Lock Variable Synchronization Mechanism

Concurrent programming employs the notion of lock variable synchronization to make sure that several threads or processes can safely access shared resources without coming into race situations or inconsistent data. It offers a mechanism to manage the order in which threads or processes are executed, enabling them to have exclusive access to shared resources when required.

In this article, we will explore the mechanism of lock variable synchronization, use cases, and an example code snippet in C as well.

Lock Variable Synchronization

Utilizing a shared variable, often known as a lock or mutex (short for mutual exclusion), to control access to crucial code segments or shared resources is the fundamental concept behind lock variable synchronization. Locks can only exist in one of two states: locked. A thread or process first examines the lock's state before attempting to access a crucial portion. If the lock is free, the thread or process can buy it, convert the lock's state to locked, and then continue with the critical section's execution. The thread or process will be halted or put to sleep if the lock is already locked and will remain so until it is unlocked.

Only one thread or process is allowed to enter a crucial part at once thanks to the lock variable synchronization mechanism. This prevents several threads from altering shared resources concurrently, which can cause data corruption or provide unpredictable consequences. Threads or processes can alternately access the crucial part by acquiring and releasing the lock, preserving data integrity and assuring sequential execution.

The following actions are commonly involved in lock variable synchronization−

Acquisition of the lock − A thread or process tries to obtain the lock by examining its current state. If the lock is locked when the lock is unlocked, the thread or process moves on to the critical area and switches the lock's status to locked. If the lock is already locked, until it is unlocked, the thread or process is either blocked or put to sleep.

Critical section execution − Execution of the critical part of code or access to shared resources is safe after a thread or process has obtained the lock and is not hampered by other threads or processes.

Lock release − The thread or process releases the lock by returning its state to unlocked after completing the crucial part. As a result, different awaiting threads or processes are able to obtain the lock and carry out their particular crucial portions.

Visual Representation of Lock Variable Synchronization

          

Use cases of Lock variable synchronization

In concurrent programming, lock variable synchronization can be used in a variety of situations when several threads or processes need to access the same resources. Typical use scenarios include −

Critical Section Protection − Lock variable synchronization makes sure that only one thread or process can execute the critical section at a time when several threads or processes need to access a critical piece of code or shared resources that shouldn't be updated concurrently. This safeguards data integrity and guards against data corruption and race situations.

Coordination of Resource Access − Lock variable synchronization is used to manage access to shared resources like hardware, files, databases, and network connections. Threads or processes can guarantee exclusive access, avoid conflicts, and safeguard the integrity of the resource by obtaining a lock prior to using it.

Producer-Consumer Problem − Lock variable synchronization can be used to create a communication and synchronization mechanism in cases where several threads or processes are involved in creating and consuming data. Before inserting data into a shared buffer, producers can lock the buffer, and consumers can lock the buffer before removing data from it. As a result, precise synchronization is guaranteed, and race conditions between producers and customers are avoided.

Parallel Task synchronization − Lock variable synchronization is frequently used in parallel programming to synchronize the execution of many processes that are currently in progress. Threads or processes can coordinate their execution by utilizing locks to make sure that some activities are finished before others begin or that certain requirements are satisfied before moving on.

Example

The C code below demonstrates the usage of a lock variable for synchronization in a multi-threaded program. The shared resource, shared_resource, is accessed and modified by multiple threads in the increment() function. Before accessing the critical section, the lock variable lock is acquired using pthread_mutex_lock(), ensuring only one thread can access the shared resource at a time.

#include <stdio.h>
#include <pthread.h>

// Shared resource
int shared_resource = 0;

// Lock variable
pthread_mutex_t lock;

// Function to increment the shared resource
void* increment(void* arg) {
   // Acquire the lock
   pthread_mutex_lock(&lock);

   // Critical section: modify the shared resource
   shared_resource++;
   printf("Shared resource value: %d\n", shared_resource);

   // Release the lock
   pthread_mutex_unlock(&lock);

   return NULL;
}

int main() {
   // Initialize the lock
   pthread_mutex_init(&lock, NULL);

   // Create multiple threads
   pthread_t threads[5];
   for (int i = 0; i < 5; i++) {
      pthread_create(&threads[i], NULL, increment, NULL);
   }

   // Wait for all threads to finish
   for (int i = 0; i < 5; i++) {
      pthread_join(threads[i], NULL);
   }

   // Destroy the lock
   pthread_mutex_destroy(&lock);

   return 0;
}

Output

Shared resource value: 1
Shared resource value: 2
Shared resource value: 3
Shared resource value: 4
Shared resource value: 5

Conclusion

A key method in concurrent programming that enables secure and organized access to shared resources is lock variable synchronization. Concurrency problems like race situations and data corruption can be avoided by using lock variables. With the use of locks, it is made sure that only one thread or process at a time can access a crucial area, protecting the integrity of the data and keeping the intended execution sequence. This method of synchronization is frequently used in a variety of situations, such as safeguarding crucial portions, coordinating resource access, managing producer-consumer relationships, facilitating parallel task synchronization, maintaining thread safety in data structures, and avoiding deadlocks. Developers can build dependable and scalable concurrent systems that efficiently use shared resources while minimizing concurrency concerns by appropriately integrating lock variable synchronization.