xclate.man

.\" $Id: xclate.man,v 2.27 2010/07/08 15:16:25 ksb Exp $
.\" by Kevin Braunsdorf
.\" $Compile: Display%h
.\" $Display: groff -tbl -Tascii -man %f | ${PAGER:-less}
.\" $Display(*): groff -tbl -T%s -man %f
.\" $Install: %b -mDeinstall %o %f && cp %f $DESTDIR/usr/local/man/man1/xclate.1
.\" $Deinstall: ${rm-rm} -f $DESTDIR/usr/local/man/[cm]a[nt]1/xclate.1*
.TH XCLATE 1L LOCAL
.SH NAME
xclate \- collate output from parallel tasks
.SH SYNOPSIS
.ds PN "xclate
\fI\*(PN\fP \-\fBm\fP [\-\fBAdnQrsv\fP] [\-\fIdepth\fP] [\-\fBH\fP\~\fIhr\fP] [\-\fBi\fP\~\fIinput\fP] [\-\fBL\fP\~\fIcap\fP] [\-\fBN\fP\~\fInotify\fP] [\-\fBO\fP\~\fIoutput\fP] [\-\fBT\fP\~\fItitle\fP] [\-\fBu\fP\~\fIunix\fP] [\-\fBW\fP\~\fIwidow\fP] [\fIutility\fP]
.br
\fI\*(PN\fP [\-\fBnQsvw\fP] [\-\fBIEDY\fP] [\-\fIdepth\fP] [\-\fBH\fP\~\fIhr\fP] [\-\fBL\fP\~\fIcap\fP] [\-\fBT\fP\~\fItitle\fP] [\-\fBu\fP\~\fIunix\fP] [\fIxid\fP]\~[\fIclient\fP]
.br
\fI\*(PN\fP \-\fBh\fP
.br
\fI\*(PN\fP \-\fBV\fP
.br

.sp
.SH DESCRIPTION
The UNIX pipe model for input/output redirection is simple and elegant
for most single-thread tasks, and scales well for some multi-thread
applications.
New issues arise when the speed of computation far exceeds the speed of
an output device.  Processes block quickly, output from one process
gets mixed into the output from another, and overall through-put is
limited to the slowest tasks using the slowest device.
.PP
\fBXclate\fP is an attempt to recover from these issues.  Processes
may output freely to a buffered stream of at least \fIcap\fP bytes
before they might block (on output).  The output from each tasks
is flushed completely before a new task is allowed to output.
While overall through-put is greater, as tasks are cleared in the order
they finish (more likely) than in the order they started (thus a
slow task may run with deferred output while several generations
of quicker tasks complete).
.PP
To accomplish this \fBxclate\fP has three modes.
.TP
Manager mode
Under \fB\-m\fP it forks a \fIutility\fP
with a special environment, then arbitrates use of the original \fIstdout\fP
channel for any descendant processes created by \fIutility\fP which
request access.  The default \fIutility\fP in this mode is a shell, either
the one specified by $SHELL, or \fI/bin/sh\fP.
A semi-permanent instance may be created when the \fIutility\fP is
specified as \fB:\fP (a single colon), see \fB\-Q\fP and \fB\-u\fP.
.TP
Filter mode -- merge output
Without \fB\-m\fP or any \fIclient\fP the program reads from \fIstdin\fP
at most \fIcap\fP bytes then waits for exclusive access to the
manager's original \fIstdout\fP.  It flushes all the buffered input, then
pumps the remainder of its \fIstdin\fP to the acquired \fIstdout\fP.
.TP
Command mode -- filter and merge output
Given a \fIclient\fP, and without \fB\-m\fP, the program buffers \fIstdin\fP,
as it would without a command, waiting for exclusive access to
the manager's \fIstdout\fP.  When it gains access to the exclusive
output it starts the given \fIclient\fP with the buffered stream as
\fIstdin\fP and the manager's \fIstdout\fP, then pumps
the remainder of its \fIstdin\fP to the new process.  When any options in
the set \fB\-I\fP, \fB\-E\fP, \fB\-D\fP are set this behavior is modified
quit a bit.
.PP
In either of the last two modes the positional parameter \fIxid\fP
is the identification for this stream, usually \fBxapply\fP's %1 or %u escape
or by default \fIxclate\fP's process id.
Other useful values are the name of a host, directory,
or device which is the topic of the output.
Specify \fB\-T\fP and \fB\-H\fP
to include a title and/or horizontal break around named
sections.

