Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.debian.user > #262616

Re: 12.2: fork() causing getline() to repeat stdin endlessly

Show all headers | View raw

On 10/23/23 10:16, Jon Leonard wrote:
> On Mon, Oct 23, 2023 at 09:31:11AM -0400, Greg Wooledge wrote:
>> On Mon, Oct 23, 2023 at 11:15:22AM +0200, Thomas Schmitt wrote:
>>> it helps to do
>>>    fflush((stdout);
>>> after each printf(), or to run before the loop:
>>>    setvbuf(stdout, NULL, _IONBF, 0);
>>>
>>> So it is obvious that the usual output buffering of printf() causes the
>>> repetitions of text.
>>
>> Yes, it looks like a buffering issue to me as well.  Or, more generally,
>> some kind of weird interaction between buffered stdio FILEs and the
>> underlying Unix file descriptors, when new processes are being fork()ed.
> 
> More specifically, fork() does not play nicely with stdio buffering.
> 
> For performance reasons, stdio tends to read and write in chunks, reducing
> the number of read() and write() calls.  Some data is stored in the stdio
> buffers, and that data is getting copied to both processes in the fork()
> call.
> 
> If you want to mix fork() and stdio, be sure to flush buffers before the
> call to fork.  Depending on the task, it may be easier to use the underlying
> read() and write() calls.
> 
> Jon Leonard

This thread seems related to a problem we've encountered when reloading 
an edited file, forcing the user to use the file->open menu to reload a 
program just edited, Using the file->reload doesn't always work, nor 
does a mouse button marked reload, they both flip a quarter to decide if 
you get the new code, or the old code that still exists in a cache 
somewhere. Probably in /tmp under a hashed name.  Is there a guaranteed 
fix afoot that can be shared?
> 
> .

Cheers, Gene Heskett.
-- 
"There are four boxes to be used in defense of liberty:
  soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
  - Louis D. Brandeis

Back to linux.debian.user | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: 12.2: fork() causing getline() to repeat stdin endlessly "Thomas Schmitt" <scdbackup@gmx.net> - 2023-10-23 10:50 +0200
  Re: 12.2: fork() causing getline() to repeat stdin endlessly "Thomas Schmitt" <scdbackup@gmx.net> - 2023-10-23 11:20 +0200
    Re: 12.2: fork() causing getline() to repeat stdin endlessly Greg Wooledge <greg@wooledge.org> - 2023-10-23 15:40 +0200
      Re: 12.2: fork() causing getline() to repeat stdin endlessly jleonard@slimy.com (Jon Leonard) - 2023-10-23 16:20 +0200
        Re: 12.2: fork() causing getline() to repeat stdin endlessly tom kronmiller <twk.personal@gmail.com> - 2023-10-23 16:40 +0200
          Re: 12.2: fork() causing getline() to repeat stdin endlessly Greg Wooledge <greg@wooledge.org> - 2023-10-23 17:20 +0200
        Re: 12.2: fork() causing getline() to repeat stdin endlessly gene heskett <gheskett@shentel.net> - 2023-10-23 18:40 +0200
          Re: 12.2: fork() causing getline() to repeat stdin endlessly <tomas@tuxteam.de> - 2023-10-23 20:10 +0200
    Re: 12.2: fork() causing getline() to repeat stdin endlessly tom kronmiller <twk.personal@gmail.com> - 2023-10-23 21:50 +0200
      Re: 12.2: fork() causing getline() to repeat stdin endlessly "Thomas Schmitt" <scdbackup@gmx.net> - 2023-10-23 22:20 +0200
        Re: 12.2: fork() causing getline() to repeat stdin endlessly Greg Wooledge <greg@wooledge.org> - 2023-10-23 22:30 +0200
          Re: 12.2: fork() causing getline() to repeat stdin endlessly "Thomas Schmitt" <scdbackup@gmx.net> - 2023-10-23 22:50 +0200
            Re: 12.2: fork() causing getline() to repeat stdin endlessly Greg Wooledge <greg@wooledge.org> - 2023-10-23 23:00 +0200
        Re: 12.2: fork() causing getline() to repeat stdin endlessly tom kronmiller <twk.personal@gmail.com> - 2023-10-24 07:20 +0200
          Re: 12.2: fork() causing getline() to repeat stdin endlessly Max Nikulin <manikulin@gmail.com> - 2023-10-24 18:10 +0200
            Re: 12.2: fork() causing getline() to repeat stdin endlessly Greg Wooledge <greg@wooledge.org> - 2023-10-24 21:30 +0200
              Re: 12.2: fork() causing getline() to repeat stdin endlessly conover@panix.com (John Conover) - 2023-10-25 01:00 +0200
              Re: 12.2: fork() causing getline() to repeat stdin endlessly jleonard@slimy.com (Jon Leonard) - 2023-10-25 04:20 +0200
              Re: 12.2: fork() causing getline() to repeat stdin endlessly Max Nikulin <manikulin@gmail.com> - 2023-10-25 04:40 +0200
              Re: 12.2: fork() causing getline() to repeat stdin endlessly <tomas@tuxteam.de> - 2023-10-25 06:30 +0200
            Re: 12.2: fork() causing getline() to repeat stdin endlessly tom kronmiller <twk.personal@gmail.com> - 2023-10-25 07:40 +0200
              Re: 12.2: fork() causing getline() to repeat stdin endlessly tom kronmiller <twk.personal@gmail.com> - 2023-10-25 08:00 +0200
  Re: 12.2: fork() causing getline() to repeat stdin endlessly Max Nikulin <manikulin@gmail.com> - 2023-10-23 18:30 +0200
    Re: 12.2: fork() causing getline() to repeat stdin endlessly Stefan Monnier <monnier@iro.umontreal.ca> - 2023-10-24 05:00 +0200

csiph-web