Andre Klemann created XGC-93:
--------------------------------
Summary: Calling DeflaterOutputStream.write(byte) byte by byte
causes blocked threads in multi session-environments
Key: XGC-93
URL: https://issues.apache.org/jira/browse/XGC-93
Project: XMLGraphicsCommons
Issue Type: Improvement
Components: postscript
Affects Versions: Trunk
Environment: WebSphere Application Server 7.0 with AIX 7.1 and JDK
1.6.0
fop.jar, Implementation-Version: 1.1, Build-Id: 20121016-224756-ICT (glenn [Mac
OS X 10.8.1 x86_64, Java 1.6.0_35-b10-428-11M3811, Target Java 1.5])
xmlgraphics-commons-1.5.jar, Implementation-Version: 1.5, Build-Id:
20121016-215324-ICT (glenn [Mac OS X 10.8.1 x86_64, Java
1.6.0_35-b10-428-11M3811])
Reporter: Andre Klemann
Fix For: Trunk
The method
org.apache.xmlgraphics.ps.ImageEncodingHelper.optimizedWriteTo(OutputStream)
from xmlgraphics-commons-1.5.jar calls the method
DeflaterOutputStream.write(byte) byte by byte (see lines 242 - 244):
private boolean optimizedWriteTo(OutputStream out)
throws IOException {
if (this.firstTileDump) {
Raster raster = image.getTile(0, 0);
DataBuffer buffer = raster.getDataBuffer();
if (buffer instanceof DataBufferByte) {
byte[] bytes = ((DataBufferByte) buffer).getData();
// see determineEncodingColorModel() to see why we permute B
and R here
if (isBGR) {
for (int i = 0; i < bytes.length; i += 3) {
out.write(bytes[i + 2]); // 242
out.write(bytes[i + 1]); // 243
out.write(bytes[i]); // 244
}
} else {
out.write(bytes);
}
return true;
}
}
return false;
}
Under WebSphere, in a multi-session environment, this leads to warnings about
possibly hanging threads:
[07.03.13 08:34:22:673 MEZ] 0000000d ThreadMonitor W WSVR0605W: Thread
"WebContainer : 1303" (00000547) has been active for 165445 milliseconds and
may be hung. There is/are 1 thread(s) in total in the server that may be hung.
at java.util.zip.Deflater.deflateBytes(Native Method)
at java.util.zip.Deflater.deflate(Deflater.java:306)
at
java.util.zip.DeflaterOutputStream.deflate(DeflaterOutputStream.java:153)
at
java.util.zip.DeflaterOutputStream.write(DeflaterOutputStream.java:112)
at
java.util.zip.DeflaterOutputStream.write(DeflaterOutputStream.java:89)
at
org.apache.xmlgraphics.ps.ImageEncodingHelper.optimizedWriteTo(ImageEncodingHelper.java:242)
...
[07.03.13 08:38:18:886 MEZ] 00000547 ThreadMonitor W WSVR0606W: Thread
"WebContainer : 1303" (00000547) was previously reported to be hung but has
completed. It was active for approximately 401662 milliseconds. There is/are
0 thread(s) in total in the server that still may be hung.
[07.03.13 08:40:22:723 MEZ] 0000002d ThreadMonitor W WSVR0605W: Thread
"WebContainer : 1323" (0000055b) has been active for 221920 milliseconds and
may be hung. There is/are 1 thread(s) in total in the server that may be hung.
at java.util.zip.Deflater.deflateBytes(Native Method)
at java.util.zip.Deflater.deflate(Deflater.java:306)
at
java.util.zip.DeflaterOutputStream.deflate(DeflaterOutputStream.java:153)
at
java.util.zip.DeflaterOutputStream.write(DeflaterOutputStream.java:112)
at
java.util.zip.DeflaterOutputStream.write(DeflaterOutputStream.java:89)
at
org.apache.xmlgraphics.ps.ImageEncodingHelper.optimizedWriteTo(ImageEncodingHelper.java:244)
...
The threads will finish their work, but this takes a long time.
The reason for this is, that the number n of calls to
java.util.zip.DeflaterOutputStream.write(byte) might be in a hight range. I
have seen cases, where n=4094496. This leads to n calls of
DeflaterOutputSteam.write(byte[] b, int off, int len), where off=0 and len=1:
public void write(byte[] b, int off, int len) throws IOException {
if (def.finished()) {
throw new IOException("write beyond end of stream");
}
if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return;
}
if (!def.finished()) {
// Deflate no more than stride bytes at a time. This avoids
// excess copying in deflateBytes (see Deflater.c)
int stride = buf.length;
for (int i = 0; i < len; i+= stride) {
def.setInput(b, off + i, Math.min(stride, len - i)); // line
116
while (!def.needsInput()) {
deflate();
// line 118
}
}
}
}
Since java.util.zip.Deflater internally uses synchronized blocks, esspecially
in setInput(byte[], int, int) and deflate(byte[], int, int), one should reduce
the number of calls to these methods as much as possible.
The number of calls of Deflater.setInput(byte[] b, int off, int len) in line
116
above could, e.g., be reduced by the factor 512 (=buffer.length), if the method
ImageEncodingHelper.optimizedWriteTo() would be written in this way:
private boolean optimizedWriteTo(OutputStream out)
throws IOException {
if (this.firstTileDump) {
Raster raster = image.getTile(0, 0);
DataBuffer buffer = raster.getDataBuffer();
if (buffer instanceof DataBufferByte) {
byte[] bytes = ((DataBufferByte) buffer).getData();
// see determineEncodingColorModel() to see why we permute B
and R here
if (isBGR) {
byte[] bytesPermutated = new byte[bytes.length];
for (int i = 0; i < bytes.length; i += 3) {
bytesPermutated[i] = bytes[i+2];
bytesPermutated[i+1] = bytes[i+1];
bytesPermutated[i+2] = bytes[i];
}
out.write(bytesPermutated);
} else {
out.write(bytes);
}
return true;
}
}
return false;
}
In this version, n calls of DeflaterOutputStream.write(byte) are replaced by
one call of DeflaterOutputStream(byte[]), which is much faster and offers less
blocking potential.
Without this optimization and with activated zlib compression in FOP 1.1, we
always got warnings from WeSphere's thread monitor, that some threads may hang.
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