fix(performance): Eliminate use of ES6 generators (shaka-project#4092)

See: shaka-project#4062 (comment) Co-authored-by: @joeyparrish Issue shaka-project#4062
joeyparrish · Apr 4, 2022 · 57c7324 · 57c7324
1 parent 8a3bed7
commit 57c7324
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diff --git a/build/conformance.textproto b/build/conformance.textproto
@@ -320,3 +320,16 @@ requirement: {
     "instead."
   whitelist_regexp: "lib/net/http_fetch_plugin.js"
 }
+
+# Disallow the use of generators, which are a major performance issue.  See
+# https://github.com/shaka-project/shaka-player/issues/4062#issuecomment-1079428268
+requirement: {
+  type: BANNED_CODE_PATTERN
+  value:
+    "/** @param {*} x */ "
+    "function *template(x) { yield x; }"
+  error_message:
+    "ES6 generators are a major performance issue!  Find another solution. "
+    "See also https://bit.ly/3wAsoj5"
+  whitelist_regexp: "node_modules/"
+}
diff --git a/lib/cea/cea708_service.js b/lib/cea/cea708_service.js
@@ -300,17 +300,19 @@ shaka.cea.Cea708Service = class {
   /**
    * Yields each non-null window specified in the 8-bit bitmap.
    * @param {number} bitmap 8 bits corresponding to each of the 8 windows.
-   * @return {!Iterable.<number>}
+   * @return {!Array.<number>}
    * @private
    */
-  * getSpecifiedWindowIds_(bitmap) {
+  getSpecifiedWindowIds_(bitmap) {
+    const ids = [];
     for (let i = 0; i < 8; i++) {
       const windowSpecified = (bitmap & 0x01) === 0x01;
       if (windowSpecified && this.windows_[i]) {
-        yield i;
+        ids.push(i);
       }
       bitmap >>= 1;
     }
+    return ids;
   }
 
   /**

diff --git a/lib/cea/sei_processor.js b/lib/cea/sei_processor.js
@@ -14,9 +14,10 @@ shaka.cea.SeiProcessor = class {
   /**
    * Processes supplemental enhancement information data.
    * @param {!Uint8Array} naluData NALU from which SEI data is to be processed.
-   * @return {!Iterable.<!Uint8Array>}
+   * @return {!Array.<!Uint8Array>}
    */
-  * process(naluData) {
+  process(naluData) {
+    const seiPayloads = [];
     const naluClone = this.removeEmu(naluData);
 
     // The following is an implementation of section 7.3.2.3.1
@@ -41,10 +42,12 @@ shaka.cea.SeiProcessor = class {
       // Payload type 4 is user_data_registered_itu_t_t35, as per the H.264
       // spec. This payload type contains caption data.
       if (payloadType == 0x04) {
-        yield naluClone.subarray(offset, offset + payloadSize);
+        seiPayloads.push(naluClone.subarray(offset, offset + payloadSize));
       }
       offset += payloadSize;
     }
+
+    return seiPayloads;
   }
 
 

diff --git a/lib/dash/segment_list.js b/lib/dash/segment_list.js
@@ -15,7 +15,6 @@ goog.require('shaka.media.SegmentIndex');
 goog.require('shaka.media.SegmentReference');
 goog.require('shaka.util.Error');
 goog.require('shaka.util.Functional');
-goog.require('shaka.util.Iterables');
 goog.require('shaka.util.ManifestParserUtils');
 goog.require('shaka.util.XmlUtils');
 goog.requireType('shaka.dash.DashParser');
@@ -222,7 +221,7 @@ shaka.dash.SegmentList = class {
     /** @type {!Array.<!shaka.media.SegmentReference>} */
     const references = [];
     let prevEndTime = info.startTime;
-    for (const i of shaka.util.Iterables.range(max)) {
+    for (let i = 0; i < max; i++) {
       const segment = info.mediaSegments[i];
       const mediaUri = ManifestParserUtils.resolveUris(
           baseUris, [segment.mediaUri]);

