Class: Internaut::SystemLock

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

Constant Summary collapse

@@enabled = 
true

Class Method Summary collapse

Class Method Details

.critical_section(unique_code_block_identifier, timeout = 60) ⇒ Object 



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# File 'lib/system_lock.rb', line 44

def self.critical_section(unique_code_block_identifier, timeout=60)
  # puts "entering cc #{Process.pid}"
  yield and return unless @@enabled

  begin
    path = "SystemLock::#{unique_code_block_identifier}"
    # puts "waiting for lock..."
    # wait until the lock is released or until we timeout

    # We use a combination of the process id and a unique app id in case the process id is the same on two different machines
    unique_process_id = UNIQUE_APPLICATION_INSTANCE_ID + Process.pid.to_s
    got_the_lock = false
    while( !got_the_lock )
      while( (cache = @@CACHE.get(path)) && (cache[0] != unique_process_id) rescue return ) do
        # puts "locked waiting.... #{path}: #{Process.pid} : #{cache.inspect}"
        sleep(0.1)
      end
      
      counter = cache && cache[1]
      counter ||= 0
      # set the lock
      set_lock_to = [unique_process_id,counter]
      # puts "attempting to grab lock: #{set_lock_to.inspect}"
      @@CACHE.set( path, set_lock_to, timeout.seconds.to_i )
      cache = @@CACHE.get(path)
      if cache && (cache[0] == unique_process_id)
        # we have to double check to make sure we actually got the lock
        # sleep(0.1)
        cache = @@CACHE.get(path)
        if cache && (cache[0] == unique_process_id)
          # puts "got the lock"
          got_the_lock = true
          
          # puts "grabbing lock: #{set_lock_to.inspect}"
          # add reference - we use ref counting for recursive calls
          set_lock_to = [unique_process_id,cache[1]+1]
          @@CACHE.set( path, set_lock_to, timeout.seconds.to_i ) 
        else
          redo
        end
      else
        # puts "redoing: #{RefCounter.get(path)}, #{unique_process_id}"
        redo
      end
    end
    # puts "acquired lock #{Process.pid}"
    CacheTest.add "entering #{Process.pid}" if Rails.env.test?

    # Do the action
    yield

    CacheTest.add "exiting #{Process.pid}" if Rails.env.test?
    # puts "leaving lock #{Process.pid}"
  # make sure we always unlock, even if there is an exception
  ensure
    cache = @@CACHE.get(path)
    if cache
      if cache[1] > 1
        
        cache[1] -= 1
        # puts "decrementing count to #{cache.inspect}"
        @@CACHE.set( path, cache)
      else
        @@CACHE.set( path, nil)
        # puts "decrementing count to nil - #{path}"
      end
    end
  end
end

.disable! ⇒ Object 



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# File 'lib/system_lock.rb', line 24

def self.disable!
  @@enabled = false
end

.enable! ⇒ Object 



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# File 'lib/system_lock.rb', line 28

def self.enable!
  @@enabled = true
end

.enabled? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/system_lock.rb', line 32

def self.enabled?
  @@enabled
end

.memcached_instance ⇒ Object 



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# File 'lib/system_lock.rb', line 40

def self.memcached_instance
  @@CACHE
end

.memcached_instance=(cache) ⇒ Object 



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# File 'lib/system_lock.rb', line 36

def self.memcached_instance= cache
  @@CACHE = cache
end