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Re: Re: Threads: Free to wrong pool

by P0w3rK!d (Pilgrim)
on Jun 06, 2003 at 15:02 UTC ( #263701=note: print w/replies, xml ) Need Help??


in reply to Re: Threads: Free to wrong pool
in thread Threads: Free to wrong pool

BrowserUK et al,

It appears that I cannot run the perl program in question with threads that I turn on and off. I create them, they run, they join, then I try to do it again and somewhere in between it blows up. Here is a similar example to what I am trying to do (and yes..it does compile). Also, attached is a modified version that blows up. Please tell me why you think it blows up? :)

-P0w3rK!d

#!/home/sam/bin/perl =pod =head1 NAME elevator.pl - a multi-threaded elevator simulator =head1 SYNOPSIS elevator.pl --elevators 3 --people 10 --floors 10 =head1 DESCRIPTION This program simulates a building with elevators and people. The people get on the elevators and ride them to their destinations. Then they get off and wait a while. Finally, the people travel to the ground floor and leave the building. Statistics are collected measuring the efficiency of the elevators from the perspective of the people. =head1 OPTIONS The following options are available to control the simulation: --elevators - number of elevators in the building (default 3) --floors - number of floors in the building (default 20) --people - number of people to create (default 10) --elevator-speed - how long an elevator takes to travel one floor, in seconds (default 1) --elevator-wait - how long an elevator waits at a floor for passeng +ers, in seconds (default 2) --people-freq - how many people are created per second (default 2 +) --people-wait - how long a person spends on their destination flo +or, in seconds (default 5) =head1 AUTHOR Sam Tregar <sam@tregar.com> =head1 COPYRIGHT AND LICENSE Copyright (C) 2002 Sam Tregar This program is free software; you can redistribute it and/or modify it under the same terms as Perl 5 itself. =head1 SEE ALSO L<threads> =cut use 5.008; # 5.8 required for stable threading use strict; # Amen use warnings; # Halleluja use threads; # pull in threading routines use threads::shared; # and variable sharing routines # get options from command line with Getopt::Long use Getopt::Long; our $NUM_ELEVATORS = 3; our $NUM_FLOORS = 20; our $NUM_PEOPLE = 10; our $ELEVATOR_SPEED = 1; our $ELEVATOR_WAIT = 2; our $PEOPLE_FREQ = 2; our $PEOPLE_WAIT = 5; GetOptions("elevators=i" => \$NUM_ELEVATORS, "floors=i" => \$NUM_FLOORS, "people=i" => \$NUM_PEOPLE, "elevator-speed=i" => \$ELEVATOR_SPEED, "elevator-wait=i" => \$ELEVATOR_WAIT, "people-freq=i" => \$PEOPLE_FREQ, "people-wait=i" => \$PEOPLE_WAIT ); die "Usage $0 [options]\n" if @ARGV; # Building State our %DOOR : shared; # a door for each elevator on each floor our @BUTTON : shared; # a button for each floor to call the elevators our %PANEL : shared; # a panel of buttons in each elevator for each f +loor # Simulation State our $FINISHED : shared = 0; # used to signal the elevators to shut do +wn # run the simulator init_building(); init_elevator(); init_people(); finish(); exit 0; # initialize building state sub init_building { # set all indicators to 0 to start the simulation for my $floor (0 .. $NUM_FLOORS - 1) { $BUTTON[$floor] = 0; for my $elevator (0 .. $NUM_ELEVATORS - 1) { $PANEL{"$elevator.$floor"} = 0; $DOOR{"$elevator.$floor"} = 0; } } } # create elevator threads sub init_elevator { our @elevators; for (0 .. $NUM_ELEVATORS - 1) { # pass each elevator thread a unique elevator id push @elevators, threads->new(\&Elevator::run, id => $_); } } # create people threads sub init_people { our @people; for (0 .. $NUM_PEOPLE - 1) { # pass each person thread a unique person id and a random # destination push @people, threads->new(\&Person::run, id => $_, dest => int(rand($NUM_FLOORS - 2)) ++ 1); # pause if we've launched enough people this second sleep 1 unless $_ % $PEOPLE_FREQ; } } # finish the simulation - join all threads and collect statistics sub finish { our (@people, @elevators); # join the people threads and collect statistics my ($total_wait, $total_ride, $max_wait, $max_ride) = (0,0,0,0); foreach my $person (@people) { my ($wait1, $wait2, $ride1, $ride2) = $person->join; $total_wait += $wait1 + $wait2; $total_ride += $ride1 + $ride2; $max_wait = $wait1 if $wait1 > $max_wait; $max_wait = $wait2 if $wait2 > $max_wait; $max_ride = $ride1 if $ride1 > $max_ride; $max_ride = $ride2 if $ride2 > $max_ride; } # tell the elevators to shut down { lock $FINISHED; $FINISHED = 1; } $_->join for @elevators; # print out statistics print "\n", "-" x 72, "\n\nSimulation Complete\n\n", "-" x 72, "\n +\n"; printf "Average Wait Time: %6.2fs\n", ($total_wait / ($NUM_PEOPL +E * 2)); printf "Average Ride Time: %6.2fs\n\n", ($total_ride / ($NUM_PEOPL +E * 2)); printf "Longest Wait Time: %6.2fs\n", $max_wait; printf "Longest Ride Time: %6.2fs\n\n", $max_ride; } ####################################################### # The Elevator Class # ####################################################### package Elevator; use threads; # pull in threading routines use threads::shared; # and variable sharing routines # state enumeration use constant STARTING => 0; use constant STOPPED => 1; use constant GOING_UP => 2; use constant GOING_DOWN => 3; # create a new Elevator object sub new { my $pkg = shift; my $self = { state => STARTING, floor => 0, dest => 0, @_, }; return bless($self, $pkg); } # run an Elevator thread, takes a numeric id as an argument and # creates a new Elevator object sub run { my $self = Elevator->new(@_); my $id = $self->{id}; # run until simulation is finished while (1) { # get next destination $self->{dest} = $self->next_dest; # stopped? if ($self->{dest} == $self->{floor}) { # state transition to STOPPED? if ($self->{state} != STOPPED) { print "Elevator $id stopped at floor $self->{dest}.