Scheduling Algorithms in Operating Systems
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Questions and Answers

What does priority ceiling aim to achieve?

  • Enhance message passing
  • Prevent priority inversions (correct)
  • Increase thread concurrency
  • Eliminate mutex ownership

    • Priority inheritance allows a low priority thread to run freely when holding a mutex.

    False

    Name a mechanism that Windows uses to prevent priority inversions.

    Random boosting

    Threads within the same process share a _________.

    <p>address space</p> Signup and view all the answers

    What is the main goal of inter-process communication?

    <p>To allow processes to synchronize their behavior</p> Signup and view all the answers

    Match the synchronization mechanisms with their descriptions:

    <p>Priority ceiling = Assigning a priority to a mutex Priority inheritance = Elevating a thread's priority temporarily Random boosting = Giving priority boosts randomly Message passing = Sending messages between processes</p> Signup and view all the answers

    Threads getting in each other’s way is a desired behavior in concurrency.

    <p>False</p> Signup and view all the answers

    What is one key question to address when supporting concurrency?

    <p>How can we make sure that threads do not get in each other’s way?</p> Signup and view all the answers

    Which of the following is NOT a communication mechanism between processes?

    <p>Semaphore</p> Signup and view all the answers

    Message passing allows processes to share memory directly.

    <p>False</p> Signup and view all the answers

    Name one primitive used in message passing.

    <p>send or receive</p> Signup and view all the answers

    In message passing, the function 'send' is used to send a message to a specified ______.

    <p>destination</p> Signup and view all the answers

    Match the communication mechanisms with their descriptions:

    <p>Message Passing = Relies on send and receive primitives Shared Memory = Allows direct memory access between processes Signals = Used to notify a process of events Semaphore = Used for controlling access to a common resource</p> Signup and view all the answers

    What happens when a caller attempts to receive a message that is not available?

    <p>The caller blocks until a message arrives</p> Signup and view all the answers

    In UNIX systems, file descriptors are used for message passing through sockets.

    <p>True</p> Signup and view all the answers

    What type of communication might 'source' in message passing refer to?

    <p>Any source</p> Signup and view all the answers

    Message passing can be used for both ______ and over-the-network communication.

    <p>inter-process communication</p> Signup and view all the answers

    What is a common use case for message passing?

    <p>Producer-consumer scenarios</p> Signup and view all the answers

    What is the purpose of a sequence identifier in message passing?

    <p>To detect multiple receptions of identical messages</p> Signup and view all the answers

    Message passing interfaces incur performance costs due to multiple copies.

    <p>True</p> Signup and view all the answers

    What function is used to create a socket in UNIX?

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

    In message passing, we need to avoid communicating with an ________ participant.

    <p>imposter</p> Signup and view all the answers

    Match the inter-process communication mechanism with its description:

    <p>Message passing = Detecting identical messages Sockets = Bound to network interface Shared memory = Allows access by multiple processes Threads = Enable lightweight process communication</p> Signup and view all the answers

    What is the main purpose of a signal in inter-process communication?

    <p>To send asynchronous notifications between processes</p> Signup and view all the answers

    Signals are always synchronous and occur in response to specific events.

    <p>False</p> Signup and view all the answers

    Which of the following is a cost associated with system calls in message passing?

    <p>Switching between user and supervisor modes</p> Signup and view all the answers

    What function is typically used to send signals to a process?

    <p>kill</p> Signup and view all the answers

    Sockets provide an interface specifically designed for file communication, not network communications.

    <p>False</p> Signup and view all the answers

    In inter-process communication, mutual exclusion ensures that shared resources are accessed by only one __________ at a time.

    <p>thread</p> Signup and view all the answers

    What are the two points where messages are typically copied in message passing?

    <p>From sender to kernel and from kernel to receiver</p> Signup and view all the answers

    Match the signal number with its corresponding reason:

    <p>KILL = Terminate a process STOP = Stop a process INT = Interrupt signal SEGV = Segmentation fault</p> Signup and view all the answers

    The process of ensuring we are communicating with the correct process is known as ________.

    <p>authentication</p> Signup and view all the answers

    What is one crucial feature provided by the OS in message passing?

    <p>Unambiguous identification of processes</p> Signup and view all the answers

    What happens in the no buffering scheme of message passing?

    <p>The sender is blocked until the message is received.</p> Signup and view all the answers

    Message passing can only implement communication locally.

