resourceloader: Make cache-eval in mw.loader.work asynchronous

This is an amended version of reverted commit 482ad8d9fb2e.

The difference is that this change is smaller.

We keep the eval as one large chunk. Not split up in <=50ms chunks and
spread out based on how fast code executes on the device. This means we keep
the issue of an irresponsive UI thread during execution, and trade it for
finishing quicker. This doesn't feel right, but is something we should change
separately, later because it has side-effects (T146510).

Doing it in one chunk is the status quo as we've had it for the last two
years. This commit merely defers the big eval chunk to one tick later so
that higher priority work may happen first (e.g. rendering).

Bug: T142129
Change-Id: I2b31b27554cd29b48d986ed6a6f698a77e59c0e5

diff --git a/resources/src/mediawiki/mediawiki.js b/resources/src/mediawiki/mediawiki.js
index f878e42..6b23439 100644 (file)
--- a/resources/src/mediawiki/mediawiki.js
+++ b/resources/src/mediawiki/mediawiki.js
@@ -1680,6 +1680,26 @@
                                }
                        }
 
+                       /**
+                        * @private
+                        * @param {string[]} implementations Array containing pieces of JavaScript code in the
+                        *  form of calls to mw.loader#implement().
+                        * @param {Function} cb Callback in case of failure
+                        * @param {Error} cb.err
+                        */
+                       function asyncEval( implementations, cb ) {
+                               if ( !implementations.length ) {
+                                       return;
+                               }
+                               mw.requestIdleCallback( function () {
+                                       try {
+                                               $.globalEval( implementations.join( ';' ) );
+                                       } catch ( err ) {
+                                               cb( err );
+                                       }
+                               } );
+                       }
+
                        /**
                         * Make a versioned key for a specific module.
                         *
@@ -1733,7 +1753,7 @@
                                 * @protected
                                 */
                                work: function () {
-                                       var q, batch, concatSource, origBatch;
+                                       var q, batch, implementations, sourceModules;
 
                                        batch = [];
 
@@ -1763,19 +1783,18 @@
 
                                        mw.loader.store.init();
                                        if ( mw.loader.store.enabled ) {
-                                               concatSource = [];
-                                               origBatch = batch;
+                                               implementations = [];
+                                               sourceModules = [];
                                                batch = $.grep( batch, function ( module ) {
-                                                       var source = mw.loader.store.get( module );
-                                                       if ( source ) {
-                                                               concatSource.push( source );
+                                                       var implementation = mw.loader.store.get( module );
+                                                       if ( implementation ) {
+                                                               implementations.push( implementation );
+                                                               sourceModules.push( module );
                                                                return false;
                                                        }
                                                        return true;
                                                } );
-                                               try {
-                                                       $.globalEval( concatSource.join( ';' ) );
-                                               } catch ( err ) {
+                                               asyncEval( implementations, function ( err ) {
                                                        // Not good, the cached mw.loader.implement calls failed! This should
                                                        // never happen, barring ResourceLoader bugs, browser bugs and PEBKACs.
                                                        // Depending on how corrupt the string is, it is likely that some
@@ -1786,16 +1805,14 @@
                                                        // something that infected the implement call itself, don't take any
                                                        // risks and clear everything in this cache.
                                                        mw.loader.store.clear();
-                                                       // Re-add the ones still pending back to the batch and let the server
-                                                       // repopulate these modules to the cache.
-                                                       // This means that at most one module will be useless (the one that had
-                                                       // the error) instead of all of them.
+
                                                        mw.track( 'resourceloader.exception', { exception: err, source: 'store-eval' } );
-                                                       origBatch = $.grep( origBatch, function ( module ) {
+                                                       // Re-add the failed ones that are still pending back to the batch
+                                                       var failed = $.grep( sourceModules, function ( module ) {
                                                                return registry[ module ].state === 'loading';
                                                        } );
-                                                       batch = batch.concat( origBatch );
-                                               }
+                                                       batchRequest( failed );
+                                               } );
                                        }
 
                                        batchRequest( batch );