.SH OPTIONS
If the program is called \fIxclate\fP then no options are forced.
The environment variable \fB$XCLATE\fP is read for command line
options, before the explicit command line.
That variable may also be changed by \fBxclate\fP for
descendent processes, see ENVIRONMENT below.
.TP
\-\fIdepth\fP
Specify a collation sequence beyond the tightest enclosing.  A \fIdepth\fP
of 0 is the default.  A \fIdepth\fP of 1 accesses the next outer
instance of \fBxclate\fP \fB\-m\fP.
.TP
\fB\-A\fP
Add the name of the controlling socket as the first line of the notification
stream.  This option is used by \fIsshw\fP to locate the service, as it
is used in global mode to manage the remote process redirection.
.TP
\fB\-d\fP
Do not link the new manager's diversion socket in the \fB$\fP\fIxclate_link\fP
environment chain.  Rather the manager socket name is recorded in
\fB$\fP\fIxclate_d\fP, while \fB$\fP\fIxclate_link\fP is left
unchanged.
When the manager socket is specified (via \fB\-u\fP \fIunix\fP) the environment
variable may be totally ignored, as you already know where the socket is.
.TP
\fB\-h\fP
Print a help message.
.TP
\fB\-i\fP \fIinput\fP
The \fIstdin\fP given to the \fI\*(PN\fP process is replaced
by this stream for the \fIutility\fP process.  The original
\fIstdin\fP is available only via the \fB\-I\fP option to client
\fIxclate\fP instances.  The \fIinput\fP specification
may be any of "|\fIcommand\fP", "<\fIfile\fP", "<>\fIfile\fP", "<&\fIfd\fP",
"<&-", "\fIfile\fP", "\fIsocket\fP" or "-" as a shorthand for "</dev/null".
.TP
\fB\-H\fP \fIhr\fP
Add a horizontal rule to end each output stream.  If a client instance
does not specify a \fIhr\fP the master's is assumed.  An explicit specification
of the empty string may over-ride this default.
See \fB\-T\fP for a list of escapes expanded.
.TP
\fB\-L\fP \fIcap\fP
Put a cap on memory based output buffer.  This limits the amount of
\fIstdin\fP \fBxclate\fP collects before it blocks waiting for
exclusive access to the manager's \fIstdout\fP.
The default is 64k, and the value may be postfixed with a scale
factor, derived from the \fBmkcmd\fP type "bytes".  The master's specification
of \fIcap\fP is assumed if none is presented on the command-line.
Use \fB\-L '?'\fP for a list of scale factors.
.TP
\fB\-m\fP
Manage output for descendant processes.
This starts a new managed output stream (the \fIstdout\fP of the
.B xclate
process itself, or the channel created by \fB\-O\fP).
In the environment of the \fIutility\fP created some variables are
installed to allow subsequent \fBxclate\fP
processes to contact the manager process to gain access to
the shared output stream (see below).
.TP
\fB\-N\fP \fInotify\fP
Send a null terminated string (the xid) to this file, process  or
file descriptor after each section is complete.  This is largely
for \fIhxmd\fP's use.  If specified as dash ("\-") the default
stream is /dev/tty, in which case the null is replaced with a newline.
The null is needed when the output is read through a pipe, and the
\fIxid\fP might contain a newline.  The same redirections available
under \fB\-W\fP are also available.
.TP
\fB\-n\fP
Do not execute commands, trace only.  This doesn't really work,
but is required by the pipefit code.  Don't try it.
.TP
\fB\-O\fP \fIoutput\fP
Specify a diversion for the collected stream, rather than \fIstdout\fP.
