module MonitorMixin
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.
Public Class Methods
# File monitor/lib/monitor.rb, line 152 def self.extend_object(obj) super(obj) obj.__send__(:mon_initialize) end
Use extend MonitorMixin
or include MonitorMixin
instead of this constructor. Have look at the examples above to understand how to use this module.
# File monitor/lib/monitor.rb, line 222 def initialize(...) super mon_initialize end
Public Instance Methods
Enters exclusive section.
# File monitor/lib/monitor.rb, line 169 def mon_enter @mon_data.enter end
Leaves exclusive section.
# File monitor/lib/monitor.rb, line 176 def mon_exit mon_check_owner @mon_data.exit end
Returns true if this monitor is locked by any thread
# File monitor/lib/monitor.rb, line 184 def mon_locked? @mon_data.mon_locked? end
Returns true if this monitor is locked by current thread.
# File monitor/lib/monitor.rb, line 191 def mon_owned? @mon_data.mon_owned? end
Enters exclusive section and executes the block. Leaves the exclusive section automatically when the block exits. See example under MonitorMixin
.
# File monitor/lib/monitor.rb, line 200 def mon_synchronize(&b) @mon_data.synchronize(&b) end
Attempts to enter exclusive section. Returns false
if lock fails.
# File monitor/lib/monitor.rb, line 160 def mon_try_enter @mon_data.try_enter end
Creates a new MonitorMixin::ConditionVariable
associated with the Monitor
object.
# File monitor/lib/monitor.rb, line 209 def new_cond unless defined?(@mon_data) mon_initialize @mon_initialized_by_new_cond = true end return ConditionVariable.new(@mon_data) end
Private Instance Methods
# File monitor/lib/monitor.rb, line 241 def mon_check_owner @mon_data.mon_check_owner end
Initializes the MonitorMixin
after being included in a class or when an object has been extended with the MonitorMixin
# File monitor/lib/monitor.rb, line 229 def mon_initialize if defined?(@mon_data) if defined?(@mon_initialized_by_new_cond) return # already initialized. elsif @mon_data_owner_object_id == self.object_id raise ThreadError, "already initialized" end end @mon_data = ::Monitor.new @mon_data_owner_object_id = self.object_id end