summaryrefslogtreecommitdiff
path: root/test/fiber/scheduler.rb
blob: 6e04409c6e6d800cb1762b6a227e5126d9659ff3 (plain)
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
185
186
187
# frozen_string_literal: true

# This is an example and simplified scheduler for test purposes.
# It is not efficient for a large number of file descriptors as it uses IO.select().
# Production Fiber schedulers should use epoll/kqueue/etc.

require 'fiber'
require 'socket'

begin
  require 'io/nonblock'
rescue LoadError
  # Ignore.
end

class Scheduler
  def initialize
    @readable = {}
    @writable = {}
    @waiting = {}

    @closed = false

    @lock = Mutex.new
    @blocking = 0
    @ready = []

    @urgent = nil
  end

  attr :readable
  attr :writable
  attr :waiting

  def next_timeout
    _fiber, timeout = @waiting.min_by{|key, value| value}

    if timeout
      offset = timeout - current_time

      if offset < 0
        return 0
      else
        return offset
      end
    end
  end

  def run
    @urgent = IO.pipe

    while @readable.any? or @writable.any? or @waiting.any? or @blocking.positive?
      # Can only handle file descriptors up to 1024...
      readable, writable = IO.select(@readable.keys + [@urgent.first], @writable.keys, [], next_timeout)

      # puts "readable: #{readable}" if readable&.any?
      # puts "writable: #{writable}" if writable&.any?

      readable&.each do |io|
        if fiber = @readable.delete(io)
          fiber.resume
        elsif io == @urgent.first
          @urgent.first.read_nonblock(1024)
        end
      end

      writable&.each do |io|
        if fiber = @writable.delete(io)
          fiber.resume
        end
      end

      if @waiting.any?
        time = current_time
        waiting, @waiting = @waiting, {}

        waiting.each do |fiber, timeout|
          if timeout <= time
            fiber.resume
          else
            @waiting[fiber] = timeout
          end
        end
      end

      if @ready.any?
        ready = nil

        @lock.synchronize do
          ready, @ready = @ready, []
        end

        ready.each do |fiber|
          fiber.resume
        end
      end
    end
  ensure
    @urgent.each(&:close)
    @urgent = nil
  end

  def close
    self.run
  ensure
    @closed = true

    # We freeze to detect any unintended modifications after the scheduler is closed:
    self.freeze
  end

  def closed?
    @closed
  end

  def current_time
    Process.clock_gettime(Process::CLOCK_MONOTONIC)
  end

  def io_wait(io, events, duration)
    unless (events & IO::READABLE).zero?
      @readable[io] = Fiber.current
    end

    unless (events & IO::WRITABLE).zero?
      @writable[io] = Fiber.current
    end

    Fiber.yield

    return true
  end

  # Used for Kernel#sleep and Mutex#sleep
  def kernel_sleep(duration = nil)
    # p [__method__, duration]
    if duration
      @waiting[Fiber.current] = current_time + duration
    end

    Fiber.yield

    return true
  end

  # Used when blocking on synchronization (Mutex#lock, Queue#pop, SizedQueue#push, ...)
  def block(blocker, timeout = nil)
    # p [__method__, blocker, timeout]
    if timeout
      @waiting[Fiber.current] = current_time + timeout
      begin
        Fiber.yield
      ensure
        # Remove from @waiting in the case #unblock was called before the timeout expired:
        @waiting.delete(Fiber.current)
      end
    else
      @blocking += 1
      begin
        Fiber.yield
      ensure
        @blocking -= 1
      end
    end
  end

  # Used when synchronization wakes up a previously-blocked fiber (Mutex#unlock, Queue#push, ...).
  # This might be called from another thread.
  def unblock(blocker, fiber)
    # p [__method__, blocker, fiber]
    @lock.synchronize do
      @ready << fiber
    end

    if io = @urgent&.last
      io.write_nonblock('.')
    end
  end

  def fiber(&block)
    fiber = Fiber.new(blocking: false, &block)

    fiber.resume

    return fiber
  end
end