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Questions and Answers
What is a characteristic of a non-preemptive kernel?
Peterson's Algorithm is used for mutual exclusion in multiprocessor systems.
False
What are the two data items shared by 2 processes in Peterson's Algorithm?
int turn and boolean flag
The TestAndSet() function is a _______________________ instruction.
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Match the synchronization hardware with its description:
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What is the purpose of a mutex lock?
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A semaphore is a 'locking' mechanism.
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What is the Bounded-Buffer Problem also known as?
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In the Producer-Consumer Problem, the _______________________ should not produce data if the buffer is full.
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What is a consequence of deadlock and starvation?
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What is the main purpose of a critical section in a program?
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A critical section can be executed by multiple processes at the same time.
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What are the three conditions to hold critical sections?
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A critical section is a part of a program that tries to access shared _______________________.
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Which of the following is a solution to the Critical Section Problem?
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A preemptive kernel allows a process to be preempted while running in user mode.
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Match the following shared resources with their descriptions:
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What is the main purpose of the rest of the section in a code for critical sections?
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What is the main characteristic of a reader process in the Readers-Writers problem?
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Multiple writers can write to the data set simultaneously in the Readers-Writers problem.
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What is the purpose of a semaphore in the solution to the Readers-Writers problem?
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A writer process requests to enter the _______________________ section.
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What is the condition for a hungry philosopher to eat in the Dining Philosophers problem?
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A reader process can enter the critical section if a writer is already inside.
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Match the following concepts with their corresponding problems:
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What is the main goal of the solution to the Readers-Writers problem?
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Study Notes
Process Synchronization
- Cooperating processes need to access shared resources (CPU, Memory, Data Structure, IO Device) in a synchronized manner.
- Critical Section is a part of the program that tries to access shared resources and needs to be executed atomically.
Conditions to Hold Critical Sections
- Processes should not be inside their critical sections at the same time.
- Processes executing outside their critical section should not block other processes.
- Processes should not be waiting for a long time to enter their critical section.
Solutions to Critical Section Problem
- Mutual Exclusion
- Progress
- Bounded Waiting
Critical Section Approaches
- Preemptive kernel - allows a process to be preempted while running in kernel mode.
- Non-preemptive kernel – does not allow a process to preempt while running in kernel mode, free of race condition.
Peterson's Algorithm or Solution
- Algorithm for mutual exclusion.
- Assumes that load and store machine-language instructions are atomic.
- Allows 2 processes to alternate between their critical sections and remainder sections.
- Requires 2 processes to share data items: int turn and boolean flag.
Synchronization Hardware
- In a uniprocessor environment: disables interrupts and uses shared variable.
- In multiprocessor systems: disabling interrupts may cause delay, uses message passing and special atomic or non-interruptible hardware instructions (TestAndSet(), Swap()).
Mutex Locks
- Kernel resource and OS "locking mechanism".
- Software solution for critical section problem.
- Locks the resources in the entry section of the code and unlocks the resources at the exit section.
Semaphores
- "Signaling" mechanism and operating system service for synchronization.
- Uses an integer variable and wait() and signal() operations.
Classic Problems of Synchronization
- Bounded-Buffer Problem or Producer-Consumer Problem
- Readers and Writers Problem
- Dining-Philosophers Problem
Bounded Buffer Problem or Producer-Consumer Problem
- Multi-process synchronization problem.
- Producer generates data and places it in a buffer, consumer consumes the data from the buffer.
- Problems:
- Producer should not produce data if buffer is full.
- Consumer should not consume data if buffer is empty.
- Producer and consumer should not access the buffer at the same time.
Readers-Writers Problem
- A data set is shared among a number of concurrent processes.
- Readers – only read the data set; they do not perform any updates.
- Writers – can both read and write.
- Only 1 writer can write at a time.
- If a process is writing, other processes cannot read or write to it.
Solution to Readers-Writers Problem
- Use of semaphores:
- Writer process requests to enter the critical section.
- If writer is allowed, it gives a true value to wait().
- If writer is not allowed, writer waits.
- Exits the critical section.
Dining Philosophers Problem
- 5 philosophers sharing a circular table and they eat and think alternatively.
- There is a bowl of rice for each of the philosophers and 5 chopsticks.
- A philosopher needs both their right and left chopstick to eat.
- A hungry philosopher may only eat if there are both chopsticks available.
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Description
Test your knowledge of process synchronization concepts, including critical sections, semaphores, and resource sharing. Questions cover Peterson's solution, synchronization hardware, and classic problems.
