HP Caliper : A Profiler

Developer rarely concern for efficiency of their programming logic. It's not a hard-and-fast observation but that's how most of amateur developer write the code. But performance is becoming critical day by day and commercial applications vie for as much performance gain as possible.

Performance can be hit for motley of reasons but application logic is what we are going to stress here. You may write a code that performs badly with cache system of your hardware or you schedule your threads inappropriately. There may be many reasons that one may not become aware unless someone find it out.

HP Caliper is one of my favorite tool that can help you with finding many causes of application slowdown. It is an Intel Itanium based tool and runs on HPUX & Linux.
Talk about its feature and I may run out of space. It can make basic profiles like sampled call-graph, flat function profile, CPU events profile. Besides it can provide call-stack profile (critical for I/O bound applications), data cache profile (to help you re-layout the data structures).

Best part is that it does not need a recompile of application or any library. Just give it a binary or attach it to a process. Run it and there you are with third party insight in to your logic. It comes with a command line interface and GUI.

Only downside is that it runs on Itanium binaries only so other users have to wait till it become available for them too.

Happy profiling!!

NUI: Mobile GUI development

I found "nui", a C++ based GUI development framework. You can develop iPhone apps as well. It runs on Linux, Windows, Mac.
http://www.libnui.net/

I also came to know about "enthought" (http://www.enthought.com/). Another GUI development framework. This guy automatically develop the GUI if you provide the class definition.

I've not tried both of these. But they both sound interesting, so thought of sharing :-)

Python questions for interview

Python is a bliss for quick development. It's a mix of C & C++ features and comes in flavor of a script. For a C/C++ developer who happen to work with Python, here are few interview questions that are frequently asked:

1. what all Python can do for you in OOP?
Python fairly supports OOP principles. You can declare and define classes that follow same philosophy of OOP(similar to C++, Java). Besides features like inheritance, polymorphism are also there.

2. Does it support operator overloading?
You can have operator overloading also.

3. What is pickling?
It's an object serialization technique. Very similar to marshaling/un-marshaling that packet data in networks.

4. Does it support function overloading?
No.

5. How do you pass variable number of arguments to a function?
def foo(*pass_many):
...
In the function you should retrieve the arguments as a tuple.

6. Difference between a tuple and list?
You know it. Tuples are immutable objects while list are mutable.

Highly recommended: http://www.learningpython.com/2008/06/21/operator-overload-learn-how-to-change-the-behavior-of-equality-operators/

Careful with both hands while using fork!

fork() is one of the most useful feature of C/Linux/UNIX. But it's like a double edged sword, so be careful with fork :-)
Of late, I got stuck in a weird problem with one of the client application(A) that interacts with another application(B). Application A was hanging when used application B; otherwise alone A runs just fine.
Now what to do? We did a thorough examination of both the applications and found that A is waiting on a pipe P. P has its write end with B and A has got the read end. But why this wait? There is no need to keep this pipe open in first place.
So here fork() comes in to picture. Actually A forks B and then B interacts with A. When A fork() B, B gets a copy of all open file descriptors(FD) of A as well. There you go!
After getting these FDs, B does not take care to close them. But A checks if any of its FD is still open. Since the file is open with B, kernel will tell A that some of your files are being accessed. So just wait :( And this wait never ends...
This was it. A simple close() call in B for all FDs worked for us. And B happily got away with A.

A word of advice: Always call exit() from child. exit() does basic clean up and calls _exit() which more work including closing all files open with child.

Just to verify, you can use this test program:

#include "fcntl.h"
#include "stdlib.h"

int main()
{
int fd = -1;
int status;
char buf[512];

fd = open("abc.txt", O_CREAT);

int pid = fork();

if(pid == 0) { // Child
puts("Child says bye");
exit(status);
} else { // Parent
sleep(1);
int ch = read(fd, buf, 16);
printf("\nRead returns %d\n", ch);
exit(status);
}
}

Lichen: Our first invention

We, a group of three friends have got our first ever invention disclosure published today. It's quite a happy moment for all of us. We started with a small idea that eventually got transformed into a serious paper :)

Title : Lichen: A Framework For Characterizing Sporadic Performance Constrictions In Non-deterministic Applications"

The idea deals with better profiling of application with a special way of sample collection.
Our paper is published in worldwide publication Research Journal. (http://www.researchdisclosure.com)