strand¶ ↑

Strand is a module that provides Thread-like behavior for Fibers in EventMachine.

Like Threads¶ ↑

Strand has an interface identical to Thread wherever possible. The specs for Strand are based on the ruby-spec for Thread

thread = Thread.new{ 1+2 }
thread.join
thread.value # => 3

strand = Strand.new{ 1+2 }
strand.join
strand.value # => 3

Fiber/EventMachine aware sleep¶ ↑

Calling ruby’s Kernel.sleep will block the EventMachine reactor, but Strand defines an EM+Fiber safe sleep.

Assuming that EventMachine is running:

s1 = Strand.new{ Strand.sleep(1) }
s2 = Strand.new{ Strand.sleep(1) }
s1.join
s2.join

# Roughly 1 second will have passed.

When run outside of the EventMachine reactor, Strand delegates to ruby’s native ::Thread so the above code would still work as expected.

Thread local, Fiber local and Strand local variables¶ ↑

Thread local storage is the same as Fiber local storage in Ruby.

Thread.current[:name] = "callie"
Fiber.current[:name]  # => "callie"
Fiber.current[:name]  = "coco"
Thread.current[:name] # => "coco"

Strand provides its own storage.

Thread.current[:name] = "callie"
Strand.current[:name] = "coco"
Thread.current[:name] # => "callie"
Strand.current[:name] # => "coco"

Strand.list¶ ↑

Ruby provides a way to get a list of all living Threads:

Thread.new{ sleep }
Thread.list # => [#<Thread:0x007f9343869da8 run>, #<Thread:0x007f934405eec8 sleep>]

There is no equivalent for finding all living Fibers.

There is a way to find all living Strands though:

Strand.new do
  Strand.new{ Strand.yield }
  Strand.list # => [#<Strand:0x70358087608460 run, #<Strand:0x70358087608280 yielded]
end

Strand.pass¶ ↑

Consider the following threaded code:

Thread.new do
  puts 1
  Thread.pass
  puts 2
  Thread.pass
  puts 3
end
Thread.new do
  puts 1
  Thread.pass
  puts 2
  Thread.pass
  puts 3
end

Or similarly:

Thread.new do
  puts 1
  sleep(0.01)
  puts 2
  sleep(0.01)
  puts 3
end
Thread.new do
  puts 1
  sleep(0.01)
  puts 2
  sleep(0.01)
  puts 3
end

How would you do that with fibers?

Fiber.new do
  puts 1
  Fiber.yield
  puts 2
  Fiber.yield
  puts 3
end.resume
Fiber.new do
  puts 1
  Fiber.yield
  puts 2
  Fiber.yield
  puts 3
end.resume

That doesn’t work. The fibers are yielding, but nothing is resuming them. The output is just:

1
1

Enter Strand.pass. It yields the fiber, but tells EventMachine to resume it on the next tick.

Strand.new do
  puts 1
  Strand.pass
  puts 2
  Strand.pass
  puts 3
end
Strand.new do
  puts 1
  Strand.pass
  puts 2
  Strand.pass
  puts 3
end

The output is:

Contributing to strand¶ ↑

Check out the latest master to make sure the feature hasn’t been implemented or the bug hasn’t been fixed yet
Check out the issue tracker to make sure someone already hasn’t requested it and/or contributed it
Fork the project
Start a feature/bugfix branch
Commit and push until you are happy with your contribution
Make sure to add specs, preferably based on ruby-spec
Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.

Copyright¶ ↑

See LICENSE.txt for further details.

lwoggardner/strand