class Ameba::Rule::Lint::SharedVarInFiber

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 variable n shared between fibers 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 { 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

Defined in:

ameba/rule/lint/shared_var_in_fiber.cr

Constant Summary

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

Constructors

Class Method Summary

Instance Method Summary

Instance methods inherited from module Ameba::AST::Util

abort?(node) abort?, control_exp_code(node : Crystal::ControlExpression, code_lines) control_exp_code, dynamic_literal?(node) : Bool dynamic_literal?, each_inline_directive(source, &block : Crystal::Token, String, Array(String) -> _) each_inline_directive, exit?(node) exit?, flow_command?(node, in_loop) flow_command?, flow_expression?(node, in_loop = false) flow_expression?, has_arguments?(node) : Bool has_arguments?, has_block?(node) : Bool has_block?, has_short_block?(node, code_lines) has_short_block?, heredoc?(node : Crystal::ASTNode, source : Source) heredoc?, literal?(node) : Bool literal?, loop?(node) loop?, name_end_location(node) name_end_location, name_location(node) name_location, name_location_or(token : Crystal::Token, name, *, adjust_location_column_number = nil)
name_location_or(node : Crystal::ASTNode, *, adjust_location_column_number = nil) name_location_or, name_size(node) name_size, node_source(node, code_lines) node_source, nodoc?(node) nodoc?, operator_method?(node) operator_method?, operator_method_name?(name : String) operator_method_name?, path_name(node : Crystal::Path, *, include_global = true) : String path_name, path_named?(node, *names : String) : Bool path_named?, raise?(node) raise?, setter_method?(node) setter_method?, setter_method_name?(name : String) setter_method_name?, short_block?(node, code_lines) short_block?, source_between(loc, end_loc, code_lines) : String | Nil source_between, static_literal?(node) : Bool static_literal?, suffix?(node) suffix?, takes_arguments?(node) : Bool takes_arguments?

Instance methods inherited from class Ameba::Rule::Base

==(other : self) ==, catch(source : Source) catch, excluded?(source, root = Dir.current) excluded?, group group, hash(hasher) hash, name name, special? special?, test(source : Source, node : Crystal::ASTNode, *opts)
test(source : Source) test

Class methods inherited from class Ameba::Rule::Base

default_severity : Ameba::Severity default_severity, group_name group_name, rule_name rule_name

Macros inherited from class Ameba::Rule::Base

issue_for(*args, **kwargs, &block) issue_for

Macros inherited from module Ameba::Config::RuleConfig

properties(&block) properties

Constructor Detail

def self.new(ctx : YAML::ParseContext, node : YAML::Nodes::Node) #

def self.new(config = nil) #

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 variable n shared between fibers 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 { 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

def self.new(*, __context_for_yaml_serializable ctx : YAML::ParseContext, __node_for_yaml_serializable node : YAML::Nodes::Node) #

Class Method Detail

def self.deprecated? #

Returns true if this rule is deprecated, false otherwise.


def self.deprecation_reason : String | Nil #

Returns the deprecation reason for this rule, if there is any.


def self.documentation_url : String #

Returns the documentation URL for this rule.

Ameba::Rule::Lint::Syntax.documentation_url
# => "https://crystal-ameba.org/api/master/Ameba/Rule/Lint/Syntax.html"

def self.parsed_doc : String | Nil #

Returns the documentation for this rule, if there is any.

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

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

def self.to_json_schema(builder : JSON::Builder) : Nil #

Instance Method Detail

def description : String #

def description=(description : String) #

def enabled=(enabled : Bool) #

def enabled? : Bool #

def excluded : Set(String) | Nil #

def excluded=(excluded : Set(String) | Nil) #

def severity : Ameba::Severity #

def severity=(severity : Ameba::Severity) #

def since_version : SemanticVersion | Nil #

def since_version=(since_version : String) #

def test(source, node, scope : AST::Scope) #

def test(source) #