Concurrency and synchronization are pivotal concepts in operating systems (OS) that enable efficient multitasking and coordination among processes or threads. Concurrency refers to the ability to execute multiple tasks simultaneously, while synchronization ensures that these tasks are executed in a coordinated and conflict-free manner. This article explores these concepts in detail, supported by schematics and code examples.
What is Concurrency?
Concurrency is the ability of an operating system to manage the execution of multiple processes or threads at the same time. It does not necessarily imply parallelism (executing tasks simultaneously on different CPUs); instead, concurrency ensures that tasks make progress by sharing CPU time effectively.
Key advantages of concurrency include:
1. Increased Efficiency: Utilizes CPU and I/O resources effectively.
2. Responsive Systems: Keeps interactive systems responsive even during heavy computation.
3. Scalability: Allows programs to scale on multi-core processors.
Challenges in Concurrency
Race Conditions: Occurs when multiple processes or threads access shared resources without proper coordination.
Deadlocks: A state where processes are stuck waiting for resources held by each other.
Starvation: One process fails to proceed because others monopolize resources.
What is Synchronization?
Synchronization is the mechanism that ensures orderly execution of concurrent tasks. It is crucial for maintaining data consistency and avoiding conflicts when processes or threads share resources.
Synchronization Mechanisms
1. Locks (Mutex): Allows one thread to access a critical section at a time.
Example: Ensures that a shared variable is updated atomically.
2. Semaphores: Signal-based mechanism to control access to resources.
Types: Binary Semaphore (acts as a mutex), Counting Semaphore.
3. Monitors: High-level constructs that combine mutual exclusion and condition variables.
4. Condition Variables: Used for thread synchronization based on specific conditions.
5. Barriers: Ensures that multiple threads reach a common execution point before proceeding.
Schematic: Concurrency and Synchronization
+———-+ +———-+
| Thread A |<–Shared—>| Thread B |
+———-+ Resource +———-+
| (Synchronized Access) |
+———–> OS Kernel <———-+
Code Example: Mutex in C for Synchronization
#include <stdio.h>
#include <pthread.h>
int counter = 0; // Shared resource
pthread_mutex_t lock; // Mutex lock
void* increment(void* arg) {
pthread_mutex_lock(&lock); // Lock before accessing the shared resource
counter++;
printf(“Thread %lu incremented counter to %d\n”, pthread_self(), counter);
pthread_mutex_unlock(&lock); // Unlock after access
return NULL;
}
int main() {
pthread_t threads[2];
pthread_mutex_init(&lock, NULL); // Initialize the mutex
// Create threads
pthread_create(&threads[0], NULL, increment, NULL);
pthread_create(&threads[1], NULL, increment, NULL);
// Wait for threads to finish
pthread_join(threads[0], NULL);
pthread_join(threads[1], NULL);
pthread_mutex_destroy(&lock); // Destroy the mutex
printf(“Final counter value: %d\n”, counter);
return 0;
}
Applications of Concurrency and Synchronization
1. Web Servers: Handle multiple client requests concurrently while ensuring data integrity.
2. Database Systems: Maintain consistency when multiple transactions access the same data.
3. Embedded Systems: Coordinate tasks in real-time systems like automotive controls.
Conclusion
Concurrency and synchronization are indispensable for designing efficient and robust operating systems. Concurrency optimizes resource usage, while synchronization ensures that tasks interact safely without conflicts. By understanding and implementing these concepts, developers can build systems that are scalable, responsive, and reliable.