This assures that no output ends up in the stream without an attending
\fBxclate\fP process.  The same diversions are allowed as for \fB\-W\fP
(below), with the exception that a dash ("\-") means to connect to
an enclosing instance of \fI\*(PN\fP, this groups all our output inside
the specified diversion.  In this case -\fIdepth\fP specifies
the depth of the desired diversion.
.TP
\fB\-Q\fP
Any manager instance started with the \fIutility\fP of ":" will continue
to process until at least one client run with this option finishes.
This allows a diversion to be started by an unrelated process tree
to complete after some client completes.  The shutdown is graceful
and allows presently connected clients to finish, as well as some
clients that may connect later.
.\" This is actually what you want, otherwise use kill(1).
\fIPtbw\fP has exactly the same notion.
.TP
\fB\-r\fP
The \fInotify\fP stream will include the exit status from each
process before the \fIxid\fP, separated with a comma.
This may not work in filter mode, as we can't see the exit code
of the process in all cases (it works for most shells).
.\" the -p option I hide helps if you are a shell wiz.
.TP
\fB\-s\fP
Totally silence subtasks with no output.  This changes the way
\fI\*(PN\fP executes some requests to place itself on
the \fBstdout\fP side of the client process, but
adds substantial speed when most tasks produce no output.
Even the title (\fB\-T\fP) and horizontal rule (\fB\-H\fP) are removed for
tasks with zero length output.  See also \fIxapply\fP, which passes this
option on to us.  Providing this option in master mode sets the option
for the whole diversion, as promised in the last release.  All \fIhxmd\fP's
send \fIxapply\fP this option to speed processing.
.TP
\fB\-T\fP \fItitle\fP
A title for each stream, some limited escapes are replaced:
.nf
	\fB%x\fP	xid
	\fB%s\fP	sequence number (like \fIxapply\fP's \fB%u\fP, in output order)
	\fB%{\fPENV\fB}\fP	the value of $ENV
	\fB%%\fP	a literal percent (%)
.fi
If the title should not have a trailing newline, make the last character
be a percent (%).
.TP
\fB\-u\fP \fIunix\fP
Specify a forced unix domain end-point.  This allows
unrelated instances of \fBxclate\fP (on the host) to share
a managed output stream.  To make this work you might have to
change the mode on the manager directory.
This option is required (in general) to make the persistent mode
(under -m with \fIutility\fP specified as a single \fB:\fP) useful.
See below.
.TP
\fB\-v\fP
Be verbose.  Show some of the commands xclate is running in pseudo-shell.
.\" This will surely confuse you more than it helps.
.TP
\fB\-V\fP
Show version information.
.TP
\fB\-w\fP
The \fIstdout\fP from the client is directed to the widow
output for the specified \fIdepth\fP.  This is most useful with
\fIdepth\fP set and multiple diversions in scope.
.TP
\fB\-W\fP \fIwidow\fP
Redirect widowed output to this file, process, or fd.
Under this option output which is not sent through a descendant \fBxclate\fP
filter process is gathered into a "widow" section at the end of the output.
The \fIwidow\fP parameter may be a process (as "|\fIcommand\fP"),
a file (as ">\fIfile\fP", or ">>\fIfile\fP", or "\fIfile\fP"),
a local (UNIX) domain socket (as "\fIsocket\fP"),
any already opened file descriptor (as ">&\fIfd\fP"),
or a dash (as "-") for \fIstderr\fP.

