Take a temporary copy of buffers provided as input. Soak testing suggests this prevents the problems seen in #6.

binding.gyp

@@ -7,11 +7,13 @@
       '<!@(PKG_CONFIG_PATH="/usr/lib/pkgconfig" pkg-config --libs vips)'
     ],
     'include_dirs': [
+      '/usr/local/include/glib-2.0',
+      '/usr/local/lib/glib-2.0/include',
       '/usr/include/glib-2.0',
       '/usr/lib/glib-2.0/include',
       '/usr/lib/x86_64-linux-gnu/glib-2.0/include'
     ],
-    'cflags': ['-fexceptions', '-O3'],
-    'cflags_cc': ['-fexceptions', '-O3']
+    'cflags': ['-fexceptions', '-pedantic', '-Wall', '-O3'],
+    'cflags_cc': ['-fexceptions', '-pedantic', '-Wall', '-O3']
   }]
 }

package.json

@@ -1,6 +1,6 @@
 {
   "name": "sharp",
-  "version": "0.1.1",
+  "version": "0.1.5",
   "author": "Lovell Fuller",
   "description": "High performance module to resize JPEG and PNG images using the libvips image processing library",
   "scripts": {

src/sharp.cc

@@ -98,46 +98,47 @@ void resize_async(uv_work_t *work) {
   int shrink_on_load = 1;
   if (inputImageType == JPEG) {
     if (shrink >= 8) {
-      factor = residual * shrink / 8;
+      factor = factor / 8;
       shrink_on_load = 8;
-      shrink = floor(factor);
-      residual = shrink / factor;
     } else if (shrink >= 4) {
-      factor = residual * shrink / 4;
+      factor = factor / 4;
       shrink_on_load = 4;
-      shrink = floor(factor);
-      residual = shrink / factor;
     } else if (shrink >= 2) {
-      factor = residual * shrink / 2;
+      factor = factor / 2;
       shrink_on_load = 2;
-      shrink = floor(factor);
-      residual = shrink / factor;
-    }
-    if (shrink_on_load > 1) {
-      g_object_unref(in);
-      in = vips_image_new();
-      if (baton->buffer_in_len > 1) {
-        if (vips_jpegload_buffer(baton->buffer_in, baton->buffer_in_len, &in, "shrink", shrink_on_load, NULL)) {
-          return resize_error(baton, in);
-        }
-      } else {
-        if (vips_jpegload((baton->file_in).c_str(), &in, "shrink", shrink_on_load, NULL)) {
-          return resize_error(baton, in);
-        }
-      }
     }
   }
+  VipsImage *shrunk_on_load = vips_image_new();
+  if (shrink_on_load > 1) {
+    // Recalculate integral shrink and double residual
+    factor = std::max(factor, 1.0);
+    shrink = floor(factor);
+    residual = shrink / factor;
+    // Reload input using shrink-on-load 
+    if (baton->buffer_in_len > 1) {
+      if (vips_jpegload_buffer(baton->buffer_in, baton->buffer_in_len, &shrunk_on_load, "shrink", shrink_on_load, NULL)) {
+        return resize_error(baton, in);
+      }
+    } else {
+      if (vips_jpegload((baton->file_in).c_str(), &shrunk_on_load, "shrink", shrink_on_load, NULL)) {
+        return resize_error(baton, in);
+      }
+    }
+  } else {
+    vips_copy(in, &shrunk_on_load, NULL);
+  }
+  g_object_unref(in);
 
   VipsImage *shrunk = vips_image_new();
   if (shrink > 1) {
     // Use vips_shrink with the integral reduction
-    if (vips_shrink(in, &shrunk, shrink, shrink, NULL)) {
-      return resize_error(baton, in);
+    if (vips_shrink(shrunk_on_load, &shrunk, shrink, shrink, NULL)) {
+      return resize_error(baton, shrunk_on_load);
     }
   } else {
-    vips_copy(in, &shrunk, NULL);
+    vips_copy(shrunk_on_load, &shrunk, NULL);
   }
-  g_object_unref(in);
+  g_object_unref(shrunk_on_load);
 
   // Use vips_affine with the remaining float part using bilinear interpolation
   VipsImage *affined = vips_image_new();
@@ -151,8 +152,8 @@ void resize_async(uv_work_t *work) {
   g_object_unref(shrunk);
 
   VipsImage *canvased = vips_image_new();
-  if (affined->Xsize != baton->width && affined->Ysize != baton->height) {
-    if (baton->crop && affined->Xsize != baton->width && affined->Ysize != baton->height) {
+  if (affined->Xsize != baton->width || affined->Ysize != baton->height) {
+    if (baton->crop) {
       // Crop
       int width = std::min(affined->Xsize, baton->width);
       int height = std::min(affined->Ysize, baton->height);
@@ -192,28 +193,28 @@ void resize_async(uv_work_t *work) {
 
