[Tcl-bugs] [ tktoolkit-Bugs-1779265 ] GUI freezes in some laptops running Windows

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Bugs item #1779265, was opened at 2007-08-22 10:57
Message generated for change (Comment added) made by mgma
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Category: 68. Win Window Operations
Group: current: 8.4.15
Status: Open
Resolution: None
Priority: 8
Private: No
Submitted By: Pablo Muñoz (pbmm)
Assigned to: Jeffrey Hobbs (hobbs)
Summary: GUI freezes in some laptops running Windows

Initial Comment:
There is a strange problem that only occurs in some notebooks running Windows. 
I have a Tcl/Tk application that executes another one using 'open |<command> r+', the pipe returned by open is used to communicate to the standard input/output of the new process. 
The second process works fine until any key is pressed when any of its windows owns the focus, then the GUI freezes. But if something is written in its 'stdin' it wakes up, then the key event is received, and everything works again. After that no more key presses causes a freeze.

This pair of Tcl files recreates the error: 
########################################## 
## File run-hello.tcl 
proc read-pipe {pipe} {
    if {![eof $pipe]} {
        puts [gets $pipe]
    } else {
        close $pipe
    }
}

set pipe [open "| tclsh.exe hello.tcl" r+]
fconfigure $pipe -buffering line
fileevent $pipe readable [list read-pipe $pipe]

package require Tk
button .b -text {Send -wake up-} -command [list puts $pipe {wake up}]
pack .b
########################################## 

########################################## 
## File hello.tcl 
proc read-pipe {pipe} {
    if {![eof $pipe]} {
        puts [gets $pipe]
    } else {
        close $pipe
    }
}
fileevent stdin readable {read-pipe stdin}

package require Tk
button .b -text Hello -command {puts Hello!}
pack .b
########################################## 

This code seems to be correct and it works fine in Unix and most Windows machines, it only hangs in some laptops running Windows. 

The laptop were I detected the bug, is a Compaq nc6400. But I know it happened also in an IBM Thinkpad.
I have tested it with some versions of tcl, and the problem has always appeared:
ActiveTcl 8.4.7
ActiveTcl 8.4.15
dqkit     8.4.13
tclkit    8.5.a6

OS version: Windows XP Professional SP2
Other info:
env(PROCESSOR_ARCHITECTURE) = x86
env(PROCESSOR_IDENTIFIER)   = x86 Family 6 Model 14 Stepping 8, GenuineIntel
env(PROCESSOR_LEVEL)        = 6
env(PROCESSOR_REVISION)     = 0e08
tcl_platform(byteOrder) = littleEndian
tcl_platform(machine)   = intel
tcl_platform(os)        = Windows NT
tcl_platform(osVersion) = 5.1
tcl_platform(platform)  = windows
tcl_platform(wordSize)  = 4


----------------------------------------------------------------------

Comment By: mgma (mgma)
Date: 2007-09-20 11:13

Message:
Logged In: YES 
user_id=1556756
Originator: NO

We've gathered some more information about the bug. Maybe you find it
useful.

First, we've detected this issue in two other laptop models: Dell Latitude
D620 and Toshiba Tecra running Windows. Sorry but we don't have additional
information about software versions, apart from the Tcl data given by
Pablo.

And also I give you some more details about the workaround found by Pablo.
Maybe it gives you some clue. When the child interpreter is blocked, if the
parent sends an end-of-line character through the pipe the child unblocks
and becomes responsive again. So what we do is to have the parent
application sending periodically a keep-alive message to the child. Once
the child interpreter has blocked and unblocked, it never blocks again when
you use the keyboard.


Kind regards,

Miguel


----------------------------------------------------------------------

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