Explore the fascinating world of computer science with a deep dive into the concept of Critical Section. This sophisticated aspect of programming plays a fundamental role in numerous computing processes, proving its overpowering importance. You will gain a lucid understanding of the principles and rules that govern Critical Sections, while uncovering common issues associated with this particular problem in operating systems. The article sheds light on the intriguing concept of Bounded Waiting in connection with Critical Sections and provides insight into real-life examples. Immerse yourself in the origin, evolution, and vital importance of Critical Section in the realm of computer science and gather some practical lessons along the way.
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Jetzt kostenlos anmeldenExplore the fascinating world of computer science with a deep dive into the concept of Critical Section. This sophisticated aspect of programming plays a fundamental role in numerous computing processes, proving its overpowering importance. You will gain a lucid understanding of the principles and rules that govern Critical Sections, while uncovering common issues associated with this particular problem in operating systems. The article sheds light on the intriguing concept of Bounded Waiting in connection with Critical Sections and provides insight into real-life examples. Immerse yourself in the origin, evolution, and vital importance of Critical Section in the realm of computer science and gather some practical lessons along the way.
Critical Section: this is the section of code in a multi-threaded program where a process can access shared resources. It is crucial that only one thread enters the critical section at a time to prevent a race condition.
Imagine running a high-traffic online newspaper. To avoid data corruption and ensure smooth interaction for every user, there must be precise control over how resources are shared amongst the different processes or threads.
Look at these principles as security guards that protect your data from getting corrupted by ensuring processes and threads honour access rules when they come into contact with shared resources.
Mutual Exclusion | Only one process can execute in the critical section at any given time. |
Progress | If no process is executing in the critical section and some processes wish to enter, only those not executing in their remainder sections can participate in deciding which will enter next, and this decision cannot be postponed indefinitely. |
Bounded Waiting | There exists a bound on the number of times that other processes are allowed to enter the critical section after a process has made a request to enter its critical section and before that request is granted. |
// Critical section code example in C programming language void critical_section() { // declaration of mutex as a global variable pthread_mutex_t mutex; // lock the mutex pthread_mutex_lock(&mutex); // critical section begins here // shared data is being accessed ... // critical section ends, unlock the mutex pthread_mutex_unlock(&mutex); }
Competition, Deadlock, and Starvation are the common issues associated with critical section problem.
Mutex Lock is an example of a nonpreemptive solution, where a global Boolean variable is used to control the access to the critical section.
// Mutex lock in C #include2. Preemptive Solutions: In contrast, a process can be interrupted in preemptive solutions. A higher priority task can "take over" the resource from another task.pthread_mutex_t mutex; // Declaration of mutex void *func(void *var) { pthread_mutex_lock(&mutex); // Lock the mutex // critical section begins // critical section ends pthread_mutex_unlock(&mutex); // Release the mutex }
An example of a preemptive solution is the Semaphore mechanism, in which a value is designated to manage access to the resource.
// Semaphore in C #includeBoth nonpreemptive and preemptive solutions have their strengths and limitations and are suitable for various application scenarios. The proper selection and implementation of these solutions are key to effectively tackling the critical section problem in an operating system.sem_t semaphore; // Declaration of semaphore void *func(void *var) { sem_wait(&semaphore); // Decrement the semaphore value // critical section begins // critical section ends sem_post(&semaphore); // Increment the semaphore value }
Bounded Waiting: A condition where each process trying to enter its critical section must be granted access in a finite amount of time, preventing the incidence of indefinite postponement.
// Peterson's algorithm making use of bounded waiting int turn; // Shared variable: int turn boolean flag[2]; // Shared variable: Boolean flag[2] void enter_region(int process) { // Process numbers are 0 and 1 int other = 1 - process; // The opposite process flag[process] = true; turn = process; while (flag[other] && turn == process) ; // do nothing } void leave_region(int process) { // Process numbers are 0 and 1 flag[process] = false; }In the realm of operating systems, bounded waiting plays a crucial role in the effective management of critical section problems. By ensuring that all processes are served within a finite waiting limit, it not only allows for efficient process execution but also contributes to overall system stability and robustness. In essence, without bounded waiting, mutual exclusion solutions for critical section problems may lead to unfortunate scenarios like starvation. The concept of bounded waiting hence prevents such pitfalls, making it a key requirement in concurrent programming.
Critical Section: A critical section is a code segment that requires mutual exclusion of access, implying that among several concurrent threads, only one can execute the code section at a time.
An everyday example of critical sections is in a banking system. Consider a scenario where two people are making a withdrawal from the same account simultaneously. Without proper control mechanisms of a critical section, one thread might read the account balance while the other thread is updating it, leading to inconsistencies.
// Example of a critical section in a banking system #includepthread_mutex_t lock; // Mutex Lock void *withdraw(void *var) { pthread_mutex_lock(&lock); // Lock the mutex // Critical section begins here balance = balance - 100; // A withdrawal is made // Critical section ends here pthread_mutex_unlock(&lock); // Unlock the mutex }
Another example is in a multi-threaded ticket booking system. If two customers try to book the last ticket at the same time, without an effectively implemented critical section, both bookings might be successful, leading to overbooking.
// Example in a ticket booking system #includeThe mutual exclusion feature of a critical section ensures only one thread performs the critical operation at a time, thus maintaining data integrity.pthread_mutex_t lock; // Mutex Lock void *book_ticket(void *var) { pthread_mutex_lock(&lock); // Lock the mutex // Critical section begins here if (available_tickets > 0) { available_tickets--; // A ticket is booked } // Critical section ends here pthread_mutex_unlock(&lock); // Unlock the mutex }
These rules are the 'flag' array and the 'turn' variable. The flag array indicates if a process wants to enter its critical section, whilst the turn variable indicates which process's turn it is to enter the critical section.
// Peterson's Algorithm int flag[2]; // Flag array int turn; void peterson_algorithm(int process) { // Process numbers are 0 and 1 int other_process = 1 - process; flag[process] = true; turn = process; while (flag[other_process] && turn == process) ; ... // Critical section flag[process] = false; ... // Remainder section }Through studying these examples, it becomes clear that the successful implementation of critical section rules is a pivotal point in concurrent programming. Therefore, understanding real-life application examples of critical sections is a decisive step towards becoming proficient in managing concurrent processes and threads.
What is a critical section in computer programming?
A critical section in computer programming is a part of a multi-process program that must not be concurrently executed by more than one process. It controls access to shared resources in a multi-threaded program to prevent race conditions.
What are the key principles for implementing a critical section in computer programming?
The principles are: no two processes may simultaneously be inside their critical region, no assumptions about speeds or number of CPUs, no process outside its critical region may block other processes and no process should wait forever to enter its critical region.
What are the benefits of implementing the critical section correctly in a computer program?
Correct implementation of the critical section prevents data corruption, enhances system performance by providing uniform access to resources, and helps maintain system processing order.
What is the critical section problem in operating systems?
The critical section problem in operating systems arises when shared resources are accessed by concurrent processes. To prevent issues, the OS must ensure that only one process accesses the resource at a time.
What are the common issues associated with the critical section problem?
The common issues with the critical section problem are competition, deadlock and starvation. These arise when multiple processes compete for the same resource, hold a part of the resource while waiting for the remainder, or cannot execute their sections due to indefinite resource allocation to other processes, respectively.
How does one counter the critical section problem in an operating system?
Countering the critical section problem involves careful synchronisation of processes, achieved by implementing mutual exclusion methodologies. These can be either nonpreemptive solutions, where a process with a resource cannot be interrupted, or preemptive solutions, where a process can be interrupted.
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