Memory management between threads in RTEMS
Gedare Bloom
gedare at rtems.org
Wed Jul 18 16:16:38 UTC 2012
Hi,
You are right to have some concern because your global variables will
need to be locked somehow (posix mutex/semaphore) since they are
accessed by both your 'main' task and the pthread that is created.
This is a correctness problem; without locking this program's behavior
is poorly defined I would guess. I assume that sharing the global
variables between 'main' and the spawned thread is the desired
behavior.
-Gedare
On Wed, Jul 18, 2012 at 11:58 AM, m.shahverdi <sspardis2 at gmail.com> wrote:
> This is my application that is written in C,I write the main code till now.
> this app is an elevator that goes up and down in a 4 floors building:
>
>
> #include<stdio.h>
> #include<stdlib.h>
> #include<string.h>
> #include<stdbool.h>
> #include<time.h>
> #include <sys/time.h>
> #include <sys/types.h>
> #include <unistd.h>
>
>
> #include <signal.h>
>
> void handler(int signo)
> {
> return;
> }
>
>
> typedef struct person prs;
> int elevator_run();
> struct person
> {
> int place;
> int distination;
> char direction;
> bool inout;// in:true,out:false
> bool exit;//if person exits true
> prs * next;
> };
> int stage[5];///////to know stop in which level
> int up_down;///////to know direct 1 for up 0 for down 2 for none
> int stop_move;/////to know if elevator is stop or no stop 0 move 1
> int current_place;
> int distination;
> time_t base;
> int xx;
> int main()
> {
> int place;
> int direct;
> int counter_in=0;
> int counter_out=0;
> int in_out;////in=1;out=0
> int dis;///to get distination of person in elevator
> prs* headin;
> prs* headout;
> prs*newnode;
> prs*nextnode;
> prs*node;
> headin=(prs*)malloc(sizeof(prs));
> headout=(prs*)malloc(sizeof(prs));
> pthread_t thread_id;
>
> pthread_create(&thread_id, NULL, elevator_run, NULL);
> struct sigaction sa;
>
> sa.sa_handler = handler;
> sigemptyset(&sa.sa_mask);
> sa.sa_flags = 0;
> sigaction(SIGALRM, &sa, NULL);
>
>
>
> if(headin==NULL)
> {
> printf("\nError in memory allocation!\n ");
> return 1;
> }
> if(headout==NULL)
> {
> printf("\nError in memory allocation!\n ");
> return 1;
> }
> int update;
> printf("This is elevator stopped at ground \n tell us your place and
> distination ");
> while(1)
> {
> update=0;
> alarm(1);
>
> if (scanf("%d", &in_out) == 1)
> {
> alarm(0); // cancel the alarm
> }
> else
> {
> continue;
> }
> // scanf("% d", & in_out);
>
>
>
> if (in_out==1)
> {
> scanf("%d",& dis);
> if(current_place==distination)
> {
> update=1;
> distination=dis;
> }
> else if((up_down==1 && distination<dis) ||(up_down==0 &&
> distination>dis))
> {
> update=1;
> stage[distination]=1;
> distination=dis;
> }
> else if((up_down==1 && current_place<dis<distination)
> ||(up_down==0 && distination<dis<current_place))
> stage[dis]=1;
> else
> {
> newnode=(prs*)malloc(sizeof(prs));
> if(newnode==NULL)
> {
> printf("\nError in memory allocation!\n ");
> return 1;
> }
> counter_in++;
> newnode->exit=false;
> newnode->distination=dis;
> newnode->next=headin->next;
> headin->next=newnode;
>
> }
> }
> else {
> scanf("%d %d",& place,& direct);
> if(direct=='q')
> return 1;
> if(stop_move==0){
> distination = place;
> printf("/////");}
> else {
> if(direct==up_down &&((up_down==1&&
> current_place<=place<=distination) ||(up_down==0&&
> current_place>=place>=distination)))
> stage[place]=1;
> if(direct==up_down && ((up_down==1 && place > distination) ||
> (up_down==0 && place < distination)))
> {
> stage[distination]=1;
> distination=place;
> update=1;
> }
> else
> {
> newnode=(prs*)malloc(sizeof(prs));
> if(newnode==NULL)
> {
> printf("\nError in memory allocation!\n ");
> return 1;
> }
> counter_out++;
> newnode->exit=false;
> newnode->next=headin->next;
> headin->next=newnode;
> newnode->place=place;
> }
>
> }
> }
> }
> }
>
>
> int elevator_run()
