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require 'concurrent/thread_safe/util'
require 'concurrent/thread_safe/util/volatile'
module Concurrent
# @!visibility private
module ThreadSafe
# @!visibility private
module Util
# Provides a cheapest possible (mainly in terms of memory usage) +Mutex+
# with the +ConditionVariable+ bundled in.
#
# Usage:
# class A
# include CheapLockable
#
# def do_exlusively
# cheap_synchronize { yield }
# end
#
# def wait_for_something
# cheap_synchronize do
# cheap_wait until resource_available?
# do_something
# cheap_broadcast # wake up others
# end
# end
# end
#
# @!visibility private
module CheapLockable
private
engine = defined?(RUBY_ENGINE) && RUBY_ENGINE
if engine == 'rbx'
# Making use of the Rubinius' ability to lock via object headers to avoid the overhead of the extra Mutex objects.
def cheap_synchronize
Rubinius.lock(self)
begin
yield
ensure
Rubinius.unlock(self)
end
end
def cheap_wait
wchan = Rubinius::Channel.new
begin
waiters = @waiters ||= []
waiters.push wchan
Rubinius.unlock(self)
signaled = wchan.receive_timeout nil
ensure
Rubinius.lock(self)
unless signaled or waiters.delete(wchan)
# we timed out, but got signaled afterwards (e.g. while waiting to
# acquire @lock), so pass that signal on to the next waiter
waiters.shift << true unless waiters.empty?
end
end
self
end
def cheap_broadcast
waiters = @waiters ||= []
waiters.shift << true until waiters.empty?
self
end
elsif engine == 'jruby'
# Use Java's native synchronized (this) { wait(); notifyAll(); } to avoid the overhead of the extra Mutex objects
require 'jruby'
def cheap_synchronize
JRuby.reference0(self).synchronized { yield }
end
def cheap_wait
JRuby.reference0(self).wait
end
def cheap_broadcast
JRuby.reference0(self).notify_all
end
else
require 'thread'
extend Volatile
attr_volatile :mutex
# Non-reentrant Mutex#syncrhonize
def cheap_synchronize
true until (my_mutex = mutex) || cas_mutex(nil, my_mutex = Mutex.new)
my_mutex.synchronize { yield }
end
# Releases this object's +cheap_synchronize+ lock and goes to sleep waiting for other threads to +cheap_broadcast+, reacquires the lock on wakeup.
# Must only be called in +cheap_broadcast+'s block.
def cheap_wait
conditional_variable = @conditional_variable ||= ConditionVariable.new
conditional_variable.wait(mutex)
end
# Wakes up all threads waiting for this object's +cheap_synchronize+ lock.
# Must only be called in +cheap_broadcast+'s block.
def cheap_broadcast
if conditional_variable = @conditional_variable
conditional_variable.broadcast
end
end
end
end
end
end
end
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