class WaitGroup

• WaitGroup
• Reference
• Object

Overview

Suspend execution until a collection of fibers are finished.

The wait group is a declarative counter of how many concurrent fibers have been started. Each such fiber is expected to call #done to report that they are finished doing their work. Whenever the counter reaches zero the waiters will be resumed.

This is a simpler and more efficient alternative to using a Channel(Nil) then looping a number of times until we received N messages to resume execution.

Basic example:

require "wait_group"
wg = WaitGroup.new(5)

5.times do
  spawn do
    do_something
  ensure
    wg.done # the fiber has finished
  end
end

# suspend the current fiber until the 5 fibers are done
wg.wait

Defined in:

Constructors

• .new(n : Int32 = 0)

Class Method Summary

• .wait(&) : Nil

  Yields a WaitGroup instance and waits at the end of the block for all of the work enqueued inside it to complete.

Instance Method Summary

• #add(n : Int32 = 1) : Nil

  Increments the counter by how many fibers we want to wait for.

• #done : Nil

  Decrements the counter by one.

• #spawn(*, name : String | Nil = nil, &block) : Fiber

  Increment the counter by 1, perform the work inside the block in a separate fiber, decrementing the counter after it completes or raises.

• #wait : Nil

  Suspends the current fiber until the counter reaches zero, at which point the fiber will be resumed.

Constructor Detail

Class Method Detail

WaitGroup.wait do |wg|
  items.each do |item|
    wg.spawn { process item }
  end
end

Instance Method Detail

wg = WaitGroup.new
wg.spawn { do_something }
wg.wait