[lug] named pipe missunderstanding

[Jason Davis]

I say reads and what i really mean is an open/close cycle of the fifo.
A writer connecting, writting some data, then disconnecting.
Each time this happens I incremented a variable. I'll try to be more clear =D

Thank You
Jason

On Tue, Feb 1, 2011 at 4:11 PM, Anthony Foiani <tkil at scrye.com> wrote:
> Jason Davis <jdavis at openactive.org> writes:
>
>> I think I have a missunderstanding about named pipes. Im using them
>> for IPC and Im losing data.
>
> Your update says that you get an inconsistent number of *reads*.
>
> Do you get an inconsistent number of *bytes*, though?  Named pipes do
> not packetize their content.
>
>  $ ls -al fedora11-i386-dvd.img
>  -rw-rw-r--. 1 tony tony 3683844096 Oct 15  2009 fedora11-i386-dvd.img
>
>  $ mkfifo my-pipe
>
>  $ dd if=my-pipe of=tmp.img bs=1M &
>  [1] 2412
>  $ dd if=fedora11-i386-dvd.img of=my-pipe bs=1M
>  3513+1 records in
>  3513+1 records out
>  3683844096 bytes (3.7 GB) copied, 227.972 s, 16.2 MB/s
>  3513+1 records in
>  3513+1 records out
>  3683844096 bytes (3.7 GB) copied, 227.966 s, 16.2 MB/s
>  [1]+  Done                    dd if=my-pipe of=tmp.img bs=1M
>
>  $ md5sum fedora11-i386-dvd.img tmp.img
>  8bb458918512bcd41a834ca05b92d252  fedora11-i386-dvd.img
>  8bb458918512bcd41a834ca05b92d252  tmp.img
>
> If the reading process happens to loop while the writing process is
> *not* writing to the pipe, the reader will see EOF.
>
> In terminal 1:
>
>  $ cat *.pdf > ../all.pdf
>
>  $ for i in *.pdf ; do dd if="$i" of=my-pipe bs=16k ; done
>  1+1 records in
>  1+1 records out
>  19070 bytes (19 kB) copied, 0.000147709 s, 129 MB/s
>  425+1 records in
>  425+1 records out
>  6976935 bytes (7.0 MB) copied, 0.128906 s, 54.1 MB/s
>  253+1 records in
>  253+1 records out
>  4153413 bytes (4.2 MB) copied, 0.0641728 s, 64.7 MB/s
>  253+1 records in
>  253+1 records out
>  4153413 bytes (4.2 MB) copied, 0.0684014 s, 60.7 MB/s
>  8+1 records in
>  8+1 records out
>  135683 bytes (136 kB) copied, 0.00947213 s, 14.3 MB/s
>  33+1 records in
>  33+1 records out
>  556324 bytes (556 kB) copied, 0.00314683 s, 177 MB/s
>
> In terminal 2:
>
>  $ dd if=my-pipe of=out1.pdf bs=1M
>  12+7 records in
>  12+7 records out
>  15438514 bytes (15 MB) copied, 0.297442 s, 51.9 MB/s
>  $ dd if=my-pipe of=out2.pdf bs=1M
>  0+3 records in
>  0+3 records out
>  1593046 bytes (1.6 MB) copied, 0.0785324 s, 20.3 MB/s
>  $ dd if=my-pipe of=out3.pdf bs=16k
>  12+1 records in
>  12+1 records out
>  201281 bytes (201 kB) copied, 0.0184194 s, 10.9 MB/s
>  $ dd if=my-pipe of=out4.pdf bs=1M
>  1+2 records in
>  1+2 records out
>  1282032 bytes (1.3 MB) copied, 0.0298385 s, 43.0 MB/s
>
> But I'm pretty sure that all the data will eventually be sent.  Using
> the same command in terminal 1 to send each file individually, I can
> use 'cat' to capture them in terminal 2:
>
>   $ rm ../all2.pdf
>
>   $ while true ; do cat my-pipe >> ../all2.pdf ; done
>   ^C
>
>   $ ls -al ../all*
>   -rw-rw-r--. 1 tony tony 60324399 Feb  1 16:08 ../all2.pdf
>   -rw-rw-r--. 1 tony tony 60324399 Feb  1 15:47 ../all.pdf
>
>   $ md5sum ../all*
>   38257d8db7a14d2d3ba69ad145697ee8  ../all2.pdf
>   38257d8db7a14d2d3ba69ad145697ee8  ../all.pdf
>
> I did have some issues using 'dd' to *receive* the data; I'm not sure
> what was going on there.
>
> HTH,
> t.
>
> _______________________________________________
> Web Page:  http://lug.boulder.co.us
> Mailing List: http://lists.lug.boulder.co.us/mailman/listinfo/lug
> Join us on IRC: irc.hackingsociety.org port=6667 channel=#hackingsociety
>