Saturday, 28 March 2015

Bad user experience on fortune.com

Experience in mobile and web should be different
While reading an article on Fortune, I found the reading space so annoyingly reduced. I guess in attempts to make a consistent mobile and web experience people are failing badly.

Saturday, 14 February 2015

Ola on the rise

The website being broken can mean either business is not moving or it is moving too fast. For Ola, the case is the latter.

Monday, 5 January 2015

Disruption in taxi business

Earlier taxi's used to be rather costly. Auto-rickshaws would be around half the price. So spending a little more time in travel and saving some money was a good option. However, looking at the fare charts of Ola and Taxi For Sure, it seems they are snatching away the market from auto-rickshaw drivers as well as from old taxi services.

Negotiating with auto-rickshaw drivers is a hard-learned skill. However as companies like Ola and Taxi For Sure are gaining market, the skill is becoming useless. The disruption in the market is achieved by use of technology to reduce wait time for taxis as well as customers.

The pain points that these technologies are addressing are:
1. Time spent in negotiation is cut off.
2. Taxi drivers are on an average better behaved than auto-rickshaw drivers.
3. Scheduling pickups is easier.
4. Payment is easy if you have a digital wallet with the taxi service.

Some issues that I face usually in Hyderabad are:
1. The driver does not know Hindi and I don't know Telugu so we are stuck on the communication part.
2. The time shown by these car service apps does not take into account the traffic.
3. The drivers usually don't know how to read maps. They need guidance to reach the pickup point and sometimes take long routes.
4. The mobile phone network is not consistent.

Often I find the driver knows a landmark near him and a landmark near my pickup point and because of language problem, I can't explain to him which way (possible shortcut) to take. So, instead of trying hard to explain, I tell him to start on the route he knows or a general route. Then I start tracking him to find where he is and call him back to tell him what to do.

Disruption in this market space is really a nice improvement. It is beneficial to customers as well as drivers. I hope to see this industry flourish.

Saturday, 16 August 2014

Finding the file or device pointed to by a file descriptor

I had been noticing that Firefox starts off with around 400mb and reaches around 1.4 gb as I keep using it throughout the day. Also, CPU utilization clocked at 25% on my i7. So, I thought of trying to mess around in the hope of finding something interesting. I found the pid using the following.

ps aux | grep firefox

I ran an strace to try and see what was keeping it so busy.

strace -p <pid_of_firefox_process>

This is what I got.

poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 4294967295) = 1 ([{fd=17, revents=POLLIN}])
read(17, "\372", 1) = 1
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 1 ([{fd=17, revents=POLLIN}])
read(17, "\372", 1) = 1
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 1 ([{fd=17, revents=POLLIN}])
read(17, "\372", 1) = 1
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 1 ([{fd=17, revents=POLLIN}])
read(17, "\372", 1) = 1
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 1 ([{fd=17, revents=POLLIN}])
read(17, "\372", 1) = 1
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 4294967295) = 1 ([{fd=17, revents=POLLIN}])
read(17, "\372", 1) = 1
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 4294967295) = 1 ([{fd=17, revents=POLLIN}])
read(17, "\372", 1) = 1
getrusage(RUSAGE_SELF, {ru_utime={17387, 398261}, ru_stime={821, 999917}, ...}) = 0
getrusage(RUSAGE_SELF, {ru_utime={17387, 438261}, ru_stime={821, 999917}, ...}) = 0
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 1 ([{fd=17, revents=POLLIN}])
read(17, "\372", 1) = 1
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
write(18, "\372", 1) = 1
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 1 ([{fd=17, revents=POLLIN}])
read(17, "\372", 1) = 1
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 4294967295) = 1 ([{fd=17, revents=POLLIN}])
read(17, "\372", 1) = 1
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 4294967295) = 1 ([{fd=17, revents=POLLIN}])
read(17, "\372", 1) = 1
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 0) = 0 (Timeout)
recvmsg(4, 0x7fff427b9fb0, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN}, {fd=4, events=POLLIN}, {fd=17, events=POLLIN}, {fd=19, events=POLLIN}], 4, 4294967295) = 1 ([{fd=17, revents=POLLIN}])

Now, I wanted to know the files pointed to by file descriptors 4, 5, 17, 19. To look those use, I read that I can use /proc filesystem. So, I just tried simply looking it up there.

ls -l /proc/<pid_of_firefox_process>/fd

The files turned out to be as follows:
  • 4 - a socket
  • 5 - anon_inode:[eventfd]
  • 17 - a pipe
  • 19 - another socket
Any suggestions are welcome. I will keep looking into the issue.

