Ruby线程

1. 创建线程

	Thread.new do
		3.times do 
			sleep 3
			puts "Thread #{Thread.current.object_id} running..."
		end
	end

ruby使用在Thread.new创建线程，线程创建后立即返回，线程也同时开始执行。ruby线程可以在创建块中使用外部变量，也可以使用本地变量，值变量在线程内部保存的是本地副本，而引用变量保存的是一个本地引用。

class Book
	attr_accessor :name
end
num = 0
count = 0
book = Book.new
book.name = 'ybur'
puts "main Thread=#{num} count=#{count} book=#{book.name}"

t.Thread.new(num,book) do |n,b|
	n+=1
	count+=1
	b.name.reverse!
	puts "new Thread:num=#{n} count=#{count} book=#{b.name}"
end
t.join
puts "main Thread:num=#{num} count=#{count} book=#{book.name}"
#=>main Thread:num=0 count=0 book=ybur
#=>new Thread:num=1 count=1 book=ruby
#=>main Thread:num=0 count=1 book=ruby

新线程中保存num的副本，在线程中更改num并不影响外部num值，而新线程对book的修改会直接影响外部book，在新线程中也可打破作用域直接访问外部count并作出修改。

常用方法

Thread.current #获取当前线程
Thread.list #所有线程列表
Thread#status #线程状态
Thread#alive?
Thread#stop?
Thread#join

线程可以将某些信息放在自身的hash表中，让别的线程访问。使用Thread#value（阻塞方法）访问线程执行最后一行代码的结果：

t=Thread.new(1,10) do |a,b|
	sleep 3
	Thread.current['plus_result']=a+b
	"thread result:#{a+b}"
end
t.join
puts "1+10=#{t['plus_result']}"
puts "#{t.value}"
#=> 1+10=11
#=> thread result:11

2. Mutex

来自ruby-doc的例子

require 'thread'
mutex=Mutex.new
count1=count2=0
difference=0
counter=Thread.new do
	loop do
		mutex.synchronize do
			count1+=1
			count2+=1
		end
	end
end
spy=Thread.new do
	loop do
		mutex.synchronize do
			difference+=(count1-count2).abs
		end
	end
end
sleep 1
mutex.lock
#=> count1 >> 21192
#=> count2 >> 21192
#=> difference >>0

3. Condition Variables

来自ruby-doc

require 'thread'
mutext=Mutex.new
cv=ConditionVariable.new
a=Thread.new {
	mutex.synchronize {
		puts "A:I have critical section, but will wait for cv"
		cv.wait mutex
		puts "A:I have critical section again! I rule!"
	}
}
puts "(Later, back at the ranch...)"
b=Thread.new {
	mutex.synchronize {
		puts "B: Now I am critical, but am done with cv"
		cv.signal
		puts "B: I am still critical, finishing up"
	}
}
a.join
b.join

produces:
A:I have critical section, but will wait for cv(Later, back at the ranch...)
B: Now I am critical,but am done with cv
B:I am still critical, finishing up
A: I have critical section again! I Rule!

在进入临界区并在cv上等待时，会释放该互斥锁mutex，从而才能让别的线程进入临界区，不至于发生死锁。

4. Queue

ruby的Queue和java的BlockingQueue十分类似。当Queue为空时，执行pop操作会导致线程挂起等待。

require 'thread'
queue=Queue.new
producer=Thread.new do 
	5.times do |i|
		sleep 4
		queue << i # operator << is alias of push
		puts "#{i} produced"
	end
end
consumer=Thread.new do 
	5.times do |i|
		value=queue.pop
		sleep 2
		puts "consumed #{value}"
	end
end

ruby还提供了一个SizedQueue，当达到队列最大长度后，执行push操作时也会导致线程挂起。

ruby
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