#2205 macosx: reading from write-only pipe hangs

[Daniel A. Steffen]

on Mac OS X, trying to read e.g. from stdout when it is a
pipe will not fail as on other platforms but block forever in
the recv() in TcpInputProc().

this has been a long standing very annoying bug that
among others things interferes with the workings of 'make
test', e.g. "test io-32.1" will hang when it tries to [read
stdout] because stdout is a pipe when io.test is run from
tests/all.tcl

I have now found an effective & simple workaround that
AFAICT does not have any negative implications on other
unices:

when creating a socket channel in Tcl_MakeFileChannel(),
the mode argument cannot be passed to
Tcl_MakeTcpClientChannel() as noted in the comments.
I've now added a static MakeTcpClientChannelMode()
taking a mode argument and use this from
Tcl_MakeFileChannel().
Tcl_MakeTcpClientChannel() simply calls through to
MakeTcpClientChannelMode() with the default mode.

so for writeonly files like stdout, the channel will now be
marked as writeonly even when it is based on a socket fd,
and thus reading from the channel will fail before the recv()
is ever attempted, thus working around the macosx
problem.

c.f. attached patch for implementation.

[Daniel A. Steffen]

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Jeff,
could you possibly take a look at reviewing this? the changes
are minor and shouldn't have any wider implications AFAICT.

it would be great if this could go into 8.4.2 as the broken 'make
test' on macosx is really annoying...

Thanks

[Daniel A. Steffen]

patch to unix/tclUnixChan.c

[Jeffrey Hobbs]

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in for 8.4.2.