ACE Tutorial 016

#!/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 1999-02-14 14:20 EST by . # Source directory was `/var/home/jcej/projects/ACE_wrappers/docs/tutorials/016'. # # Existing files will *not* be overwritten unless `-c' is specified. # # This shar contains: # length mode name # ------ ---------- ------------------------------------------ # 422 -rw-rw-r-- hdr # 51 -rw-rw-r-- bodies # 2917 -rw-rw-r-- page01.pre # 1351 -rw-rw-r-- page02.pre # 248 -rw-rw-r-- page03.pre # 310 -rw-rw-r-- page04.pre # 606 -rw-rw-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 _sh31855; 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 016 X ACE Tutorial 016 X Making ACE_Condition easier to use X

SHAR_EOF $shar_touch -am 1029153498 '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 \ || $echo 'hdr:' 'MD5 check failed' 34600093c989939b7a2a6806f2b18f22 hdr SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'hdr'`" test 422 -eq "$shar_count" || $echo 'hdr:' 'original size' '422,' 'current size' "$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 Condition_i.h Condition_i.cpp condition.cpp SHAR_EOF $shar_touch -am 1029153398 '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 \ || $echo 'bodies:' 'MD5 check failed' 53b96616ae101b38fd1e30b2ab8707a2 bodies SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'bodies'`" test 51 -eq "$shar_count" || $echo 'bodies:' 'original size' '51,' 'current size' "$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' && The ACE framework has quite a few objects for syncronizing your threads and even processes. We've mentioned a few in passing already: X ACE_Thread_Mutex and ACE_Barrier for instance.

Another interesting one is the ACE_Condition template. By using an ACE_Condition you can have your code wait for an arbitrary condition to occur. That condition is "embodied" in a variable of your choice. That variable can, in turn, be any data type you wish. This makes ACE_Condition much more flexible than a simple mutex, barrier or semaphore.

In this tutorial, I'll create a wrapper class around the ACE_Condition and the assorted housekeeping items necessary to make it work. I'll use a simple integer as the condition variable but keep in mind that you can use any data type you want.

Kirthika's abstract:

Pizza-delivery metaphor: (courtesy Dr.Schmidt)

Five pizza delivery boys use the same van. While the van is unavailable, the boys go to sleep. When the van returns and the keys are returned, the current user of the van nudges the other sleeping boys to wake up and fight for the keys. Once the keys are obtained and the pizza is ready and out of the kitchen, the boy with the pizza and the keys can now deliver it.

This tutorial makes use of a wrapper class around the ACE_Condition and uses a integer value as the condition. The four kinds of condition implemented are: !=, >=, <=, == by using C++ operator overloading. Guards are used within the methods to make sure that the method is thread-safe. Once the thread completes its job, it broadcasts to the waiting on it.

An ACE_Task is used to stress test the various conditions. A test object is created for each condition and the main thread waits until the condition becomes true. For instance: <= condition: Five threads are spwaned which in turn increment the condition variable, which is initialised to 1 by 2. Remember that you are waiting on the <= condition. So once 3 threads have been thru it, the value becomes 6 and the condition becomes true!

This simple example shows us how to program and use the Condition variable for synchronisation.

SHAR_EOF $shar_touch -am 0214140699 '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 \ || $echo 'page01.pre:' 'MD5 check failed' 37032e8a180a426e2677f3c2848162bb page01.pre SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page01.pre'`" test 2917 -eq "$shar_count" || $echo 'page01.pre:' 'original size' '2917,' 'current size' "$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' && We'll look first at the declaration of the wrapper class.

The way you use ACE_Condition is something like this:

First, the setup...
- Create a variable using your choice of data types
- Create a mutex that will provide thread-safe access to that variable
- Create an ACE_Condition that uses the mutex
Waiting for the condition...

Setting the condition...

the_mutex.acquire();
the_variable = some_new_value_or_state;
the_condition.signal() OR the_condition.broadcast()

The problem I have is remembering to setup everything and co-ordinate the locking, waiting and signaling. Even if I remember it all correctly it just makes my application code more complex than it should be.

To help out with that, I've created the class below to encapsulate the three elements necessary for the condition to work. I've then added methods for manipulation of the condition variable and waiting for the condition to occur.

SHAR_EOF $shar_touch -am 1029191498 '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 \ || $echo 'page02.pre:' 'MD5 check failed' d3230a58558843154d2363ce940dbb9b page02.pre SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page02.pre'`" test 1351 -eq "$shar_count" || $echo 'page02.pre:' 'original size' '1351,' 'current size' "$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' && Ok, now we'll take a look at the definition of the class. You already know how to use an ACE_Condition & it's not really that difficult. Still, imagine how much more cluttered your code would be if it had to include the mess I've got below!

SHAR_EOF $shar_touch -am 1029162998 '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 \ || $echo 'page03.pre:' 'MD5 check failed' 51c4ebc7f5c67e072fed8f76bd7be62d page03.pre SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page03.pre'`" test 248 -eq "$shar_count" || $echo 'page03.pre:' 'original size' '248,' 'current size' "$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' && We finally get to the main() application. I create a simple Task derivative that will serve as a baseclass for other objects that test specific functions of the Condition class. Notice how easy it is to integrate a Condition into the application without keeping track of three related member variables.

SHAR_EOF $shar_touch -am 1029185698 'page04.pre' && chmod 0664 '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 \ || $echo 'page04.pre:' 'MD5 check failed' a2b2c42216f88e006a18d37adcb31c1d page04.pre SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page04.pre'`" test 310 -eq "$shar_count" || $echo 'page04.pre:' 'original size' '310,' 'current size' "$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' && And that's all...

For general use, it would make sense to convert Condition into a template and get rid of some of the operators that don't make sense. Using an integer as the condition type probably isn't realistic since you could just use a semaphore or barrier for that case. Still, the Tutorial shows the basics and provides a foundation on which you can create a more useful class for your application.

SHAR_EOF $shar_touch -am 1029192198 'page05.pre' && chmod 0664 '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 \ || $echo 'page05.pre:' 'MD5 check failed' 3926547773016bf56d809fae9170625e page05.pre SHAR_EOF else shar_count="`LC_ALL= LC_CTYPE= LANG= wc -c < 'page05.pre'`" test 606 -eq "$shar_count" || $echo 'page05.pre:' 'original size' '606,' 'current size' "$shar_count!" fi fi rm -fr _sh31855 exit 0