Process Synchronization

1. Introduction

• Definition of Process Synchronization:

Process synchronization is the coordination of multiple processes in a system to ensure that
they execute in a way that avoids conflicts, data corruption, or unintended side effects. It
becomes particularly important in multitasking or multiprocessor systems where more than
one process executes at the same time.

• Multitasking Systems:
In an operating system, multiple processes may run simultaneously. When these processes
need to share resources like memory or CPU, synchronization is necessary to ensure that no
two processes interfere with each other.

• Critical Sections:
The part of a program that accesses shared resources is referred to as the critical section.
Synchronization mechanisms are used to ensure that only one process at a time can execute
in its critical section, thus avoiding conflicts or inconsistency.

• Need for Synchronization:

Without synchronization, processes can cause problems such as race conditions, deadlocks,
data inconsistency, and incorrect results. These issues arise due to improper management of
resources and scheduling.

2. Need for Process Synchronization

Synchronization is necessary for the following reasons:

1. Shared Resource Access:

• Processes in a system often need to access common resources (like memory, files,
printers, etc.). Without synchronization, multiple processes accessing these
resources simultaneously could lead to inconsistencies or data corruption. For
example, if two processes modify the same data at the same time, the result may be
unpredictable.

• Example: If two processes are updating a bank account balance at the same time,
without synchronization, one process might overwrite the changes made by the
other, leading to incorrect balance calculation.

2. Avoiding Race Conditions:

• A race condition occurs when two or more processes attempt to modify shared data
at the same time, and the outcome depends on the timing of these events.
Synchronization ensures that processes execute in a predictable order.

• Example: Two processes incrementing a counter variable without synchronization

may result in one of the increments being lost, as both processes may read and
update the counter simultaneously.

3. Data Integrity:
 • Synchronization prevents data corruption by ensuring that processes do not access
shared data concurrently. It ensures that once a process modifies shared data, no
other process can change that data until it has been properly handled.

• Example: If one process is writing to a file while another is reading from it,
synchronization ensures that the reading process does not access the file before the
writing process is finished.

4. Deadlock Prevention:

• Deadlock occurs when two or more processes are unable to proceed because each
one is waiting for the other to release a resource. Without synchronization, deadlock
can cause processes to wait indefinitely, blocking further execution.

• Synchronization mechanisms are used to prevent or resolve deadlocks by controlling

the way processes request and release resources.

• Example: If Process A holds Resource 1 and waits for Resource 2, while Process B
holds Resource 2 and waits for Resource 1, both processes are deadlocked. Proper
synchronization ensures processes do not get stuck in such situations.

5. Starvation Prevention:

• Starvation occurs when a process is indefinitely delayed from accessing resources

because other processes continuously get access to those resources. Synchronization
ensures that every process gets a fair chance to execute and access resources.

• Example: In a CPU scheduling system, if a high-priority process is constantly

executing, a low-priority process may never get a chance to execute, resulting in
starvation. Proper synchronization ensures that processes are given an equitable
amount of resources.

6. Efficient Resource Utilization:

• Synchronization ensures that shared resources are used efficiently. It prevents

both overutilization (where one process consumes all the resources)
and underutilization (where resources are left idle) by managing the access of
multiple processes to the resources.

• Example: In a printer-sharing scenario, synchronization ensures that one process

uses the printer at a time and avoids conflicts in print jobs.

3. Inter-Process Communication (IPC)

Inter-Process Communication (IPC) is the mechanism that allows processes to communicate with
each other and synchronize their actions in a multitasking system. IPC plays a vital role in process
synchronization by enabling processes to exchange data and coordinate their execution without
conflicts.

1. Types of IPC Mechanisms:

There are several IPC methods used for process communication:

• Shared Memory:
 • In shared memory systems, processes communicate by accessing a common
area of memory.

• Multiple processes can read from and write to the same memory location.
However, synchronization is necessary to ensure that only one process
accesses the shared memory at a time to avoid corruption.

• Message Passing:

• In message passing, processes communicate by sending and receiving

messages. This method is typically used in systems where processes do not
share memory.

• Messages are sent through message queues, and synchronization is

necessary to ensure that messages are received in the correct order and that
processes are not blocked waiting for messages.

• Pipes:

• Pipes are used for communication between related processes. Data flows in
one direction, and one process writes to the pipe while another reads from
it.

• Named Pipes can be used for communication between unrelated processes.

• Sockets:

• Sockets allow processes to communicate over a network. Processes can

exchange data by sending and receiving messages through socket
connections.

• Synchronization is necessary to manage network communication and ensure

reliable data exchange.

2. Role of IPC in Synchronization:

• IPC mechanisms provide a structured way for processes to share data, but they
require synchronization to prevent data inconsistency.

• Synchronization mechanisms like semaphores, mutexes, and condition variables are

used to control access to shared resources, ensuring that communication between
processes happens in an orderly and conflict-free manner.

4. Producer-Consumer Problem

The Producer-Consumer Problem is a classic synchronization problem that involves two types of
processes: the producer and the consumer.

1. Problem Overview:

• The producer generates data and places it into a shared buffer.

• The consumer retrieves and processes the data from the buffer.

• The challenge is to synchronize the producer and consumer so that:

 • The producer does not add data to the buffer when it is full (buffer
overflow).

• The consumer does not try to retrieve data from the buffer when it is empty
(buffer underflow).

2. Synchronization Solution:

• To solve this problem, synchronization tools such as semaphores or mutexes are

used to coordinate the producer and consumer actions.

• A semaphore is used to count the number of items in the buffer and to manage the
availability of buffer space:

• Full semaphore: Tracks the number of items currently in the buffer.

• Empty semaphore: Tracks the number of empty slots in the buffer.

• A mutex is used to ensure mutual exclusion so that only one process (either
producer or consumer) can access the buffer at any given time.

3. Steps in Synchronization:

• Producer process:

1. Checks if there is space in the buffer using the empty semaphore.

2. Waits if the buffer is full.

3. Adds an item to the buffer and signals that there is one more item in the buffer using
the full semaphore.

• Consumer process:

1. Checks if there is data in the buffer using the full semaphore.

2. Waits if the buffer is empty.

3. Retrieves an item from the buffer and signals that there is now an empty slot in the buffer
using the empty semaphore.