fork and duplicate window manager connections

From: Ken Taylor (google_at_kjt.us)
Date: 06/28/04 

Date: 28 Jun 2004 14:26:28 -0700

Running wish with expect extension, I note that when a forked client
exits, the window manager connection is destroyed. Here's a simple
test case that demonstrates the behavior:

#!/usr/local/bin/wish
package require Expect

frame .f
pack .f

text .f.main -width 80 -height 5
text .f.sub -width 80 -height 5
pack .f.main -side top -expand yes -fill x
pack .f.sub -side bottom -expand yes -fill x

wm title . "wish/fork test"

.f.main insert end "Starting Sub from [pid]...\n"
update idletasks

if {[catch exp_fork subPid]} {
    error "Couldn't create subprocess - $subPid"
}

if {$subPid < 0} {
    error "Couldn't create subprocess."
}

if {$subPid == 0} {
    .f.sub insert end "Sub pausing 10 seconds in [pid]...\n"
    update idletasks
    after 10000
    exit 0
}

.f.main insert end "Main giving subp time to exit.\n"
update idletasks
after 12000

.f.main insert end "Sub should have exited at this point.\n"
update idletasks

tkwait window .

####

Here's a typical error message produced by the window server
irrespective of wether the subprocess interacts with the window
manager:

/home/kjt> ./wishtest.tcl
X Error of failed request: BadDrawable (invalid Pixmap or Window
parameter)
  Major opcode of failed request: 53 (X_CreatePixmap)
  Resource id in failed request: 0x4c0000d
  Serial number of failed request: 148
  Current serial number in output stream: 123
}

A similar problem described on the perl/Tk usergroup requires the
child process
to call a Core::Exit routine. Do we get something similar available
with Wish/Expect?
    http://groups.google.com/groups?q=Tk+fork+Core::Exit&hl=en&lr=&ie=UTF-8&selm=40C0A471.7000502%40gmx.net&rnum=4

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