java - ImageIO thread-safety

Question

I see in the javax.imageio spec that thread-safety is not a goal, despite I've seen several examples using ImageIO.read() and ImageIO.write() for uploading/sanitizing images in a web environment.

So, my question is, despite what the spec says, is ImageIO thread-safe?

Answer 1

ImageIO is not thread safe (or at least one of it's plugins is not), in at least one of my environments. I am in the process of debugging an issue where png and jpg files don't get loaded correctly (sometimes solid gray, sometimes inverted colors, sometimes random colors, etc) when ImageIO.read() is invoked from multiple threads. I also occasionally get ConcurrentModificationExceptions like:

java.util.ConcurrentModificationException
at java.util.Vector$Itr.checkForComodification(Vector.java:1184)
at java.util.Vector$Itr.next(Vector.java:1137)
at sun.java2d.cmm.ProfileDeferralMgr.activateProfiles(ProfileDeferralMgr.java:93)
at java.awt.color.ICC_Profile.getInstance(ICC_Profile.java:777)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.setImageData(JPEGImageReader.java:657)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.readImageHeader(Native Method)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.readNativeHeader(JPEGImageReader.java:609)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.checkTablesOnly(JPEGImageReader.java:347)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.gotoImage(JPEGImageReader.java:481)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.readHeader(JPEGImageReader.java:602)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.readInternal(JPEGImageReader.java:1059)
at com.sun.imageio.plugins.jpeg.JPEGImageReader.read(JPEGImageReader.java:1039)
at javax.imageio.ImageIO.read(ImageIO.java:1448)
at javax.imageio.ImageIO.read(ImageIO.java:1308)
at com.foo.bar.MyTestLoadThread.loadImage(MyTestLoadThread.java:241)
...
at java.lang.Thread.run(Thread.java:745)

I am not able to replicate this behavior in all environments so it may be JVM specific. But here are the details of the env. where I see it fail:

• OS : Ubuntu 14.04
• java -version :
  java version "1.8.0_33"
  Java(TM) SE Runtime Environment (build 1.8.0_33-b05)
  Java HotSpot(TM) Client VM (build 25.33-b05, mixed mode)