Homework 3
Submission date: 31/12/2003 17:00
Teaching assistants in charge:
 Vadim Drabkin, dvadim@cs.technion.ac.il, phone 04-8293371
 Artiom Myaskovskey artiom@cs.technion.ac.il, phone 04-8294619
All emails regarding this assignment must have the subject
cs234120hw3.
1. Introduction
In this assignment your task is to write a job dispatcher.
Every job will contain several tasks. The dispatcher will read the jobs from the pipe and
(immediately) distribute them among its workers.
The workers should perform the tasks according to the rules below.
From this assignment you will learn how to work with threads, protect and synchronize
the common data structures, and to use pipes to communicate between threads.
2. General Description
You must write a dispatcher with a configurable number of workers.
The dispatcher reads job messages from the input pipe and forwards the tasks that
appear in the job description to the workers according to the instructions that appear in
the job message.
“Tasks pool” is a data structure that contains the tasks that the worker has to execute.
You should decide how to implement it.
Every worker chooses from its “tasks pool” a task according to the rules described below
and executes it. The worker that finishes the last task of the job writes the output of the
whole job (output of all tasks in the job) to the output pipe.
The user can stop all the workers by sending “PAUSE” to the dispatcher input pipe.
It will cause all the workers to stop accepting any new tasks and wait (the workers will
finish the task they worked on and stop).
The user can resume all the workers by sending “RESUME” to the dispatcher’s input
pipe. It will cause all the workers to start looking for the next task to perform.
The user can abort dispatcher by sending "ABORT" to the dispatcher's input pipe.
It will cause all the workers finish all their tasks and then exit. The dispatcher will not
add any new tasks and it will wait until all workers finish their tasks and then exit.
3. Detailed Description
Your program will consist of a number of threads:
 “main thread” – “dispatcher” – reads messages from the input pipe. The
message that the dispatcher gets from the pipe is either a command
(“PAUSE” or “RESUME”) or job description. The “dispatcher” parses the
message and if the message type is “JOB”, forwards the tasks to the
workers according to the rules described below. The “dispatcher” has it’s
own FIFO (input pipe).
 “workers” – threads that perform the tasks. The number of “workers” is
a configurable. Every “worker” has its own ID and “tasks pool”. The
“dispatcher” adds the tasks to worker’s “tasks pool”. The “worker”
chooses the task from the “tasks pool” according to the rules described
below. Every “worker” has its own FIFO pipe. The “workers”
communicate only via these pipes.
There are two kinds of jobs that the “worker” can perform:
 “Regular job”
 “Master job”
A “Master job” is a special kind of job. A “Master job” contains only one task. We will call
it “Master task”. When a “Master task” is executed no other task is allowed to be
executed. After the dispatcher parses a “Master job”, all workers should finish executing
the current task and then the worker that should execute the “Master task”, executes it,
while the other workers wait for its completion. “Master jobs” should be executed in the
order, they were received. Two “Master jobs” can’t be executed at the same time.
A “Regular job” can contain several tasks.
Every “Regular job” contains:
 JOB_PRIORITY – the priority of the job (All tasks in a job have the job’s priority).
 N – the number of tasks to perform.
 T1 T2… TN (where Ti is Task_i).
Every