.SH "COMMAND MODE OPTIONS"
These options will let you blow your foot completely off, placing it into orbit.
.\" It is not an accident that they spell "improvised explosive device".
They are not used by most automation, but allow for some very clever
shell scripts (see sapply):
.TP
\fB\-I\fP
The \fIclient\fP is started with \fBstdin\fP connected to the
master's \fBstdin\fP.  No buffering of \fBstdin\fP can be provided.
.TP
\fB\-E\fP
The \fIclient\fP is started with \fBstderr\fP connected to the
master's \fBstderr\fP.
.TP
\fB\-D\fP
The \fIclient\fP is launched from the same current working
directory as the master's.  Really, even if that directory is
hidden under a mount point.  See \fIfchdir\fP(2).
.TP
\fB\-Y\fP
Change the controlling tty to the new \fIstdin\fP, \fIstdout\fP,
or \fIstderr\fP (in that order).  See \fItty\fP(4).
.PP
These are the inspiration for the \fIescrow\fP wrapper.  I'll even
claim that \fIxclate\fP is the first true wrapper, and inspired
all the others.

.SH ENVIRONMENT
Since \fBxclate\fP is intended to be recursive, a provision is
made in the processing of environment variables for passing
options to nested \fBxclate\fP processes.
.TP
$xcl_link
The environment variable \fB$xcl_link\fP is set to the number
of nested \fBxclate\fP processes presently running.

.TP
$xcl_1, $xcl_2, ...
Each manager instance of \fBxclate\fP sets a variable (named for the value
of $xcl_link established when it started) to the path to the
unix domain socket used to chat with that instance.

.TP
$xcl_d
The path to the unix domain socket for the tightest enclosing instance
of \fIxclate\fP \fB\-m\fP with \fB\-d\fP in effect.

.TP
$XCLATE and $XCLATE_1, $XCLATE_2, \fI...\fP
After reading command line options from variable \fB$XCLATE\fP,
any master (\fB\-m\fP) process removes it
from the environment
(before executing \fIutility\fP in the child process).
It then installs the variable \fB$XCLATE\fP_\fInesting\fP in its place,
if it is present in the environment.  This allows header and
horizontal rule options to be set before they are needed, for
example before any \fIxapply\fP commands are started.
.TS
l l.
$XCLATE	read by the first manger instance
$XCLATE_1	read by the children of the first manager
$XCLATE_1	read by the second manager, if not reset.
$XCLATE_2	read by the children of the second manager
\...	and so on...
.TE

