Module: MonitorMixin
Relationships & Source Files | |
Namespace Children | |
Classes:
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Extension / Inclusion / Inheritance Descendants | |
Included In:
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Defined in: | lib/monitor.rb |
Overview
In concurrent programming, a monitor is an object or module intended to be used safely by more than one thread. The defining characteristic of a monitor is that its methods are executed with mutual exclusion. That is, at each point in time, at most one thread may be executing any of its methods. This mutual exclusion greatly simplifies reasoning about the implementation of monitors compared to reasoning about parallel code that updates a data structure.
You can read more about the general principles on the Wikipedia page for Monitors
Examples
Simple object.extend
require 'monitor.rb'
buf = []
buf.extend(MonitorMixin)
empty_cond = buf.new_cond
# consumer
Thread.start do
loop do
buf.synchronize do
empty_cond.wait_while { buf.empty? }
print buf.shift
end
end
end
# producer
while line = ARGF.gets
buf.synchronize do
buf.push(line)
empty_cond.signal
end
end
The consumer thread waits for the producer thread to push a line to buf while buf.empty?
. The producer thread (main thread) reads a line from ARGF and pushes it into buf then calls empty_cond.signal
to notify the consumer thread of new data.
Simple Class include
require 'monitor'
class SynchronizedArray < Array
include MonitorMixin
def initialize(*args)
super(*args)
end
alias :old_shift :shift
alias :old_unshift :unshift
def shift(n=1)
self.synchronize do
self.old_shift(n)
end
end
def unshift(item)
self.synchronize do
self.old_unshift(item)
end
end
# other methods ...
end
SynchronizedArray
implements an Array with synchronized access to items. This Class is implemented as subclass of Array which includes the MonitorMixin
module.
Class Method Summary
Instance Method Summary
-
#mon_enter
(also: #enter)
Enters exclusive section.
-
#mon_exit
(also: #exit)
Leaves exclusive section.
-
#mon_synchronize
(also: #synchronize)
Enters exclusive section and executes the block.
-
#mon_try_enter
(also: #try_mon_enter)
Attempts to enter exclusive section.
-
#new_cond
Creates a new ConditionVariable associated with the receiver.
-
#synchronize
Alias for #mon_synchronize.
-
#try_mon_enter
(also: #try_enter)
Alias for #mon_try_enter.
-
#initialize(*args)
private
Use
extend MonitorMixin
orinclude MonitorMixin
instead of this constructor. - #mon_check_owner private
- #mon_enter_for_cond(count) private
- #mon_exit_for_cond private
-
#mon_initialize
private
Initializes the
MonitorMixin
after being included in a class or when an object has been extended with theMonitorMixin
.
Class Method Details
.extend_object(obj)
[ GitHub ]# File 'lib/monitor.rb', line 160
def self.extend_object(obj) super(obj) obj.__send__(:mon_initialize) end
Instance Method Details
#initialize(*args) (private)
Use extend MonitorMixin
or include MonitorMixin
instead of this constructor. Have look at the examples above to understand how to use this module.
# File 'lib/monitor.rb', line 234
def initialize(*args) super mon_initialize end
#mon_check_owner (private)
[ GitHub ]# File 'lib/monitor.rb', line 247
def mon_check_owner if @mon_owner != Thread.current raise ThreadError, "current thread not owner" end end
#mon_enter Also known as: #enter
Enters exclusive section.
# File 'lib/monitor.rb', line 185
def mon_enter if @mon_owner != Thread.current @mon_mutex.lock @mon_owner = Thread.current @mon_count = 0 end @mon_count += 1 end
#mon_enter_for_cond(count) (private)
[ GitHub ]# File 'lib/monitor.rb', line 253
def mon_enter_for_cond(count) @mon_owner = Thread.current @mon_count = count end
#mon_exit Also known as: #exit
Leaves exclusive section.
# File 'lib/monitor.rb', line 197
def mon_exit mon_check_owner @mon_count -=1 if @mon_count == 0 @mon_owner = nil @mon_mutex.unlock end end
#mon_exit_for_cond (private)
[ GitHub ]# File 'lib/monitor.rb', line 258
def mon_exit_for_cond count = @mon_count @mon_owner = nil @mon_count = 0 return count end
#mon_initialize (private)
Initializes the MonitorMixin
after being included in a class or when an object has been extended with the MonitorMixin
# File 'lib/monitor.rb', line 241
def mon_initialize @mon_owner = nil @mon_count = 0 @mon_mutex = Mutex.new end
#mon_synchronize Also known as: #synchronize
Enters exclusive section and executes the block. Leaves the exclusive section automatically when the block exits. See example under MonitorMixin
.
#mon_try_enter Also known as: #try_mon_enter
Attempts to enter exclusive section. Returns false
if lock fails.
# File 'lib/monitor.rb', line 168
def mon_try_enter if @mon_owner != Thread.current unless @mon_mutex.try_lock return false end @mon_owner = Thread.current @mon_count = 0 end @mon_count += 1 return true end
#new_cond
Creates a new ::MonitorMixin::ConditionVariable associated with the receiver.
# File 'lib/monitor.rb', line 225
def new_cond return ConditionVariable.new(self) end
#synchronize
Alias for #mon_synchronize.
# File 'lib/monitor.rb', line 219
alias synchronize mon_synchronize
#try_mon_enter Also known as: #try_enter
Alias for #mon_try_enter.
# File 'lib/monitor.rb', line 180
alias try_mon_enter mon_try_enter