diff --git a/lib/hls/hls_parser.js b/lib/hls/hls_parser.js
@@ -30,7 +30,6 @@ goog.require('shaka.util.CmcdManager');
 goog.require('shaka.util.Error');
 goog.require('shaka.util.FakeEvent');
 goog.require('shaka.util.Functional');
-goog.require('shaka.util.Iterables');
 goog.require('shaka.util.LanguageUtils');
 goog.require('shaka.util.ManifestParserUtils');
 goog.require('shaka.util.MimeUtils');
@@ -1869,8 +1868,8 @@ shaka.hls.HlsParser = class {
     // Create SegmentReferences for the partial segments.
     const partialSegmentRefs = [];
     if (this.lowLatencyMode_ && hlsSegment.partialSegments.length) {
-      const enumerate = (it) => shaka.util.Iterables.enumerate(it);
-      for (const {i, item} of enumerate(hlsSegment.partialSegments)) {
+      for (let i = 0; i < hlsSegment.partialSegments.length; i++) {
+        const item = hlsSegment.partialSegments[i];
         const pPreviousReference = i == 0 ?
           previousReference : partialSegmentRefs[partialSegmentRefs.length - 1];
         const pStartTime = (i == 0) ? startTime : pPreviousReference.endTime;
@@ -1891,6 +1890,9 @@ shaka.hls.HlsParser = class {
             this.parseByteRange_(pPreviousReference, pByterange);
         }
         const pUri = item.getAttributeValue('URI');
+        if (!pUri) {
+          continue;
+        }
         const pAbsoluteUri = shaka.hls.Utils.constructAbsoluteUri(
             absoluteMediaPlaylistUri, pUri);
 
@@ -2066,8 +2068,8 @@ shaka.hls.HlsParser = class {
     /** @type {!Array.<!shaka.media.SegmentReference>} */
     const references = [];
 
-    const enumerate = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {i, item} of enumerate(hlsSegments)) {
+    for (let i = 0; i < hlsSegments.length; i++) {
+      const item = hlsSegments[i];
       const previousReference = references[references.length - 1];
       const startTime =
           (i == 0) ? firstStartTime : previousReference.endTime;

diff --git a/lib/hls/manifest_text_parser.js b/lib/hls/manifest_text_parser.js
@@ -13,7 +13,6 @@ goog.require('shaka.hls.Segment');
 goog.require('shaka.hls.Tag');
 goog.require('shaka.hls.Utils');
 goog.require('shaka.util.Error');
-goog.require('shaka.util.Iterables');
 goog.require('shaka.util.StringUtils');
 goog.require('shaka.util.TextParser');
 
@@ -82,8 +81,9 @@ shaka.hls.ManifestTextParser = class {
     const tags = [];
     // Initialize to "true" to skip the first element.
     skip = true;
-    const enumerate = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {i, item: line, next} of enumerate(lines)) {
+    for (let i = 0; i < lines.length; i++) {
+      const line = lines[i];
+      const next = lines[i + 1];
       // Skip comments
       if (shaka.hls.Utils.isComment(line) || skip) {
         skip = false;

diff --git a/lib/media/adaptation_set.js b/lib/media/adaptation_set.js
@@ -8,7 +8,6 @@ goog.provide('shaka.media.AdaptationSet');
 
 goog.require('goog.asserts');
 goog.require('shaka.log');
-goog.require('shaka.util.Iterables');
 goog.require('shaka.util.MimeUtils');
 
 
@@ -215,7 +214,7 @@ shaka.media.AdaptationSet = class {
     codecsA.sort();
     codecsB.sort();
 