.SH EXAMPLES
.TP
\fBxclate\fP \-vV
Show version information and any details in the present environment.
.TP
\fBxclate\fP \-L \e? -V
Display the table of suffixes supported by \fB\-L\fP, and
some version information.
.TP
\fBxclate\fP \fB\-vm\fP  tasks
Assuming that the file \fItasks\fP is a shell script that had a list of
(long running) background jobs in it, for example:
.nf
	xclate \-T%x passwd sort /etc/passwd &
	xclate \-T%x  group sort /etc/group &
	...
	wait
.fi
The output of this command would be the output of the jobs in some
order, with each output section contiguous.
.TP
\fBxapply\fP \fB\-m\fP \-P5 ...
Wrap a controlled environment around an \fBxapply\fP process.
There is some real hoodoo going on here, and you don't want to
mess with it until you can use \fBxclate\fP very well.
.TP
\fBxclate\fP \-m \fBxapply\fP  \-P5 '...  |\fBxclate\fP %u' ...
This puts the pixie dust on the \fBxapply\fP by hand, and is
in effect exactly what \fBxapply\fP does under \fB\-m\fP.
This is akin to making home-made distilled spirits
(as is one is apt to get blown-up, poisoned, or shot by the law).
.TP
\fBxclate\fP \-m \fBxapply\fP \-m \-P6 '...' ...
Force a new \fBxclate\fP manager into the process tree for this
instance of \fIxapply\fP.
Nested instances of \fBxapply\fP share a common manager by default,
by explicitly starting a new managed stream we can group all the
output of this \fIxapply\fP together in the common output.
.TP
eval chmod 0750 \e${xcl_$xcl_link%/\e*}
A \fBksh\fP spell to make the present manager socket visible to
our group.
.TP
eval chmod 0750 \e`dirname \e${xcl_$xcl_link}\e`
The same spell under Borne shell, or csh.
.TP
xclate \-\- \-\- ls
The spell to skip the \fIxid\fP, one double-dash to end
the options, one to skip the optional \fIxid\fP.
It is better form to put a meaningful \fIxid\fP on each stream,
as the default of question-mark ("?") is silly.
.TP
xclate \-mr \-N /tmp/log.0 \fIprogram\fP ; tr '\000' '\n' /tmp/log.0
Run a collated \fIprogram\fP, then replay the exit codes and \fIxid\fP for each task.
.TP
.nf
xclate \-mu /var/run/cheater : >>/var/log/cheater &
.fi
Start a persistent diversion on the socket \fB/var/run/cheater\fP.
Clients that can connect to that socket can write messages
into \fB/var/log/cheater\fP, until someone issues a client
with \fB\-Q\fP set.
.TP
.nf
xclate \-m \-i "/etc/motd"  tr '[A\-Z]' '[a\-z]'
.fi
A force \fIxclate\fP to open \fB/etc/motd\fP as \fIstdin\fP to
a tr(1).
.TP
.nf
xclate \-mi "\-" <$DATA xapply \fI...\fP
.fi
All child processes of the \fIxapply\fP may try to acquire a file descriptor
on the $DATA file with "xclate -I".  Note \fBXapply\fP doesn't implement this
since this option would serialize all of the child processes.
.TP
.nf
xclate \-mi "$SOCK_TMP" nc log.example.com 4321
.fi
Use xclate to connect to the local domain socket \fI$SOCK_TMP\fP,
use that as \fIstdin\fP to a netcat to \fBlog.example.com\fP on
port 4321.
.TP
.nf
xclate \-mi "$SOCK_TMP" sh -c "exec nc log.example.com 4321 1>&0"
.fi
Same as the above, with a duplex connection to force the replies back to
the UNIX-domain socket.
Use \fBnc -l -U $SOCK_TMP\fP to create a local end-point
(in a window).  In another start a network listener with \fBnc -l -p 4321\fP.
In a third window run the above command on the same host as
the local end-point, please replace "log.example.com" with the name of
the host running the listener.  You should be bidirectionally connected
between the two windows.  An interrupt (^C) in the "nc -l -U" window
or in the xclate window breaks the connection.


.SH BUGS
This program is very confusing to novice users.  The complex file
descriptor manipulations lead to cries of pain and massive denial.
While \fBxclate\fP can be used over the top of a shell, it is
considered "poor form" to leave one of those just lying around.

.PP
The "command mode" is more useful (most of the time) with input
redirected from \fB/dev/null\fP.  This is parallel to the bug where
ssh (or rsh) reads input it never needs.  There is not a command
line option to do that, because I think "</dev/null" is clear,
and sometimes you'd like to input text from your terminal.

.PP
The options \fB\-O\fP, \fB\-W\fP, and \fB\-N\fP do not truncate
any file they are told to open, unless you prefix it with a greater-than
symbol (>), which must be quoted from the shell.

.PP
The name is a play on "xapply", "escalate" and "collate", and that's
a bug all by itself.

.PP
Some programmers are confused when \fIxclate\fP's \fB%s\fP is
not in sync with \fIxapply\fP's \fB%u\fP, this
results from 2 root causes: races between subtasks in an \fIxapply\fP
with a large parallel factor, and races between peer instances of
\fIxclate\fP managed tasks unrelated to those started by \fIxapply\fP.
The use of \fB%s\fP, in general, is just to let some applications re-sort
the collated output as a post-processing filter.

.SH AUTHOR
Kevin S Braunsdorf
.br
NPCGuild.org
.br
xclate at ksb.npcguild.org

.SH "SEE ALSO"
sh(1), csh(1), xapply(1)'s \fB\-m\fP, \fB\-s\fP and \fB\-u\fP options,
environ(7), mkcmd(1L), cat(1), hxmd(8L), escrow(1L), ptbw(1L), dicer(5),
nc(1)
.\" and soon wrapw, escrow