File::write uses nonblocking IO when MRI uses blocking #5663
Description
Environment
- jruby 9.2.6.0 (2.5.3) 2019-02-11 15ba00b OpenJDK 64-Bit Server VM 25.201-b09 on 1.8.0_201-b09 +jit [linux-x86_64]
- RHEL 7.6
Expected Behavior
MRI waits if nobody is reading the other side of a pty pair:
2.5.3 :001 > require 'pty'
=> true
2.5.3 :002 > m,s = PTY.open
=> [#<IO:masterpty:/dev/pts/15>, #<File:/dev/pts/15>]
2.5.3 :003 > 20.times{|i| puts "writing #{i}"; s.write("_" * 1000) }
writing 0
writing 1
writing 2
writing 3
writing 4
writing 5
writing 6
writing 7
writing 8
<hang until ctrl-c>
Actual Behavior
However JRuby appears to use non-blocking IO and thus throws an exception:
jruby-9.2.6.0 :001 > require 'pty'
=> true
jruby-9.2.6.0 :002 > m,s = PTY.open; nil
=> nil
jruby-9.2.6.0 :003 > 20.times{|i| puts "writing #{i}"; s.write("_" * 1000) }
writing 0
writing 1
writing 2
writing 3
writing 4
writing 5
writing 6
writing 7
writing 8
writing 9
writing 10
writing 11
writing 12
Traceback (most recent call last):
9: from /home/byteit101/.rvm/rubies/jruby-9.2.6.0/bin/irb:13:in `<main>'
8: from org/jruby/RubyKernel.java:1179:in `catch'
7: from org/jruby/RubyKernel.java:1179:in `catch'
6: from org/jruby/RubyKernel.java:1411:in `loop'
5: from org/jruby/RubyKernel.java:1047:in `eval'
4: from (irb):3:in `evaluate'
3: from (irb):3:in `block in evaluate'
2: from org/jruby/RubyIO.java:1429:in `write'
1: from org/jruby/RubyIO.java:1472:in `write'
SystemCallError (Unknown error (SystemCallError) - No message available)
jruby-9.2.6.0 :004 >
It took me a bit to figure out that the errno was EAGAIN (Resource temporarily unavailable) (not sure why that wasn't in the exception message, another issue?)
I found this as the surprise exception causes a compatibility issue with Pry in a Pty to exit on large output (think ENV inspection, ~12k on my machine) in JRuby, but not under MRI as MRI never throws here.