task contains:
function_index (index of the function that should be performed)
ID of the worker
Index of the data set
Input/Output:
The input pipe from which the dispatcher reads the messages will be FIFO. It’s name
will be “/tmp/hw3_inputpipe”.
The output pipe to which the workers write the output will also be FIFO. It’s name will
be “/tmp/hw3_outputpipe”.
Both pipes should be created by the dispatcher.
Program arguments:
Synopsis:
./dispatcher nw file1 file2 file3 file4
Where
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nw – number of “workers”
file1 – name of file that contains
file2 – name of file that contains
file3 – name of file that contains
file4 – name of file that contains
Data
Data
Data
Data
Set
Set
Set
Set
1
2
3
4
Data sets:
A data Set is a binary file that contains 4 bytes of data (Note that the size of int is
exactly 4 bytes).
Functions:
There will be 4 different functions. Each of the functions gets as input an integer and
returns an integer.
Each function is of the following type: typedef int (*func)(int input);
In the program, the functions should be declared as follows:
typedef int (*func_type)(int input);
extern func_type func_arr[4];
Function definitions will be defined in external file “func.o”.
For your tests you should write these functions by yourself.
Message format conventions:
 Bold is used for constant strings that appear in message
 Italic is for parameters
 numbers after underscores are parameter lengths (in bytes)
 <SEP> stands for ';' - separates between fields in message
 <EOM> stands for '#' – end of message mark.
Message example:
MESSAGE_TYPE=VALUE1<SEP>
where VALUE1={PAUSE,RESUME}
Here 'MESSAGE_TYPE=' is a constant string and VALUE1 is a string
parameter that can get one of two values: 'PAUSE' or 'RESUME'.
The dispatcher can get messages of one of 2 types:
1. Command
Format: MESSAGE_TYPE=VALUE <EOM>
where VALUE ={PAUSE,RESUME,ABORT};
2. Job message
Format:
MESSAGE_TYPE=VALUE1 <SEP>
JOB_TYPE=VALUE2 <SEP>
JOB_PRIORITY=VALUE3<SEP>
TASKS_NUMBER=VALUE4 <SEP>
Description of each task.
Appears VALUE4 times
TASK_START<SEP>
WORKER_ID=VALUE5 <SEP>
FUNCTION_INDEX=VALUE6<SEP>
DATASET_INDEX=VALUE7<SEP>
TASK_END<SEP>
<EOM>
Where :
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VALUE1 = {JOB}
VALUE2 = { REGULAR,MASTER}
VALUE3 = 1..100 .
VALUE4 = integer. Remark: This parameter sets the number of
tasks that appear in this job.
 VALUE5 = 1..{maximum number of “workers”}.
 VALUE6 = 1..4
 VALUE7 = 1..4
Remark: all numbers are written in ASCII.
For example: if VALUE5 = 48 then string in the message will be
'VALUE5=48' and not 'VALUE5=0' ('0' ASCII value is 48)
Rules:
1) The tasks in each job should be executed in the order they appear within the job.
Message example:
MESSAGE_TYPE=JOB;
JOB_TYPE=REGULAR;
JOB_PRIORITY=4
TASKS_NUMBER=2;
TASK_START;
WORKER_ID=9;
FUNCTION_INDEX=4;
DATASET_INDEX=3;
TASK_END;
TASK_START;
WORKER_ID=7;
FUNCTION_INDEX=1;
DATASET_INDEX=2;
TASK_END;#
It means that the job contains 2 tasks and that the first task should execute function
number 4 on data set number 3 and it will be executed on worker number 9.The second
task should execute function number 1 on data set number 2 and it will be executed on
worker number 7. The second task can’t be started before the first task of the same job
is finished. You should think how to implement it.
2) If there is no “Master job” waiting, the worker chooses from its “tasks pool”, the task
with highest priority and starts executing it (after it checked the conditions of rule
number 1). Notice that a task with low priority can be starved by tasks with higher
priority. The worker won’t start executing a new task until it finishes executing the
current task.
3) If the worker has in its queue two tasks with the same priority, the tasks should be
started in the order they were received.
4. Remarks


As soon as the dispatcher gets the input (jobs) from the pipe, it forwards the
tasks to the workers’ queues and the workers remove the tasks from the queue
after they have performed them.
The dispatcher shouldn’t communicate with workers in any way except for
adding the tasks to the workers’ queues.
5. Submission

You should electronically submit a zip file that contains the source files
and the makefile. It’s name should be “Makefile”. The makefile will create
an executable with name “dispatcher”.

You should also submit a printed version of the source code.

A file named “submitters.txt” which includes students ID's and names in
the following format:
i. Israeli Israel 123456789
ii. Israeli Israela 987654321
iii. Ben-Israeli Zion 543627189
May God Be With You,
The course staff.