ACE Tutorial 014

#!/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 1999-02-10 22:17 EST by . # Source directory was `/var/home/jcej/projects/ACE_wrappers/docs/tutorials/014'. # # Existing files will *not* be overwritten unless `-c' is specified. # # This shar contains: # length mode name # ------ ---------- ------------------------------------------ # 414 -rw-r--r-- hdr # 44 -rw-r--r-- bodies # 2609 -rw-r--r-- page01.pre # 231 -rw-r--r-- page02.pre # 651 -rw-r--r-- page03.pre # 439 -rw-r--r-- page04.pre # 1079 -rw-r--r-- page05.pre # 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 _sh28285; 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' && X X X ACE Tutorial 014 X ACE Tutorial 014 X ACE_Stream Tutorial, Of Sorts X

SHAR_EOF $shar_touch -am 1012190598 'hdr' && chmod 0644 '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 \ || $echo 'hdr:' 'MD5 check failed' 25304aa689283dcbed9531b68e7ae2b9 hdr SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'hdr'`" test 414 -eq "$shar_count" || $echo 'hdr:' 'original size' '414,' 'current size' "$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 Task.h Task.cpp EndTask.h stream.cpp SHAR_EOF $shar_touch -am 1020193698 'bodies' && chmod 0644 '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 \ || $echo 'bodies:' 'MD5 check failed' 43305b4b15975a1e4cbd99b6d3592c12 bodies SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'bodies'`" test 44 -eq "$shar_count" || $echo 'bodies:' 'original size' '44,' 'current size' "$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' && X

ACE_Stream is handy when you have several ACE_Task objects that you would like to link together. X

An intermediate class you we will deal with is the ACE_Module. X

The basic plan is to wrap your Task into a Module, push the Module onto the Stream. Do this for each Task, X and then inject Message_Blocks into the Stream. X

Each Task then processes the Message_Block, and forwards it on to the next Task in the Stream. X

If you are not already familiar with Message_Blocks and Message_Queues, I highly suggest that you check out Tutorials 10-13. X

Streams can be used for both downstream and upstream movement of messages. Used this way mirrors closely the way System V STREAMS work. But you don't have to use them bidirectionally. In this tutorial, we only use one direction of the Stream. Down. X

This tutorial is contributed by Bob McWhirter (bob@netwrench.com) X

Kirthika's abstract:

The task implementation makes use of flags to decide on whether to close the main task or the service thread. The svc () method follows the golden rule of copying message blocks before putting them on the queue until it comes across a hang-up message. It then puts the message back on the queue for its peers to obtain it and exits.

Any message put onto the Tail module is an error. So a customised derivative of the Task class is created, which collects all the garbage messages put onto the Tail. This End_Task is put into the Stream at the start itself such that no modules whould ever follow it!

Then the other modules are pushed from the Tail-end into the Stream. This is because we are interested in writing and not reading. (Picture this to be a FIFO (queue) with head and tail nodes such that the nodes are removed from the front and put into the queue from the back)

Each module then opens up the task which spawns threads and begins to shove messgaes down the stream. Once we have got all the messages into the stream, our job is completed and we shut down the Stream.

A simple way to wade down the stream...;)

SHAR_EOF $shar_touch -am 0210221599 'page01.pre' && chmod 0644 '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 \ || $echo 'page01.pre:' 'MD5 check failed' 23c8c084825939056b1c9226d4ab54c1 page01.pre SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page01.pre'`" test 2609 -eq "$shar_count" || $echo 'page01.pre:' 'original size' '2609,' 'current size' "$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' &&

You find pretty soon that anytime you work with ACE_Task<> you X have to create a derivative. The Task.h header simply provides X that derivative with the overrides we'll need in our application.

SHAR_EOF $shar_touch -am 1012190598 'page02.pre' && chmod 0644 '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 \ || $echo 'page02.pre:' 'MD5 check failed' 4568ed757f3dbc1cebb7dc10d4768894 page02.pre SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page02.pre'`" test 231 -eq "$shar_count" || $echo 'page02.pre:' 'original size' '231,' 'current size' "$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' &&

Before we get to main() let's take a look at the Task implementation. X While we've overridden several methods, the real work is done in X the close() and svc() methods.

Notice how close() figures out if it is being called by the shutdown X of the ACE_Stream or by the exit of svc(). The magic here is X provided by the flags parameter. By handling the stream X shutdown in this way, we don't have to do anything strange in X svc(). We also don't end up with extra hangup messages in the X queue when the dust all settles down.

Like our other tutorials, svc() looks for a hangup and processes data.

SHAR_EOF $shar_touch -am 1012190598 'page03.pre' && chmod 0644 '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 \ || $echo 'page03.pre:' 'MD5 check failed' 5c35812c1251ef1e8214fa9d9a18d496 page03.pre SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page03.pre'`" test 651 -eq "$shar_count" || $echo 'page03.pre:' 'original size' '651,' 'current size' "$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' &&

As stated in the comments below, the default action of the task at the X stream tail is to treat any received data as an error. In our X implementation it will often happen that data gets through to X the tail. How, then, do we handle this without creating an X error condition? Simple: Create a custom Task for use as the X stream tail that doesn't consider it an error to receive data.

Read on...

SHAR_EOF $shar_touch -am 1012190598 'page04.pre' && chmod 0644 'page04.pre' || $echo 'restore of' 'page04.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 \ || $echo 'page04.pre:' 'MD5 check failed' c6eaa0dbd1216734dcf83f5283d433f3 page04.pre SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page04.pre'`" test 439 -eq "$shar_count" || $echo 'page04.pre:' 'original size' '439,' 'current size' "$shar_count!" fi fi # ============= page05.pre ============== if test -f 'page05.pre' && test "$first_param" != -c; then $echo 'x -' SKIPPING 'page05.pre' '(file already exists)' else $echo 'x -' extracting 'page05.pre' '(text)' sed 's/^X//' << 'SHAR_EOF' > 'page05.pre' &&

Now we come to main(). In the previous task-chain tutorial X every thread pool had to have the same number of threads. This X time around, we leverage the construction method of ACE_Stream X and ACE_Module to customize the thread-pool size in each X ACE_Task of the stream.

Remember EndTask from the previous page? We create one here and push X it into the stream to take care of cleaning up the messages. X Technically, we could have replaced the default Tail task X created by the ACE framework but it seems to make more sense to X just push our "tail" onto the stream like the other tasks. The X caveat to this method is that you must be sure you don't push() X any other Modules behind the EndTask!

Once the stream of modules containing tasks is all setup then we can X put() some data into the stream for processing. The clever use X of Task::close() makes shutting downt the stream easier than X ever. No messing with hangup messages at the application level, X just close() when you're done! What could be simpler?

SHAR_EOF $shar_touch -am 1012190598 'page05.pre' && chmod 0644 'page05.pre' || $echo 'restore of' 'page05.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 \ || $echo 'page05.pre:' 'MD5 check failed' e1c3ef1d521db6daf9e432fb5582607d page05.pre SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page05.pre'`" test 1079 -eq "$shar_count" || $echo 'page05.pre:' 'original size' '1079,' 'current size' "$shar_count!" fi fi rm -fr _sh28285 exit 0