File downloaders are programs used for downloading files from the Internet.here

you will implement two different types of multi-process downloaders (i.e., file downloaders that

comprise multiple processes):

1. a serial file downloader which downloads files one by one.

2. a parallel file downloader which downloads multiple files in parallel.

You will then compare the performance of the two types of downloaders.

Both downloaders will use the Linux wget program in order to perform the actual downloading.

The usage of the wget is simple: wget . For example, running from command line

the following command:

wget http://releases.ubuntu.com/15.04/ubuntu-15.04-desktop-amd64.iso

will download the Ubuntu Linux iso image to the current directory. Before proceeding with the

assignment, you may want to take a moment to experiment with the wget command.

In your program, the parent process shall first read the file, urls.txt, containing the URLs of the

files to be downloaded. urls.txt shall have the following format:

.

.

.

For example:

http://releases.ubuntu.com/cosmic/ubuntu-18.10-desktop-amd64.iso

http://releases.ubuntu.com/cosmic/ubuntu-18.10-live-server-amd64.iso

Next, the parent process shall fork the child processes. Each created child process shall use the

execlp() system call to replace its executable image with that of the wget program. The two types

downloaders are described in detail below.

The two downloaders shall be implemented as separate programs. The serial downloader

program shall be called serial.c (or .cpp extension if you use C++). The parallel downloader

program shall be called parallel.c (or .cpp extension if you use C++).

Serial Downloader

The serial downloader shall download files one by one. After the parent process has read and

parsed the urls.txt file, it shall proceed as follows:

1. The parent process forks off a child process.

2. The child uses execlp("/usr/bin/wget", "wget", , NULL) system call in

order to replace its program with wget program that will download the first file in urls.txt

(i.e. the file at URL ).

3. The parent executes a wait() system call until the child exits.

4. The parent forks off another child process which downloads the next file specified in

urls.txt.

5. Repeat the above steps until all files are downloaded.

Parallel Downloader

1. The parent forks off n children, where n is the number of URLs in urls.txt.

2. Each child executes execlp("/usr/bin/wget", "wget", , NULL) system

call where each is a distinct URL in urls.txt.

3. The parent calls wait() (n times in a row) and waits for all children to terminate.

4. The parent exits.

Performance Comparison

Use the time program to measure the execution time for the two downloaders. For example:

time ./serial

real 0m10.009s

user 0m0.008s

sys 0m0.000s

The column titled real gives the execution time in seconds. Please get the execution times for

both downloaders using the following urls.txt file:

http://releases.ubuntu.com/cosmic/ubuntu-18.10-desktop-amd64.iso

http://releases.ubuntu.com/cosmic/ubuntu-18.10-live-server-amd64.iso

Your execution times should be submitted along with your code.

In your submission, please include the answers to the following questions (you may need to do

some research):

1. In the output of time, what is the difference between real, user, and sys times?

2. Which is longer: user time or sys time? Use your knowledge to explain why.

3. When downloading the files above, which downloader finishes faster? Why do you think

that is?

4. Repeat the experiment for 10 files (any reasonably large-sized files, e.g., 100 MB, will

do). Is the downloader in the previous question still faster? If not so, why do you think

that is?