-    for (const i of shaka.util.Iterables.range(codecsA.length)) {
+    for (let i = 0; i < codecsA.length; i++) {
       if (codecsA[i] != codecsB[i]) {
         return false;
       }

diff --git a/lib/media/mp4_segment_index_parser.js b/lib/media/mp4_segment_index_parser.js
@@ -11,8 +11,6 @@ goog.require('shaka.log');
 goog.require('shaka.media.InitSegmentReference');
 goog.require('shaka.media.SegmentReference');
 goog.require('shaka.util.Error');
-goog.require('shaka.util.Functional');
-goog.require('shaka.util.Iterables');
 goog.require('shaka.util.Mp4Parser');
 
 
@@ -123,8 +121,7 @@ shaka.media.Mp4SegmentIndexParser = class {
     let unscaledStartTime = earliestPresentationTime;
     let startByte = sidxOffset + box.size + firstOffset;
 
-    for (const _ of shaka.util.Iterables.range(referenceCount)) {
-      shaka.util.Functional.ignored(_);
+    for (let i = 0; i < referenceCount; i++) {
       // |chunk| is 1 bit for |referenceType|, and 31 bits for |referenceSize|.
       const chunk = box.reader.readUint32();
       const referenceType = (chunk & 0x80000000) >>> 31;

diff --git a/lib/media/time_ranges_utils.js b/lib/media/time_ranges_utils.js
@@ -6,8 +6,6 @@
 
 goog.provide('shaka.media.TimeRangesUtils');
 
-goog.require('shaka.util.Iterables');
-
 
 /**
  * @summary A set of utility functions for dealing with TimeRanges objects.
@@ -157,7 +155,7 @@ shaka.media.TimeRangesUtils = class {
       return [];
     }
     const ret = [];
-    for (const i of shaka.util.Iterables.range(b.length)) {
+    for (let i = 0; i < b.length; i++) {
       ret.push({start: b.start(i), end: b.end(i)});
     }
     return ret;

diff --git a/lib/polyfill/all.js b/lib/polyfill/all.js
@@ -7,7 +7,6 @@
 goog.provide('shaka.polyfill');
 
 goog.require('shaka.log');
-goog.require('shaka.util.Iterables');
 
 
 /**
@@ -40,8 +39,8 @@ shaka.polyfill = class {
    */
   static register(polyfill, priority) {
     const newItem = {priority: priority || 0, callback: polyfill};
-    const enumerate = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {i, item} of enumerate(shaka.polyfill.polyfills_)) {
+    for (let i = 0; i < shaka.polyfill.polyfills_.length; i++) {
+      const item = shaka.polyfill.polyfills_[i];
       if (item.priority < newItem.priority) {
         shaka.polyfill.polyfills_.splice(i, 0, newItem);
         return;

diff --git a/lib/util/buffer_utils.js b/lib/util/buffer_utils.js
@@ -6,8 +6,6 @@
 
 goog.provide('shaka.util.BufferUtils');
 
-goog.require('shaka.util.Iterables');
-
 
 /**
  * @summary A set of BufferSource utility functions.
@@ -45,7 +43,7 @@ shaka.util.BufferUtils = class {
 
     const uint8A = shaka.util.BufferUtils.toUint8(arr1);
     const uint8B = shaka.util.BufferUtils.toUint8(arr2);
-    for (const i of shaka.util.Iterables.range(arr1.byteLength)) {
+    for (let i = 0; i < arr1.byteLength; i++) {
       if (uint8A[i] != uint8B[i]) {
         return false;
       }

diff --git a/lib/util/ebml_parser.js b/lib/util/ebml_parser.js
@@ -11,7 +11,6 @@ goog.require('goog.asserts');
 goog.require('shaka.util.BufferUtils');
 goog.require('shaka.util.DataViewReader');
 goog.require('shaka.util.Error');
-goog.require('shaka.util.Iterables');
 
