Synchronization Examples

The Synchronization is an important concept in operating systems that ensures the smooth and coordinated execution of processes and threads. It is the task of coordinating the execution of processes in such a way that no two processes can access the same shared data and resource. It is a critical part of operating system design which ensures that processes or threads can safely share resources without interfering with each other. Synchronization is important because it helps in avoiding Data inconsistency between multiple processes or threads, Deadlocks and Race conditions. It is generally used in multi-processing systems, where process concurrently attempt to access the same shared resource of piece of data.

Primary Terminologies

Deadlock

Deadlock is a bug present in process or thread synchronization method. It is a condition where two or more processes are waiting for some resource availability which will never be available as it is required by another process which is busy with some other processes. These are said to be in a deadlock situation.

Mutex

Mutex means “mutual exclusion”. It is synchronization primitive that is used to prevent multiple threads to simultaneously access shared resources. Only one thread or process can enter the critical section of code at a time. So, it ensures that resources are not accessed by multiple processes or threads concurrently.

Semaphores

It is a synchronization method. It is an integer value that is equal to number of resources. It is used to control access to a shared resource by multiple processes or threads. It maintains a counter and when counter reaches zero then further attempts to acquire the semaphore are blocked until its value become greater than zero. These are of two types:

Binary semaphore
Counting semaphore

Race Condition

Race condition occurs when two or more threads or processes can access the shared data and try to change it at same time. Because in thread scheduling algorithms, we can swap between threads at any time. We do not know the order in which threads attempt to access the shared data and change the data. So, both threads are racing to access and change the data cause the race condition.

Critical Section

Refers to segment of the code where processes/threads access shared resources such as common variable, file and perform read/write operation on them. Mutex and semaphore methods are used to ensure that only one thread/process can access critical section at a time.

Examples

Producer-Consumer Problem

It is also known as bounded buffer problem. Here, we have two threads one is producer thread and other is consumer thread. Critical section (buffer) is a shared resource. We do not want that inconsistency will be produced so we want synchronization between producer and consumer thread.

Producer must not insert the data when the buffer is full.
Consumer must not pick/remove data when the buffer is empty.

Solution (with the help of semaphores) => we will use both binary and counting semaphores here. So, we will take as:

m, mutex => used to acquire lock on buffer.
empty => a counting semaphore with initial value is n. Used to track empty slots.
full => tracks filled slots and initial value is zero.

Producer  solution 

do{
      wait(empty); // wait until empty > 0 then empty->value

      wait(mutex);
      // critical section => add data to buffer
      signal(mutex);
      signal(full); // increment full->value
}while(true)

Consumers solution

do{
      wait(full); // wait until full > 0 then fill -- 

      wait(mutex);
      //remove data from buffer
      Signal(mutex);
      Signal(empty);
      // increment empty
} while(true)

Reader-Writer Problem

Here, we want synchronization that at one time only one writer can write and multiple readers can read. Here, we have two threads one is Read and other is Write/Update.

If there are more than one readers reading then there is no issue.
If there are more than one writers or one writer and some other thread(r/w) occur parallelly then Race condition will arise there and data will become inconsistent.

Solution (using semaphores)

mutex (binary semaphore) => to ensure mutual exclusion, when read count (rc) is updated. No two threads modify read count at same time.
wrt (write) => Binary semaphore common for both reader and writer.
read count (rc) => integer = {0} initially, tracks how many readers are reading in critical section.

Writer solution 

do {
      wait(wrt);
      // do write operation
      signal(wrt);
} while(true);

Reader solution

do {
wait(mutex); // to mutex read count unable
rc++;
if(rc == 1)
wait(wrt) // ensure no writer thread can enter if there is even one reader
signal(mutex)
// critical section => reader is reading
wait(mutex);
rc–; // a reader leaves
if(rc == 0) // no reader is left in critical section
signal(wrt) // writer can enter into critical section now
signal(mutex) // reader leaves
} while(true)

Conclusion

In conclusion, synchronization in operating systems is essential for managing shared resources, preventing conflicts, and ensuring system stability. Through mechanisms like mutexes and semaphores, processes and threads coordinate access to critical sections of code, maintaining data integrity and preventing race conditions. Examples such as the producer-consumer and reader-writer problems illustrate the practical significance of synchronization in real-world scenarios. Despite challenges like deadlocks and performance overhead, understanding and implementing synchronization techniques are crucial for building reliable and efficient computing systems. Ultimately, synchronization is a cornerstone of modern computing, enabling the seamless execution of concurrent tasks and the smooth operation of operating systems.

Frequently Asked Questions on Synchronization Examples – FAQs

How do mutex locks work?

Only one process or thread at a time can access the critical section of code. If another process or thread request the resource, the requesting process or thread must wait until the resource has been released. Threads or processes attempting to access the resource while it is locked will be blocked until it becomes available.

What are condition variables used for?

Conditional variables are synchronization premitives that lets the thread to wait until certain condition meets. It works with locks. They are mainly used in producer-consumer scenarios or when thread needs to wait for another thread to complete a task.

What is the purpose of synchronization in operating systems?

Synchronization ensures the data integrity by preventing the race conditions and ensures the proper ordered execution of concurrent processes. It provide facility to share resources among different threads or processes while avoiding deadlock and starvation situations. Methods such as mutex locks, semaphores and conditional variable play a crucial role in managing shared resources and coordinating interaction between threads.

Article Tags :

Operating Systems