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#!/bin/sh
# This is a shell archive (produced by GNU sharutils 4.2).
# To extract the files from this archive, save it to some FILE, remove
# everything before the `!/bin/sh' line above, then type `sh FILE'.
#
# Made on 2000-03-19 15:00 EST by <jcej@chiroptera.tragus.org>.
# Source directory was `/home/jcej/projects/ACE_wrappers/docs/tutorials/013'.
#
# Existing files will *not* be overwritten unless `-c' is specified.
#
# This shar contains:
# length mode name
# ------ ---------- ------------------------------------------
# 386 -rw-rw-r-- hdr
# 89 -rw-rw-r-- bodies
# 2412 -rw-rw-r-- page01.pre
# 432 -rw-rw-r-- page02.pre
# 1424 -rw-rw-r-- page03.pre
# 1048 -rw-rw-r-- page04.pre
# 268 -rw-rw-r-- page05.pre
# 914 -rw-rw-r-- page06.pre
# 1360 -rw-rw-r-- page07.pre
# 860 -rw-rw-r-- page08.pre
# 204 -rw-rw-r-- page02.pst
# 704 -rw-rw-r-- page04.pst
# 385 -rw-rw-r-- page06.pst
# 369 -rw-rw-r-- page07.pst
#
save_IFS="${IFS}"
IFS="${IFS}:"
gettext_dir=FAILED
locale_dir=FAILED
first_param="$1"
for dir in $PATH
do
if test "$gettext_dir" = FAILED && test -f $dir/gettext \
&& ($dir/gettext --version >/dev/null 2>&1)
then
set `$dir/gettext --version 2>&1`
if test "$3" = GNU
then
gettext_dir=$dir
fi
fi
if test "$locale_dir" = FAILED && test -f $dir/shar \
&& ($dir/shar --print-text-domain-dir >/dev/null 2>&1)
then
locale_dir=`$dir/shar --print-text-domain-dir`
fi
done
IFS="$save_IFS"
if test "$locale_dir" = FAILED || test "$gettext_dir" = FAILED
then
echo=echo
else
TEXTDOMAINDIR=$locale_dir
export TEXTDOMAINDIR
TEXTDOMAIN=sharutils
export TEXTDOMAIN
echo="$gettext_dir/gettext -s"
fi
touch -am 1231235999 $$.touch >/dev/null 2>&1
if test ! -f 1231235999 && test -f $$.touch; then
shar_touch=touch
else
shar_touch=:
echo
$echo 'WARNING: not restoring timestamps. Consider getting and'
$echo "installing GNU \`touch', distributed in GNU File Utilities..."
echo
fi
rm -f 1231235999 $$.touch
#
if mkdir _sh32654; then
$echo 'x -' 'creating lock directory'
else
$echo 'failed to create lock directory'
exit 1
fi
# ============= hdr ==============
if test -f 'hdr' && test "$first_param" != -c; then
$echo 'x -' SKIPPING 'hdr' '(file already exists)'
else
$echo 'x -' extracting 'hdr' '(text)'
sed 's/^X//' << 'SHAR_EOF' > 'hdr' &&
<HTML>
<HEAD>
X <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
X <META NAME="Author" CONTENT="James CE Johnson">
X <TITLE>ACE Tutorial 013</TITLE>
</HEAD>
<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#000FFF" VLINK="#FF0F0F">
X
<CENTER><B><FONT SIZE=+2>ACE Tutorial 013</FONT></B></CENTER>
X
<CENTER><B><FONT SIZE=+2>Multiple thread pools</FONT></B></CENTER>
SHAR_EOF
$shar_touch -am 03191459100 'hdr' &&
chmod 0664 'hdr' ||
$echo 'restore of' 'hdr' 'failed'
if ( md5sum --help 2>&1 | grep 'sage: md5sum \[' ) >/dev/null 2>&1 \
&& ( md5sum --version 2>&1 | grep -v 'textutils 1.12' ) >/dev/null; then
md5sum -c << SHAR_EOF >/dev/null 2>&1 \
|| $echo 'hdr:' 'MD5 check failed'
abef9831eba4051526151ff2343730d7 hdr
SHAR_EOF
else
shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'hdr'`"
test 386 -eq "$shar_count" ||
$echo 'hdr:' 'original size' '386,' 'current size' "$shar_count!"
