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Koichi SasadaandClaude Opus 4.8
ca20425fd5
`fiber_current()` reads `GET_EC()`, which the compiler may inline as a thread-pointer-relative TLS access whose base is cached in a callee-saved register. `coroutine_transfer` preserves callee-saved registers across the stack switch, so when a fiber's coroutine resumes on a different native thread (M:N scheduler migration), the cached thread pointer is stale and `fiber_current()` returns another thread's execution context. `fiber_switch()` calls `fiber_current()` right after the transfer. With `-DRUBY_DEBUG=1` this trips `VM_ASSERT(ec == rb_current_ec_noinline())` in `rb_current_execution_context`; in release builds it silently uses the wrong (or NULL) EC. Only reproduces with >= 2 Ractors (a single Ractor does not migrate the coroutine). Read the current EC through `rb_current_ec_noinline()` in `fiber_current()`, which forces a fresh thread-pointer load. fiber_current() is only used by the (cold) fiber machinery, so the non-inlined read costs nothing on hot paths. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
64 lines
1.3 KiB
Ruby
64 lines
1.3 KiB
Ruby
show_limit %q{
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fibers = []
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begin
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fiber = Fiber.new{Fiber.yield}
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fiber.resume
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fibers << fiber
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raise Exception, "skipping" if fibers.count >= 10_000
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rescue Exception => error
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puts "Fiber count: #{fibers.count} (#{error})"
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break
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end while true
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}
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assert_equal %q{ok}, %q{
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Fiber.new{
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}.resume
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:ok
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}
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assert_equal %q{ok}, %q{
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100.times.collect{Fiber.new{}}
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:ok
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}
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assert_equal %q{ok}, %q{
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fibers = 1000.times.collect{Fiber.new{Fiber.yield}}
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fibers.each(&:resume)
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fibers.each(&:resume)
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:ok
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}
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assert_normal_exit %q{
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at_exit { Fiber.new{}.resume }
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}
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assert_normal_exit %q{
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Fiber.new(&Object.method(:class_eval)).resume("foo")
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}, '[ruby-dev:34128]'
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# [Bug #21400]
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assert_normal_exit %q{
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Thread.new { Fiber.current.kill }.join
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}
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# fiber_current() must not read a stale (cached) TLS execution context after a
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# fiber's coroutine migrates between native threads under the M:N scheduler.
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# Needs >= 2 Ractors so coroutines actually migrate; sleep drives the migration.
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assert_equal 'ok', %q{
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Warning[:experimental] = false
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2.times.map do
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Ractor.new do
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200.times do
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f = Fiber.new { Fiber.yield; 1 }
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f.resume
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sleep(0.0003) # block -> M:N native-thread migration
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f.resume rescue nil
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end
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:ok
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end
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end.each(&:value)
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:ok
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}
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