\n" +; $self->{state} = STOPPED; } # wait for passengers $self->open_door; sleep $ELEVATOR_WAIT; } elsif ($self->{dest} > $self->{floor}) { # state transition to GOING UP? if ($self->{state} != GOING_UP) { print "Elevator $id going up to floor $self->{dest}.\n +"; $self->{state} = GOING_UP; $self->close_door; } # travel to next floor up sleep $ELEVATOR_SPEED; $self->{floor}++; } else { # state transition to GOING DOWN? if ($self->{state} != GOING_DOWN) { print "Elevator $id going down to floor $self->{dest}. +\n"; $self->{state} = GOING_DOWN; $self->close_door; } # travel to next floor down sleep $ELEVATOR_SPEED; $self->{floor}--; } # simulation over? { lock $FINISHED; return if $FINISHED; } } } # choose the next destination floor by looking at BUTTONs and PANELs sub next_dest { my $self = shift; my ($id, $state, $floor) = @{$self}{('id', 'state', 'floor')}; lock @BUTTON; lock %PANEL; # look up from current floor unless travelling down. Head # for the first activated button or panel if ($state == GOING_UP || $state == STOPPED) { for ($floor .. ($NUM_FLOORS - 1)) { return $_ if $BUTTON[$_] or $PANEL{"$id.$_"}; } } # look down from current floor for ($_ = $floor; $_ >= 0; $_--) { return $_ if $BUTTON[$_] or $PANEL{"$id.$_"}; } # look up again if going down and nothing found if ($state == GOING_DOWN) { for ($floor .. ($NUM_FLOORS - 1)) { return $_ if $BUTTON[$_] or $PANEL{"$id.$_"}; } } # stop if nothing found return $floor; } # open the elevator doors sub open_door { my $self = shift; lock %DOOR; $DOOR{"$self->{id}.$self->{floor}"} = 1; cond_broadcast(%DOOR); } # close the elevator doors sub close_door { my $self = shift; lock %DOOR; $DOOR{"$self->{id}.$self->{floor}"} = 0; } ####################################################### # The Person Class # ####################################################### package Person; use threads; # pull in threading routines use threads::shared; # and variable sharing routines # create a new Person object sub new { my $pkg = shift; my $self = { @_, floor => 0, elevator => 0 }; return bless($self, $pkg); } # run a Person thread, takes an id and a destination floor as # arguments. Creates a Person object. sub run { my $self = Person->new(@_); my $id = $self->{id}; # wait for elevator going up my $wait_start1 = time; $self->wait; my $wait1 = time - $wait_start1; # board the elevator, wait for arrival destination floor and get o +ff my $ride_start1 = time; $self->board; $self->ride; $self->disembark; my $ride1 = time - $ride_start1; # spend some time on the destination floor and then head back sleep $PEOPLE_WAIT; $self->{dest} = 0; # wait for elevator going down my $wait_start2 = time; $self->wait; my $wait2 = time - $wait_start2; # board the elevator, wait for arrival destination floor and get o +ff my $ride_start2 = time; $self->board; $self->ride; $self->disembark; my $ride2 = time - $ride_start2; # return wait and ride times return ($wait1, $wait2, $ride1, $ride2); } # wait for an elevator sub wait { my $self = shift; print "Person $self->{id} waiting on floor 1 for elevator ", "to floor $self->{dest}.\n"; while(1) { $self->press_button(); lock(%DOOR); cond_wait(%DOOR); for (0 .. $NUM_ELEVATORS - 1) { if ($DOOR{"$_.$self->{floor}"}) { $self->{elevator} = $_; return; } } } } # signal an elevator to come to this floor sub press_button { my $self = shift; lock @BUTTON; $BUTTON[$self->{floor}] = 1; } # get on an elevator sub board { my $self = shift; lock @BUTTON; lock %PANEL; $BUTTON[$self->{floor}] = 0; $PANEL{"$self->{elevator}.$self->{dest}"} = 1; } # ride to the destination sub ride { my $self = shift; print "Person $self->{id} riding elevator $self->{elevator} ", "to floor $self->{dest}.\n"; lock %DOOR; cond_wait(%DOOR) until $DOOR{"$self->{elevator}.$self->{dest}"}; } # get off the elevator sub disembark { my $self = shift; print "Person $self->{id} getting off elevator $self->{elevator} " +, "at floor $self->{dest}.\n"; lock %PANEL; $PANEL{"$self->{elevator}.$self->{dest}"} = 0; $self->{floor} = $self->{dest}; }
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Modified example below>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