    <p>False</p> Signup and view all the answers

    What is the purpose of sending an acknowledgement message in message passing?

    <p>To confirm that a message has arrived at the receiver.</p> Signup and view all the answers

    In message passing, data can be ___ between address spaces when messages are sent.

    <p>copied</p> Signup and view all the answers

    Match the following message passing schemes with their characteristics:

    <p>No buffering = Sender blocks until message is received Buffering with N elements = Sender can send messages until buffer is full Acknowledgement = Receiver confirms message receipt Data loss = Messages may not arrive over a network</p> Signup and view all the answers

    What is a limitation of message passing over networks?

    <p>It may suffer from data loss and increased security risks.</p> Signup and view all the answers

    Message passing embeds synchronization semantics.

    <p>True</p> Signup and view all the answers

    What happens when the buffer is full in the buffering scheme of message passing?

    <p>Senders are blocked until messages are consumed by receivers.</p> Signup and view all the answers

    The function used by the producer to generate data is called ___ .

    <p>generate_data</p> Signup and view all the answers

    Which of the following functions does the consumer use to process received messages?

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

    Study Notes

    Scheduling and Priority Mechanisms

    • Priority Inversion: The rationale behind scheduling algorithms can fail if a high-priority thread is unable to run due to a lower-priority thread holding a resource.
    • Priority Ceiling Protocol: Assigns a high priority to mutexes, ensuring that any thread holding it has priority above threads needing the mutex, thus preventing priority inversions.
    • Priority Inheritance Protocol: Temporarily boosts the priority of a low-priority thread that holds a mutex needed by a higher-priority thread, allowing swift mutex release while maintaining system priorities.
    • Random Boosting: Mechanism that randomly increases the priority of mutex holders to expedite critical section completion; used by Windows operating systems to mitigate priority inversions.

    Supporting Concurrency

    • Three essential considerations for concurrency support:
      • Processes must communicate effectively.
      • Ensuring threads operate without interference.
      • Synchronizing thread behavior.

    Inter-Process Communication (IPC)

    • Shared Address Space: Threads within the same process can share memory, simplifying information exchange.
    • Message Acknowledgment: Messages typically include sequence identifiers to manage received messages and detect duplicates.
    • Authentication: Ensures proper identification of processes during communication to prevent interactions with unauthorized entities.
    • Performance Costs: Message passing can incur overhead from multiple copies of messages and context switching between user and kernel modes.

    Sockets

    • Sockets are special files in UNIX that bind to network interfaces, providing a tailored API for message passing and network communication.
    • They enable data exchange via buffers and variables, aiding communication between isolated processes.

    Message Passing

    • Basics: Operates on send and receive primitives implemented as system calls.
      • send(destination, &message): Sends a message to a specified destination.
      • receive(source, &message): Receives a message from a specified source.
    • Communication can occur between local processes or over a network through sockets.
    • Synchronizing Semantics: Message passing inherently incorporates synchronization due to its communication nature.

    Message Passing: Buffers

    • No Buffering: The sender blocks until the message is received with no intermediate storage.
    • Buffered Communication: The kernel maintains a limited queue of messages, allowing senders to transmit without blocking until the buffer is full.

    Message Passing: Limitations

    • Data Loss: When communicating over networks, messages may get lost; acknowledgments can help confirm receipt and trigger retransmission if necessary.
    • Security Risks: Increased vulnerabilities when handling messages over networks, necessitating robust communication protocols.

    Signals

    • Signal Mechanism: Asynchronous notifications sent between processes that invoke a signal handler based on signal numbers (e.g., KILL, STOP).
    • Sending Signals: Executed through the kill(pid_t pid, int sig_nr) function.
    • Signal Handling: Processes manage signals via defined signal handlers, which can be modified using functions like signal() or sigaction().
    • Synchronicity: Signals operate asynchronously; they can be triggered at any time, usually upon interrupts or system calls.
    • Signal Count: Processes cannot track the number of signals received before handling, as they are represented only in a bitmask.

    Deadlocks

    • Mutual Exclusion: Access to shared resources must be controlled, permitting only one thread at a time to avoid deadlocks.

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    Description

    This quiz covers key concepts in scheduling algorithms, focusing on priority ceiling and priority inheritance mechanisms. Understand how these methods help prevent priority inversions and manage thread priorities effectively. Test your knowledge on the implications of mutexes in real-time systems.

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