Difference Between Lock variable and Turn variable in Operating System
In operating systems, effective and reliable synchronization mechanisms play a vital role in managing concurrency and coordinating the activities of multiple processes or threads. Two essential tools for synchronization are lock variables and turn variables, each serving distinct purposes and having unique characteristics. In this article, we will explore the key differences between lock variable and turn variables
Lock Variable
A lock variable, also called a mutex (mutual exclusion), serves as a synchronization primitive to protect critical sections of code against simultaneous access by multiple processes or threads. It ensures exclusive access to shared resources, effectively preventing race conditions and conflicts. When a process or thread needs to access a resource protected by a lock variable, it must request the lock. If another process already holds the lock, the requesting process will be required to wait until the lock is released.
Lock variables, in their various forms like binary semaphores or mutexes, serve as crucial tools for coordinating processes’ access to shared resources. By ensuring that only one process can enter the critical section at a time, lock variables enable efficient and synchronized utilization of these resources.
Turn Variable
A turn variable serves as a synchronization primitive in determining the sequential access to a shared resource by processes or threads. It often works alongside other synchronization mechanisms like semaphores or condition variables to implement a fair scheduling policy. The turn variable essentially acts as a queue or waiting list, dictating the order in which processes gain access to the resource.
Processes or threads are arranged in a queue based on a predefined order. The turn variable determines which process from the queue is given access. This system guarantees that each process takes its turn to access the resource, effectively preventing starvation and ensuring fairness.
Difference between Lock and Turn Variable
Feature |
Lock Variable |
Turn Variable |
---|---|---|
Purpose |
Lock variables are primarily used to provide mutual exclusion, preventing concurrent access by multiple processes or threads to a shared resource. |
Turn variables are employed to ensure fair scheduling among multiple processes or threads. They specify the order in which processes will access the resource, promoting fairness. |
Core Mechanism |
Lock variables use a blocking mechanism. When a process/thread requests a lock and it’s already held, the requesting process is blocked and waits until the lock becomes available. |
Turn variables use a queue or waiting list mechanism. Processes are placed in the queue based on a predefined order, and the turn variable determines which process from the queue gets access. |
Fairness |
Lock variables may lead to potential fairness issues if not used carefully. They may favor one process or thread over others, leading to possible contention problems. |
Turn variables are explicitly designed to ensure fairness. They prevent starvation and provide each process with an equal opportunity to access the shared resource. |
Complexity |
Lock variables are generally simpler to implement and use. They are well-suited for scenarios where the main concern is preventing concurrent access. |
Turn variables are more complex to implement. They are often used in conjunction with other synchronization primitives such as semaphores or condition variables to establish a fair scheduling. |
Examples |
Mutexes, binary semaphores, critical sections, and semaphores with locking mechanisms. |
Turn variables are typically used in conjunction with semaphores or condition variables to implement fair resource allocation. |
Conclusion
Lock variables and turn variables are two distinct synchronization mechanisms in operating systems. Lock variables ensure exclusive access to shared resources but may cause fairness issues. On the other hand, turn variables prioritize fair scheduling, preventing resource starvation and ensuring equitable resource access.
The choice between them depends on the specific needs of the application: lock variables are suitable for scenarios where fairness is less critical, while turn variables are ideal for ensuring fairness among multiple processes.
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