interacting with a process with redirected stdin/stdout/stderr

[Timothee Cour]

On Tue, Jul 16, 2013 at 10:01 AM, Anthony Goins <neontotem at gmail.com> wrote:

> On Monday, 15 July 2013 at 06:46:52 UTC, timotheecour wrote:
>
>> On Monday, 15 July 2013 at 03:49:10 UTC, Timothee Cour wrote:
>>
>>> I'm trying to interact with a process using std.process and
>>> redirected stdin/stdout/stderr.
>>> What would be the recommended way?
>>>
>>> For example:
>>> ----
>>> auto pipes=pipeShell("myprocess",**Redirect.all);
>>> while(true){
>>>  pipes.stdin.rawWrite(some_**command);
>>>  foreach (line; pipes.stdout.byLine) {
>>>    //do something with line
>>>  }
>>> }
>>> ----
>>>
>>> This doesn't work because it might block inside pipes.stdout.byLine, as
>>> the
>>> process is requesting more inputs to be written to its stdin before
>>> outputting more bytes to its stdout.
>>>
>>> What's the right approach?
>>> * fcntl(fd, F_SETFL, O_NONBLOCK); didn't seem to work
>>> * reading pipes.stdout inside a separate thread?
>>> In that second case, how to cleanly dispose of a blocked thread when we
>>> no
>>> longer need it?
>>>
>>> Any detailed example would help.
>>> Thanks!
>>>
>>
>>
>>
>> I tried using a separate thread for reading the process' stdout. It
>> works, except that sometimes the output is shuffled out of order.
>>
>> Is there anything buggy in this:
>>
>> ----
>> __gshared string output;
>>
>> void readBlocking(){
>> while ((c = fgetc(filepointer)) >= 0)
>>       output~=cast(char) c;
>> //NOTE: i can use something more efficient here but that's beside the
>> question
>> }
>>
>> thread = new Thread(& readBlocking);
>> output=null;
>> while(true){
>>         Thread.sleep(...);
>>         if(condition) break;
>> }
>> //now output is shuffled out of order sometimes
>> ----
>>
>> Furthermore, is there a standard way to tell when a process is waiting
>> for stdin input ? (cf condition above). Currently I'm checking whether
>> 'output' was modified within a timeout period T, but that's fragile and
>> incurs of penalty of T at least.
>>
>
> Are you looking for select() or poll()
> Poll I believe is posix only but I think select is more widely available.
> Not much of an answer but I hope it helps
>
>

Thanks, I had actually used select to solve another problem I had:
[std.process: how to process stdout chunk by chunk without waiting for
process termination]
That should work for here as well.

I think std.process is a bit limited currently, I keep having to implement
basic stuff it doesn't support.
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