On 10 Dec 2009, at 03:24, Anil Pinto wrote:
Hi Anil
(Didn't see a response for this one come in, so far on fop-us...@... Apologies
if the reply comes a bit late.)
> We have FOP (0.95) embedded in a multithreaded environment to create many
> PDFs almost simultaneously.
>
> We hav been using this configuration for 6 months plus now. I noticed the
> following trace for the first time and it caught my attention, as I thought
> we have followed all the multithreaded requirements required by FOP.
It is pointing to a bug in FOP, due to a slight oversight in making use of
java.awt.ICC_Profile, IIC.
>
> java.util.ConcurrentModificationException
> at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
> at java.util.AbstractList$Itr.next(AbstractList.java:343)
> at
> sun.awt.color.ProfileDeferralMgr.activateProfiles(ProfileDeferralMgr.java:75)
> at java.awt.color.ICC_Profile.getInstance(ICC_Profile.java:756)
> at java.awt.color.ICC_Profile.getInstance(ICC_Profile.java:996)
Checking the Javadocs, there is no mention anywhere of the multi-thread
(un)safety of ICC_Profile or the call to getInstance(). So, I think we can only
safely assume that this means it is unsafe.
> at
> org.apache.fop.pdf.PDFICCBasedColorSpace.setupsRGBColorProfile(PDFICCBasedColorSpace.java:140)
Seen that it is a static method calling another static method, the chances of
anything bad happening are very slim, but so you stumbled upon it. :(
Seems a perfect example of a race condition, though: you mean this is the first
time in all those 6 months that this error occurred? Very slim indeed, then!
As for the good news (I hope I am correct about this):
FOP can solve this easily, either by making setupsRGBProfile() a synchronized
method, or by performing only the call to ICC_Profile.getInstance() in a
synchronized block. My preference goes in the direction of the latter, as that
limits the synchronization overhead to the single call into the AWT library,
which is causing the issue. The rest of the method appears safe for concurrent
runs, at first glance.
The (minor) downside is that we would have to introduce a new static final to
synchronize the calls on.
Very quick patch below (vs current trunk; don't know if it can be applied to
0.95 without small changes...).
HTH!
Regards,
Andreas
---
Index: src/java/org/apache/fop/pdf/PDFICCBasedColorSpace.java
===================================================================
--- src/java/org/apache/fop/pdf/PDFICCBasedColorSpace.java (revision
679326)
+++ src/java/org/apache/fop/pdf/PDFICCBasedColorSpace.java Wed Jan 13
20:29:07 CET 2010
@@ -34,6 +34,8 @@
private PDFICCStream iccStream;
private String explicitName;
+ private static final Object _S = new Object();
+
/**
* Constructs a the ICCBased color space with an explicit name (ex.
"DefaultRGB").
* @param explicitName an explicit name or null if a name should be
generated
@@ -137,7 +139,9 @@
InputStream in = PDFDocument.class.getResourceAsStream("sRGB Color
Space Profile.icm");
if (in != null) {
try {
+ synchronized (_S) {
- profile = ICC_Profile.getInstance(in);
+ profile = ICC_Profile.getInstance(in);
+ }
} catch (IOException ioe) {
throw new RuntimeException(
"Unexpected IOException loading the sRGB profile: " +
ioe.getMessage());
---
