Ruby on Rails 入门之：(19) ruby线程同步控制

在Ruby中，提供三种实现同步的方式，分别是：

1. 通过Mutex类实现线程同步

2. 监管数据交接的Queue类实现线程同步

3. 使用ConditionVariable实现同步控制

1. 通过Mutex类实现线程同步
通过Mutex类实现线程同步控制，如果在多个线程钟同时需要一个程序变量，可以将这个变量部分使用lock锁定。
代码如下：
[ruby]
#encoding:gbk
require "thread"
puts "Synchronize Thread"

@num=200
@mutex=Mutex.new

def buyTicket(num)
    @mutex.lock
        if @num>=num
            @num=@num-num
            puts "you have successfully bought #{num} tickets"
        else
            puts "sorry,no enough tickets"
        end
    @mutex.unlock
end

ticket1=Thread.new 10 do
    10.times do |value|
    ticketNum=15
    buyTicket(ticketNum)
    sleep 0.01
    end
end

ticket2=Thread.new 10 do
    10.times do |value|
    ticketNum=20
    buyTicket(ticketNum)
    sleep 0.01
    end
end

sleep 1
ticket1.join
ticket2.join

程序运行的输出：
[ruby]
Synchronize Thread
you have successfully bought 15 tickets
you have successfully bought 20 tickets
you have successfully bought 15 tickets
you have successfully bought 20 tickets
you have successfully bought 15 tickets
you have successfully bought 20 tickets
you have successfully bought 15 tickets
you have successfully bought 20 tickets
you have successfully bought 15 tickets
you have successfully bought 20 tickets
you have successfully bought 15 tickets
sorry,no enough tickets
sorry,no enough tickets
sorry,no enough tickets
sorry,no enough tickets
sorry,no enough tickets
sorry,no enough tickets
sorry,no enough tickets
sorry,no enough tickets
sorry,no enough tickets
除了使用lock锁定变量，还可以使用try_lock锁定变量，还可以使用Mutex.synchronize同步对某一个变量的访问。

2. 监管数据交接的Queue类实现线程同步
Queue类就是表示一个支持线程的队列，能够同步对队列末尾进行访问。不同的线程可以使用统一个对类，但是不用担心这个队列中的数据是否能够同步，另外使用SizedQueue类能够限制队列的长度
SizedQueue类能够非常便捷的帮助我们开发线程同步的应用程序，应为只要加入到这个队列中，就不用关心线程的同步问题。

经典的生产者消费者问题：
[ruby]
#encoding:gbk
require "thread"
puts "SizedQuee Test"

queue = Queue.new

producer = Thread.new do
    10.times do |i|
        sleep rand(i) # 让线程睡眠一段时间
        queue << i
        puts "#{i} produced"
    end
end

consumer = Thread.new do
    10.times do |i|
        value = queue.pop
        sleep rand(i/2)
        puts "consumed #{value}"
    end
end

consumer.join

程序的输出：
[ruby]
SizedQuee Test
0 produced
1 produced
consumed 0
2 produced
consumed 1
consumed 2
3 produced
consumed 34 produced

consumed 4
5 produced
consumed 5
6 produced
consumed 6
7 produced
consumed 7
8 produced
9 produced
consumed 8
consumed 9

3. 使用ConditionVariable实现同步控制
使用 ConditonVariable进行同步控制，能够在一些致命的资源竞争部分挂起线程直到有可用的资源为止。

[ruby]
#encoding:gbk
require "thread"
puts "thread synchronize by ConditionVariable"

mutex = Mutex.new
resource = ConditionVariable.new

a = Thread.new {
    mutex.synchronize {
        # 这个线程目前需要resource这个资源
        resource.wait(mutex)
        puts "get resource"
    }
}

b = Thread.new {
    mutex.synchronize {
        #线程b完成对resourece资源的使用并释放resource
        resource.signal
    }
}

a.join
puts "complete"

mutex 是声明的一个资源，然后通过ConditionVariable来控制申请和释放这个资源。
b 线程完成了某些工作之后释放资源resource.signal,这样a线程就可以获得一个mutex资源然后进行执行。
执行结果：
[html]
thread synchronize by ConditionVariable
get resource
complete

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