Class: Laziest::Group

Inherits:
Promise
  • Object
show all
Defined in:
lib/laziest/group.rb

Instance Method Summary collapse

Constructor Details

#initialize(enumerator, &block) ⇒ Group 



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
 
# File 'lib/laziest/group.rb', line 5

def initialize enumerator, &block
  @hash = {}
  @lazy_arrays = {}
  @buffers = ::Hash.new{|h,k|h[k]=[]}
  @enumerator = enumerator
  @group_block = block
  @enum_mutex = ::Mutex.new
  super() do
    # Any existing lazy arrays can simply be forced, since
    # they're on a different mutex now:
    @lazy_arrays.each do |arr|
      arr.__force__
    end
    # And just in case there aren't any lazy arrays:
    ::Kernel.loop do
      val = enumerator.next
      key = yield val
      (@hash[key] ||= []) << val
    end
    # Strip out anything that turned out to be empty.
    @hash.delete_if {|k,v| v.empty?}
    # clear potentially-expensive GC-able stuff.
    @lazy_arrays = nil
    @buffers = nil
    @group_block = nil
    # safe because we already forced all existing lazy arrays, and we're
    # holding the global mutex which prevents any new ones from being built
    @enum_mutex = nil
    @hash
  end
end

Instance Method Details

#[](key) ⇒ Object 



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
 
# File 'lib/laziest/group.rb', line 37

def [] key
  return super unless @result.equal?(NOT_SET) && @error.equal?(NOT_SET)
  @mutex.synchronize do
    @enum_mutex.synchronize do
      # for good measure -- for once, we really _don't_ want to do _any_ of
      # this once the hash's promise resolves.
      return super unless @result.equal?(NOT_SET) && @error.equal?(NOT_SET)
      if @lazy_arrays.has_key?(key)
        @lazy_arrays[key]
      else
        # Note: This enumerator is only ever passed to ArrayPromise.
        # It is not actually a valid enumerator, as it entirely lacks
        # support for rewinding.
        enum = ::Enumerator.new do |yielder|
          @enum_mutex.synchronize do
            buffer = @buffers[key]
            ::Kernel.loop do
              if buffer.empty?
                # At this point, @enumerator.next may throw StopIteration.
                # Which will break the loop, which will end our iteration,
                # which is fine. (A call to our enumerator.each would also
                # result in a StopIteration.)
                v = @enumerator.next
                k = @group_block.call v
                if k == key
                  # We shouldn't hold the lock when we yield.
                  ::Laziest::MutexUtil.unsynchronize @enum_mutex do
                    yielder << v
                  end
                elsif @hash.has_key? k
                  # Buffer data for the lazy array to read later
                  if @lazy_arrays.has_key? k
                    @buffers[k] << v
                  else
                    @hash[k] << v
                  end
                else
                  # We know a lazy array doesn't exist unless the hash exists
                  @hash[k] = [v]
                end
              else
                v = buffer.shift
                ::Laziest::MutexUtil.unsynchronize @enum_mutex do
                  yielder << v
                end
              end
            end
          end
        end
        @hash[key] = [] unless @hash.has_key? key
        @lazy_arrays[key] = ArrayPromise.new enum, @hash[key], true
      end
    end
  end
end