#!/home/sam/bin/perl =pod =head1 NAME elevator.pl - a multi-threaded elevator simulator =head1 SYNOPSIS elevator.pl --elevators 3 --people 10 --floors 10 =head1 DESCRIPTION This program simulates a building with elevators and people. The people get on the elevators and ride them to their destinations. Then they get off and wait a while. Finally, the people travel to the ground floor and leave the building. Statistics are collected measuring the efficiency of the elevators from the perspective of the people. =head1 OPTIONS The following options are available to control the simulation: --elevators - number of elevators in the building (default 3) --floors - number of floors in the building (default 20) --people - number of people to create (default 10) --elevator-speed - how long an elevator takes to travel one floor, in seconds (default 1) --elevator-wait - how long an elevator waits at a floor for passeng +ers, in seconds (default 2) --people-freq - how many people are created per second (default 2 +) --people-wait - how long a person spends on their destination flo +or, in seconds (default 5) =head1 AUTHOR Sam Tregar <sam@tregar.com> =head1 COPYRIGHT AND LICENSE Copyright (C) 2002 Sam Tregar This program is free software; you can redistribute it and/or modify it under the same terms as Perl 5 itself. =head1 SEE ALSO L<threads> =cut use 5.008; # 5.8 required for stable threading use strict; # Amen use warnings; # Halleluja use threads; # pull in threading routines use threads::shared; # and variable sharing routines # get options from command line with Getopt::Long use Getopt::Long; our $NUM_ELEVATORS = 5; our $NUM_FLOORS = 20; our $NUM_PEOPLE = 10; our $ELEVATOR_SPEED = 1; our $ELEVATOR_WAIT = 2; our $PEOPLE_FREQ = 2; our $PEOPLE_WAIT = 5; GetOptions("elevators=i" => \$NUM_ELEVATORS, "floors=i" => \$NUM_FLOORS, "people=i" => \$NUM_PEOPLE, "elevator-speed=i" => \$ELEVATOR_SPEED, "elevator-wait=i" => \$ELEVATOR_WAIT, "people-freq=i" => \$PEOPLE_FREQ, "people-wait=i" => \$PEOPLE_WAIT ); die "Usage $0 [options]\n" if @ARGV; # Building State our %DOOR : shared; # a door for each elevator on each floor our @BUTTON : shared; # a button for each floor to call the elevators our %PANEL : shared; # a panel of buttons in each elevator for each f +loor # Simulation State our $FINISHED : shared = 0; # used to signal the elevators to shut do +wn # run the simulator init_building(); while() { print "Running...\n"; init_elevator(); #init_people(); sleep(5); finish(); } exit 0; # initialize building state sub init_building { # set all indicators to 0 to start the simulation for my $floor (0 .. $NUM_FLOORS - 1) { $BUTTON[$floor] = 0; for my $elevator (0 .. $NUM_ELEVATORS - 1) { $PANEL{"$elevator.$floor"} = 0; $DOOR{"$elevator.$floor"} = 0; } } } # create elevator threads sub init_elevator { our @elevators; for (0 .. $NUM_ELEVATORS - 1) { # pass each elevator thread a unique elevator id push @elevators, threads->new(\&Elevator::run, id => $_); } } # finish the simulation - join all threads and collect statistics sub finish { our (@elevators); { lock $FINISHED; $FINISHED = 1; } $_->join for @elevators; } ####################################################### # The Elevator Class # ####################################################### package Elevator; use threads; # pull in threading routines use threads::shared; # and variable sharing routines # state enumeration use constant STARTING => 0; use constant STOPPED => 1; use constant GOING_UP => 2; use constant GOING_DOWN => 3; # create a new Elevator object sub new { my $pkg = shift; my $self = { state => STARTING, floor => 0, dest => 0, @_, }; return bless($self, $pkg); } # run an Elevator thread, takes a numeric id as an argument and # creates a new Elevator object sub run { my $self = Elevator->new(@_); my $id = $self->{id}; # run until simulation is finished while (1) { # get next destination $self->{dest} = $self->next_dest; # stopped? if ($self->{dest} == $self->{floor}) { # state transition to STOPPED? if ($self->{state} != STOPPED) { print "Elevator $id stopped at floor $self->{dest}.\n" +; $self->{state} = STOPPED; } # wait for passengers $self->open_door; sleep $ELEVATOR_WAIT; } elsif ($self->{dest} > $self->{floor}) { # state transition to GOING UP? if ($self->{state} != GOING_UP) { print "Elevator $id going up to floor $self->{dest}.\n +"; $self->{state} = GOING_UP; $self->close_door; } # travel to next floor up sleep $ELEVATOR_SPEED; $self->{floor}++; } else { # state transition to GOING DOWN? if ($self->{state} != GOING_DOWN) { print "Elevator $id going down to floor $self->{dest}. +\n"; $self->{state} = GOING_DOWN; $self->close_door; } # travel to next floor down sleep $ELEVATOR_SPEED; $self->{floor}--; } # simulation over? { lock $FINISHED; return if $FINISHED; } } } # choose the next destination floor by looking at BUTTONs and PANELs sub next_dest { my $self = shift; my ($id, $state, $floor) = @{$self}{('id', 'state', 'floor')}; lock @BUTTON; lock %PANEL; # look up from current floor unless travelling down. Head # for the first activated button or panel if ($state == GOING_UP || $state == STOPPED) { for ($floor .. ($NUM_FLOORS - 1)) { return $_ if $BUTTON[$_] or $PANEL{"$id.$_"}; } } # look down from current floor for ($_ = $floor; $_ >= 0; $_--) { return $_ if $BUTTON[$_] or $PANEL{"$id.$_"}; } # look up again if going down and nothing found if ($state == GOING_DOWN) { for ($floor .. ($NUM_FLOORS - 1)) { return $_ if $BUTTON[$_] or $PANEL{"$id.$_"}; } } # stop if nothing found return $floor; } # open the elevator doors sub open_door { my $self = shift; lock %DOOR; $DOOR{"$self->{id}.$self->{floor}"} = 1; cond_broadcast(%DOOR); } # close the elevator doors sub close_door { my $self = shift; lock %DOOR; $DOOR{"$self->{id}.$self->{floor}"} = 0; }

