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Bug #15644

closed

ThreadsWait problems with Thread#report_on_exception

Added by kke (Kimmo Lehto) over 5 years ago. Updated over 2 years ago.

Status:
Closed
Assignee:
keiju (Keiju Ishitsuka)
Target version:
-
ruby -v:
ruby 2.6.1p33 (2019-01-30 revision 66950) [x86_64-darwin18]
Backport:
2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
[ruby-core:91703]
Tags:
patch, ext

Description

Using ThreadsWait with Thread.report_on_exception is confusing.

ThreadsWait spawns a new thread for waiting on a thread:

  # thwait.rb:87
  def join_nowait(*threads)
    threads.flatten!
    @threads.concat threads
    for th in threads
      Thread.start(th) do |t|
        begin
          t.join
        ensure
          @wait_queue.push t
        end
      end
    end
  end

The t.join in ThreadsWait will re-raise the exceptions that happen in the thread being waited on.

If the thread being waited on was using report_on_exception = false, the wait thread will report the exception and the report_on_exception = false effectively did nothing, as you still got an exception report.

If the thread was using report_on_exception = true, both threads will report the exception, so you get it twice.

I think this could be fixed by always setting report_on_exception = false for the wait thread.

Example 1

require 'thwait'

thread = Thread.new do
  Thread.current.report_on_exception = false
  sleep 1
  raise "Foo"
end

ThreadsWait.all_waits(thread) do |terminated_thread|
  puts "Thread #{terminated_thread} terminated"
end

Expected result

No exception reports

Actual result

The wait thread will report the exception:

#<Thread:0x00007fa57d092d68@/Users/user/.rbenv/versions/2.6.1/lib/ruby/2.6.0/thwait.rb:91 run> terminated with exception (report_on_exception is true):

Example 2

require 'thwait'

thread = Thread.new do
  sleep 1
  raise "Foo"
end

ThreadsWait.all_waits(thread) do |terminated_thread|
  puts "Thread #{terminated_thread} terminated"
end

Expected result

One exception report

Actual result

Two exception reports:

#<Thread:0x00007f9f83053320@test.rb:3 run> terminated with exception (report_on_exception is true):
#<Thread:0x00007f9f830530a0@/Users/user/.rbenv/versions/2.6.1/lib/ruby/2.6.0/thwait.rb:91 run> terminated with exception (report_on_exception is true):
Traceback (most recent call last):
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