Slow performance on windows

[johnv-git]

Running on an i7 Windows 7 box, this runs cpu at 20%. It'd be nice to use all available cpu and finish 5x faster. But perhaps a gm limitation?

It looks like grunt-imagemin pegs the cpu, so whatever they're doing in terms of pipeline seems like the right thing.

[andismith]

Can you try with the latest version (0.1.7)? It includes some performance updates.

[johnv-git]

Much improved in 0.1.7. Looks to be 4x faster than 0.1.6. I still have idle cpu, so there is room for even more improvement. Perhaps an option to select the number of concurrent threads? (Assuming gm allows multiple concurrent invocations.)

[johnv-git]

I took a look at the async routines and tuned the cpu usage by using a combination of series() and parallelLimit(). So where you accumulate the resize tasks into series, I'm accumulating them into resizeseries and then parallelize that at some concurrency level. 3 runs nicely on my box without pegging the cpu.

In practice its a one-time hit as long as you write to a tmp dir that isn't cleaned between rebuilds and use options.newFilesOnly = true. But maybe this helps someone?

        // Run resize operations in parallel at a specified concurrency.
        options.concurrency = 3;
        series.push(function(callback) {
            async.parallelLimit(resizeseries, options.concurrency, callback);
        });
        series.push(function(callback) {
          outputResult(tally[sizeOptions.id], sizeOptions.name);
          return callback();
        });

[johnv-git]

Here's a patch that I'm running locally. Works nicely with concurrency set to 3.

--- node_modules/grunt-responsive-images/tasks/responsive_images.bak    2015-10-05 18:03:11.564669200 -0700
+++ node_modules/grunt-responsive-images/tasks/responsive_images.js     2015-10-10 01:44:57.365276300 -0700
@@ -35,6 +35,7 @@
     customIn: null,
     customOut: null,
     sharpen: null,
+    concurrency: 1,            // Simultaneous gm processes to invoke.  CPU Cores - 1 is a reasonable choice.
     sizes: [{
       name: 'small',
       width: 320
@@ -470,6 +472,7 @@
     options.units = _.extend(_.clone(DEFAULT_UNIT_OPTIONS), options.units);

     options.sizes.forEach(function(s) {
+      var resizeseries = [];

       var sizeOptions = _.extend({}, options, s);

@@ -512,7 +515,7 @@
           // remove pixels from the value so the gfx process doesn't complain
           sizeOptions = removeCharsFromObjectValue(sizeOptions, ['width', 'height'], 'px');

-          series.push(function(callback) {
+          resizeseries.push(function(callback) {

             if (sizeOptions.newFilesOnly) {
               if (isFileNewVersion(srcPath, dstPath)) {
@@ -528,6 +531,10 @@
           });
         });

+        // Run resize operations in parallel at a specified concurrency.
+        series.push(function(callback) {
+            async.parallelLimit(resizeseries, options.concurrency, callback);
+        });
         series.push(function(callback) {
           outputResult(tally[sizeOptions.id], sizeOptions.name);
           return callback();

[johnv-git]

Added as pull#99