update (broquaint): added <readmore> tag

Replies are listed 'Best First'.
Re: Re: Re: Threads: Free to wrong pool
by BrowserUk (Pope) on Jun 06, 2003 at 15:39 UTC

    Geez. One copy and an indication of the 4 lines you had changed and how would have been more than enough!

    The reason the modified code fails, is because it wasn't designed to be run in a loop, and you have made no changes to allow it to run in a loop.

    The first problem, one of several, is that the our'd array @elevators is initialised in init_elevator() with the handles of the threads used to runs the elevators are pushed onto this array, but they are never removed. So on the second run, a second set of thread handles are push onto the array, and when finish() is called, it attempts to join to all the threads in the array, accept the handles for the first set are still there, but the associated thread are not. Then went away the first time finish() was called. So you are calling join on non-existant threads, so it blows up in your face.

    It probably shouldn't blow up, but it is still programmer error. When you re-start the code, you need to ensure that all the globals, our vars, are re-set to ther initial state.

    There are many other globals used. There are several other problems with the design of this program too. Not a great design, but it is meant as a demonstration of the concepts rather than working level code.


    Examine what is said, not who speaks.
    "Efficiency is intelligent laziness." -David Dunham
    "When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller


      Sorry about the example. This is not my code. I wsa trying to use it as an example to figure out why my threads were crashing. Thanks for your efforts :)

        If you posted your code then you might get help.


        Examine what is said, not who speaks.
        "Efficiency is intelligent laziness." -David Dunham
        "When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller


Re: Re: Re: Threads: Free to wrong pool
by P0w3rK!d (Pilgrim) on Jun 06, 2003 at 15:39 UTC
    I tried running #2 and put a breakpoint at finish(). The threads were running fine:

    When I stepped over finish, the application crashed as follows:

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