Expose libvips thread pool size

README.md

@@ -365,6 +365,18 @@ sharp.cache(200); // { current: 75, high: 99, memory: 200, items: 500 }
 sharp.cache(50, 200); // { current: 49, high: 99, memory: 50, items: 200}
 ```
 
+#### sharp.concurrency([threads])
+
+`threads`, if provided, is the Number of threads _libvips'_ should create for image processing. The default value is the number of CPU cores. A value of `0` will reset to this default.
+
+This method always returns the current concurrency.
+
+```javascript
+var threads = sharp.concurrency(); // 4
+sharp.concurrency(2); // 2
+sharp.concurrency(0); // 4
+```
+
 #### sharp.counters()
 
 Provides access to internal task counters.

index.js

@@ -430,6 +430,16 @@ module.exports.cache = function(memory, items) {
   return sharp.cache(memory, items);
 };
 
+/*
+  Get and set size of thread pool
+*/
+module.exports.concurrency = function(concurrency) {
+  if (Number.isNaN(concurrency)) {
+    concurrency = null;
+  }
+  return sharp.concurrency(concurrency);
+};
+
 /*
   Get internal counters
 */

src/sharp.cc

@@ -775,6 +775,20 @@ NAN_METHOD(cache) {
   NanReturnValue(cache);
 }
 
+/*
+  Get and set size of thread pool
+*/
+NAN_METHOD(concurrency) {
+  NanScope();
+
+  // Set concurrency
+  if (args[0]->IsInt32()) {
+    vips_concurrency_set(args[0]->Int32Value());
+  }
+  // Get concurrency
+  NanReturnValue(NanNew<Number>(vips_concurrency_get()));
+}
+
 /*
   Get internal counters (queued tasks, processing tasks)
 */
@@ -807,6 +821,7 @@ extern "C" void init(Handle<Object> target) {
   NODE_SET_METHOD(target, "metadata", metadata);
   NODE_SET_METHOD(target, "resize", resize);
   NODE_SET_METHOD(target, "cache", cache);
+  NODE_SET_METHOD(target, "concurrency", concurrency);
   NODE_SET_METHOD(target, "counters", counters);
 }
 

tests/parallel.js

@@ -1,37 +1,39 @@
-var sharp = require("../index");
-var fs = require("fs");
-var path = require("path");
-var assert = require("assert");
-var async = require("async");
-
-var inputJpg = path.join(__dirname, "fixtures/2569067123_aca715a2ee_o.jpg"); // http://www.flickr.com/photos/grizdave/2569067123/
-var width = 720;
-var height = 480;
-
-var timer = setInterval(function() {
-  console.dir(sharp.cache());
-}, 100);
-
-async.mapSeries([1, 1, 2, 4, 8, 16, 32, 64, 128], function(parallelism, next) {
-  var start = new Date().getTime();
-  async.times(parallelism,
-    function(id, callback) {
-      sharp(inputJpg).resize(width, height).toBuffer(function(err, buffer) {
-        buffer = null;
-        callback(err, new Date().getTime() - start);
-      });
-    },
-    function(err, ids) {
-      assert(!err);
-      assert(ids.length === parallelism);
-      var mean = ids.reduce(function(a, b) {
-        return a + b;
-      }) / ids.length;
-      console.log(parallelism + " parallel calls: fastest=" + ids[0] + "ms slowest=" + ids[ids.length - 1] + "ms mean=" + mean + "ms");
-      next();
-    }
-  );
-}, function() {
-  clearInterval(timer);
-  console.dir(sharp.cache());
-});
+var sharp = require("../index");
+var fs = require("fs");
+var path = require("path");
+var assert = require("assert");
+var async = require("async");
+
+var inputJpg = path.join(__dirname, "fixtures/2569067123_aca715a2ee_o.jpg"); // http://www.flickr.com/photos/grizdave/2569067123/
+var width = 720;
+var height = 480;
+
+sharp.concurrency(1);
+
+var timer = setInterval(function() {
+  console.dir(sharp.counters());
+}, 100);
+
+async.mapSeries([1, 1, 2, 4, 8, 16, 32, 64, 128], function(parallelism, next) {
+  var start = new Date().getTime();
+  async.times(parallelism,
+    function(id, callback) {
+      sharp(inputJpg).resize(width, height).toBuffer(function(err, buffer) {
+        buffer = null;
+        callback(err, new Date().getTime() - start);
+      });
+    },
+    function(err, ids) {
+      assert(!err);
+      assert(ids.length === parallelism);
+      var mean = ids.reduce(function(a, b) {
+        return a + b;
+      }) / ids.length;
+      console.log(parallelism + " parallel calls: fastest=" + ids[0] + "ms slowest=" + ids[ids.length - 1] + "ms mean=" + mean + "ms");
+      next();
+    }
+  );
+}, function() {
+  clearInterval(timer);
+  console.dir(sharp.counters());
+});

tests/unit.js

@@ -28,6 +28,13 @@ var inputGif = path.join(fixturesPath, "Crash_test.gif"); // http://upload.wikim
 sharp.cache(0); // Disable
 sharp.cache(50, 500); // 50MB, 500 items
 
+// Ensure concurrency can be set
+var defaultConcurrency = sharp.concurrency();
+sharp.concurrency(16);
+assert.strictEqual(16, sharp.concurrency());
+sharp.concurrency(0);
+assert.strictEqual(defaultConcurrency, sharp.concurrency());
+
 async.series([
   // Resize with exact crop
   function(done) {