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Full Discussion: File read/ write operation
Operating Systems Linux File read/ write operation Post 302425274 by jim mcnamara on Thursday 27th of May 2010 02:07:23 PM
Old 05-27-2010
Short answer, yes, it is possible.

In order to keep the reader consistent you have to employ some kind of IPC - sockets, shared memory, mutex, file locking. Example: the reader tries to read whenever it feels like it, it will probably hit an EOF, which is not the real EOF, because reader did not wait for writer to finish.

Check out the flock() (advisory lock) call.
edit -
My bad - you are writing perl (probably). A better perler than me will have to advise about flock.
 

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PROGRESS(1)						    BSD General Commands Manual 					       PROGRESS(1)

NAME
progress -- feed input to a command, displaying a progress bar SYNOPSIS
progress [-ez] [-b buffersize] [-f file] [-l length] [-p prefix] cmd [args ...] DESCRIPTION
The progress utility opens a pipe to cmd and feeds an input stream into it, while displaying a progress bar to standard output. If no file- name is specified, progress reads from standard input. Where feasible, progress fstat(2)s the input to determine the length, so a time esti- mate can be calculated. If no length is specified or determined, progress simply displays a count of the data and the data rate. The options are as follows: -b buffersize Read in buffers of the specified size (default 64k). An optional suffix (per strsuftoll(3)) may be given. -e Display progress to standard error instead of standard output. -f file Read from the specified file instead of standard input. -l length Use the specified length for the time estimate, rather than attempting to fstat(2) the input. An optional suffix (per strsuftoll(3)) may be given. -p prefix Print the given ``prefix'' text before (left of) the progress bar. -z Filter the input through gunzip(1). If -f is specified, calculate the length using gzip -l. EXIT STATUS
progress exits 0 on success. EXAMPLES
The command progress -zf file.tar.gz tar xf - will extract the file.tar.gz displaying the progress bar as time passes: 0% | | 0 0.00 KiB/s --:-- ETA 40% |******** | 273 KiB 271.95 KiB/s 00:01 ETA 81% |*********************** | 553 KiB 274.61 KiB/s 00:00 ETA 100% |*******************************| 680 KiB 264.59 KiB/s 00:00 ETA If it is preferred to monitor the progress of the decompression process (unlikely), then progress -f file.tar.gz tar zxf - could be used. The command dd if=/dev/rwd0d ibs=64k | progress -l 120g dd of=/dev/rwd1d obs=64k will copy the 120 GiB disk wd0 (/dev/rwd0d) to wd1 (/dev/rwd1d), displaying a progress bar during the operation. SEE ALSO
ftp(1), strsuftoll(3) HISTORY
progress first appeared in NetBSD 1.6.1. The dynamic progress bar display code is part of ftp(1). AUTHORS
progress was written by John Hawkinson <jhawk@NetBSD.org>. ftp(1)'s dynamic progress bar was written by Luke Mewburn. BUGS
Since the progress bar is displayed asynchronously, it may be difficult to read some error messages, both those produced by the pipeline, as well as those produced by progress itself. BSD
June 6, 2007 BSD
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