The Java Fork-Join Pool: A Computation Model for Parallelism

Question 1

The _ in Java provides a powerful and efficient mechanism for parallelizing tasks, particularly those amenable to the “divide and conquer” approach.

Answer 1

Fork-Join framework

Its internal workings are designed to maximize performance and scalability by leveraging multi-core processors and a sophisticated work-stealing algorithm.

Question 2

The fork-join pool supports a style of parallel programming that solves problems by _.

Solve (problem)
—if problem is small enough
——solve problem directly (sequential algorithm)
—else
——split problem into independent parts
——fork new sub-tasks to solve each part
——join all sub-tasks
——compose result from sub-results

Answer 2

divide and conquer

Question 3

Java Fork-Join Pool Computation Model
1. Splitting a task into sub-tasks creates the tasks by using the fork()ing
2. Solving the sub-tasks in parallel
▪ Implemented by fork-join framework
▪ Java execution environment,
▪ Operating System
▪ Hardware
▪ Subtask can run parallel on different cores
▪ can run concurrently in different threads on a single-core
3. Waiting for them to complete
4. Merging the results can use calls to join() to merge all sub-task results together

Answer 3

Noted

Question 4

_ implements an Executor Service.

Answer 4

Fork-Join Pool

Question 5

_ is the basis for Java Executor framework subclasses.

Answer 5

Executor Service

Question 6

_ is the other implementation of ExecutorService executes in runnable or callable.

Answer 6

AbstractExecutorService

Question 7

The purpose of ForkJoinPool in contrast, is to
execute _.

Answer 7

ForkJoinTasks

Question 8

Each _ has its own stack, registers, etc.

Answer 8

worker thread

Question 9

Fork() does not run the task immediately, but instead places it on the _.

Answer 9

work queue

Question 10

Unlike thread.join(), ForkJoinTasks.join() doesn’t simply _ the calling thread. It uses _ to thread to run tasks.

Answer 10

block, workers

Question 11

When a worker thread encounters a _, it processes other tasks until it notices that target sub-task is done.

Answer 11

join()

Question 12

Programs rarely use the ForkJoinTask class directly, but instead, extend one of its subclasses & override compute() Three Classes:
* RecursiveAction – used for computations that do not return results
* RecursiveTask – used for computations that do return results
* CountedCompleter – used for computations in which completed actions trigger other actions

Answer 12

Noted

Question 13

ForkJoinPool enables a _ client to process ForkJoinTasks

Answer 13

non-ForkJoinTask

The client inserts new tasks onto a shared queue used to fee “work stealing queues managed by worker threads.

Question 14

The goal of “work-stealing” is to maximize _.

Answer 14

processor core utilization

Question 15

Each worker thread in a forkjoinpool runs in a _ that scans from sub-tasks to execute.

Answer 15

loop

• The goal for the work thread is to keep as busy as possible.
• The worker threads only block waiting for work if no (sub-) tasks are available to run therefore, the working thread checks multi-input sources for (sub-) tasks to execute.

Question 16

The Fork-Join Framework Internal

If the tasks run by a worker thread call fork(), the new tasks is pushed on the _ of the worker’s deque. The way this works is that a worker thread processes the elements on its deque in LIFO order.

Answer 16

head

It then pops (sub-)tasks from the head of its deque and runs them to completion.

Question 17

The WorkQueue deque that implements workstealing minimizes _.

Answer 17

locking contention

Question 18

CONCLUSION:

The fork-join Pool computation model is a valuable tool for parallelizing tasks, particularly those that can be divided into independent subtasks the Fork-Join framework’s internal workings are carefully designed to maximize performance and scalability in parallel programming. Its work-stealing algorithm, efficient task management, and high-level abstraction make it a valuable tool for tackling complex computational problems.

Answer 18

Noted