Class: FSDB::Modex

Inherits:
Object
  • Object
show all
Defined in:
lib/fsdb/modex.rb,
lib/fsdb/faster-modex.rb

Overview

Modex is a modal exclusion semaphore, like in syncronizer.rb. The two modes are shared (SH) and exclusive (EX). Modex is not nestable.

Defined Under Namespace

Modules: ForkSafely

Constant Summary collapse

SH = 
:SH
EX = 
:EX

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Modex

Returns a new instance of Modex.



35
36
37
38
39
40
 
# File 'lib/fsdb/modex.rb', line 35

def initialize
  @waiting  = []
  @locked   = []
  @mode     = nil
  @first    = true
end

Instance Method Details

#lock(mode) ⇒ Object

the block is executed in the exclusive context



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
 
# File 'lib/fsdb/modex.rb', line 59

def lock mode
  Thread.exclusive do
    thread = Thread.current
    raise ThreadError if @locked.include?(thread)

    if @mode == mode and mode == SH and @waiting.empty? # strict queue
      @locked << thread
    elsif not @mode
      @mode = mode
      @locked << thread
    else
      @waiting << thread << mode
      Thread.stop
      Thread.critical = true
    end
    
    yield if block_given?

#      if @mode != mode
#        raise "@mode == #{@mode} but mode == #{mode}"
#      end
#
#      if @mode == EX and @locked.size > 1
#        raise "@mode == EX but @locked.size == #{@locked.size}"
#      end

    self
  end
end

#remove_dead ⇒ Object

:nodoc:



136
137
138
139
140
141
142
143
144
145
146
147
148
 
# File 'lib/fsdb/modex.rb', line 136

def remove_dead # :nodoc:
  Thread.exclusive do
    waiting = @waiting; @waiting = []
    until waiting.empty?
    
      t = waiting.shift; m = waiting.shift
      @waiting << t << m if t.alive?
    end
    
    @locked = @locked.select {|t| t.alive?}
    wake_next_waiter if @locked.empty?
  end
end

#synchronize(mode, do_when_first = nil, do_when_last = nil, arg = nil) ⇒ Object 



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
 
# File 'lib/fsdb/modex.rb', line 102

def synchronize mode, do_when_first = nil, do_when_last = nil, arg = nil
  lock mode do
    if @first
      @first = false
      
      if do_when_first
        if mode == SH
          @mode = EX
        end

        Thread.nonexclusive { do_when_first[arg] }

        if mode == SH
          @mode = SH
          wake_waiting_sharers
        end
      end
    end
  end
  
  yield
  
ensure
  unlock do
    if @locked.size == 1
      if do_when_last
        @mode = EX
        Thread.nonexclusive { do_when_last[arg] }
      end
      @first = true
    end
  end
end

#try_lock(mode) ⇒ Object 



42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
 
# File 'lib/fsdb/modex.rb', line 42

def try_lock mode
  Thread.exclusive do
    thread = Thread.current
    raise ThreadError if @locked.include?(thread)

    if @mode == mode and mode == SH and @waiting.empty? # strict queue
      @locked << thread
      true
    elsif not @mode
      @mode = mode
      @locked << thread
      true
    end
  end
end

#unlock ⇒ Object

the block is executed in the exclusive context

Raises:

  • (ThreadError) 


90
91
92
93
94
95
96
97
98
99
100
 
# File 'lib/fsdb/modex.rb', line 90

def unlock
  raise ThreadError unless @mode
  
  Thread.exclusive do
    yield if block_given?
    @locked.delete Thread.current
    wake_next_waiter if @locked.empty?
  end

  self
end