddles the given time', async () => {
-      segmentPrefetch.deleteOnGet(false);
       segmentPrefetch.prefetchSegmentsByTime(references[0].startTime);
       segmentPrefetch.evict(5);
       await expectSegmentsPrefetched(0);
@@ -177,7 +176,6 @@ describe('SegmentPrefetch', () => {
     });
 
     it('segments that end before the provided time', async () => {
-      segmentPrefetch.deleteOnGet(false);
       segmentPrefetch.prefetchSegmentsByTime(references[0].startTime);
       segmentPrefetch.evict(21);
       for (let i = 0; i < 2; i++) {

diff --git a/test/test/util/fake_segment_prefetch.js b/test/test/util/fake_segment_prefetch.js
@@ -39,9 +39,6 @@ shaka.test.FakeSegmentPrefetch = class {
     /** @private {number} */
     this.prefetchPosTime_ = 0;
 
-    /** @private {boolean} */
-    this.deleteOnGet_ = true;
-
     /** @private {number} */
     this.segmentNum_ = 0;
   }
@@ -97,11 +94,6 @@ shaka.test.FakeSegmentPrefetch = class {
     this.evictions_.push(time);
   }
 
-  /** @override */
-  deleteOnGet(newDeleteOnGet) {
-    this.deleteOnGet_ = newDeleteOnGet;
-  }
-
   /**
    * @override
    * @param {shaka.media.InitSegmentReference|