Redis Gem (Ruby) 中的 Rescue Timeout::Error

Question

我需要拯救从 Redis 库中提出的 Timeout::Error，但我遇到了问题，拯救该特定类似乎不起作用。

begin
  Redis.new( { :host => "127.0.0.X" } )
rescue Timeout::Error => ex
end

=> Timeout::Error: Timeout::Error from /Users/me/.rvm/gems/ree-1.8.7-2011.03@gowalla/gems/redis-2.2.0/lib/redis/connection/hiredis.rb:23:in `connect'

当我试图拯救 Exception 时它仍然不起作用

begin
  Redis.new( { :host => "127.0.0.X" } )
rescue Exception => ex
end

=> Timeout::Error: Timeout::Error from /Users/me/.rvm/gems/ree-1.8.7-2011.03@gowalla/gems/redis-2.2.0/lib/redis/connection/hiredis.rb:23:in `connect'

如果我尝试手动引发异常，我可以拯救它，但不知道为什么当它从 Redis Gem (2.2.0) 中调用时我无法拯救它。

begin
  raise Timeout::Error
rescue Timeout::Error => ex
  puts ex 
end

Timeout::Error
=> nil 

任何线索如何挽救这个异常？

Answer 1

你在 irb 中运行了这段代码，对吧？你得到的异常实际上并不是由Redis.new 提出的。它是由inspect 方法引发的，irb 调用该方法以显示您刚刚键入的表达式的值。

只需查看堆栈跟踪（我缩短了路径以使其清晰可见）：

ruby-1.8.7-p330 :009 >   Redis.new(:host => "google.com")
Timeout::Error: time's up!
    from /.../SystemTimer-1.2.3/lib/system_timer/concurrent_timer_pool.rb:63:in `trigger_next_expired_timer_at'
    from /.../SystemTimer-1.2.3/lib/system_timer/concurrent_timer_pool.rb:68:in `trigger_next_expired_timer'
    from /.../SystemTimer-1.2.3/lib/system_timer.rb:85:in `install_ruby_sigalrm_handler'
    from /..../lib/ruby/1.8/monitor.rb:242:in `synchronize'
    from /.../SystemTimer-1.2.3/lib/system_timer.rb:83:in `install_ruby_sigalrm_handler'
    from /.../redis-2.2.2/lib/redis/connection/ruby.rb:26:in `call'
    from /.../redis-2.2.2/lib/redis/connection/ruby.rb:26:in `initialize'
    from /.../redis-2.2.2/lib/redis/connection/ruby.rb:26:in `new'
    from /.../redis-2.2.2/lib/redis/connection/ruby.rb:26:in `connect'
    from /.../SystemTimer-1.2.3/lib/system_timer.rb:60:in `timeout_after'
    from /.../redis-2.2.2/lib/redis/connection/ruby.rb:115:in `with_timeout'
    from /.../redis-2.2.2/lib/redis/connection/ruby.rb:25:in `connect'
    from /.../redis-2.2.2/lib/redis/client.rb:227:in `establish_connection'
    from /.../redis-2.2.2/lib/redis/client.rb:23:in `connect'
    from /.../redis-2.2.2/lib/redis/client.rb:247:in `ensure_connected'
    from /.../redis-2.2.2/lib/redis/client.rb:137:in `process'
... 2 levels...
    from /.../redis-2.2.2/lib/redis/client.rb:46:in `call'
    from /.../redis-2.2.2/lib/redis.rb:90:in `info'
    from /..../lib/ruby/1.8/monitor.rb:242:in `synchronize'
    from /.../redis-2.2.2/lib/redis.rb:89:in `info'
    from /.../redis-2.2.2/lib/redis.rb:1075:in `inspect'
    from /..../lib/ruby/1.8/monitor.rb:242:in `synchronize'
    from /.../redis-2.2.2/lib/redis.rb:1074:in `inspect'
    from /..../lib/ruby/1.8/irb.rb:310:in `output_value'
    from /..../lib/ruby/1.8/irb.rb:159:in `eval_input'
    from /..../lib/ruby/1.8/irb.rb:271:in `signal_status'
    from /..../lib/ruby/1.8/irb.rb:155:in `eval_input'
    from /..../lib/ruby/1.8/irb.rb:154:in `eval_input'
    from /..../lib/ruby/1.8/irb.rb:71:in `start'
    from /..../lib/ruby/1.8/irb.rb:70:in `catch'
    from /..../lib/ruby/1.8/irb.rb:70:in `start'
    from /..../bin/irb:17

正如您在上面看到的，异常发生在inspect 内部，而不是Redis.new。当您在 Redis 对象上调用 inspect 时，它实际上并不仅仅打印出它的状态，它实际上做了很多事情。在这种情况下，inspect 尝试连接到服务器并在超时时抛出异常。这对我来说似乎是一个非常糟糕的设计，也许我们应该向 Redis gem 的维护者提交错误报告。

这导致了 IRB 中一些有趣的行为：

• 键入 Redis.new(:host => "google.com") 会导致如上所示的异常
• 键入 Redis.new(:host => "google.com"); 'hello' 会得到“=> "hello"”

如果您想捕获此异常，请尝试在 begin/rescue/end 块内调用 ensure_connected。