Bug #10540
closedYielded fibers do not execute ensure blocks
Description
When a thread has paused fibers, if an exception occurs anywhere in the thread, ensure
blocks in the paused fibers do not execute.
The effect of this is that block-scoped resources (like File.open, Mutex#synchronize, ActiveRecord transactions) can easily leak due to non-local effects. This may result in strange effects, like checking connections back into a connection pool that are in the wrong state, where the correct state was guarded with an ensure
block.
Here is a very simple repro of this situation:
Thread.new {
Fiber.new {
begin
puts "YIELD"
Fiber.yield
ensure
puts "UNWIND"
end
}.resume
raise
}
Expected result: YIELD
is printed, followed by UNWIND
Actual result: YIELD
is printed, but UNWIND
is never printed
Updated by normalperson (Eric Wong) almost 10 years ago
This seems unfortunate. I'm not sure if there's a good way to do
this automatically with current APIs because Fiber
s require
explicit scheduling.
Perhaps storing Fiber
s in Thread.current
and having a
terminate_all_fibers
method can be helpful:
Thread.new do
begin
do_something_which_creates_fibers
ensure
# all thread-local fibers are resumed until they're dead
terminate_all_fibers
end
end
Updated by ko1 (Koichi Sasada) almost 10 years ago
- Assignee set to ko1 (Koichi Sasada)
- Target version set to 2.6
This issue is a known bug.
[Bug #595]: Fiber ignores ensure clause
(3 digits!)
Rubinius supports it.
This feature is not impossible, but a bit difficult because there are two ENSURE points.
- Owner thread is terminated.
-
Fiber
object is collected.
In this issue, (1) is pointed out. It is easy to implement by sending EXIT exception for owned fibers.
However, (2) is a problem. We can not use finalizers for each fibers because it is too late (in finalizer, Fiber object should be already terminated). To solve this issue, we need to separate fiber handler and fiber cotext itself. In other words, it is possible, but tough hack.
And another issue is compatibility. It is too late to fix this issue for 2.2.
I try to implement this fix and apply in early 2015.
Updated by ko1 (Koichi Sasada) almost 8 years ago
- Related to Bug #595: Fiber ignores ensure clause added