[ruby-core:58545] [ruby-trunk - Feature #9145][Open] Queue#pop(true) return nil if empty instead of raising ThreadError

[ruby-core:58545] [ruby-trunk - Feature #9145][Open] Queue#pop(true) return nil if empty instead of raising ThreadError

[jsc (Justin Collins)]

Issue #9145 has been reported by jsc (Justin Collins).

----------------------------------------
Feature #9145: Queue#pop(true) return nil if empty instead of raising ThreadError
https://bugs.ruby-lang.org/issues/9145

Author: jsc (Justin Collins)
Status: Open
Priority: Normal
Assignee: 
Category: lib
Target version: 


I propose the non-blocking form of Queue#pop behave like Array#pop and return nil when empty.

Current behavior is to raise a ThreadError, with a message indicating the queue is empty.

For example:

q = Queue.new
begin
  loop do
    next_item = q.pop(true)
  end
rescue ThreadError
  # queue is empty...or maybe something bad happened
end

Instead, this could be

q = Queue.new
while next_item = q.pop(true)
end

Alternatively, raise an exception that is a subclass of ThreadError with a more specific name, such as "QueueEmpty". This would be a small improvement while remaining compatible with existing code.


-- 
http://bugs.ruby-lang.org/

[ruby-core:58546] [ruby-trunk - Feature #9145][Feedback] Queue#pop(true) return nil if empty instead of raising ThreadError

[Glass_saga (Masaki Matsushita)]

Issue #9145 has been updated by Glass_saga (Masaki Matsushita).

Category changed from lib to ext
Status changed from Open to Feedback

I think we can't change default behavior of Queue#pop(true) because some code expects ThreadError to be raised.
However, it may be possible to introduce new keyword argument like following:

q = Queue.new
while next_item = q.pop(true, exception: false) # it doesn't raise ThreadError and returns nil.
  # do something
end
----------------------------------------
Feature #9145: Queue#pop(true) return nil if empty instead of raising ThreadError
https://bugs.ruby-lang.org/issues/9145#change-43126

Author: jsc (Justin Collins)
Status: Feedback
Priority: Normal
Assignee: 
Category: ext
Target version: 


I propose the non-blocking form of Queue#pop behave like Array#pop and return nil when empty.

Current behavior is to raise a ThreadError, with a message indicating the queue is empty.

For example:

q = Queue.new
begin
  loop do
    next_item = q.pop(true)
  end
rescue ThreadError
  # queue is empty...or maybe something bad happened
end

Instead, this could be

q = Queue.new
while next_item = q.pop(true)
end

Alternatively, raise an exception that is a subclass of ThreadError with a more specific name, such as "QueueEmpty". This would be a small improvement while remaining compatible with existing code.


-- 
http://bugs.ruby-lang.org/

[ruby-core:58547] Re: [ruby-trunk - Feature #9145][Feedback] Queue#pop(true) return nil if empty instead of raising ThreadError

[Eric Wong]

"Glass_saga (Masaki Matsushita)" <glass.saga@gmail.com> wrote:
> I think we can't change default behavior of Queue#pop(true) because some code expects ThreadError to be raised.
> However, it may be possible to introduce new keyword argument like following:
> 
> q = Queue.new
> while next_item = q.pop(true, exception: false) # it doesn't raise ThreadError and returns nil.
>   # do something
> end

+1 to that.  All non-blocking methods (I/O or not) should support
exception: false to avoid (expensive/noisy-on-$DEBUG=$true) exceptions.

[ruby-core:58556] [ruby-trunk - Feature #9145] Queue#pop(true) return nil if empty instead of raising ThreadError

[jsc (Justin Collins)]

Issue #9145 has been updated by jsc (Justin Collins).


Glass_saga (Masaki Matsushita) wrote:
> I think we can't change default behavior of Queue#pop(true) because some code expects ThreadError to be raised.
> However, it may be possible to introduce new keyword argument like following:
> 
> q = Queue.new
> while next_item = q.pop(true, exception: false) # it doesn't raise ThreadError and returns nil.
>   # do something
> end

That would work for me.
----------------------------------------
Feature #9145: Queue#pop(true) return nil if empty instead of raising ThreadError
https://bugs.ruby-lang.org/issues/9145#change-43134

Author: jsc (Justin Collins)
Status: Feedback
Priority: Normal
Assignee: 
Category: ext
Target version: 


I propose the non-blocking form of Queue#pop behave like Array#pop and return nil when empty.

Current behavior is to raise a ThreadError, with a message indicating the queue is empty.

For example:

q = Queue.new
begin
  loop do
    next_item = q.pop(true)
  end
rescue ThreadError
  # queue is empty...or maybe something bad happened
end

Instead, this could be

q = Queue.new
while next_item = q.pop(true)
end

Alternatively, raise an exception that is a subclass of ThreadError with a more specific name, such as "QueueEmpty". This would be a small improvement while remaining compatible with existing code.


