[PD-dev] Shell and long-term instability

[Mathieu Bouchard]

On Mon, 26 Nov 2007, Hans-Christoph Steiner wrote:

> Yeah, [shell] definitely acts strangely sometimes.

[shell] uses system() instead of the commented-out execvp(). This requires 
the child to exit by itself. This is done using a call to exit(). exit() 
calls all exit handlers registered by atexit(), which includes some that 
are registered by gcc/glibc that call fclose() on all remaining 
filehandles. fclose() calls fflush() prior to destructing the filehandle. 
fflush() may contain duplicate data that is sent a second time completely 
out of sync with what the main process is sending through the same socket. 
It is the same socket because fork() copies all low-level filehandles (int 
fd) from one process to the other, with the exact same destination. Thus 
when the sys_gui() buffer is not empty during a fork(), an exit() will 
garble the tk command socket's data, which may happen in a way that an 
open brace is sticking in the air or whatever can freeze pd.tk, i don't 
know what it is in particular.

I believe that _exit() does not flush the filehandles. The manpage says it 
closes files, but they must mean only "int fd", whose buffers are shared 
between all owning processes, unlike "FILE *" buffers.

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| Mathieu Bouchard - tél:+1.514.383.3801, Montréal QC Canada