Class: FSDB::Modex

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

Overview

Modex is a modal exclusion semaphore. 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.



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# File 'lib/fsdb/modex.rb', line 11

def initialize
  @waiting  = []
  @locked   = []
  @mode     = nil
  @first    = true
  @m        = Mutex.new
end

Instance Method Details

#lock(mode) ⇒ Object

the block is executed in the exclusive context



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# File 'lib/fsdb/modex.rb', line 38

def lock mode
  @m.synchronize do
    thread = Thread.current
    raise ThreadError, "nesting not allowed" 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
      @m.unlock
      Thread.stop
      @m.lock
    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:



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# File 'lib/fsdb/modex.rb', line 125

def remove_dead # :nodoc:
  @m.synchronize 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 



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# File 'lib/fsdb/modex.rb', line 91

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

        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
        nonexclusive { do_when_last[arg] }
      end
      @first = true
    end
  end
end

#try_lock(mode) ⇒ Object 



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# File 'lib/fsdb/modex.rb', line 19

def try_lock mode
  @m.synchronize do
    thread = Thread.current
    raise ThreadError, "nesting not allowed" 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
    else
      false
    end
  end
end

#unlock ⇒ Object

the block is executed in the exclusive context

Raises:

  • (ThreadError) 


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# File 'lib/fsdb/modex.rb', line 70

def unlock
  raise ThreadError, "already unlocked" unless @mode
  
  @m.synchronize do
    if block_given?
      begin
        yield
      ensure
        @locked.delete Thread.current
      end
    
    else
      @locked.delete Thread.current
    end
    
    wake_next_waiter if @locked.empty?
  end

  self
end