Ruby on Rails 入门之：(20) ruby线程控制的join

所有的编程语言中的线程控制都使用了join，可能鉴于英语和汉语的差异，这个函数功能让我们理解起来相当的费解。

join方法给出的解释是：挂起当前线程，执行指定的线程.那么，到底是挂起哪个线程，执行哪个线程。

看看代码来解释：

[ruby]
i=1
puts "hello thread"
puts Time.new

#round=5
#while i<round
#   puts "the #{i}th round"
#   i=i+1
#end

thread1=Thread.start 10 do |value|
    while i<value
        puts "#{i}\n"
        i=i+1
        sleep(0.1);
    end
end
thread1.join

thread2=Thread.start do
    10.times do |a|
        puts "the #{a+1} output\n"
        sleep(0.1);
    end
end

thread2.join

i=1
puts "hello thread"
puts Time.new

#round=5
#while i<round
# puts "the #{i}th round"
# i=i+1
#end

thread1=Thread.start 10 do |value|
  while i<value
  puts "#{i}\n"
  i=i+1
  sleep(0.1);
end
end
thread1.join

thread2=Thread.start do
10.times do |a|
puts "the #{a+1} output\n"
sleep(0.1);
end
end

thread2.join
第一个thread1.join, 意思是挂起主线程，执行我们指定的线程，即thread1，所以可以这样理解，哪个线程调用join函数，就是执行哪个线程，而挂起执行这个线程之前的线程。

看看上面程序的输出结果：

[html]
watkins@watkins:~/temp/workspace/ruby$ ruby thread1.rb
hello thread
Wed Oct 10 12:07:28 +0800 2012
1
2
3
4
5
6
7
8
9
the 1 output
the 2 output
the 3 output
the 4 output
the 5 output
the 6 output
the 7 output
the 8 output
the 9 output
the 10 output
watkins@watkins:~/temp/workspace/ruby$

watkins@watkins:~/temp/workspace/ruby$ ruby thread1.rb
hello thread
Wed Oct 10 12:07:28 +0800 2012
1
2
3
4
5
6
7
8
9
the 1 output
the 2 output
the 3 output
the 4 output
the 5 output
the 6 output
the 7 output
the 8 output
the 9 output
the 10 output
watkins@watkins:~/temp/workspace/ruby$

可以看到，直到线程thread1执行完毕之后才执行的thread2.

那么如果没有使用join会获得什么样的输出呢？看看

[ruby]
i=1
puts "hello thread"
puts Time.new

#round=5
#while i<round
#   puts "the #{i}th round"
#   i=i+1
#end

thread1=Thread.start 10 do |value|
    while i<value
        puts "#{i}\n"
        i=i+1
        sleep(0.1);
    end
end
#thread1.join

thread2=Thread.start do
    10.times do |a|
        puts "the #{a+1} output\n"
        sleep(0.1);
    end
end

thread2.join

i=1
puts "hello thread"
puts Time.new

#round=5
#while i<round
# puts "the #{i}th round"
# i=i+1
#end

thread1=Thread.start 10 do |value|
  while i<value
  puts "#{i}\n"
  i=i+1
  sleep(0.1);
end
end
#thread1.join

thread2=Thread.start do
10.times do |a|
puts "the #{a+1} output\n"
sleep(0.1);
end
end

thread2.join
这时候获得的输出是thread1和thread2混合的输出：

[html]
watkins@watkins:~/temp/workspace/ruby$ ruby thread1.rb
hello thread
Wed Oct 10 12:39:16 +0800 2012
1
the 1 output
the 2 output
2
the 3 output
3
the 4 output
4
the 5 output
5
the 6 output
6
the 7 output
7
the 8 output
8
the 9 output
9
the 10 output
watkins@watkins:~/temp/workspace/ruby$

watkins@watkins:~/temp/workspace/ruby$ ruby thread1.rb
hello thread
Wed Oct 10 12:39:16 +0800 2012
1
the 1 output
the 2 output
2
the 3 output
3
the 4 output
4
the 5 output
5
the 6 output
6
the 7 output
7
the 8 output
8
the 9 output
9
the 10 output
watkins@watkins:~/temp/workspace/ruby$

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