-- 
http://bugs.ruby-lang.org/

[ruby-core:58562] Re: [ruby-trunk - Feature #9145][Feedback] Queue#pop(true) return nil if empty instead of raising ThreadError

[Joel VanderWerf]

On 11/23/2013 08:30 PM, Glass_saga (Masaki Matsushita) wrote:
> I think we can't change default behavior of Queue#pop(true) because some code expects ThreadError to be raised.
> However, it may be possible to introduce new keyword argument like following:
>
> q = Queue.new
> while next_item = q.pop(true, exception: false) # it doesn't raise ThreadError and returns nil.
>    # do something
> end

Or what about a new method, Queue#pop?, which is always non-blocking and 
non-raising. It would behave like:

class Queue
   def pop?
     pop(true)
   rescue ThreadError
     nil
   end
end

q = Queue.new

q << 1
q << 2
q << 3

while x=q.pop?
   p x
end

__END__
output:
1
2
3

[ruby-core:58564] [ruby-trunk - Feature #9145] Queue#pop(true) return nil if empty instead of raising ThreadError

[drbrain (Eric Hodel)]

Issue #9145 has been updated by drbrain (Eric Hodel).


Note that the current behavior allows you to distinguish between a nil in the queue (returns nil) and no value in the queue (raises ThreadError)
----------------------------------------
Feature #9145: Queue#pop(true) return nil if empty instead of raising ThreadError
https://bugs.ruby-lang.org/issues/9145#change-43140

Author: jsc (Justin Collins)
Status: Feedback
Priority: Normal
Assignee: 
Category: ext
Target version: 


I propose the non-blocking form of Queue#pop behave like Array#pop and return nil when empty.

Current behavior is to raise a ThreadError, with a message indicating the queue is empty.

For example:

q = Queue.new
begin
  loop do
    next_item = q.pop(true)
  end
rescue ThreadError
  # queue is empty...or maybe something bad happened
end

Instead, this could be

q = Queue.new
while next_item = q.pop(true)
end

Alternatively, raise an exception that is a subclass of ThreadError with a more specific name, such as "QueueEmpty". This would be a small improvement while remaining compatible with existing code.


-- 
http://bugs.ruby-lang.org/

[ruby-core:81738] [Ruby trunk Feature#9145][Closed] Queue#pop(true) return nil if empty instead of raising ThreadError

[glass.saga]

Issue #9145 has been updated by Glass_saga (Masaki Matsushita).

Status changed from Feedback to Closed

Currently, Queue#pop takes non_block flag. 

----------------------------------------
Feature #9145: Queue#pop(true) return nil if empty instead of raising ThreadError
https://bugs.ruby-lang.org/issues/9145#change-65440

* Author: jsc (Justin Collins)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
I propose the non-blocking form of Queue#pop behave like Array#pop and return nil when empty.

Current behavior is to raise a ThreadError, with a message indicating the queue is empty.

For example:

q = Queue.new
begin
  loop do
    next_item = q.pop(true)
  end
rescue ThreadError
  # queue is empty...or maybe something bad happened
end

Instead, this could be

q = Queue.new
while next_item = q.pop(true)
end

Alternatively, raise an exception that is a subclass of ThreadError with a more specific name, such as "QueueEmpty". This would be a small improvement while remaining compatible with existing code.



-- 
https://bugs.ruby-lang.org/

[ruby-core:81739] Re: [Ruby trunk Feature#9145][Closed] Queue#pop(true) return nil if empty instead of raising ThreadError

[Eric Wong]

glass.saga@gmail.com wrote:
> Issue #9145 has been updated by Glass_saga (Masaki Matsushita).
> 
> Status changed from Feedback to Closed
> 
> Currently, Queue#pop takes non_block flag. 

No, I don't think this should be closed.

I think Justin's point was:

Currently, it is impossible to know if a queue is closed
(permanent condition) or if it is empty (temporary condition).
So at the very least, a different exception should be raised:

Justin Collins wrote:
	> Alternatively, raise an exception that is a subclass of
	> ThreadError with a more specific name, such as "QueueEmpty".
	> This would be a small improvement while remaining compatible
	> with existing code.



On a side note, relying on exceptions for flow control has all
the same performance and $DEBUG noise problems it did with
IO#*_nonblock [ruby-core:38666] [Feature #5138]

But thinking of an efficient API for that is tricky :<

[ruby-core:84576] [Ruby trunk Feature#9145] Queue#pop(true) return nil if empty instead of raising ThreadError

[uwe]

Issue #9145 has been updated by uwe@kubosch.no (Uwe Kubosch).


How about a block form where the block is called with the popped element?  The method would return false if called with non_block set to true if the queue is empty.

q = Queue.new
q << 1
q << 2
q << 3

while q.pop(true){|x| p x}


----------------------------------------
Feature #9145: Queue#pop(true) return nil if empty instead of raising ThreadError
https://bugs.ruby-lang.org/issues/9145#change-69116

* Author: jsc (Justin Collins)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
I propose the non-blocking form of Queue#pop behave like Array#pop and return nil when empty.

Current behavior is to raise a ThreadError, with a message indicating the queue is empty.

For example:

q = Queue.new
begin
  loop do
    next_item = q.pop(true)
  end
rescue ThreadError
  # queue is empty...or maybe something bad happened
end

Instead, this could be

q = Queue.new
while next_item = q.pop(true)
end

Alternatively, raise an exception that is a subclass of ThreadError with a more specific name, such as "QueueEmpty". This would be a small improvement while remaining compatible with existing code.



-- 
https://bugs.ruby-lang.org/