Task Parallelism and Manager-Worker Parallelism

Question 1

What is the purpose of MPI_ANY_SOURCE and MPI_ANY_TAG?

Answer 1

• MPI_ANY_SOURCE allows receiving from an unspecified source
• MPI_ANY_TAG allows receiving from an unspecified tag

Question 2

Why define a new communicator instead of using MPI_COMM_WORLD?

Answer 2

To limit communication to a subset of processes.

Question 3

What are the steps to create a new communicator?

Answer 3

1. Get world group handle (MPI_Comm_group)
2. Create a new group (MPI_Group_incl or MPI_Group_excl)
3. Create a communicator (MPI_Comm_create)
4. Get rank in new communicator (MPI_Comm_rank)
5. Perform communication
6. Free the group and communicator (MPI_Group_free, MPI_Comm_free)

Question 4

What does MPI_Group_incl do?

Answer 4

Creates a new group including specific processes.

Question 5

What does MPI_Group_excl do?

Answer 5

Creates a new group excluding specific processes.

Question 6

What does MPI_Group_union do?

Answer 6

Combines two groups, keeping all unique members.

Question 7

What does MPI_Group_intersection do?

Answer 7

Creates a group containing only common members.

Question 8

What does MPI_Group_difference do?

Answer 8

Creates a group containing processes in the first group but not in the second.

Question 9

How does the Manager-Worker model work in MPI?

Answer 9

1. The manager assigns work to worker processes 2. Workers request more work when finished

Question 10

What function is used to request work in the Mandelbrot Manager-Worker model?

Answer 10

MPI_Recv(&nextProc, 1, MPI_INT, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);

Question 11

How do workers signal completion?

Answer 11

Workers send a request, receive a task, and exit if the received task is a special end flag.

Question 12

What are two OpenMP work-sharing constructs besides parallel for? When is each used?

Answer 12

1. sections - When there are multiple, independent, tasks that can execute concurrently
2. single - Ensures that only thread executes a block of code

Question 13

When are OpenMP tasks useful?

Answer 13

For recursive algorithms and traversing linked lists.

Question 14

How does OpenMP handle tasks?

Answer 14

One thread generates tasks, and other threads execute them.

Question 15

What OpenMP directive ensures only one thread generates tasks?

Answer 15

#pragma omp single

Question 16

When using a single construct, which thread executes the code?

Answer 16

It can be any thread