A simple hard drive today is capable of things that sound like some outlandish technology. Just try to do some file I/O in your application and do it with many threads.
Say you have 4 threads, A,B,C, and D. And request to do I/O comes in A then B and so on. If you check the return status of these threads, the ordering might be surprising. Thread D may return before A. How?
Disk have a technology called Native Command Ordering. So they take your request in and process them on a single, simple logic:
-> Serve the one which you can do fastest.
This depends on the head position of the disk. The request that can be served with minimal movement of head, is served first.
Tuesday, October 13, 2009
Sunday, October 4, 2009
A few 'why' answered
There are certain 'why' that we may have missed, so I am trying to attend them...one by one.
o Why do we need hash table?
Of course, for better, faster search. It could even get us an element in O(1).
But we need to use hash because if given data is in a form which can't be ordered; we need hashing. Example can be images. How will you order a set of images and search any.
Hashing comes to help here. It generates a unique(ideally) hash key for given such data. We save these keys in a hash table. So searching an image is now searching a key in hash table. Keys are generated with a hash function. More about that later.
To be continued with more whys.
o Why do we need hash table?
Of course, for better, faster search. It could even get us an element in O(1).
But we need to use hash because if given data is in a form which can't be ordered; we need hashing. Example can be images. How will you order a set of images and search any.
Hashing comes to help here. It generates a unique(ideally) hash key for given such data. We save these keys in a hash table. So searching an image is now searching a key in hash table. Keys are generated with a hash function. More about that later.
To be continued with more whys.
Tuesday, September 22, 2009
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!!
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!!
Friday, August 28, 2009
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 :-)
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 :-)
Monday, August 17, 2009
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/
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/
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