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
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
|
module Concurrent
module Edge
# @!macro [attach] atomic_markable_reference
#
# An atomic reference which maintains an object reference along with a mark bit
# that can be updated atomically.
#
# @see http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/AtomicMarkableReference.html
# java.util.concurrent.atomic.AtomicMarkableReference
class AtomicMarkableReference < ::Concurrent::Synchronization::Object
private(*attr_atomic(:reference))
# @!macro [attach] atomic_markable_reference_method_initialize
def initialize(value = nil, mark = false)
super()
self.reference = ImmutableArray[value, mark]
end
# @!macro [attach] atomic_markable_reference_method_compare_and_set
#
# Atomically sets the value and mark to the given updated value and
# mark given both:
# - the current value == the expected value &&
# - the current mark == the expected mark
#
# @param [Object] expected_val the expected value
# @param [Object] new_val the new value
# @param [Boolean] expected_mark the expected mark
# @param [Boolean] new_mark the new mark
#
# @return [Boolean] `true` if successful. A `false` return indicates
# that the actual value was not equal to the expected value or the
# actual mark was not equal to the expected mark
def compare_and_set(expected_val, new_val, expected_mark, new_mark)
# Memoize a valid reference to the current AtomicReference for
# later comparison.
current = reference
curr_val, curr_mark = current
# Ensure that that the expected marks match.
return false unless expected_mark == curr_mark
if expected_val.is_a? Numeric
# If the object is a numeric, we need to ensure we are comparing
# the numerical values
return false unless expected_val == curr_val
else
# Otherwise, we need to ensure we are comparing the object identity.
# Theoretically, this could be incorrect if a user monkey-patched
# `Object#equal?`, but they should know that they are playing with
# fire at that point.
return false unless expected_val.equal? curr_val
end
prospect = ImmutableArray[new_val, new_mark]
compare_and_set_reference current, prospect
end
alias_method :compare_and_swap, :compare_and_set
# @!macro [attach] atomic_markable_reference_method_get
#
# Gets the current reference and marked values.
#
# @return [ImmutableArray] the current reference and marked values
def get
reference
end
# @!macro [attach] atomic_markable_reference_method_value
#
# Gets the current value of the reference
#
# @return [Object] the current value of the reference
def value
reference[0]
end
# @!macro [attach] atomic_markable_reference_method_mark
#
# Gets the current marked value
#
# @return [Boolean] the current marked value
def mark
reference[1]
end
alias_method :marked?, :mark
# @!macro [attach] atomic_markable_reference_method_set
#
# _Unconditionally_ sets to the given value of both the reference and
# the mark.
#
# @param [Object] new_val the new value
# @param [Boolean] new_mark the new mark
#
# @return [ImmutableArray] both the new value and the new mark
def set(new_val, new_mark)
self.reference = ImmutableArray[new_val, new_mark]
end
# @!macro [attach] atomic_markable_reference_method_update
#
# Pass the current value and marked state to the given block, replacing it
# with the block's results. May retry if the value changes during the
# block's execution.
#
# @yield [Object] Calculate a new value and marked state for the atomic
# reference using given (old) value and (old) marked
# @yieldparam [Object] old_val the starting value of the atomic reference
# @yieldparam [Boolean] old_mark the starting state of marked
#
# @return [ImmutableArray] the new value and new mark
def update
loop do
old_val, old_mark = reference
new_val, new_mark = yield old_val, old_mark
if compare_and_set old_val, new_val, old_mark, new_mark
return ImmutableArray[new_val, new_mark]
end
end
end
# @!macro [attach] atomic_markable_reference_method_try_update!
#
# Pass the current value to the given block, replacing it
# with the block's result. Raise an exception if the update
# fails.
#
# @yield [Object] Calculate a new value and marked state for the atomic
# reference using given (old) value and (old) marked
# @yieldparam [Object] old_val the starting value of the atomic reference
# @yieldparam [Boolean] old_mark the starting state of marked
#
# @return [ImmutableArray] the new value and marked state
#
# @raise [Concurrent::ConcurrentUpdateError] if the update fails
def try_update!
old_val, old_mark = reference
new_val, new_mark = yield old_val, old_mark
unless compare_and_set old_val, new_val, old_mark, new_mark
fail ::Concurrent::ConcurrentUpdateError,
'AtomicMarkableReference: Update failed due to race condition.',
'Note: If you would like to guarantee an update, please use ' \
'the `AtomicMarkableReference#update` method.'
end
ImmutableArray[new_val, new_mark]
end
# @!macro [attach] atomic_markable_reference_method_try_update
#
# Pass the current value to the given block, replacing it with the
# block's result. Simply return nil if update fails.
#
# @yield [Object] Calculate a new value and marked state for the atomic
# reference using given (old) value and (old) marked
# @yieldparam [Object] old_val the starting value of the atomic reference
# @yieldparam [Boolean] old_mark the starting state of marked
#
# @return [ImmutableArray] the new value and marked state, or nil if
# the update failed
def try_update
old_val, old_mark = reference
new_val, new_mark = yield old_val, old_mark
return unless compare_and_set old_val, new_val, old_mark, new_mark
ImmutableArray[new_val, new_mark]
end
# Internal/private ImmutableArray for representing pairs
class ImmutableArray < ::Array
def self.new(*args)
super(*args).freeze
end
end
end
end
end
|