> {
>
> time_t current;
> int i;
> int y=0;
> //float x=1;
> for(i=0;i<5;i++)
> stage[i]=0;
> up_down=1;
> stop_move=0;/////to know if elevator is stop or no
> current_place=0;
> distination=0;
>
> while(1)
> {
>
> if(stop_move==1)
> {
> if(up_down==1)
> {
>
> current=time(NULL);
>
> if(current==base + 5)
> {
> base=current;
> y=y+1;
> }
> // printf("y = %f" ,y);
> }
> else
> {
> current=time(NULL);
>
> if(current==base + 5)
> {
> base=current;
> y=y-1;
> }
> }
> }
> if(stop_move==0 && distination > current_place)
> {
> stop_move=1;
> base=time(NULL);
> up_down=1;
> printf("salam");
> }
> if(stop_move==0 && distination < current_place)
> {
> stop_move=1;
> base=time(NULL);
> up_down=0;
> }
>
> if(y == 0) {current_place=0;if(distination==0) stop_move=0;}
> if(y == 1 && current_place !=1) { printf("place1"); current_place=1;
> if(distination==1) stop_move=0;}
> if(y == 2 && current_place != 2)
> {current_place=2;printf("place2");if(distination==2) stop_move=0;}
> if(y == 3 && current_place != 3)
> {current_place=3;printf("place3");if(distination==3) stop_move=0;}
> if(y == 4 && current_place != 4)
> {current_place=4;printf("place4");if(distination==4) stop_move=0;}
>
>
> }
> }
>
> On Wed, Jul 18, 2012 at 8:11 PM, Till Straumann <strauman at slac.stanford.edu>
> wrote:
>>
>> Maybe you could share some example code so that we understand
>> what exactly you're trying to do?
>>
>> T.
>>
>>
>> On 07/18/2012 10:37 AM, m.shahverdi wrote:
>>
>> These two threads have some common fields that I use mutex on these fields
>> but in general I read in c_user document of RTEMS that this OS has a flat
>> memory and I'm worry about unsafe access to memory that each thread allocate
>> in the beginning of execution.
>>
>> On Wed, Jul 18, 2012 at 7:42 PM, Thomas Doerfler
>> <Thomas.Doerfler at embedded-brains.de> wrote:
>>>
>>> Hi,
>>>
>>> funny topic: one question, many different answers, none of them is
>>> wrong ;-)
>>>
>>> Maybe you can specify, what you expect from a "memory protection"
>>> mechanism:
>>> - A way to synchronize two threads, so only one is allowed to
>>> access/write to a memory area?
>>> - A way to detect, when a thread inadvertedly tries to access/write to
>>> another thread's private area?
>>> - Something different?
>>>
>>> wkr,
>>>
>>> Thomas.
>>>
>>> Am 18.07.2012 16:20, schrieb m.shahverdi:
>>> > Hi, I have an application with two threads but I don't know how to
>>> > protect memory of each thread against other thread.please help me.
>>> >
>>> > thanks
>>> >
>>> >
>>> >
>>> > _______________________________________________ rtems-users mailing
>>> > list rtems-users at rtems.org
>>> > http://www.rtems.org/mailman/listinfo/rtems-users
>>> >
>>>
>>>
>>> --
>>> IMD Ingenieurbuero fuer Microcomputertechnik
>>> Thomas Doerfler Herbststrasse 8
>>> D-82178 Puchheim Germany
>>> email: Thomas.Doerfler at imd-systems.de
>>> PGP public key available on request
>>>
>>>
>>> --
>>> --------------------------------------------
>>> embedded brains GmbH
>>> Thomas Doerfler
>>> Obere Lagerstrasse 30
>>> D-82178 Puchheim
>>> Germany
>>> email: Thomas.Doerfler at embedded-brains.de
>>> Phone: +49-89-18908079-2
>>> Fax: +49-89-18908079-9
>>> PGP: Public key available on request.
>>>
>>> Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
>>>
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>>
>>
>>
>>
>> --
>>
>> به "هوالحی" زنده می کند؛
>>
>> آنسان که می میراند به "هوالممیت"..
>>
>> ما را به "هوالشهید" است که مدام می میراند و زنده می کند..
>>
>>
>>
>>
>
>
>
> --
>
> به "هوالحی" زنده می کند؛
>
> آنسان که می میراند به "هوالممیت"..
>
> ما را به "هوالشهید" است که مدام می میراند و زنده می کند..
>
>
>
> _______________________________________________
> rtems-users mailing list
> rtems-users at rtems.org
> http://www.rtems.org/mailman/listinfo/rtems-users
>
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