java.lang.OutOfMemory Exception with Multithreaded Image Generate - multithreading

Question

I am trying to copy a lot of images with Java ImageIO. Each copy resizes the original picture. As the size of image set is huge (60,000). I try to use multi thread to solve the problem. Here is the code:
package generate.image
import scala.util.Random._
import scala.math._
import java.io.File
import java.io.PrintWriter
import java.util.concurrent.{ExecutorService, TimeUnit, Executors}
import java.awt.Image
import java.awt.image.BufferedImage
import javax.imageio.ImageIO
class ImageResizer{
def resizeImage(srcImgPath: String, distImgPath: String, width: Int, height: Int){
val srcFile: File = new File(srcImgPath)
val srcImg: Image = ImageIO.read(srcFile)
val buffImg: BufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB)
buffImg.getGraphics().drawImage(
srcImg.getScaledInstance(width, height, Image.SCALE_SMOOTH), 0,
0, null
)
ImageIO.write(buffImg, "JPEG", new File(distImgPath))
}
}
class ImageWorker(imgSrc: String, imgName: String, width: Int, height: Int) extends Runnable{
override def run(): Unit = {
val resizer = new ImageResizer()
resizer.resizeImage(imgSrc, imgName, width, height);
}
}
object ImageGenerate {
def main(args:Array[String]): Unit = {
// parameters
val dirName = args(0)
val images = new File(dirName).listFiles.filter(_.getName.endsWith(".JPEG"))
val imgCnt = images.length
// threadpool
val pool = Executors.newFixedThreadPool(25)
// copy with norm
for(i <- 0 until imgCnt){
for(cnt <- 1 to 20){
val width = nextInt(200) + 300
val height = nextInt(200) + 300
val imgSrc: String = images(i).getAbsolutePath
val imgName: String = "img/%s_%d_%d_%d.JPEG".format(splitFilename(images(i).getName), width, height, cnt)
pool.execute(new ImageWorker(imgSrc, imgName, width, height))
}
}
pool.shutdown()
pool.awaitTermination(Long.MaxValue, TimeUnit.NANOSECONDS)
}
// split file name
def splitFilename(fileName: String) = {
fileName.substring(0, fileName.lastIndexOf("."))
}
}
ImageResizer does the copy work. It reads an image into BufferedImage, resizes it into a new BufferedImage, and finally writes to a JPEG file.
ImageWorker does the thread work. It is executed by the worker threads in the ExecuteServive.
ImageGenerate does the dispatching work. It reads all the image files in the args(0) (first arg), generates new random width and height, and submit a new job to pool.
Compile and run: scalac ImageGenerate.scala scala generate.image.ImageGenerate test. The sizes of images are 150kb in average.
As is running, the program throws java.lang.OutOfMemoryError.
Sometimes, there is a Exception in thread "pool-1-thread-36" java.lang.OutOfMemoryError: GC overhead limit exceeded error.
If I set the parameter -J-Xmx2048m, the program will run smoothly. However, I only run 400 images. Is there any optimization for my code?
Thanks for sharing your idea, best wishes.

Answer 1

You should be calling dispose()
Something like this (untested)
val graphics = buffImg.getGraphics()
graphics.drawImage(
srcImg.getScaledInstance(width, height, Image.SCALE_SMOOTH), 0,
0, null
)
ImageIO.write(buffImg, "JPEG", new File(distImgPath))
graphics.dispose()