[Tcl-bugs] [ tcl-Bugs-653218 ] Channels CloseProc() not called on close

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Bugs item #653218, was opened at 2002-12-13 06:54
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Category: 24. Channel System
Group: 8.4.1
Status: Open
Resolution: None
Priority: 5
Submitted By: Rolf Schroedter (schroedter)
Assigned to: Andreas Kupries (andreas_kupries)
Summary: Channels CloseProc() not called on close

Initial Comment:

If there is pending BG output for a non-blocking channel 
then Tcl_DriverCloseProc() is not called when the 'close' 
command is invoked.

That can be seen from generic/tclIO.c : 
Tcl_Unregister_Channel():
    if (!(statePtr->flags & BG_FLUSH_SCHEDULED)) {
        ...

This can be very bad if channel's output is stalled, e.g. a 
serial port blocked by handshake:

% puts "Tcl $tcl_patchLevel"
Tcl 8.4b1
% set chan [open com1: r+]
fileaaf550
% fconfigure $chan -buffering none -blocking 0
% fconfigure $chan -mode 1200,n,8,1 -handshake rtscts
% ### 2 outputs: "hello world" \x0D\x0A, BG_FLUSH
% puts $chan "hello world"
% puts "Queue: [fconfigure $chan -queue]"
Queue: 0 13
% after 1000
% puts "Queue: [fconfigure $chan -queue]"
Queue: 0 13
% close $chan
% set chan [open com1: r+]
couldn't open "com1:": permission denied
% 

This problem occurs also for slow output without 
handshake:

% puts "Tcl $tcl_patchLevel"
Tcl 8.4b1
% set chan [open com1: r+]
fileaaf768
% fconfigure $chan -buffering none -blocking 0
% # Explicitely reset handshake=none
% fconfigure $chan -mode 1200,n,8,1 -handshake none
% puts $chan "hello world"
% puts $chan "hello world"
% close $chan
% set chan [open com1: r+]
couldn't open "com1:": permission denied


For Tcl < 8.4. this has never been observed for serial 
ports, because serial output has already been blocking.


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>Comment By: Don Porter (dgp)
Date: 2002-12-13 08:51

Message:
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Is this related to FR 525783 ?

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Comment By: Donal K. Fellows (dkf)
Date: 2002-12-13 08:17

Message:
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When I have time (maybe, just maybe, over Xmas) I'll be
advancing a TIP on behaviour-on-close of serial channels.

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Comment By: Rolf Schroedter (schroedter)
Date: 2002-12-13 06:58

Message:
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user_id=99573

This bahaviour may be interpretet not as a bug,
but as a feature of the channel system.

But then we need an additional option 
        [fconfigure $chan -flushonclose 0]
(default=1) for channels like serial ports.

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