Ton Hospel wrote:
>In article <[EMAIL PROTECTED]>,
> Steve Hay <[EMAIL PROTECTED]> writes:
>
>
>>Adding some debug, I find that $sel->can_read() is returning an empty
>>list. If I change
>>
>> while (my @ready = $sel->can_read) {
>> foreach my $fh (@ready) { # loop through buffered handles
>> ...
>> }
>> }
>>
>>to
>>
>> foreach my $fh ($outfh, $errfh) {
>> ...
>> }
>>
>>then the output is now as expected.
>>
>>Presumably IO::Select->can_read() doesn't work on Win32 because it uses
>>a 4-arg select(), which is only implemented for sockets on Win32. Is
>>the above change safe, or did we need to call can_read() for some
>>reason? Would the proposed "selectable pipes" change have any impact on
>>this?
>>
>>
>>
>The case where the above type of change is dangerous is when the source
>tries to write more than can be buffered in the communication channel to
>err_fh and only then bothers to write to $out_fh. In that case you will
>deadlock. the source will wait until enough gets drained from err_fh so it
>can write again, and you will wait on $out_fh, which hasn't gotten anything
>yet and now never will.
>
>So whether that is relevant for your case depends on what you're running
>(how it uses its output channels).
>
I don't know what commands are being run by IPC::Cmd and whether or not
they would be likely to be affected by these problems, but I guess
removing the can_read() check isn't ideal if it *can* cause problems,
even if it doesn't affect us now -- we'd only be storing up problems for
the future.
Does anyone know if the selectable pipes work that Nicholas mentioned
would be likely to make the 4-arg select(), and hence can_read(), work?
I don't really know what would be involved in finishing off the work in
question, but if someone can give me some pointers then I'm willing to
give it a go.
Alternatively, Nicholas also mentioned the possibility of converting the
C code to Perl (and indeed, actually did so) and putting that into
IPC::Run. Again, I've no idea how to fit that Perl code into IPC::Run
(or IPC::Cmd). Can someone help out?
- Steve
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