fix(performance): Eliminate use of ES6 generators

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/"
+}

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;
   }
 
   /**

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;
   }
 
 

lib/util/iterables.js

@@ -80,12 +80,14 @@ shaka.util.Iterables = class {
    * Returns an iterable that contains numbers in the range [0, end).
    *
    * @param {number} end The exclusive end of the list.
-   * @return {!Iterable.<number>}
+   * @return {!Array.<number>}
    */
-  static* range(end) {
+  static range(end) {
+    const counters = [];
     for (let i = 0; i < end; i++) {
-      yield i;
+      counters.push(i);
     }
+    return counters;
   }
 
   /**
@@ -96,11 +98,17 @@ shaka.util.Iterables = class {
    * - 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)}>}
+   * @return {!Array.<{
+   *           i: number,
+   *           item: T,
+   *           prev: (T|undefined),
+   *           next: (T|undefined)
+   *         }>}
    * @template T
    */
-  static* enumerate(iterable) {
+  static enumerate(iterable) {
+    const enumeration = [];
+
     // 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.
@@ -109,7 +117,7 @@ shaka.util.Iterables = class {
     let item = undefined;
     for (const next of iterable) {
       if (i >= 0) {
-        yield {i, item, prev, next};
+        enumeration.push({i, item, prev, next});
       }
       i++;
       prev = item;
@@ -118,7 +126,9 @@ shaka.util.Iterables = class {
     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};
+      enumeration.push({i, prev, item, next: undefined});
     }
+
+    return enumeration;
   }
 };