IPC - Inter-process communication
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Semaphores : Provides a synchronizing mechanism for processes that are accessing the same resources. No data is passed with a semaphore ; it simply coordinates access to shared ressources.
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Shared Memory : Proccesses can exchange values in the shared memory One process will create a portion of memory wich other process can access.
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Message Queue : It is an structured amd ordered list of memory segments where proccesses store or retrieve data.
key_t ftok(char *pathname, int proj_id);
create IPC identifier from path name
int shmget(key_t key, size_t size, int shmflg);
will get or create a segment of shared memory
void *shmat(int shmid, const void *shmaddr, int shmflg);
will map the segment of shared memory
int shmctl(int shmid, int cmd, struct shmid_ds *buf);
will apply the cmd instruction, like remove the memory.
int semget (key_t key, int nsems, int semflg);
will get or create a sepahore linked to the key
int semop(int semid, struct sembuf *sops, unsigned nsops);
atomic array of operations on a semaphore set.
int semctl (int semid, int semno, int cmd, ...);
control operations on a semaphore set. Like remove semaphore or set a value.
int msgget(key_t key, int msgflg);
will get or create a message queue.
int msgctl(int msqid, int cmd, struct msqid_ds *buf);
will apply the cmd instruction, like remove the message queue.
int msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg);
will send a message on the Message Queue
ssize_t msgrcv(int msqid, void *msgp, size_t msgsz, long msgtyp, int msgflg);
will receive a message on the Message Queue