[mapguide-internals] Patch for ticket 2596 (Constant crashes under high load/many concurrent requests)

[Jackie Ng]

Hi All,

I've attached a patch for ticket 2596

https://trac.osgeo.org/mapguide/ticket/2596

This patch should fix instability issues in mgserver as a result of high
load.

>From the ticket description, mgserver crashes under high load from many
concurrent QUERYMAPFEATURES requests to an Oracle layer (with the King
Oracle provider).

I was able to reproduce this on an Oracle XE 11g instance on a MapGuide
Server on Windows using an Apache/Tomcat web tier configuration with one
layer pointing to an oracle table and hammering the containing map with a
200 concurrent sample QUERYMAPFEATURES requests using ApacheBench.

Intense debugging revealed corrupted STL strings being passed to FDO feature
queries, which then manifest as access violations when put under the VS
debugger and produces log entries similar to the ticket description (the
king oracle provider not finding a class definition is because of a garbage
class name string being passed to it), other errors being logged included
std::length_errors.

Having being reminded of this thread from many years back
(http://osgeo-org.1560.x6.nabble.com/std-string-not-thread-safe-on-Linux-td4210940.html),
I scanned the MapGuide codebase for cases where STL strings were being
assigned to class members as-is instead of assigning its c_str()'d result.
It turns out the whole MdfModel project is full of classes where this was
the case (raw STL string assignment to class members).

This patch modifies all affected MdfModel classes to assign c_str() on all
class members for any STL string inputs. 

The patch also modifies MgUtil so that some previously static const STL
string members have been replaced with raw #define'd string literals, as I
suspected ParseQualifiedClassName()/FormatQualifiedClassName() would be
called from multiple threads and I didn't want to risk possibility of STL
string corruption from multiple threads trying to concat from the same
static STL string member.

I have yet to see mgserver crash under the same load tests after this patch
was applied.

Please review. Thanks.

- Jackie



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