OK, but I still cannot seem to find out if there is output available. Try:
julia> function test_redirect(f::Function)
stdout_orig = STDOUT
rd, wr = redirect_stdout()
f()
close(wr)
nb = nb_available(rd)
redirect_stdout(stdout_orig)
nb
end
test_redirect (generic function with 1 method)
julia> println(test_redirect(()->println("Some output")))
0
julia> println(test_redirect(()->run(`echo Some output`)))
0
julia> println(test_redirect(()->nothing))
0
So whether there is anything there or not nb_available returns 0?
What do you recommend instead of readavailable?
Bob
On Tue, Jun 3, 2014 at 9:00 AM, Jameson Nash <[email protected]> wrote:
> You need to close the pipe you called stdin before trying to read from
> stdout. Otherwise, the answers you get are correct -- readavailable can
> return whatever it wants. It is not know if all data written to the pipe is
> available until the write end is closed, and the read end sees an eof
>
> readavailable is a badly defined function. Don't use it.
>
> eof needs to block if there is no data available since it can't answer
> that question until the stream is closed (eof) or there is more data (!eof)
>
>
>
> On Tuesday, June 3, 2014, Bob Nnamtrop <[email protected]> wrote:
>
>> I am having an issue detecting if STDOUT is empty after I redirect it.
>> I'm using an external C program may or may not write to STDOUT. Thus, I
>> need to know if there is anything there before I readavailable from it
>> (since readavailable blocks if the pipe is empty). Here is some code to
>> show the issue (I redirect STDOUT and send nothing to it and try to check
>> if there is anything there):
>>
>> julia> stdout_orig = STDOUT
>> TTY(open, 0 bytes waiting)
>>
>> julia> stdout, stdin = redirect_stdout()
>> (Pipe(open, 0 bytes waiting),Pipe(open, 0 bytes waiting))
>>
>> julia> if !eof(stdout)
>> out = readavailable(stdout)
>> end
>>
>> This last command blocks on eof(stdout), which makes it worthless for
>> this purpose. Is it suppose to block when there is nothing in the Pipe? The
>> help for eof says "If the stream is not yet exhausted, this function will
>> block to wait for more data if necessary, and then return "false". " I'm
>> not sure how to interpret this. The behavior of eof seems like a bug to me.
>>
>> So looking at the docs I figure I can use nb_available instead but it
>> doesn't seem to be reliable when the pipe is used by external programs. For
>> example (restarting julia):
>>
>> julia> stdout, stdin = redirect_stdout()
>> (Pipe(open, 0 bytes waiting),Pipe(open, 0 bytes waiting))
>>
>> julia> stdout, stdin = redirect_stdout()
>> (Pipe(open, 0 bytes waiting),Pipe(open, 0 bytes waiting))
>>
>> julia> run(`echo Some output`)
>>
>> julia> nb_available(stdout)
>> 0
>>
>> This should have returned 12. Adding flush_cstdio() doesn't help.
>> nb_available seems to work if you use julia programs to write to STDOUT but
>> not for external programs. Is this a bug?
>>
>> Am I missing something?
>>
>> Thanks,
>> Bob
>>
>> ps Here is my version:
>>
>> julia> versioninfo()
>> Julia Version 0.3.0-prerelease+3407
>> Commit 152b3d3 (2014-06-02 21:29 UTC)
>> Platform Info:
>> System: Darwin (x86_64-apple-darwin13.2.0)
>> CPU: Intel(R) Core(TM)2 Duo CPU T9550 @ 2.66GHz
>> WORD_SIZE: 64
>> BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY)
>> LAPACK: libopenblas
>> LIBM: libopenlibm
>>
>>
>>
