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Re: Go - deadlocked processes causing memory leaks

Hi all
  1. Is this (the whole thread, starting with Rick’s question 29March2015) so important that it should be updated in the original stackoverflow thread?
  2. Or in some way added to golang-nuts, or better golang-dev?
  3. If not, is there a place where it could be posted? 
  4. If so, should it be anonymized or edited?
  5. Or is it already on some Occam Family open thread (or else) out there?
  6. Or is this news to us only, and the Go people are content with their present solution?
  7. An easy solution could be to make a pdf of it and place it somewhere, and then refer this somewehere?
  8. Any other question in need of an answer?
Øyvind


31. mar. 2015 kl. 14.05 skrev Kerridge, Jon <J.Kerridge@xxxxxxxxxxxx>:

Hi,
version 1.4.2 does not help; in fact the effect is even worse.

I am developing the code using Eclipse with the plugin goclipse in a Windows 7 system (my normal system)

When I ran my code it started and produced some output, albeit slowly.  It then stopped and caused my PC to hang such that Cntrl-Alt-Del did not work and I had to resort to switching off the PC using the power switch!!

If anyone wants the code they can find it at https://bitbucket.org/jkerridge/gows 

Jon



Professor Jon Kerridge
School of Computing
Edinburgh Napier University
Merchiston Campus
Edinburgh EH10 5DT
 
0131 455 2777
 
From: occam-com-request@xxxxxxxxxx [occam-com-request@xxxxxxxxxx] on behalf of Kerridge, Jon [J.Kerridge@xxxxxxxxxxxx]
Sent: 30 March 2015 10:46
To: Roger Shepherd; Jim Whitehead II
Cc: Rick Beton; Occam Family
Subject: RE: Go - deadlocked processes causing memory leaks

That is my experience!!

I shall now try the latest 1.4 release of the language to see if there have been any changes to the run time to get rid of the problem I found.

I will let you know

Jon



Professor Jon Kerridge
School of Computing
Edinburgh Napier University
Merchiston Campus
Edinburgh EH10 5DT
 
0131 455 2777
 
From: occam-com-request@xxxxxxxxxx [occam-com-request@xxxxxxxxxx] on behalf of Roger Shepherd [rog@xxxxxxxx]
Sent: 30 March 2015 09:35
To: Jim Whitehead II
Cc: Rick Beton; Occam Family
Subject: Re: Go - deadlocked processes causing memory leaks

So the memory leak is, arguably, correct behaviour then?

Roger
--
Roger Shepherd




On 29 Mar 2015, at 22:01, Jim Whitehead II <jnwhiteh@xxxxxxxxx> wrote:

There is no such thing as a goroutine going out of scope, there's no process hierarchy. It's spawned in a flat tree and will continue to block indefinitely. Yes it would be possible for the garbage collector to determine that a channel send could never succeed on that channel but the semantics of what to do after that are very difficult to specify.

- Jim

On Sun, 29 Mar 2015 at 22:19 Roger Shepherd <rog@xxxxxxxx> wrote:

On 29 Mar 2015, at 17:35, Rick Beton <rick.beton@xxxxxxxxx> wrote:

Hi Roger,

see notes inserted below...

On 29 March 2015 at 17:01, Roger Shepherd <rog@xxxxxxxx> wrote:

I think I understand the explanation in Stack Overflow. Essentially this says that if a one-buffered channel is used, the sending process won’t block even if the receiver is dead, and the process and channel will be garbage collected. Presumably in the implementation, a process’s memory is reclaimed only when it terminates, whereas dangling channels are garbage collected.


That is a reasonable interpretation. Go has quite straightforward memory model, using the stack as much as possible and the garbage-collected heap otherwise. Anything that goes out of scope is reclaimed either by being on the stack (and the stack pointer is moved), or by having no more references to it. This applies to both the channel and the goroutine in the specific example.

 


In the example, isn't it the case that with the zero-buffered channel the channel and the grouting go out of scope and should be garbage collected? So there is a bug, as the Stack Overflow post suggests.

Roger
--
Roger Shepherd
rog@xxxxxxxx

Øyvind TEIG 
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