Task_Comm_part1_RTS_course_Masters_degree.ppsx

Task Communication and Synchronization
Task Communications- Page 1
EEC682– Spring 2025
Inter-task communication is an important service that must be
provided by any real-time kernel. This communication is needed
to:

to:
 exchange data between tasks.
 avoid problems resulting from access to common resources.
 satisfy task precedence constraints.

to:
Some communication mechanisms, such as semaphores, require
a shared memory among tasks. The method of message passing
is more general.
 exchange data between tasks.
 avoid problems resulting from access to common resources.
 satisfy task precedence constraints.

Message queues and mailboxes

A minimum set of system calls that handle message passing is the
following:
send (destination, &message)
receive (source, &message)

following:
A message sent but not yet received is queued by the system.
Queue will have a pre-specified maximum capacity.

following:
Many design options exist for the message format, addressing
methods, synchronization modes, and queuing discipline. All
these can affect program timing.
A message sent but not yet received is queued by the system.
Queue will have a pre-specified maximum capacity.

Message Format
Typically, message is a sequence of bytes with fixed or variable
length. Correct interpretation of message content is the
responsibility of the communicating tasks, not the operating
system.

Message Format
system.

Addressing Method
 Direct addressing: using task id.
Allows only one-to-one communication.
Message Format
system.

Addressing Method
 Direct addressing: using task id.
Allows only one-to-one communication.
 Indirect addressing : using mailboxes
Allows many-to-one, one-to-many or many-to-many modes.
Message Format
system.

Mailbox
s R
Mailbox
s
R1
Rn
S1
Sm
Mailbox
R1
Rn
Mailbox
S1
Sm
R
One to many
One to one Many to one
Many to many

If no message is available, the receiver will typically be blocked
until one arrives. Alternatively, it can return immediately with
an error code.

Example (1): Mutual exclusion using messages
Using messages, how to control access to resource (e.g. data)
that cannot be accessed by more than one task at the same time

Example (1): Mutual exclusion using messages
To access resource, any task will use the following sequence:
receive(Access_box,&msg);
Access_resource;
send(Access_box,&msg);
Using messages, how to control access to resource (e.g. data)
that cannot be accessed by more than one task at the same time

Example (2): Bounded buffer problem
A buffer of size n with reader and writer tasks running at
different speeds.

different speeds.
buffer
writer Reader

different speeds.
Reader task
send(writer,’empty’);
receive(writer,’full’);
Read_data_item;

different speeds.
Reader task
receive(reader,’empty’);
send(writer,’empty’);
receive(writer,’full’);
Read_data_item;
Writer task
Write_data_item;
send(reader,’full’);

in asynchronous send, sender will continue operation
regardless of whether the message was received or not.
Message Synchronization Modes
an error code.
Sender can operate in one of two modes:

In synchronous send, the sender will be blocked until it
receives an acknowledgment from the receiver.
an error code.

an error code.
In synchronous send, the sender will be blocked until it
receives an acknowledgment from the receiver.

Task_Comm_part1_RTS_course_Masters_degree.ppsx

More Related Content

Similar to Task_Comm_part1_RTS_course_Masters_degree.ppsx (20)

Recently uploaded (20)

Task_Comm_part1_RTS_course_Masters_degree.ppsx