Description
Learning Objectives
The primary learning objectives of this assignment include learning to use concurrent programming
abstractions including POSIX message passing and inter-process communication. Additional
learning objectives include being able to reason about concurrent execution of programs.
Specifications
1. Using POSIX message passing (message queues) write an application that communicates
temperature values between various processes.
2. There will be 7 processes. Each one an instance of the same executable.
a. You will run 7 instances of the process and they will be identified by a unique
number as the first argument that will be passed in at the command prompt, numbers
0 to 6.
b. Each process will create their own mailbox with a different number. For each process
provided numbers 0 to 6 they create a mailbox /70 for 0, /71 for 1, etc.
c. Additionally, the program will be provided with a floating point number as the
second argument indicating the temperature.
d. In the first step of this assignment the processes will create, in this order, processes 6,
5, 4, 3, 2, 1, 0 with a small delay in-between to ensure that each process’s respective
message queues have been created.
e. These processes will communicate as a binary tree. While each process opens and
creates its own mailbox it will communicate with 1, 2 or 3 other mailboxes. It will
open the mailbox of its parent and children if they exist.
i. Process 0 is parent to process 1 and 2
ii. Process 1 is parent to process 3 and 4 and child to process 0
iii. Process 2 is parent to process 5 and 6 and child to process 0
iv. Processes 3 and 4 are children to process 1
v. Processes 5 and 6 are children to process 2
f. Each process will accept the following 2 command line parameters
./external
For example,
./external 6 100.0
./external 5 45.0
./external 4 120.0
./external 3 67.7
./external 2 20.0
./external 1 36.9
./external 0 98.6
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ECE-3574: Applied Software Engineering, Spring 2016
Homework 5
3. The whole idea of the system is as follows:
a. Processes 6 through 0 create their own mailbox and wait on their own mailbox to
receive a message to start, except 0 which starts itself. You may wait on the start
message to connect to the other mailboxes or count on a startup delay between the
processes.
b. After process 0 starts it should send a message indicating its current temperature.
c. When a process receives a temperature from its parent it will calculate its value
according to the following equation and transmit this number to its children
down_temp = (temp + parent_temp)/2.0
d. Processes 3, 4, 5 and 6 do not, and cannot, transmit their temperature to their
children. Instead they transmit its down_temp back to their parent.
e. When a process receives a temperature from its children it will calculate its value
according to the following equation and transmit this number to its parent
up_temp = (temp + child_a_temp + child_b_temp)/3.0
f. Process 0 does not, and cannot, transmit its temperature to its parent. Instead, if it
still unstable as discussed later, it will transmit its up_temp back to its children.
g. When down_temp and up_temp are calculated it immediately becomes the node’s
temperature.
h. When up_temp is calculated it must be printed to output.
4. In the case where the up_temp is less than 1/100th degree different from the temp for process
0 it is no longer unstable and it should send a signal, which other processes must propagate,
that will cause each process to print a message indicating that it’s the final temperature and
then exit the process.
5. When printing the calculated up_temp value it should print
Process #
Where
6. When printing the final temperature for each process it should print
Process #
Where
difference in the text. This is used to indicate that the exit message is received and
propagated properly.
Example
Let the initial temperatures be the following:
Process 0 temp = 0.0
Process 1 temp = 100.0
Process 2 temp = 200.0
Process 3 temp = 300.0
Process 4 temp = 400.0
Process 5 temp = 500.0
Process 6 temp = 600.0
Iteration P0 P1 P2 P3 P4 P5 P6
initial 0 100 200 300 400 500 600
1 133.333 150 250 175 225 300 350
2 176.852 161.111 236.111 158.333 183.333 245.833 270.833
3 190.072 169.599 223.765 163.657 176.157 226.157 238.657
4 194.004 176.526 215.415 171.746 177.996 216.538 222.788
5 195.166 181.801 209.694 178.506 181.631 210.624 213.749
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ECE-3574: Applied Software Engineering, Spring 2016
Homework 5
6 195.509 185.678 205.682 183.495 185.057 206.527 208.09
7 195.61 188.488 202.833 187.044 187.825 203.561 204.343
8 195.64 190.511 200.798 189.547 189.937 201.391 201.782
9 195.649 191.964 199.342 191.311 191.506 199.805 200.001
final 195.649 191.964 199.342 191.311 191.506 199.805 200.001
Note that you may omit the output for iteration 9 as long there is text which indicates that it is
printing the final temperature for a given process. Also note that only process 0 needs to have a
temperature that changes no more than 0.01 degrees.
Notes
1. Standard error checking for command line arguments is required. If wrongly formatted
parameters are entered, the process must print out an error message
2. External IDs in the correct range are expected. If an incorrect ID is entered on the command
line, again, the program must print out an error message
3. It is an error to try to run a process with the same ID twice. You can detect this by using the
IPC_EXCL (exclusive) flag when creating the mailboxes. Detect this and all other errors
and properly report them.
4. There is no specific requirement in using Blocking or Non-blocking send/receive functions
for the mailboxes. A non-blocking implementation will be granted with an extra-credit of 10.
5. When using message queue there are a few functions that you’ll likely want to use to
manipulate these queues. From the terminal you can type “man
function name is any of the following and get documentation for any of these commands:
• mq_open
• mq_close
• mq_unlink
• mq_send
• mq_receive
• mq_getattr
• mq_setattr
Note that the header for these functions is given in the documentation and mentions that you
need to link with librt. This can be done by adding a line in your *.pro file: “LIBS += -lrt” or
by adding -lrt to the gcc command line compilation tool.
Grading
Qt Style: 10%
Programs work as specified: 90%
