I am trying to write a C++ program to delete the shared memory segments. I know it can be done from cmd prompt using
ipcs -m | awk '{ print $2 }' | xargs ipcrm -m
But I am trying to do it using C++ so that I create a shared memory garbage collector.
The idea is to delete shared memory segments that are not attached to any process( nattach ==0) or the status == NULL
I finally have the the answer to my own question. It can be done using shmctl flags.
shmctl(0,SHM_INFO,&shm_info);
gives number of segments currently present.
shmctl(i , SHM_STAT , &shm_segment)
gives the segment id
it can also be accessed by shm_segment.shm_id
#include <sys/shm.h>
int delete_segment(int seg_id){
if ((shmctl(seg_id,IPC_RMID,0))==-1){
std::cout<<" ERROR(C++)with shmctl(IPC_RMID): "<<strerror(errno)<<std::endl;
return -1;
}else//on success
return 0;
}
void clean_segments(){
struct shmid_ds shm_info;
struct shmid_ds shm_segment;
int max_id = shmctl(0,SHM_INFO,&shm_info);
if (max_id>=0){
for (int i=0;i<=max_id;++i) {
int shm_id = shmctl(i , SHM_STAT , &shm_segment);
if (shm_id<=0)
continue;
else if (shm_segment.shm_nattch==0){
delete_segment(shm_id);
}
}
}
return result;
}