fi
fi
# ============= bodies ==============
if test -f 'bodies' && test "$first_param" != -c; then
$echo 'x -' SKIPPING 'bodies' '(file already exists)'
else
$echo 'x -' extracting 'bodies' '(text)'
sed 's/^X//' << 'SHAR_EOF' > 'bodies' &&
PAGE=2
message_queue.cpp
mld.h mld.cpp
block.h
block.cpp
task.h task.cpp
work.h work.cpp
SHAR_EOF
$shar_touch -am 1114230198 'bodies' &&
chmod 0664 'bodies' ||
$echo 'restore of' 'bodies' 'failed'
if ( md5sum --help 2>&1 | grep 'sage: md5sum \[' ) >/dev/null 2>&1 \
&& ( md5sum --version 2>&1 | grep -v 'textutils 1.12' ) >/dev/null; then
md5sum -c << SHAR_EOF >/dev/null 2>&1 \
|| $echo 'bodies:' 'MD5 check failed'
826e1e15e593f64228b867cb6143f179 bodies
SHAR_EOF
else
shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'bodies'`"
test 89 -eq "$shar_count" ||
$echo 'bodies:' 'original size' '89,' 'current size' "$shar_count!"
fi
fi
# ============= page01.pre ==============
if test -f 'page01.pre' && test "$first_param" != -c; then
$echo 'x -' SKIPPING 'page01.pre' '(file already exists)'
else
$echo 'x -' extracting 'page01.pre' '(text)'
sed 's/^X//' << 'SHAR_EOF' > 'page01.pre' &&
<P>
<HR WIDTH="100%">
<P>
My intent with this tutorial was to derive from ACE_Data_Block instead
of ACE_Message_Block so that we could leverage the reference counting
nature of that object.
<P>
Along the way, I sort of got distracted... What I ended up with is a
poor excuse for ACE_Stream that implements a simple state machine.
<P>
The application is built around a thread pool where the pool's svc()
method takes work units from the message queue for processing. As
each unit is taken from the queue, the process() method is invoked to
do some work. The twist is that after processing the message, we
enqueue it into another thread pool to do more work. This continues
through a chain of thread pools until the last where the unit's fini()
method is called for finishing up any outstanding work.
<P>
The chain of thread pools is uni-directional using a singly-linked
list of Task derivatives. Each pool has the same number of tasks in
order to keep things simple.
<P>
Kirthika's abstract:
<UL>
In this tutorial, a singly linked list of thread-pools, each of which is
a subtask and which acts as the finite state machine node, is used to
simulate a finite state machine.
<P>
A task is created with a number of subtasks. Once the message block is
obtained from the queue, it is verified to see whether a task has a
subtask. If so, it is forwarded to the subtask. Thus the mesage
traverses over the whole list. As a safety measure for destroying the
block after it goes through the whole list, an effective and simple
Memory Leak Detector has been implemented. It is a counter which
increments when the object where it resides is created and decrements on
its deletion.
<P>
Another optimisation from the previous tutorials on Message Queues, is
the bundling of the Data block within the Message Block. The Data block
provides reference counting, so duplication of data is avoided. It is
deleted only when its reference count drops to zero. Now updating
this count between threads call for synchronisation and in comes the
ACE_Mutex, a lock which takes care that the counting is thread-safe.
<P>
Although the example isn't a full-fledged Finite State Machine,
i.e. it has to be tweaked to be able to jump states on different inputs,
it definitely proves to be a great lesson and introduces us to quite a
few new ACE classes and the ways they can be mixed and matched to
produce the end-system desired.
</ul>
SHAR_EOF
$shar_touch -am 03191459100 'page01.pre' &&
chmod 0664 'page01.pre' ||
$echo 'restore of' 'page01.pre' 'failed'
if ( md5sum --help 2>&1 | grep 'sage: md5sum \[' ) >/dev/null 2>&1 \
&& ( md5sum --version 2>&1 | grep -v 'textutils 1.12' ) >/dev/null; then
md5sum -c << SHAR_EOF >/dev/null 2>&1 \
|| $echo 'page01.pre:' 'MD5 check failed'
a78a6c7a7841ee5d8ce2a87a55cd456f page01.pre
SHAR_EOF
else
shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page01.pre'`"
test 2412 -eq "$shar_count" ||
$echo 'page01.pre:' 'original size' '2412,' 'current size' "$shar_count!"
fi
fi
# ============= page02.pre ==============
if test -f 'page02.pre' && test "$first_param" != -c; then
$echo 'x -' SKIPPING 'page02.pre' '(file already exists)'
else
$echo 'x -' extracting 'page02.pre' '(text)'
sed 's/^X//' << 'SHAR_EOF' > 'page02.pre' &&
X
X
<P>
<HR WIDTH="100%">
<P>
We'll go back to our tradition of looking at main() first. The only
change here from our "normal" thread pool is the ability to specify
the number of subtasks for the pool. (Each subtask is another thread
pool in the chain. I suppose I should have named that better...)
