embedded - Semaphore in Ada -

this assignment , have been asked implement semaphore in ada description below.

however have implemented semaphore.adb , called semaphore in producerconsumer_sem.adb created.

i output following.

1. i'm not sure if initialization of semaphore correct s: countingsemaphore(1,1);.

2. i don't know call s.wait , s.signal randomly called s.wait before producer put item in buffer x := i; , s.signal after x := i;. correct way?

producer-consumer problem program producerconsumer.adb implements non-reliable implemen- tation of producer-consumer problem, data lost. in following, use 3 different communication mechanisms achieve reliable implementation of producer-consumer problem.

semaphore

the ada language not directly provide library functions semaphore. however, semaphores can implemented means of protected object. create package specification semaphore in file semaphores.ads , corresponding package body in file semaphores.adb implements counting semaphore. skeletons package available on course page.

use semaphore package reliable implementation of producer- consumer problem. modify file producerconsumer.adb , save final code producerconsumer_sem.adb. in order use semaphore package shall installed in same directory producerconsumer_sem.adb. can accessed by

with semaphores; use semaphores;

the output:

output: 1 1 1 2 2 3 4 4 5 6 6 7 7 8 9 9 9 10 11 11 11 12 12 13 13 13 14 15 15 16 16 17 18 18 18 19 20 20 21 21 22 22 23 24 24 24 24 25 25 26 27 27 28 29 29 30 30 31 31 32 32 33 33 33 34 35 35 35 36 36 37 37 37 38 38 38 39 40 40 40

the package

package semaphores    protected type countingsemaphore(max: natural; initial: natural)        entry wait;       entry signal;    private       count : natural := initial;       maxcount : natural := max;    end countingsemaphore; end semaphores; 

the semaphore implemented semaphores.adb.

package body semaphores    protected body countingsemaphore    entry wait when count > 0     begin     count := count - 1;      end wait;       entry signal when count < maxcount     begin     count := count + 1;      end signal;    end countingsemaphore; end semaphores; 

the producerconsumer_sem.adb

with ada.text_io; use ada.text_io;  ada.real_time; use ada.real_time;  ada.numerics.discrete_random;  semaphores; use semaphores;  procedure producerconsumer_sem     x : integer; -- shared variable    n : constant integer := 40; -- number of produced , comsumed variables     s: countingsemaphore(1,1);    --s1: countingsemaphore(1,1);     pragma volatile(x); -- volatile object reads , updates of                        -- object whole performed directly                        -- memory (ada reference manual, c.6)     --random delays    subtype delay_interval integer range 50..250;    package random_delay new ada.numerics.discrete_random    (delay_interval);    use random_delay;    g : generator;     task producer;     task consumer;     task body producer       next : time;    begin       next := clock;       in 1..n loop          -- write x          s.wait;          x := i;          s.signal;          --next 'release' in 50..250ms          next := next + milliseconds(random(g));          put_line(integer'image(x));          delay until next;       end loop;    end;     task body consumer       next : time;    begin       next := clock;       in 1..n loop          -- read x          s.wait;          put_line(integer'image(x));          s.signal;          next := next + milliseconds(random(g));          delay until next;       end loop;    end;  begin -- main task      null; end producerconsumer_sem; 

on macos, fsf gcc 7.1.0 , gnat gpl 2017, changed put_lines puts , got pretty-much answer state in question.

the question says create semaphore.ads, .adb. work on windows, , may work on macos, won’t work on linux, because of gnat’s file naming convention (see end of this; it’s idea habit of using lower-case file names).

if want ensure 1 task has access x @ time, don’t think there’s wrong wait, signal calls, though when put delay 0.1 @ beginning of producer, first value output 151619216 (because x isn’t initialized). however! if point communicate 1 update x @ time (as implied names producer/consumer), should

• initialize semaphore count of 0 (and max of 1). makes binary semaphore.
• in consumer, wait (i.e. remove signal)
• in producer, signal (i.e. remove wait). also, remove put avoid confusion!