PDP Chapter 6: Programming using message passing paradigm
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PDP Chapter 6: Programming using message passing paradigm

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Questions and Answers

What is a key drawback of non-buffered blocking message passing operations?

  • It can lead to considerable idling overhead. (correct)
  • It's faster than buffered operations.
  • It requires more memory than buffered operations.
  • It guarantees no message loss.
  • How do buffered blocking message passing operations mitigate the issue of idling?

  • By allowing the sender to proceed without waiting for the receiver. (correct)
  • By eliminating the use of buffers entirely.
  • By ensuring that all messages are sent instantaneously.
  • By forcing the receiver to wait for acknowledgments.
  • What can result from the handshake process in non-buffered blocking sends?

  • Improved data security during transmission.
  • Reduced data integrity issues.
  • Enhanced bandwidth utilization.
  • Increased potential for deadlocks. (correct)
  • What is the main consequence of using bounded buffer sizes in message passing?

    <p>It can significantly impact performance.</p> Signup and view all the answers

    What is a characteristic of the buffered blocking message passing operations?

    <p>The sender copies data into a buffer and then can continue processing.</p> Signup and view all the answers

    Why is it beneficial to use buffers at both sending and receiving ends?

    <p>To manage the flow of data between sender and receiver more efficiently.</p> Signup and view all the answers

    What is one of the primary reasons for using non-buffered blocking communication?

    <p>To ensure immediate feedback between sender and receiver.</p> Signup and view all the answers

    What challenge can arise if senders and receivers do not reach their communication points simultaneously in non-buffered operations?

    <p>Significant idling overhead may occur.</p> Signup and view all the answers

    What is a key characteristic of the message-passing paradigm in parallel programming?

    <p>Data must be explicitly partitioned and placed.</p> Signup and view all the answers

    Which model is most commonly used in message-passing programs?

    <p>Single program multiple data (SPMD)</p> Signup and view all the answers

    What does the send operation's semantics dictate regarding the value received by a process?

    <p>It must be the initially set value of the sender process.</p> Signup and view all the answers

    Which of the following best describes the asynchronous paradigm in message-passing programs?

    <p>Tasks execute independently, interspersed with synchronization points.</p> Signup and view all the answers

    How can deadlocks be avoided in message-passing systems?

    <p>By allowing processes to communicate only in a strict order.</p> Signup and view all the answers

    What is a primary function of MPI?

    <p>To facilitate message passing between distributed processes.</p> Signup and view all the answers

    Which function prototype correctly describes a receive operation in MPI?

    <p>receive(void *recvbuf, int nelems, int source)</p> Signup and view all the answers

    In the loosely synchronous model, what aspect of task execution is highlighted?

    <p>Tasks can execute independently with occasional synchronization.</p> Signup and view all the answers

    What is the primary purpose of the MPI_Status structure in the MPI_Recv operation?

    <p>To provide information about the source, tag, and errors.</p> Signup and view all the answers

    Which function is used to determine the number of items received in an MPI message?

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

    In the example provided, what condition causes a deadlock when processes are using MPI_Send?

    <p>One process sends before the other receives.</p> Signup and view all the answers

    Which of the following best describes a common method to avoid deadlocks in MPI?

    <p>Implement a protocol to manage the sequence of sends and receives.</p> Signup and view all the answers

    What is the role of the 'tag' parameter in MPI_Send and MPI_Recv calls?

    <p>To distinguish between different messages from the same source.</p> Signup and view all the answers

    In the context of MPI, what does it mean when a send operation is termed 'blocking'?

    <p>The send operation cannot proceed until the receive operation is complete.</p> Signup and view all the answers

    What should the length of the message be in relation to the length field specified in MPI_Recv?

    <p>Less than or equal to the length field specified.</p> Signup and view all the answers

    Which of the following data types can be used with the MPI_Send and MPI_Recv functions?

    <p>MPI_INT, MPI_FLOAT, and any user-defined type.</p> Signup and view all the answers

    Study Notes

    Message Passing Operations

    • Message passing is a fundamental concept in parallel and distributed processing. It allows processes to communicate and exchange data.
    • Non-Buffered Blocking Send/Receive: This method relies on processes waiting for each other to complete their send/receive operations. It poses challenges due to idling and deadlocks.
    • Buffered Blocking Send/Receive: This method utilizes buffers to avoid idling and deadlocks. The sender first copies data into a buffer, then returns. The receiver receives the data from the buffer.
    • Buffered Blocking transfers can be implemented with or without communication hardware with send and receive buffers.
    • Bounded Buffer Sizes: Limiting the size of buffers can impact performance.

    Programming Using Message Passing Paradigm

    • Message-Passing Programming Principles: The logical view of a machine supporting message passing comprises multiple processes with separate address spaces.
    • Message-Passing Programming Constraints: Data must be explicitly partitioned and placed, requiring cooperation between processes for data access.
    • Asynchronous and Loosely Synchronous Paradigms: Message-passing programs can adopt these paradigms for process execution.
    • Single Program Multiple Data (SPMD) Model: This model is widely used where a single program is executed on multiple processes, each with its own data.

    Send and Receive Operations

    • Prototypes of Send and Receive Operations:
      • send(void *sendbuf, int nelems, int dest) sends data to a destination process.
      • receive(void *recvbuf, int nelems, int source) receives data from a source process.
    • Send and Receive Semantics: The value received by the destination process in a send operation must correspond to the value sent.
    • Receive Length: The receiver only accepts messages with a length equal to or less than the specified length field.

    Sending and Receiving Messages

    • Status Variable: Provides information about the MPI_Recv operation, including source, tag, and error details.
    • MPI_Get_count Function: Returns the number of data items received.

    Avoiding Deadlocks

    • Deadlock Scenarios: Circular wait conditions occur when processes are blocked, waiting for each other to release resources.
    • Breaking Deadlock: Modifying the order of send/receive operations, such as using non-blocking operations or introducing asynchronous communication, etc. can prevent deadlocks.

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    Description

    This quiz covers the essential concepts of message passing operations in parallel and distributed processing. It explores various methods like non-buffered blocking and buffered blocking send/receive, along with the implications of bounded buffer sizes on performance. Test your understanding of these crucial principles in message-passing programming.

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