Fiber#alive? returns true even when already finished #4838
Description
It looks to be related to #1789 and #1949.
Environment
jruby 9.1.13.0 (2.3.3) 2017-09-06 8e1c115 Java HotSpot(TM) 64-Bit Server VM 25.151-b12 on 1.8.0_151-b12 +jit [mswin32-x86_64]
Windows 10 Home
Expected Behavior
Fiber#alive? returns false for all the calls in the following code.
require "fiber"
def check(&block)
1000.times.map do
fiber = Fiber.new(&block)
fiber.resume
fiber.alive?
end
end
results = [
check {},
check { "Text" },
check { Fiber.new {} },
check { sleep(0.001) },
]
puts ["", "FALSE", "TRUE"].join("\t")
results.each_with_index do |r, i|
puts ["test#{i}", r.count(false), r.count(true)].join("\t")
endOn CRuby:
$ ruby check_fiber_alive.rb
FALSE TRUE
test0 1000 0
test1 1000 0
test2 1000 0
test3 1000 0
Actual Behavior
On JRuby, the results can be true.
$ jruby check_fiber_alive.rb
FALSE TRUE
test0 998 2
test1 999 1
test2 288 712
test3 987 13
The code sometimes runs into NullPointerException.
$ jruby check_fiber_alive.rb
Unhandled Java exception: java.lang.NullPointerException
java.lang.NullPointerException: null
alive at org/jruby/ext/fiber/ThreadFiber.java:243
__alive__ at org/jruby/ext/fiber/ThreadFiber.java:229
call at org/jruby/ext/fiber/ThreadFiber$INVOKER$i$0$0$__alive__.gen:-1
call at org/jruby/internal/runtime/methods/AliasMethod.java:56
call at org/jruby/runtime/callsite/CachingCallSite.java:129
invokeOther16:alive? at check_fiber_alive.rb:7
block in check at check_fiber_alive.rb:7
yieldDirect at org/jruby/runtime/CompiledIRBlockBody.java:156
yield at org/jruby/runtime/BlockBody.java:114
yield at org/jruby/runtime/Block.java:165
call at org/jruby/RubyEnumerable.java:846
yieldSpecific at org/jruby/runtime/CallBlock19.java:77
yieldSpecific at org/jruby/runtime/Block.java:134
times at org/jruby/RubyFixnum.java:299
call at org/jruby/RubyFixnum$INVOKER$i$0$0$times.gen:-1
call at org/jruby/internal/runtime/methods/JavaMethod.java:498
finvoke at org/jruby/RubyClass.java:522
invoke at org/jruby/runtime/Helpers.java:395
callMethod at org/jruby/RubyBasicObject.java:393
each at org/jruby/RubyEnumerator.java:323
call at org/jruby/RubyEnumerator$INVOKER$i$each.gen:-1
finvoke at org/jruby/RubyClass.java:512
invoke at org/jruby/runtime/Helpers.java:383
callEach19 at org/jruby/RubyEnumerable.java:116
collectCommon at org/jruby/RubyEnumerable.java:838
map at org/jruby/RubyEnumerable.java:830
call at org/jruby/RubyEnumerable$INVOKER$s$0$0$map.gen:-1
callBlock at org/jruby/runtime/callsite/CachingCallSite.java:139
call at org/jruby/runtime/callsite/CachingCallSite.java:145
invokeOther20:map at check_fiber_alive.rb:4
check at check_fiber_alive.rb:4
call at org/jruby/internal/runtime/methods/CompiledIRMethod.java:90
cacheAndCall at org/jruby/runtime/callsite/CachingCallSite.java:328
callBlock at org/jruby/runtime/callsite/CachingCallSite.java:141
call at org/jruby/runtime/callsite/CachingCallSite.java:145
invokeOther28:check at check_fiber_alive.rb:15
<main> at check_fiber_alive.rb:15
invokeWithArguments at java/lang/invoke/MethodHandle:-1
load at org/jruby/ir/Compiler.java:95
runScript at org/jruby/Ruby.java:828
runNormally at org/jruby/Ruby.java:747
runNormally at org/jruby/Ruby.java:765
runFromMain at org/jruby/Ruby.java:578
doRunFromMain at org/jruby/Main.java:417
internalRun at org/jruby/Main.java:305
run at org/jruby/Main.java:232
main at org/jruby/Main.java:204
Workaround:
Fiber#alive? looks to return false as expected by adding a short sleep between resume and alive? calls.