Computer Science Chapter 6: Synchronization Tools
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Questions and Answers

What is the primary issue that arises from concurrent access to shared data?

  • Increased execution speed
  • Improved resource allocation
  • Data inconsistency (correct)
  • Simplified process management
  • Which synchronization tool is specifically designed to allow multiple threads to lock resources in a controlled manner?

  • Monitors
  • Semaphores
  • Mutex locks (correct)
  • Condition variables
  • In the context of the critical-section problem, what does a race condition primarily refer to?

  • An inconsistency in shared data due to improper synchronization (correct)
  • An immediate resource release by a process
  • The competition for a limited number of resources
  • A scenario where multiple processes complete their execution simultaneously
  • Which of the following provides a hardware solution to the critical-section problem?

    <p>Memory barriers (C)</p> Signup and view all the answers

    What is the role of semaphores in process synchronization?

    <p>To provide a counter for resource availability (D)</p> Signup and view all the answers

    What issue arises from the race condition in the context of process creation?

    <p>The same process identifier could be assigned to multiple processes. (D)</p> Signup and view all the answers

    What is the primary goal of a critical section protocol?

    <p>Ensure that only one process can execute in its critical section at a time. (C)</p> Signup and view all the answers

    Which requirement for solving the critical-section problem ensures that no process is indefinitely delayed in entering its critical section?

    <p>Progress (B)</p> Signup and view all the answers

    What does mutual exclusion imply in the context of the critical section problem?

    <p>Only one process can execute in its critical section at any given moment. (D)</p> Signup and view all the answers

    In a system with multiple processes, what can occur if proper synchronization is not maintained during critical section execution?

    <p>Data inconsistency and unpredictable behavior. (C)</p> Signup and view all the answers

    What principle does bounded waiting address in critical section management?

    <p>Limit the time any process can wait to enter a critical section (A)</p> Signup and view all the answers

    What problem arises when only disabling interrupts in a critical section solution?

    <p>It could result in starvation if the critical section executes for a long time (C)</p> Signup and view all the answers

    In the software solution using the variable 'turn', what does the variable indicate?

    <p>Which process is permitted to run next (B)</p> Signup and view all the answers

    What does the algorithm for Process Pi ensure about the variable 'turn'?

    <p>Turn must never be both 0 and 1 at the same time (A)</p> Signup and view all the answers

    Which condition is required for mutual exclusion in the software solution?

    <p>A process can enter only if 'turn' equals its identifier (D)</p> Signup and view all the answers

    In a system with two CPUs, which of the following is a potential issue with disabling interrupts?

    <p>Processes could enter critical sections through both CPUs simultaneously (D)</p> Signup and view all the answers

    What issue is specifically highlighted when discussing long-running critical sections?

    <p>Some processes may starve while waiting to enter (C)</p> Signup and view all the answers

    What is a key assumption made about the load and store machine-language instructions in the software solution?

    <p>They execute atomically and cannot be interrupted (C)</p> Signup and view all the answers

    What challenge does the Progress requirement address in critical section solutions?

    <p>Guaranteeing that no process can monopolize the critical section indefinitely (D)</p> Signup and view all the answers

    Flashcards

    Race Condition

    A situation where multiple processes try to access and modify shared data concurrently, leading to unpredictable and potentially incorrect results.

    Critical Section

    A set of instructions that must be executed atomically, meaning that either all instructions complete successfully or none of them do. It guarantees that if a process is interrupted while executing the critical section, the data will be left in a consistent state.

    Synchronization

    A method used to protect shared resources from simultaneous access by multiple processes. It ensures mutual exclusion, guaranteeing that a process can only access a resource if it is not currently being used by another process.

    Synchronization Tools

    A mechanism that allows processes to communicate and coordinate their actions safely, ensuring data consistency and preventing race conditions.

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    Memory Barrier

    A technique used to guarantee that changes to shared memory made by one processor are visible to other processors. Memory barriers ensure that the order of memory operations is maintained, preventing race conditions and ensuring data consistency.

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    Critical Section Problem

    The problem of designing a protocol to ensure that only one process can access the shared resource (critical section) at a time, preventing data corruption due to simultaneous access.

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    Critical Section Solution

    A set of rules or mechanisms that govern access to shared resources, ensuring that only one process can access the critical section at any given time. These rules are crucial to protect data integrity and prevent race conditions.

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    Mutual Exclusion

    A requirement for any solution to the critical section problem. It ensures that at any given time, only one process can be executing its critical section, preventing multiple processes from accessing and modifying shared data simultaneously. Imagine a one-lane tunnel where only one car can pass at a time, avoiding head-on collisions.

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    Bounded Waiting

    Ensures that a process doesn't wait forever to enter its critical section. There's a limit on how many times other processes can enter their critical sections after a process requests entry.

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    Interrupt-based Solution

    This method disables interrupts during the critical section, preventing other processes from interrupting and causing data inconsistency. It's not ideal for longer critical sections.

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    Software Solution 1

    This solution aims to prevent race conditions in a two-process scenario. Atomic instructions like load and store are used, and a shared variable turn determines who gets to enter the critical section.

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    Process Pi Algorithm

    The process waits until it's its turn to enter the critical section, indicated by the turn variable. It then sets turn to the other process' number, allowing the other process to enter the critical section.

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    Process Pj Algorithm

    This process waits for its turn based on the turn variable. After entering the critical section, it sets turn to the other process' number, giving them access.

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    Progress Requirement

    This requirement ensures that all processes eventually get a chance to enter their critical sections. The solution should prevent any process from being continuously blocked.

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    Starvation

    It refers to the situation where a process is continuously denied access to the critical section while other processes are allowed entry. This can happen despite the mutual exclusion and bounded waiting being satisfied.

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    Multi-CPU Problem

    This situation arises when there are multiple CPUs. Interrupts can be disabled on one CPU, but the critical section code might be executing on another CPU, leading to potential violations of mutual exclusion.

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    Study Notes

    Chapter 6: Synchronization Tools

    • Synchronization tools are used to manage concurrent processes and access to shared data

    • Concurrent execution of processes may result in data inconsistency, requiring mechanisms for orderly execution

    • The critical-section problem aims to solve concurrent access conflicts to shared data

    • The critical section is where a process accesses the shared data

    • Mutual exclusion ensures that only one process can access the critical section at a time

    • Progress ensures that a process wishing to enter the critical section cannot be indefinitely postponed

    • Bounded waiting guarantees a bound on the number of times other processes are allowed to enter the critical section before the requesting process is granted access

    • Peterson's solution is a two-process solution to the critical-section problem, ensuring mutual exclusion, progress, and bounded waiting, but is not guaranteed to work correctly in modern architecture without memory barriers due to instruction reordering

    • Software solutions to critical section problems require atomic operations or hardware support

    • Modern architectures may reorder instructions, affecting the execution of processes

    • Interrupt-based solutions can be problematic due to potential issues like starvation or the duration of critical section access

    • To improve performance, processes and/or compilers may reorder operations which have no dependencies.

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    Explore the key concepts of synchronization tools used in managing concurrent processes in computer science. Understand the critical-section problem and mechanisms like mutual exclusion, progress, and bounded waiting. Dive into solutions like Peterson's and their implications on modern architecture.

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