DevDisasters
Modular Process Improvement
After nearly eight years of working as a C++ developer at Rik V.'s insurance company, a certain coworker was finally laid off.
One task that fell to Rik was to run an application that his former colleague wrote, which compared two directories and put any files that had changed into a third. This was a semi-frequent task, and one that his coworker had devoted quite a bit of time to each month.
Performance Issues
The first time Rik ran the application, he noticed that it was taking an exorbitant amount of time to complete. After five minutes, it barely scratched the surface of the directories, so Rik took off for lunch and returned later to see that the app had run for 43 minutes. Curious as to how a directory comparison could take so long, he peeked at the code. Here's what he found:
long ReadBinaryFile(CString
strFile, BYTE** pResult)
{
BYTE* pBuffer[256];
BYTE* pResultBuffer = NULL;
long nLenResultBuffer = 0;
CFile file;
if(!file.Open(strFile,
CFile::modeRead)) {
return NULL;
}
UINT nBytesRead = 256;
while(nBytesRead)
{
nBytesRead =
file.Read(pBuffer, 255);
if(nBytesRead)
{
BYTE* pNewBuffer =
new BYTE[nBytesRead
+ nLenResultBuffer];
ZeroMemory(pNewBuffer,
nBytesRead
+ nLenResultBuffer);
memcpy(pNewBuffer,
pResultBuffer,
nLenResultBuffer);
memcpy(pNewBuffer
+ nLenResultBuffer,
pBuffer, nBytesRead);
delete[] pResultBuffer;
pResultBuffer = pNewBuffer;
nLenResultBuffer
+= nBytesRead;
}
}
*pResult = pResultBuffer;
return nLenResultBuffer;
}
"I was stunned," Rik said, as he relayed the situation to Doug, who was in the next cubicle. "For a 5MB file, his code would require 20,000-plus loops, 20,000-plus memory allocations of gradually increasing size, and at least 40,000 memcopy operations. And that's just for one file!"
Do-Over
Not knowing whether to laugh or cry, Rik decided to take the safe approach and just rewrite it.
After rewriting, he restarted the app-and it finished in less than 20 seconds. With a couple of logic tweaks elsewhere in the code, he got this down to 13 seconds-from 40 minutes.
"I'm not sure if the guy was a moron or a genius," Rik told Doug. On one hand, the code was absolutely appalling. On the other, it gave the former coworker the opportunity to say: "Sorry, the application is still running; I've got to wait for it to finish"-and then go back to reading the newspaper.
About the Author
Alex Papadimoulis is a managing partner at Inedo LLC and publisher of the Web site "Worse Than Failure" (WorseThanFailure.com). He writes the DevDisasters page in every issue of Redmond Developer News.