1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
|
require 'concurrent/constants'
require_relative 'locals'
module Concurrent
# A `FiberLocalVar` is a variable where the value is different for each fiber.
# Each variable may have a default value, but when you modify the variable only
# the current fiber will ever see that change.
#
# This is similar to Ruby's built-in fiber-local variables (`Thread.current[:name]`),
# but with these major advantages:
# * `FiberLocalVar` has its own identity, it doesn't need a Symbol.
# * Each Ruby's built-in fiber-local variable leaks some memory forever (it's a Symbol held forever on the fiber),
# so it's only OK to create a small amount of them.
# `FiberLocalVar` has no such issue and it is fine to create many of them.
# * Ruby's built-in fiber-local variables leak forever the value set on each fiber (unless set to nil explicitly).
# `FiberLocalVar` automatically removes the mapping for each fiber once the `FiberLocalVar` instance is GC'd.
#
# @example
# v = FiberLocalVar.new(14)
# v.value #=> 14
# v.value = 2
# v.value #=> 2
#
# @example
# v = FiberLocalVar.new(14)
#
# Fiber.new do
# v.value #=> 14
# v.value = 1
# v.value #=> 1
# end.resume
#
# Fiber.new do
# v.value #=> 14
# v.value = 2
# v.value #=> 2
# end.resume
#
# v.value #=> 14
class FiberLocalVar
LOCALS = FiberLocals.new
# Creates a fiber local variable.
#
# @param [Object] default the default value when otherwise unset
# @param [Proc] default_block Optional block that gets called to obtain the
# default value for each fiber
def initialize(default = nil, &default_block)
if default && block_given?
raise ArgumentError, "Cannot use both value and block as default value"
end
if block_given?
@default_block = default_block
@default = nil
else
@default_block = nil
@default = default
end
@index = LOCALS.next_index(self)
end
# Returns the value in the current fiber's copy of this fiber-local variable.
#
# @return [Object] the current value
def value
LOCALS.fetch(@index) { default }
end
# Sets the current fiber's copy of this fiber-local variable to the specified value.
#
# @param [Object] value the value to set
# @return [Object] the new value
def value=(value)
LOCALS.set(@index, value)
end
# Bind the given value to fiber local storage during
# execution of the given block.
#
# @param [Object] value the value to bind
# @yield the operation to be performed with the bound variable
# @return [Object] the value
def bind(value)
if block_given?
old_value = self.value
self.value = value
begin
yield
ensure
self.value = old_value
end
end
end
protected
# @!visibility private
def default
if @default_block
self.value = @default_block.call
else
@default
end
end
end
end
|
