Memory management between threads in RTEMS
Till Straumann
strauman at slac.stanford.edu
Fri Jul 20 13:36:12 UTC 2012
It means that there are no 'processes' as e.g., in unix.
Processes have independent address spaces and cannot
access each other's. Hence, there is no way for process 'A'
to overwrite and corrupt memory 'malloc()'ed by process 'B'.
RTEMS is a 'single process' with multiple threads which are
assumed to collaborate (and not try to destroy each other).
Threads under RTEMS behave like multiple threads in a
single unix program. All threads can access all of the memory
(and other resources).
HTH
- T.
On 07/20/2012 06:14 AM, m.shahverdi wrote:
> According to RTEMS POSIX API User’s Guide"RTEMS provides no memory
> protection"! so what does thismean?
>
> On Wed, Jul 18, 2012 at 8:46 PM, Gedare Bloom <gedare at rtems.org
> <mailto:gedare at rtems.org>> wrote:
>
> 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
> <mailto: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"Mosset, Robyn" <robyn at slac.stanford.edu>"Mosset, Robyn"
> <robyn at slac.stanford.edu>
> > 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 <mailto: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
> <mailto: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 <mailto: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
> <mailto: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
> <mailto: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.
> >>>
> >>> _______________________________________________
> >>> rtems-users mailing list
> >>> rtems-users at rtems.org <mailto:rtems-users at rtems.org>
> >>> http://www.rtems.org/mailman/listinfo/rtems-users
> >>
> >>
> >>
> >>
> >> --
> >>
> >> 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 <mailto:rtems-users at rtems.org>
> > http://www.rtems.org/mailman/listinfo/rtems-users
> >
>
>
>
>
> --
>
> به "هوالحی" زنده می کند؛
>
> آنسان که می میراند به "هوالممیت"..
>
> ما را به "هوالشهید" است که مدام می میراند و زنده می کند..
>
>
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