CS342 Project 2: Task Communication and Synchronization

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Part A: Processes [35 points]
Objective: Practice process IPC, shared memory, synchronization.
In this part, you will develop the same application in project 1, but this time
you will use shared memory, instead of intermediate files, to pass information from
child processes to the parent process. Hence, again you will develop a multi-process
application that will generate a value histogram for the values sitting in a set of input
ascii text files, one value per line. Values can be an integers or real numbers. The
program will be called syn_phistogram and will take the following parameters:
syn_phistogram minvalue maxvalue bincount N file1 … fileN outfile
Here, minvalue is the minimum value that exists in the given set of input files,
and maxvalue is the maximum value. bincount is the number of bins in the histogram.
Let w denote bin-width. Then w = (maxvalue – minvalue) / bincount. The first bin
will give the count of values in range [minvalue, minvalue+w); the second bin will
give the count of values in range [minvalue+w, minvalue+2w); and so on. The last bin
will be inclusive [] in both ends. N is the number of input files. file1 … fileN are the
names of these input files. outfile is the output file. An example invocation of the
program can be like the following:
syn_phistogram 0 500000 20 3 f1.txt f2.txt f3.txt out.txt
As in project 1, your program will create another child process for each input
file to generate a histogram for the values in that input file. Hence there will be N
child processes working concurrently on the N input files. Each child will generate a
histogram for the values in its input file. The generated histogram will be put into a
shared memory this time, instead of outputting to an intermediate file. There will be
one shared memory region that is shared between parent and all children. The shared
memory segment will be just large enough to hold one histogram. Each child will use
the same shared memory segment. When a child has the histogram ready, it will put
the histogram into shared memory, and the parent will receive the histogram from the
shared memory. In this way the histogram content will be passed from child to the
parent. Parent will process the histogram (merge it to its histogram or copy it to its
own memory). Then, another child can use the shared memory, When another child
has finished preparing its histogram, that child will put the content into the shared
memory (and overwrite the previous content in the shared memory). Then the parent
can receive the content form shared memory again and process it. In this way, each
child will prepare a histogram and will pass the content to the parent. Parent will
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collect those and will build a single combined histogram. Then the parent will print
out the combined histogram into the output file.
Parent and children must be synchronized in accessing (reading from or
writing into) the shared memory. For example, while a child is copying its histogram
into shared memory (i.e., accessing and writing into shared memory), another child
should not access and write into the shared memory at the time. Similarly, while a
child is copying its histogram into shared memory, the parent should not access and
read the shared memory at the same time. After copying of histogram into shared
memory is finished, the parent can access the shared memory and read the content.
You should also not allow a child to overwrite the histogram of another child before
parent has received the histogram. That means, after a child X has put its histogram
into shared memory, another child Y can not write into shared memory, until the
parent has retrieved the histogram of child X.
You will use POSIX semaphores for synchronization. Type “man
sem_overview” at commad line of Linux to get information about POSIX
semaphores. You can also find a lot of information in Internet about POSIX
semaphores and their usage.
You will use POSIX shared memory as IPC among processes. Type “man
shm_overview” at commad line of Linux to get information about POSIX shared
memory interface. You can also find a lot of information in Internet about POSIX
shared memory and its usage.
The output file will contain the combined histogram. Each output line will
contain information about a separate bin in the following format: binnumber: count.
Bin numbers will start at 1. For example, if the are 10 bins, the following can be a
possible output.
1: 30
2: 50
3: 60
4: 40
5: 30
6: 20
7: 15
8: 10
9: 5
10: 3
Part B: Threads [35 points]
Objective: Practice developing multi-threaded applications, sharing information
among threads, and synchronization.
In this part, you will develop a similar application as in part A. But this time,
for each input file, there will be a separate worker thread reading the input file. This
time, a worker thread will not build a histogram, but will just pass the values that it
reads from its input file to the main thread. The main thread will build a combined
histogram. To pass values form worker threads to the main thread, a single shared
linked list will be used. That means in your program, you will define a linked list as a
global variable (structure) to be accessed by all threads (worker threads and main
thread). Initially, the list is empty.
A worker thread will read the values from its input file in batches of B values
each. When a worker thread has retrieved B values from its input file, the worker
thread will add (i.e., append) these values into the linked list. Then, the worker thread
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will read another batch of B values from its input file, and then add them again. A
worker thread will continue reading and passing values like this until the file is
completely read.
Meanwhile, the main thread will receive the values from the linked list in
batches of B values each and will generate the combined histogram. All worker
threads and the main thread will run concurrently. After values are received and the
histogram is build, it will be written to the output file.
The program will be called syn_thistogram and will be invoked with the
following parameters:
syn_thistogram minvalue maxvalue bincount N file1 … fileN outfile B
All parameters are the same with syn_phistogram program except we have
now another parameter B. This is the batch size. It can be a value between 1 and 100.
As said, a thread will collect B values from its input file before appending them to the
linked list. If B is 1, values are read and appended one by one. If B is bigger than 1,
The last batch may contain less than B values.
You will use POSIX pthreads mutex and condition variables to synchronize
the threads. That means, one at a time the threads should access the shared linked list.
For example, while a thread is appending a batch of B values into the linked list,
another thread can not concurrently append, or the main thread can not concurrently
retrieve. After the addition of B number of values (a batch) is finished, then another
thread can add its batch of values, or the main thread can retrieve a batch of values.
An example invocation can be as follows:
syn_thistogram 100 40000 6 3 file1.txt file2.txt file3.txt file4.txt o.txt 50
Part C: Experiments [20 points]
Objective: Practice designing and conducting experiments and applying knowledge
and skills acquired in the Probability and Statistics course.
Do some timing experiments to measure the running time (turnaround time) of
the syn_thistogram program for various values of B. You can use various input
sizes. At the end, decide whether batch size affects the running time of the
application or not. If you find that batch size affects, try to find out and discuss the
relationship.
Submission
Put all your files into a project directory named with your ID (one of the IDs
of team members), tar the directory (using tar xvf), zip it (using gzip) and upload it
to Moodle. For example, a student with ID 20140013 will create a directory named
20140013, will put the files there, tar and gzip the directory and upload the file. The
uploaded file will be 20140013.tar.gz. Include a README.txt file as part of your
upload. It will have the names and IDs of group members, at least. Include also a
Makefile to compile your programs. We want to type just make and obtain the
executables. Do not forget to put your report (PDF form) into your project directory.
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Additional Information and Clarifications
• POSIX thread synchronization functions to solve critical section problem are
pthread_mutex_init, pthread_mutex_lock, pthread_mutex_unlock. To solve other
synchronization issues you may use condition variables with the following
functions: pthread_cond_init, pthread_cond_wait, pthread_cond_signal,
pthread_cond_broadcast.