ruby类实例变量不是线程安全吗？

Question

我只是想知道类实例变量是否是线程安全的。 最近，我陷入了由自定义ORM模型引起的数据库锁定问题。 （无论如何，没有活动记录或续集模型，只是我自己创建的ORM的简单版本）。

为了简单起见，我在这里只包含了一个简单的版本：

我使用一个简单的类实例变量来保存数据库实例（可能是一个Sequel :: Database对象）。

class TestORM
  class << self
    attr_accessor :db 
    def self.db=( db )
      @db = db
    end 
  end 
end

我为它创建一个测试脚本来验证这个db是否是线程安全的。

require 'test_orm.rb'
t1 = Thread.new do  
  db = 'db string 1'
  p "Thread 1: before assign, thread = #{Thread.current.object_id}, TestORM.db.object_id = #{TestORM.db.object_id}"
  TestORM.db = db
  p "Thread 1: after assign, thread = #{Thread.current.object_id}, TestORM.db.object_id = #{TestORM.db.object_id}"
  sleep( 0.5 )
  p "Thread 1: TestORM.db.object_id =  #{TestORM.db.object_id}"
end 
t2 = Thread.new do  
  db = 'db string 2'      
  p "Thread 2: before assign, thread = #{Thread.current.object_id}, TestORM.db.object_id = #{TestORM.db.object_id}"
  TestORM.db = db
  p "Thread 2: after assign, thread = #{Thread.current.object_id}, TestORM.db.object_id = #{TestORM.db.object_id}"
  sleep( 0.5 )
  p "Thread 2: TestORM.db.object_id =  #{TestORM.db.object_id}"
end

t1.join
t2.join

运行上面的代码产生以下结果：

"Thread 1: before assign, thread = 70332471940100, TestORM.db.object_id = 4"
"Thread 2: before assign, thread = 70332471939980, TestORM.db.object_id = 4"
"Thread 1: after assign, thread = 70332471940100, TestORM.db.object_id = 70332471939840"
"Thread 2: after assign, thread = 70332471939980, TestORM.db.object_id = 70332471939520"
"Thread 1: TestORM.db.object_id =  70332471939520"
"Thread 2: TestORM.db.object_id =  70332471939520"

从上面的结果看，类实例变量似乎不是线程安全的，因为线程2覆盖了线程1的TestORM.db实例。

这种包装的任何提示或任何解决方案？

红宝石版：红宝石1.9.2p320

Answer 1

TestORM是线程之间的常量共享。 也就是说，您正在更改同一个对象。

如果您使用的是实例，则可以使用不同的实例，每个线程一个。 由于您创建了该ORM，我建议您将实例用于不同的DB; 所以你的代码看起来像这样：

require 'test_orm.rb'
t1 = Thread.new do  
  db = 'db string 1'
  orm = TestORM.new   
  p "Thread 1: before assign, thread = #{Thread.current.object_id}, orm.db.object_id = #{orm.db.object_id}"
  orm.db = db
  p "Thread 1: after assign, thread = #{Thread.current.object_id}, orm.db.object_id = #{orm.db.object_id}"
  sleep( 0.5 )
  p "Thread 1: orm.db.object_id =  #{orm.db.object_id}"
end 
t2 = Thread.new do  
  db = 'db string 2'
  orm = TestORM.new   
  p "Thread 2: before assign, thread = #{Thread.current.object_id}, orm.db.object_id = #{orm.db.object_id}"
  orm.db = db
  p "Thread 2: after assign, thread = #{Thread.current.object_id}, orm.db.object_id = #{orm.db.object_id}"
  sleep( 0.5 )
  p "Thread 2: orm.db.object_id =  #{orm.db.object_id}"
end

您可能希望在initialize定义数据库：

orm = TestORM.new(db)