[xml] xmlReadFile/xmlReadMemory - Performance or Concurrency problem

[Martin Trappel <0xCDCDCDCD gmx at>]

Hi there.

I could use a few wild guesses, because I've quite run out of them:
* libxml2 2.6.27
* Windows XPsp2

I have a process that is running approx 30 threads where one of this 
threads is doing some calculations and network communication with a 
hardware device. This one is the only thread that spends a measureable 
time doing anything, i.e. it takes about 10% cpu).
So far, no libxml2 involved.

Now, in an additional thread, I start up a libxml parser to parse a 4MB 
xml file. (When tested in isolation parsing of this file takes approx 
200-300ms).
In this process, the parsing (xmlReadFile, or xmlReadMemory call with 
file read into memory) takes btw. 2 sec and 12 sec. That ain't the 
problem and of course I expected it to take longer due to heavy load.
The problem now is, that the xmlRead* call takes 99% cpu resources which 
causes the other thread to slow down so much that it fails due to a 
fixed timeout for msg processing we have.

What is really interesting now is, that when I add some artificial 
cpu-load before or after xmlReadFile (some dummy calculations in a loop 
for 10 seconds) that takes up 99% cpu as well, but the msg processing in 
the other thread ain't aborted.

Could this be due to many heap-allocations from 
xmlReadFile/xmlReadMemory? Some other process global resource that could 
be the cause?

any guesses welcome!
cheers,
Martin