90 lines
2.6 KiB
C
90 lines
2.6 KiB
C
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/***********************************************************************************
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Code Inherited from Anon
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Massively Modified by Prawar Poudel, 3 Feb 2020 (pp0030@uah.edu)
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************************************************************************************/
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/types.h>
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#include <sys/ipc.h>
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#include <sys/shm.h>
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#include "header.h"
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/*
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Process C creates a shared memory segment
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Process C attaches a pointer to the shared memory segment created
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.. then it writes an integer value and a character value to it
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.. it prints the character value for the integer number of times
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.. then it waits on Process D to update the value of integer and the character
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.. .. this will be indicated by the flag value being set to 1 by Process D
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.. after the same printing operation is done, Process C will detach and delete the shared memory segment
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*/
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main(void)
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{
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int i, id ;
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struct info *ctrl;
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// create the shared memory segment
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// .. id is the file identifier of the shared memory segment
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// .. if the key is shared, any process can attach to this shared memory segment
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// .. 0666 is the file permission for the shared memory segment
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if ( (id = shmget( key,MSIZ,IPC_CREAT | 0666) ) < 0 )
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{
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//error…;
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printf("error 1\n");
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exit(1) ;
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}
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// attach a local pointer to the shared memory segment created
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// .. exit if fails
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if ( (ctrl = (struct info *) shmat( id, 0, 0)) <= (struct info *) (0) ){
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//error … ;
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printf("error 2\n");
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exit(1) ; }
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// put some initial data in the shared memory so that we will just print the things before Process D is run
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ctrl->c = 'a';
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ctrl->length = 10;
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ctrl->flag = 0;
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// print the character ctrl->c for ctrl->length times in a single line
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for (i = 0 ; i <ctrl->length ; i++ )
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{
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putchar (ctrl->c);
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putchar (' ');
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}
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putchar('\n');
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// flushing stdout just in case
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fflush(stdout);
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// signal Process D that Process C is ready for next round, which will be printed below
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ctrl->flag = 2;
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// wait for the flag to be set in processB to 1
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// .. flag is 0 right now
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// .. once processB starts to run, it will set the flag to 1
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while(ctrl->flag!=1);
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// print the character ctrl->c for ctrl->length times in a single line
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for (i = 0 ; i <ctrl->length ; i++ )
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{
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putchar (ctrl->c);
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putchar (' ');
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}
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putchar ('\n');
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// flushing stdout just in case
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fflush(stdout);
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//now detach the pointer from the shared memory
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shmdt(ctrl);
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//let us delete the shared memory
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shmctl(id,IPC_RMID,NULL);
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//job done
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}
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