A customer encounters a performance problem with ImageIO.
Using the attached test case, here the time it takes to write an image
to a file (PNG):

  local display -> DISPLAY set to :0
  remote display -> DISPLAY set to remote machine:0

                  local display remote display
  jdk1.5.0_04 ~3 sec ~36 min
  jdk1.4.2_08 ~3 sec ~39 min


pstack shows the following:

  ...
  b2bc047c XGetImage (1c4128, e0002f, 2e2, 4d, 1, 1) + a0
  fde27ea0 ???????? (fde75940, 2a36a8, ffbfd9c0, 1, 0, 20) + 4b267ac4
  fde27c38 ???????? (37618, 2a36a8, ffbfd9c0, 1c6170, 1, 3c4) + 4b26785c
  b30f5d44 Java_sun_awt_image_DataBufferNative_getElem (37618, ffbfda98, 2e2, 4d, ffbfda94, 2a36a8) + 64
  f8850798 * *sun/awt/image/DataBufferNative.getElem(IILsun/java2d/SurfaceData;)I+0
  f8850c10 * sun/awt/image/IntegerInterleavedRaster.verify(Z)V+432 (line 551)
  f8851720 * *java/awt/image/SinglePixelPackedSampleModel.getDataElements(IILjava/lang/Object;Ljava/awt/image/DataBuffer;)Ljava/lang/Object;+196 (line 404)
  f8857404 * *java/awt/image/SampleModel.getDataElements(IIIILjava/lang/Object;Ljava/awt/image/DataBuffer;)Ljava/lang/Object;+369 (line 402)
   ...


I tracked down (jdk1.5.0_04 src) to the following call where
getDataElements is eventually called for each pixel. In the remote case,
it further translates to XGetImage call per pixel, which could be
the cause for bad performance:


SampleModel:
334 public Object getDataElements(getDataElements(int x, int y, int w, int h,
335 Object obj, DataBuffer data) {:
....

400 for (int i=y; i<y+h; i++) {
401 for (int j=x; j<x+w; j++) {
402 o = getDataElements(j, i, o, data);
403 itemp = (int[])o;
404 for (int k=0; k<numDataElems; k++) {
405 idata[cnt++] = itemp[k];
406 }
407 }