class Ameba::Rule::Lint::SharedVarInFiber

• Ameba::Rule::Lint::SharedVarInFiber
• Ameba::Rule::Base
• Reference
• Object

Overview

A rule that disallows using shared variables in fibers, which are mutated during iterations.

In most cases it leads to unexpected behaviour and is undesired.

For example, having this example:

n = 0
channel = Channel(Int32).new

while n < 3
  n = n + 1
  spawn { channel.send n }
end

3.times { puts channel.receive } # => # 3, 3, 3

The problem is there is only one shared between fibers variable n and when channel.receive is executed its value is 3.

To solve this, the code above needs to be rewritten to the following:

n = 0
channel = Channel(Int32).new

while n < 3
  n = n + 1
  m = n
  spawn do { channel.send m }
end

3.times { puts channel.receive } # => # 1, 2, 3

This rule is able to find the shared variables between fibers, which are mutated during iterations. So it reports the issue on the first sample and passes on the second one.

There are also other techniques to solve the problem above which are officially documented

YAML configuration example:

Lint/SharedVarInFiber:
  Enabled: true

Included Modules

• YAML::Serializable
• YAML::Serializable::Strict

Defined in:

Constant Summary

MSG = "Shared variable `%s` is used in fiber"

Constructors

• .new(ctx : YAML::ParseContext, node : YAML::Nodes::Node)
• .new(config = nil)

  A rule that disallows using shared variables in fibers, which are mutated during iterations.

Class Method Summary

• .parsed_doc : String | Nil

  Returns documentation for this rule, if there is any.

Instance Method Summary

• #description : String
• #description=(description : String)
• #enabled=(enabled : Bool)
• #enabled? : Bool
• #excluded : Array(String) | Nil
• #excluded=(excluded : Array(String) | Nil)
• #severity : Ameba::Severity
• #severity=(severity : Ameba::Severity)
• #test(source, node, scope : AST::Scope)
• #test(source)

Constructor Detail

n = 0
channel = Channel(Int32).new

while n < 3
  n = n + 1
  spawn { channel.send n }
end

3.times { puts channel.receive } # => # 3, 3, 3

n = 0
channel = Channel(Int32).new

while n < 3
  n = n + 1
  m = n
  spawn do { channel.send m }
end

3.times { puts channel.receive } # => # 1, 2, 3

Lint/SharedVarInFiber:
  Enabled: true

Class Method Detail

module Ameba
  # This is a test rule.
  # Does nothing.
  class MyRule < Ameba::Rule::Base
    def test(source)
    end
  end
end

MyRule.parsed_doc # => "This is a test rule.\nDoes nothing."

Instance Method Detail