[erlang-patches] Patch for erl shell (unix/ttsl_drv.c) SIGWINCH handling (R12B-1 31-Dec-2007)

[Patrick Mahoney]

This is an attempt to fix the problem described by Matthew
Dempsky:
http://erlang.org/pipermail/erlang-questions/2007-December/031962.html

The erl shell in Unix does not properly handle terminal
resize events which can result in a misplaced cursor and
other confusion.

This patch adds two functions to the file
erts/emulator/drivers/unix/ttsl_drv.c

winch() is registered as the handler for SIGWINCH which is
  received on terminal resize events.  winch() sets a global
  flag "cols_needs_update = TRUE".

update_cols() is run at the start of each function that uses
  the COL() or LINE() macros for calculating cursor positions,
  namely the del_chars(), write_buf(), and move_cursor()
  functions.  It checks the "cols_needs_update" flag, and sets
  the "cols" global var to the number returned by
  ttysl_get_widow_size().

  If the terminal is resized after update_cols() but before
  use of the COL() macro, then we'll have the same incorrect
  cursor problems during that function.

We don't run ttysl_get_window_size() from the SIGWINCH
handler because it uses ioctl() which is not listed as a
"safe" function for use in signal handlers in the signal(7)
man page.

That said, the solution would be more elegant if we did call
ttysl_get_window_size() from the signal handler, avoiding
the polling done by update_cols().  The ncurses source
includes a simple test/view.c program that does use ioctl()
in its SIGWINCH handler.  It states "This uses functions
that are 'unsafe', but it seems to work on SunOS and Linux."
Doing this in erl works for me on Linux, but I have no idea
on which platforms if may fail.

I've only tested this with R12B-1 on Linux 2.6.22.

-- 
Patrick Mahoney	<pat@REDACTED>
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