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我只是想知道类实例变量是否是线程安全的。最近，我遇到了一个由自定义 ORM 模型引起的数据库锁定问题。（反正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，我只是在这里包装了一个简单的版本：

我使用一个简单的类实例变量来保存一个数据库实例（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

我为它创建了一个测试脚本来验证这个数据库是否是线程安全的。

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"

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

关于这种包装的任何提示或任何解决方案？

红宝石版本：红宝石1.9.2p320

4

1 回答 1

2

TestORM是线程之间共享的常量。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。既然你创建了那个 ORM，我建议你为不同的数据库使用实例；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

您可能希望在以下位置定义您的数据库initialize：

orm = TestORM.new(db)
于 2013-01-30T12:05:51.537 回答