R devel - Jul 2013 - Ctrl+C in R will terminate the child process which is spawned by using "pipe"

Hi, all,

I pressed Ctrl+C in R process, and found that the child process which was
spawned by using "pipe" is terminated due to this.
Are there any way to work around it, so that the child process can run
happily without being terminated? Or can we block the signal for the child
process?

1. I used pipe to spawn one C++ process, which will running in a loop
without exiting immediately.

z <- pipe("./mytest", open =
"r+")
> z
description       class        mode        text      opened    can read
 "./mytest"      "pipe"        "r+"     
"text"    "opened"       "yes"
  can write
       "no"

2. When I press "Ctrl+C" in the current R shell, I found the forked
child
process was also terminated. Are there any way to work around it?

====================
Rong "Jessica", Li (ÀîÈÙ)
Platform Symphony TET, CSTL, IBM Systems &Technology Group, Development
Tel:86-10-82451010  Email:ronglli@cn.ibm.com
	[[alternative HTML version deleted]]

On Jul 2, 2013, at 11:46 AM, Rong lI Li wrote:
> 
> Hi, all,
> 
> I pressed Ctrl+C in R process, and found that the child process which was
> spawned by using "pipe" is terminated due to this.
> Are there any way to work around it, so that the child process can run
> happily without being terminated? Or can we block the signal for the child
> process?
> 
Yes, simply handle the INT signal in your C++ process and do what you deem
appropriate (which does include the option of doing nothing / ignoring).

Other option is to do a double-fork ( fork -> if (fork()) exit) so you
disassociate the child from the parent group or to possibly use setsid(), both
as to not share the terminal with the parent.

Cheers,
Simon

> 1. I used pipe to spawn one C++ process, which will running in a loop
> without exiting immediately.
> 
> z <- pipe("./mytest", open = "r+")
>> z
> description       class        mode        text      opened    can read
> "./mytest"      "pipe"        "r+"     
"text"    "opened"       "yes"
>  can write
>       "no"
> 
> 2. When I press "Ctrl+C" in the current R shell, I found the
forked child
> process was also terminated. Are there any way to work around it?
> 
> ====================> 
> Rong "Jessica", Li (????)
> Platform Symphony TET, CSTL, IBM Systems &Technology Group, Development
> Tel:86-10-82451010  Email:ronglli at cn.ibm.com
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

If you are on a Unix-like machine try using the setsid command to
run your command in a 'session' of its own.  E.g.,

  > z <- pipe("setsid /usr/bin/yes", open="r")
  > length(readLines(z, n=1e6))
  [1] 1000000
  > # hit control-C
  > length(readLines(z, n=1e6))
  [1] 1000000
  > length(readLines(z, n=1e6))
  [1] 1000000
  > close(z)

as opposed to

  > z <- pipe("/usr/bin/yes", open="r")
  > length(readLines(z, n=1e6))
  [1] 1000000
  > # hit control-C
  > length(readLines(z, n=1e6)) # this reads what is left in the stdin buffer
  [1] 34240
  > length(readLines(z, n=1e6))
  [1] 0
  > close(z)

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

> -----Original Message-----
> From: r-devel-bounces at r-project.org [mailto:r-devel-bounces at
r-project.org] On Behalf
> Of Rong lI Li
> Sent: Tuesday, July 02, 2013 8:46 AM
> To: r-devel at r-project.org
> Subject: [Rd] Ctrl+C in R will terminate the child process which is spawned
by using "pipe"
> 
> 
> Hi, all,
> 
> I pressed Ctrl+C in R process, and found that the child process which was
> spawned by using "pipe" is terminated due to this.
> Are there any way to work around it, so that the child process can run
> happily without being terminated? Or can we block the signal for the child
> process?
> 
> 1. I used pipe to spawn one C++ process, which will running in a loop
> without exiting immediately.
> 
> z <- pipe("./mytest", open = "r+")
> > z
> description       class        mode        text      opened    can read
>  "./mytest"      "pipe"        "r+"     
"text"    "opened"       "yes"
>   can write
>        "no"
> 
> 2. When I press "Ctrl+C" in the current R shell, I found the
forked child
> process was also terminated. Are there any way to work around it?
> 
> ====================> 
> Rong "Jessica", Li (????)
> Platform Symphony TET, CSTL, IBM Systems &Technology Group, Development
> Tel:86-10-82451010  Email:ronglli at cn.ibm.com
> 	[[alternative HTML version deleted]]

Hi, all,

My previous question is: "how to make the child process run happily without
being terminated, after hit Ctrl+C in R".

For this, I tried both "setsid" and blocking signals in the child
process.
Both of them can solve this issue.
Considering the compatibility between Unix/Linux platform and windows
platform, I choose to use block signals in the child process.

Thanks again for all your help!

====================
Rong "Jessica", Li
Platform Symphony TET, CSTL, IBM Systems &Technology Group, Development
Tel:86-10-82451010  Email:ronglli@cn.ibm.com
	[[alternative HTML version deleted]]