A patch to fix a spawn read bug

Brought to you by: andreas_kupries, hobbs, libes, pyssling

#4 A patch to fix a spawn read bug

Status: open

Owner: Andreas Kupries

Labels: None

Priority: 7

Updated: 2002-10-15

Created: 2002-10-15

Creator: H.J. Lu

Private: No

Please see

http://gcc.gnu.org/ml/gcc/2002-10/msg00804.html

for links to the detailed bug descriptions.

Discussion

H.J. Lu - 2002-10-15

A patch

expect-read.patch

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Jeffrey Hobbs - 2002-10-15

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This should be verified against the latest sources and then
applied (assuming no conflicts).

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Jeffrey Hobbs - 2002-10-15

priority: 5 --> 7

assigned_to: nobody --> andreas_kupries
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H.J. Lu - 2002-10-15

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The patch was generated against today's CVS. However, I
haven't built it since
it has to be built in the combined tcl/expect tree. I can
give it a try.

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Andreas Kupries - 2002-10-16

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Please do.

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H.J. Lu - 2002-10-19

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I rebuilt expect 5.38.0 with my patch on RedHat 7.3.
Everything seems to work fine.

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Andreas Kupries - 2002-10-21

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Good. Still, 'seems' is a bit vague. I guess it is passing the
testsuite, and your own application does behave well now. Is
this guess true ?

Also, is it possible to condense your problem into a new
testcase we can add to the testsuite ? Failing for expect
without, and passing with the patch applied ?

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H.J. Lu - 2002-10-21

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You are right.

I guess you can extract a testcase based on my
RedHat bug report. But I am afraid I don't have
the time to send you one.

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Andreas Kupries - 2002-10-25

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I asked Don Libes to review your patch.
Enclosed his answer:

-----
I do not find that bug report convincing (and the code appears
to be solving a non-problem; Expect isn't line-oriented to
begin but the code clearly believes it is). In any case, the
simple example he showed that fails could be due to pty
behavior warned about in the expect man page:

Some implementations of ptys are designed so that the
kernel
throws away any unread output after 10 to 15 seconds
(actual
number is implementation-dependent) after the process
has
closed the file descriptor. Thus Expect programs such as

spawn date
sleep 20
expect

will fail. To avoid this, invoke non-interactive programs
with exec rather than spawn. While such situations are
con-
ceivable, in practice I have never encountered a situation
in which the final output of a truly interactive program
would be lost due to this behavior.

Don

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