Issue #16509 has been reported by jmaino (Jim Maino).

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Bug #16509: puts from EM within a thread seem to be missing linefeed when run in ruby 2.7.0 console
https://bugs.ruby-lang.org/issues/16509

* Author: jmaino (Jim Maino)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 2.7.0
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
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This is strange, and I'm hoping I explain it sufficiently - but I've upgraded to ruby 2.7.0 and I'm seeing missing linefeeds in puts outputs from EM that's within a thread.

I did not see this problem when running in ruby 2.6.5's console output - it seems to be related to my move to 2.7.0.

I've simplified this to reproduce this as folllows. If I run the following EM without being inside of a thread, then I get an OK output - example:

irb(main):042:1* EventMachine.run do
irb(main):043:1* EM.add_periodic_timer(1) { puts "Tick ..." }
irb(main):044:1*
irb(main):045:2* EM.add_timer(3) do
irb(main):046:2* puts "I waited 3 seconds"
irb(main):047:2* EM.stop_event_loop
irb(main):048:1* end
irb(main):049:0> end
Tick ...
Tick ...
I waited 3 seconds
=> nil

Note all of the strings that are output from the puts commands within the EM loop are fully left-justified in the output.
But if I wrap this in a thread, the output lines appear to be missing the linefeed, but do have the CR - such that the successive puts strings are not left justified as they sequence, and build from the X-offset that ended the previous puts string output.

irb(main):001:1* Thread.new do
irb(main):002:2* EventMachine.run do
irb(main):003:2* EM.add_periodic_timer(1) { puts "Tick ..." }
irb(main):004:2*
irb(main):005:3* EM.add_timer(3) do
irb(main):006:3* puts "I waited 3 seconds"
irb(main):007:3* EM.stop_event_loop
irb(main):008:2* end
irb(main):009:1* end
irb(main):010:0> end
=> #<Thread:0x000055cf1a8482c8 (irb):1 run>
irb(main):011:0> Tick ...
_________________________Tick ...
_______________________________ I waited 3 seconds

Is there something that's known to have changed that is causing this?
Can others reproduce this as well?
I can't tell is this is EM's or ruby's - so any help would really be appreciated.
However, the folks over at eventmachine think this belongs to ruby and not themselves.

I only see this from puts statements within the EM loop within a Thread.
If the wrapping Thread is not there, there's no issue.
If there's just a sequence of puts in a Thread and no EM loop, there's no issue.

It seems as if there's something about the combo of a Thread wrapping an EM loop that's making the underlying puts misbehave.

Thanks,
-Jim



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