Wednesday, 16 July 2014

Invoke a rake task multiple times from another

To invoke a rake task within another, one can do the following:

Rake::Task['namespace:task_name'].invoke

However, if you need to run a task multiple times, the following will not work.

n.times do
    Rake::Task['namespace:task_name'].invoke
end

It only executes the task once. This behaviour is useful when you are loading dependent tasks. For example, if there are two tasks that depend upon :environment task, this behaviour ensures :environment is loaded only once. However, the above code is written with a different intension. To make it work correctly, the rake task has to be re-enabled. The way to do it is as follows:

n.times do
    task = Rake::Task['namespace:task_name'].invoke

    task.reenable
    task.invoke
end

Thursday, 5 June 2014

Writing files in a specific encoding in Ruby

Recently, I was trying to create PDF files of barcodes. I was using barby gem for generating barcodes. When I tried to write the generated PDF, I found that the PDF string was in ASCII-8BIT encoding while my console was in UTF-8 which was causing Ruby to attempt writing in UTF-8 encoding causing errors. So, to write to the file in ASCII-8BIT, I had to specify that while opening the file. I achieved that using the following and I could write to the file correctly.

f = File.open("test.pdf", "w:ASCII-8BIT")
f.write the_pdf_string
f.close

Sunday, 25 May 2014

Compiling in Emacs

I use Emacs for development in C. I was trying out some algorithms and I had used some functions from math.h. I had included the header of course. However, when I wanted to compile I knew I would have to use the -lm flag to include math.h in the compilation. I use M-x compile for compilation. It usually asks me to enter the name of the executable to be built. In that same line, I added the CFLAGS=-lm part to the end of that line and the compilation worked fine. So instead of

make -k application

my compilation command looked like the following.

make -k application CFLAGS=-lm

Wednesday, 14 May 2014

Do not save VBS file in UTF8 encoding

Recently, I had to run a VB script as suggested here. I do not have much experience on Windows; but I often keep my source code in utf8. I also have my IDE set to it. So, when I saved the script I opted for utf8. However, when I ran the script, I got a strange error. Since, I had opted specifically for utf8 overriding the default, I tried saving in the default character encoding, i.e. ASCII and the script ran fine. Reading about it, I can see that ASCII and utf-16 are supported. So, lesson learned: do not use utf8 on windows.

Sunday, 16 March 2014

Starting with Lisp

Just for some fun and relaxation, I decided to start doing some Lisp. I had set up SLIME a few months backs while I was starting some book but I had not done much. I decided to use SBCL because I had read that is usually fast. The reason I was using SLIME is that the back arrow key does not work when I use the SBCL REPL and that is very annoying to me because I type both opening and closing parentheses together and type the rest of the code in between. To setup SLIME, a lot of documentation is available online so I wont re-iterate. Just for reference, the SLIME section of the .emacs file is as follows:

(setq inferior-lisp-program "/usr/bin/sbcl")
(add-to-list 'load-path "/usr/share/emacs/site-lisp/slime/")
(require 'slime)
(slime-setup)

Once I was in SLIME REPL, I started writing a few s-expression to get a hang of it.

(+ 1 2)

(print 'hello)

(format t "hello world")


After that, I started writing a simple function that returns the nth number in the Fibonacci sequence. I came up with the following.


(defun foo (n)
    (cond
     ((= n 1) 0)
     ((= n 2) (+ 1 (foo (- n 1))))
     (+ (foo (- n 1)) (foo (- n 2)))))


And I started testing it.


(foo 1)

(foo 2)
(foo 3)


The result for n = 3 was wrong. The reason lay in the last section of cond. I intended it to be default but I had not specified the condition for it. So, I corrected it as follows.

(defun foo (n)
    (cond
     ((= n 1) 0)
     ((= n 2) (+ 1 (foo (- n 1))))
     (t (+ (foo (- n 1)) (foo (- n 2))))))

Now, the method was returning correct values. Clearly, it is a bad implementation. So, I thought the calls to foo should be memoized. I could go ahead and try writing my own memoization but I wanted to see what Common Lisp had to offer. However, before doing that I wanted to know whether memoization will be beneficial. So, I wanted to benchmark the memoized and the plain versions. Our good friend Google helped me out. I was able to start profiling using SBCL's built-in package sb-prof.


(in-package :cl-user)
(require :sb-sprof)
(declaim (optimize speed))
(sb-sprof:with-profiling (:max-samples 1000
                          :report :flat
                          :loop nil)
  (foo 100))


I was a little doubtful that I should not be trying for the 100th Fibonacci number but still I went ahead with it and even after some minutes, it was going on. So, I now I decided to kill the profiling. Ctrl+C Ctrl+C came in handy. I started low this time. From 10, 15, 25, I reached up to 40 at which value it took around 6 seconds.


(sb-sprof:with-profiling (:max-samples 1000
                          :report :flat
                          :loop nil)
  (foo 40))


Now, I was ready to test a memoized version of the function and see how much benefit I can get. I remembered reading some code by Peter Norvig in Python which used a decorator to achieve generic memoization. So, I thought Lisp ought to have something similar. I found a nice memoization API. However, I had to install the package and I did not want to delve into that because I did not find any packages for Arch. So, I decided to settle for a less robust implementation.

(defun Basic-Memo (Function)
  "Takes a normal function object and returns an `equivalent' memoized one"
  (let ((Hash-Table (make-hash-table)))
    #'(lambda (Arg)
    (multiple-value-bind (Value Foundp)
        (gethash Arg Hash-Table)
      (if
        Foundp
        Value
        (setf (gethash Arg Hash-Table) (funcall Function Arg))))) ))

(defun Basic-Memoize (Function-Name)
  "Memoize function associated with Function-Name. Simplified version"
  (setf (symbol-function Function-Name)
    (Basic-Memo (symbol-function Function-Name))))

(Basic-Memoize 'foo)
Now, the 1000th Fibonacci number was also easily calculated. When I tried to the above profiling code for (foo 1000), I was getting error for the run being too short. Trying for 10000th Fibonacci number, I got 0.01 seconds.