[ruby-core:53909] [ruby-trunk - Feature #6154] Eliminate extending WaitReadable/Writable at runtime

Issue #6154 has been updated by headius (Charles Nutter).


charliesome: Yeah, I was thinking about that as I created this patch.

It's possible, but it introduces a rather strange oddity: you'll have multiple exceptions floating around that look like singletons but are actually the same singleton class. If anyone adds methods to them it will add methods to all of them, but there's no way to know you're doing it. I believe this would mean you can't create proper isolated singleton instances/classes of these exception objects.

Are there other places in MRI where this pattern is used? If it's not being done elsewhere, I'd be reluctant to do it here.

The only behavior you have to change from Ruby land would be not testing for EAGAIN == exception. EAGAIN#===, WaitReadable#===, kind_of? and so on work just as they did before. I had to change the tests only because assert_raise does an == check internally (and it arguably should do === or kind_of? since that's closer to what rescue does).
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Feature #6154: Eliminate extending WaitReadable/Writable at runtime
https://bugs.ruby-lang.org/issues/6154#change-38125

Author: headius (Charles Nutter)
Status: Assigned
Priority: Normal
Assignee: headius (Charles Nutter)
Category: core
Target version: next minor


The nonblocking IO operations started extending WaitReadable or WaitWritable into the Errno::EAGAIN instance some time during the 1.9 series. This has a rather high cost, since a singleton class must be created and the global method cache must be flushed.

The attached patch instead creates two new classes of the following form, and raises them rather than raising a singleton EAGAIN:

class IO::EAGAINReadable < Errno::EAGAIN
  include WaitReadable
end

class IO::EAGAINWritable < Errno::EAGAIN
  include WaitWritable
end

The performance of repeatedly doing unsuccessful nonblocking reads improves by about 20%:

BEFORE:

system ~/projects/ruby $ ./ruby2.0.0 -rbenchmark -rsocket -e "sock = TCPSocket.new('localhost', 22); 10.times { puts Benchmark.measure { 100_000.times { begin; sock.read_nonblock(10); rescue IO::WaitReadable; end } } }"
  1.210000   0.110000   1.320000 (  1.328921)
  1.220000   0.120000   1.340000 (  1.326136)
  1.220000   0.110000   1.330000 (  1.334026)
  1.230000   0.110000   1.340000 (  1.349927)
  1.310000   0.130000   1.440000 (  1.426608)
  1.210000   0.110000   1.320000 (  1.333530)
  1.220000   0.120000   1.340000 (  1.330352)
  1.230000   0.110000   1.340000 (  1.350455)
  1.220000   0.120000   1.340000 (  1.327550)
  1.220000   0.110000   1.330000 (  1.337785)

AFTER:

system ~/projects/ruby $ ./ruby2.0.0 -rbenchmark -rsocket -e "sock = TCPSocket.new('localhost', 22); 10.times { puts Benchmark.measure { 100_000.times { begin; sock.read_nonblock(10); rescue IO::WaitReadable; end } } }"
  0.980000   0.110000   1.090000 (  1.092166)
  1.010000   0.120000   1.130000 (  1.129877)
  1.090000   0.120000   1.210000 (  1.202066)
  0.960000   0.110000   1.070000 (  1.076274)
  0.970000   0.100000   1.070000 (  1.078000)
  0.970000   0.110000   1.080000 (  1.078156)
  0.970000   0.110000   1.080000 (  1.078005)
  0.970000   0.110000   1.080000 (  1.078266)
  0.980000   0.110000   1.090000 (  1.093039)
  1.000000   0.110000   1.110000 (  1.112519)

This benchmark does not show the hidden cost of constantly invalidating the global method cache.

I also modified a similar case in OpenSSL, where it previously created an SSLError and extended WaitReadable into it.


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