执行过期异常导致 Ruby 线程崩溃，但 Timeout::Error 被处理

Question

任何人都可以解释为什么当对方法的调用如下所示时我可能会看到这个堆栈（由 HTTParty::post 请求引起）：

begin
  response = HTTParty::post(url, options)
rescue
  logger.warn("Could not post to #{url}")      
rescue Timeout::Error
  logger.warn("Could not post to #{url}: timeout")      
end

堆栈：

/usr/local/lib/ruby/1.8/timeout.rb:64:in `timeout'
/usr/local/lib/ruby/1.8/net/protocol.rb:134:in `rbuf_fill'
/usr/local/lib/ruby/1.8/net/protocol.rb:104:in `read_all'
/usr/local/lib/ruby/1.8/net/http.rb:2228:in `read_body_0'
/usr/local/lib/ruby/1.8/net/http.rb:2181:in `read_body'
/usr/local/lib/ruby/1.8/net/http.rb:2206:in `body'
/usr/local/lib/ruby/1.8/net/http.rb:2145:in `reading_body'
/usr/local/lib/ruby/1.8/net/http.rb:1053:in `request_without_newrelic_trace'
[GEM_ROOT]/gems/newrelic_rpm-3.1.1/lib/new_relic/agent/instrumentation/net.rb:20:in `request'
[GEM_ROOT]/gems/newrelic_rpm-3.1.1/lib/new_relic/agent/method_tracer.rb:242:in `trace_execution_scoped'
[GEM_ROOT]/gems/newrelic_rpm-3.1.1/lib/new_relic/agent/instrumentation/net.rb:19:in `request'
/usr/local/lib/ruby/1.8/net/http.rb:1037:in `request_without_newrelic_trace'
/usr/local/lib/ruby/1.8/net/http.rb:543:in `start'
/usr/local/lib/ruby/1.8/net/http.rb:1035:in `request_without_newrelic_trace'
[GEM_ROOT]/gems/newrelic_rpm-3.1.1/lib/new_relic/agent/instrumentation/net.rb:20:in `request'
[GEM_ROOT]/gems/newrelic_rpm-3.1.1/lib/new_relic/agent/method_tracer.rb:242:in `trace_execution_scoped'
[GEM_ROOT]/gems/newrelic_rpm-3.1.1/lib/new_relic/agent/instrumentation/net.rb:19:in `request'
[GEM_ROOT]/gems/httparty-0.7.8/lib/httparty/request.rb:69:in `perform'
[GEM_ROOT]/gems/httparty-0.7.8/lib/httparty.rb:390:in `perform_request'
[GEM_ROOT]/gems/httparty-0.7.8/lib/httparty.rb:358:in `post'
[GEM_ROOT]/gems/httparty-0.7.8/lib/httparty.rb:426:in `post'

如您所见，我正在处理 Timeout::Error 异常。这是在 Ruby 1.8.7 中。我很清楚，在 Ruby 1.8.7 中，StandardException 和 TimeoutException 有不同的继承树，所以我处理了这两个，但似乎没有什么区别。

Answer 1

当您省略rescue 中的异常类时，它将捕获任何StandardError。由于Timeout::Error 是StandardError 的子类，因此它将被第一个rescue 语句捕获。如果你想单独捕获它，你必须把它放在省略的前面：

begin
  response = HTTParty::post(url, options)
rescue Timeout::Error
  logger.warn("Could not post to #{url}: timeout")      
rescue
  logger.warn("Could not post to #{url}")      
end