I've still got the custom Message_Block so that, at this level, we
don't even know about custom Data_Blocks.
<P>
<HR WIDTH="100%">
SHAR_EOF
$shar_touch -am 03191459100 'page02.pre' &&
chmod 0664 'page02.pre' ||
$echo 'restore of' 'page02.pre' 'failed'
if ( md5sum --help 2>&1 | grep 'sage: md5sum \[' ) >/dev/null 2>&1 \
&& ( md5sum --version 2>&1 | grep -v 'textutils 1.12' ) >/dev/null; then
md5sum -c << SHAR_EOF >/dev/null 2>&1 \
|| $echo 'page02.pre:' 'MD5 check failed'
6f4a2e24d7d776b1ec17a07f00f409f8 page02.pre
SHAR_EOF
else
shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page02.pre'`"
test 432 -eq "$shar_count" ||
$echo 'page02.pre:' 'original size' '432,' 'current size' "$shar_count!"
fi
fi
# ============= page03.pre ==============
if test -f 'page03.pre' && test "$first_param" != -c; then
$echo 'x -' SKIPPING 'page03.pre' '(file already exists)'
else
$echo 'x -' extracting 'page03.pre' '(text)'
sed 's/^X//' << 'SHAR_EOF' > 'page03.pre' &&
X
X
<P>
<HR WIDTH="100%">
<P>
I did eventually create that ACE_Data_Block derivative that I wanted.
My purpose in doing so was to use the reference-counting
that is provided by ACE_Data_Block and ACE_Message_Block interactions.
X When you're working with an object in a single
thread, it's generally not so difficult to manage it's lifetime.
That is, it doesn't tend to go out of scope or get destroyed unless
you do it on purpose.
<P>
On the other hand, if you're passing data between several threads, it
is easy to loose track of who "owns" the data at any one time. All
too frequently, data will be deleted by one thread while another is
still using it. Reference counting can prevent that. The rule of
thumb is that you increment the reference count of the object when you
hand it off to a new thread. You then decrement the count when you're
done with the object and let the object delete itself when there are
no more references.
<P>
To prove that all of that works correctly in the tutorial, I've
created a cheap Memory Leak Detector object. All mld instances
reference a thread-safe counter that is incremented when the mld is
constructed and decremented when destructed. I then insert an mld
into each of my dynamically created objects. If I get to the end of
main() and the counter isn't zero then I either didn't delete enough
or I deleted too many times.
<P>
Simple, cheap, effective.
<P>
<HR WIDTH="100%">
SHAR_EOF
$shar_touch -am 03191459100 'page03.pre' &&
chmod 0664 'page03.pre' ||
$echo 'restore of' 'page03.pre' 'failed'
if ( md5sum --help 2>&1 | grep 'sage: md5sum \[' ) >/dev/null 2>&1 \
&& ( md5sum --version 2>&1 | grep -v 'textutils 1.12' ) >/dev/null; then
md5sum -c << SHAR_EOF >/dev/null 2>&1 \
|| $echo 'page03.pre:' 'MD5 check failed'
545e09ebf801bfaea60bb1fb07c7ec9f page03.pre
SHAR_EOF
else
shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page03.pre'`"
test 1424 -eq "$shar_count" ||
$echo 'page03.pre:' 'original size' '1424,' 'current size' "$shar_count!"
fi
fi
# ============= page04.pre ==============
if test -f 'page04.pre' && test "$first_param" != -c; then
$echo 'x -' SKIPPING 'page04.pre' '(file already exists)'
else
$echo 'x -' extracting 'page04.pre' '(text)'
sed 's/^X//' << 'SHAR_EOF' > 'page04.pre' &&
X
X
<P>
<HR WIDTH="100%">
<P>
Let's look now at the changes to our ACE_Message_Block derivative and
the new ACE_Data_Block derivative.
<P>
The important thing to remember is that the data block (not the
message block) is reference counted. When you instantiate a new
ACE_Message_Block, it will create one or more ACE_Data_Block objects
to contain the data you need. Optionally, you can provide it with a
pointer to a data block.
<P>
When you finish with a message block, you should use the release()
method to make it go away. Do not ever <em>delete</em> an instance of
a message block! When you invoke release(), the message block will
invoke release() on the data block(s) it contains. If the block's
reference count goes to zero as a result then the block will <em>delete</em>
itself.
<P>
To increment the reference count of a data block, use the
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