为什么 ruby​​ 1.9.2 中的分叉会中断 memcached 连接，但在 1.8.7 中不会？

Question

在将大型项目从 1.8.7 升级到 1.9.2 时，我发现了一个无法解释的错误。即使在分叉代码中未使用 memcached 连接，fork 操作似乎也会中断 memcached 连接。这是一个 IRB 会话，在 1.9.2 中显示错误，在 1.8.7 中显示没有错误。谁能解释为什么 1.8.7 中没有 ServerIsMarkedDead 错误，而 1.9.2 中却有？

MBPR:$ rvm list

rvm rubies

   ruby-1.8.7-p370 [ i686 ]
=* ruby-1.9.2-p320 [ x86_64 ]

# => - current
# =* - current && default
#  * - default

MBPR:$ irb
irb(main):001:0>     require 'rubygems'
=> false
irb(main):002:0>     require 'memcached'
=> true
irb(main):003:0>     mc = Memcached.new("localhost:11211", :timeout => 1.0)
=> #<Memcached:0x007fc91082abc8 @struct=#<Rlibmemcached::MemcachedSt:0x007fc91082a948>, @options={:hash=>:fnv1_32, :no_block=>false, :noreply=>false, :distribution=>:consistent_ketama, :ketama_weighted=>true, :buffer_requests=>false, :cache_lookups=>true, :support_cas=>false, :tcp_nodelay=>false, :show_backtraces=>false, :retry_timeout=>30, :timeout=>1.0, :rcv_timeout=>1.0, :poll_timeout=>1.0, :connect_timeout=>4, :prefix_key=>"", :prefix_delimiter=>"", :hash_with_prefix_key=>true, :default_ttl=>604800, :default_weight=>8, :sort_hosts=>false, :auto_eject_hosts=>true, :server_failure_limit=>2, :verify_key=>true, :use_udp=>false, :binary_protocol=>false, :credentials=>nil, :experimental_features=>false, :exception_retry_limit=>5, :exceptions_to_retry=>[Memcached::ServerIsMarkedDead, Memcached::ATimeoutOccurred, Memcached::ConnectionBindFailure, Memcached::ConnectionFailure, Memcached::ConnectionSocketCreateFailure, Memcached::Failure, Memcached::MemoryAllocationFailure, Memcached::ReadFailure, Memcached::ServerEnd, Memcached::ServerError, Memcached::SystemError, Memcached::UnknownReadFailure, Memcached::WriteFailure, Memcached::SomeErrorsWereReported]}, @default_ttl=604800, @not_found=#<Memcached::NotFound: Memcached::NotFound>, @not_stored=#<Memcached::NotStored: Memcached::NotStored>>
irb(main):004:0>     mc.set "foo", 1, 100
=> nil
irb(main):005:0>     mc.get "foo"    
=> 1
irb(main):006:0>     pid1 = fork do
irb(main):007:1*     end
=> 9682
irb(main):008:0>     sleep 1
=> 1
irb(main):009:0>     mc.get "foo"    
Memcached::ServerIsMarkedDead: Key {"foo"=>"localhost:11211:8"}
    from /Users/me/.rvm/gems/ruby-1.9.2-p320@global/gems/memcached-1.5.0/lib/memcached/memcached.rb:630:in `reraise'
    from /Users/me/.rvm/gems/ruby-1.9.2-p320@global/gems/memcached-1.5.0/lib/memcached/memcached.rb:608:in `check_return_code'
    from /Users/me/.rvm/gems/ruby-1.9.2-p320@global/gems/memcached-1.5.0/lib/memcached/memcached.rb:517:in `get'
    from (irb):9
    from /Users/me/.rvm/rubies/ruby-1.9.2-p320/bin/irb:12:in `<main>'
irb(main):010:0> 

在 1.8.7 中

MBPR:$ rvm use 1.8.7
Using /Users/me/.rvm/gems/ruby-1.8.7-p370
MBPR:$ irb
1.8.7 :001 >     require 'rubygems'
 => true 
1.8.7 :002 >     require 'memcached'
 => true 
1.8.7 :003 >     mc = Memcached.new("localhost:11211", :timeout => 1.0)
 => #<Memcached:0x10fc65dd0 @not_stored=#<Memcached::NotStored: Memcached::NotStored>, @servers=["localhost:11211:8"], @not_found=#<Memcached::NotFound: Memcached::NotFound>, @default_ttl=604800, @struct=#<Rlibmemcached::MemcachedSt:0x10fc65808>, @options={:cache_lookups=>true, :retry_timeout=>30, :rcv_timeout=>1.0, :exception_retry_limit=>5, :show_backtraces=>false, :binary_protocol=>false, :hash_with_prefix_key=>true, :server_failure_limit=>2, :exceptions_to_retry=>[Memcached::ServerIsMarkedDead, Memcached::ATimeoutOccurred, Memcached::ConnectionBindFailure, Memcached::ConnectionFailure, Memcached::ConnectionSocketCreateFailure, Memcached::Failure, Memcached::MemoryAllocationFailure, Memcached::ReadFailure, Memcached::ServerError, Memcached::SystemError, Memcached::UnknownReadFailure, Memcached::WriteFailure], :no_block=>false, :distribution=>:consistent_ketama, :timeout=>1.0, :ketama_weighted=>true, :prefix_delimiter=>"", :auto_eject_hosts=>true, :support_cas=>false, :hash=>:fnv1_32, :buffer_requests=>false, :poll_timeout=>1.0, :default_ttl=>604800, :sort_hosts=>false, :verify_key=>true, :tcp_nodelay=>false, :connect_timeout=>4, :default_weight=>8, :credentials=>nil, :use_udp=>false}> 
1.8.7 :004 >     mc.set "foo", 1, 100
 => nil 
1.8.7 :005 >     mc.get "foo"    
 => 1 
1.8.7 :006 >     pid1 = fork do
1.8.7 :007 >         end
 => 9799 
1.8.7 :008 >     sleep 1
 => 1 
1.8.7 :009 >     mc.get "foo"    
 => 1 
1.8.7 :010 > 

Answer 1

这是关于fork 的UNIX 进程模型的基础。这两个程序是完全一样的克隆，唯一区别另一个的方法是调用fork 的结果。

当进程完成时，克隆将像主节点一样终止任何连接。在一个版本的 Ruby 中不会发生这种情况可能是一个错误。

这就是为什么在打开连接之前分叉可能是一个好主意，而在打开连接之后分叉需要特殊处理。