 
 /**
@@ -157,7 +156,8 @@ shaka.util.EbmlParser = class {
     }
 
     let value = 0;
-    for (const {item, i} of shaka.util.Iterables.enumerate(vint)) {
+    for (let i = 0; i < vint.length; i++) {
+      const item = vint[i];
       if (i == 0) {
         // Mask out the first few bits of |vint|'s first byte to get the most
         // significant bits of |vint|'s value. If |vint| is 8 bytes wide then
@@ -267,7 +267,7 @@ shaka.util.EbmlElement = class {
 
     let value = 0;
 
-    for (const i of shaka.util.Iterables.range(this.dataView_.byteLength)) {
+    for (let i = 0; i < this.dataView_.byteLength; i++) {
       const chunk = this.dataView_.getUint8(i);
       value = (256 * value) + chunk;
     }

diff --git a/lib/util/iterables.js b/lib/util/iterables.js
@@ -75,50 +75,4 @@ shaka.util.Iterables = class {
     }
     return out;
   }
-
-  /**
-   * Returns an iterable that contains numbers in the range [0, end).
-   *
-   * @param {number} end The exclusive end of the list.
-   * @return {!Iterable.<number>}
-   */
-  static* range(end) {
-    for (let i = 0; i < end; i++) {
-      yield i;
-    }
-  }
-
-  /**
-   * Iterates over an iterable object and includes additional info about each
-   * item:
-   * - The zero-based index of the element.
-   * - The next item in the list, if it exists.
-   * - The previous item in the list, if it exists.
-   *
-   * @param {!Iterable.<T>} iterable
-   * @return {!Iterable.<
-   *     {i: number, item: T, prev: (T|undefined), next: (T|undefined)}>}
-   * @template T
-   */
-  static* enumerate(iterable) {
-    // Since we want the "next" item, we need to skip the first item and return
-    // elements one in the past.  So as we iterate, we are getting the "next"
-    // element and yielding the one from the previous iteration.
-    let i = -1;
-    let prev = undefined;
-    let item = undefined;
-    for (const next of iterable) {
-      if (i >= 0) {
-        yield {i, item, prev, next};
-      }
-      i++;
-      prev = item;
-      item = next;
-    }
-    if (i != -1) {
-      // If it's still -1, there were no items.  Otherwise we need to yield
-      // the last item.
-      yield {i, prev, item, next: undefined};
-    }
-  }
 };
diff --git a/lib/util/mp4_box_parsers.js b/lib/util/mp4_box_parsers.js
@@ -7,8 +7,6 @@
 goog.provide('shaka.util.Mp4BoxParsers');
 
 goog.require('shaka.util.DataViewReader');
-goog.require('shaka.util.Functional');
-goog.require('shaka.util.Iterables');
 
 shaka.util.Mp4BoxParsers = class {
   /**
@@ -125,8 +123,7 @@ shaka.util.Mp4BoxParsers = class {
       reader.skip(4);
     }
 
-    for (const _ of shaka.util.Iterables.range(sampleCount)) {
-      shaka.util.Functional.ignored(_);
+    for (let i = 0; i < sampleCount; i++) {
       /** @type {shaka.util.ParsedTRUNSample} */
       const sample = {
         sampleDuration: null,

diff --git a/lib/util/mp4_parser.js b/lib/util/mp4_parser.js
@@ -9,8 +9,6 @@ goog.provide('shaka.util.Mp4Parser');
 goog.require('goog.asserts');
 goog.require('shaka.log');
 goog.require('shaka.util.DataViewReader');
-goog.require('shaka.util.Functional');
-goog.require('shaka.util.Iterables');
 
 
 /**
@@ -229,8 +227,7 @@ shaka.util.Mp4Parser = class {
     // start position.  The header size varies.
     const headerSize = shaka.util.Mp4Parser.headerSize(box);
     const count = box.reader.readUint32();
-    for (const _ of shaka.util.Iterables.range(count)) {
-      shaka.util.Functional.ignored(_);
+    for (let i = 0; i < count; i++) {
       box.parser.parseNext(box.start + headerSize, box.reader, box.partialOkay);
       if (box.parser.done_) {
         break;