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How to synchronize between processes
In order to synchronize the task between processes the user must have some mechanism to communicate the state of the processes. The user can use the following pattern to achieve the same using semaphore:
- Create a semaphore using semget.
- When a process wants to synchronize with some other process, the first process can create the semaphore and set the semval with some condition.
- Once the other process has finished its task, satisfy the condition for which the other process is waiting for.
- Delete the semaphore.
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Example
Process 1:
#include <sys/sem.h>
#define SEM_KEY 1000
int main()
{
int semid = semget(SEM_KEY, 1, IPC_CREAT);
int ret = semctl(semid, 0, SETVAL, 1);
struct sembuf st = {0, 0, 0};
ret = semop(semid, &st, 1); // process -1 is blocked over here.
ret = semctl(semid, 1, IPC_RMID);
return 0;
}
Process 2:
#include <sys/sem.h>
#define SEM_KEY 1000
int main()
{
int semid = semget(SEM_KEY, 1, IPC_CREAT);
struct sembuf st = {0, -1, 0};
TInt ret = semop(semid, &st, 1); // unblocking the process 1
return 0;