   if (baton->file_out == "__jpeg") {
     // Write JPEG to buffer
-    if (vips_jpegsave_buffer(canvased, &baton->buffer_out, &baton->buffer_out_len, "strip", TRUE, "Q", 80, "optimize_coding", TRUE, "interlace", baton->progessive, NULL)) {
-      return resize_error(baton, canvased);
+    if (vips_jpegsave_buffer(sharpened, &baton->buffer_out, &baton->buffer_out_len, "strip", TRUE, "Q", 80, "optimize_coding", TRUE, "interlace", baton->progessive, NULL)) {
+      return resize_error(baton, sharpened);
     }
   } else if (baton->file_out == "__png") {
     // Write PNG to buffer
-    if (vips_pngsave_buffer(canvased, &baton->buffer_out, &baton->buffer_out_len, "strip", TRUE, "compression", 6, "interlace", baton->progessive, NULL)) {
-      return resize_error(baton, canvased);
+    if (vips_pngsave_buffer(sharpened, &baton->buffer_out, &baton->buffer_out_len, "strip", TRUE, "compression", 6, "interlace", baton->progessive, NULL)) {
+      return resize_error(baton, sharpened);
     }
   } else if (is_jpeg(baton->file_out))  {
     // Write JPEG to file
-    if (vips_jpegsave(canvased, baton->file_out.c_str(), "strip", TRUE, "Q", 80, "optimize_coding", TRUE, "interlace", baton->progessive, NULL)) {
-      return resize_error(baton, canvased);
+    if (vips_jpegsave(sharpened, baton->file_out.c_str(), "strip", TRUE, "Q", 80, "optimize_coding", TRUE, "interlace", baton->progessive, NULL)) {
+      return resize_error(baton, sharpened);
     }
   } else if (is_png(baton->file_out)) {
     // Write PNG to file
-    if (vips_pngsave(canvased, baton->file_out.c_str(), "strip", TRUE, "compression", 6, "interlace", baton->progessive, NULL)) {
-      return resize_error(baton, canvased);
+    if (vips_pngsave(sharpened, baton->file_out.c_str(), "strip", TRUE, "compression", 6, "interlace", baton->progessive, NULL)) {
+      return resize_error(baton, sharpened);
     }
   } else {
     (baton->err).append("Unsupported output " + baton->file_out);
   }
-  g_object_unref(canvased);
+  g_object_unref(sharpened);
   vips_thread_shutdown();
 }
 
@@ -222,10 +223,15 @@ void resize_async_after(uv_work_t *work, int status) {
 
   resize_baton *baton = static_cast<resize_baton*>(work->data);
 
+  // Free temporary copy of input buffer
+  if (baton->buffer_in_len > 0) {
+    g_free(baton->buffer_in);
+  }
+
   Handle<Value> argv[2] = { Null(), Null() };
   if (!baton->err.empty()) {
     // Error
-    argv[0] = String::New(baton->err.data(), baton->err.size());
+    argv[0] = scope.Close(String::New(baton->err.data(), baton->err.size()));
   } else if (baton->buffer_out_len > 0) {
     // Buffer
     Buffer *slowBuffer = Buffer::New(baton->buffer_out_len);
@@ -233,7 +239,7 @@ void resize_async_after(uv_work_t *work, int status) {
     Local<Object> globalObj = Context::GetCurrent()->Global();
     Local<Function> bufferConstructor = Local<Function>::Cast(globalObj->Get(String::New("Buffer")));
     Handle<Value> constructorArgs[3] = { slowBuffer->handle_, v8::Integer::New(baton->buffer_out_len), v8::Integer::New(0) };
-    argv[1] = bufferConstructor->NewInstance(3, constructorArgs);
+    argv[1] = scope.Close(bufferConstructor->NewInstance(3, constructorArgs));
     g_free(baton->buffer_out);
   }
 
@@ -250,8 +256,12 @@ Handle<Value> resize(const Arguments& args) {
   baton->file_in = *String::Utf8Value(args[0]->ToString());
   if (args[1]->IsObject()) {
     Local<Object> buffer = args[1]->ToObject();
-    baton->buffer_in = Buffer::Data(buffer);
-    baton->buffer_in_len = Buffer::Length(buffer);
+    // Take temporary copy of input buffer
+    if (Buffer::Length(buffer) > 0) {
+      baton->buffer_in_len = Buffer::Length(buffer);
+      baton->buffer_in = g_malloc(baton->buffer_in_len);
+      memcpy(baton->buffer_in, Buffer::Data(buffer), baton->buffer_in_len);
+    }
   }
   baton->file_out = *String::Utf8Value(args[2]->ToString());
   baton->width = args[3]->Int32Value();
@@ -287,6 +297,6 @@ extern "C" void init(Handle<Object> target) {
   vips_init("");
   AtExit(at_exit);
   NODE_SET_METHOD(target, "resize", resize);
-};
+}
 
-NODE_MODULE(sharp, init);
+NODE_MODULE(sharp, init)

tests/parallel.js

@@ -0,0 +1,29 @@
+var sharp = require("../index");
+var fs = require("fs");
+var assert = require("assert");
+var async = require("async");
+
+var inputJpg = __dirname + "/2569067123_aca715a2ee_o.jpg"; // http://www.flickr.com/photos/grizdave/2569067123/
+var width = 720;
+var height = 480;
+
+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.resize(inputJpg, sharp.buffer.jpeg, width, height, 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() {});