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Interprocess Communication

Interprocess Communication. CSE 380 Lecture Note 8 Insup Lee. Interprocess communication. Shared Memory Message Passing Signals. Shard Memory. Process 1. Process 2. Process 3. Shared memory. Shared Memory in Solaris.

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Interprocess Communication

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  1. Interprocess Communication CSE 380 Lecture Note 8 Insup Lee CSE 380

  2. Interprocess communication • Shared Memory • Message Passing • Signals CSE 380

  3. Shard Memory Process 1 Process 2 Process 3 Shared memory CSE 380

  4. Shared Memory in Solaris • Processes can share the same segment of memory directly when it is mapped into the address space of each sharing process • Faster communication • System calls: • int shmget(key_t key, size_t size, int shmflg) : creates a new region of shared memory or returns an existing one • void *shmat(int shmid, const void *shmaddr, int shmflg) : attaches a shared memory region to the virtual address space of the process • int shmdt(char *shmaddr):detaches a shared region • Mutual exclusion must be provided by processes using the shared memory CSE 380

  5. Message Passing message CSE 380

  6. Design Attributes • Naming • Process id, mailbox • Buffering • Size: zero, bounded, unbounded • Place: kernel space, user space • Send operation • Synchronous vs. asynchronous • Receive operation • Blocking vs. non-blocking CSE 380

  7. Interprocess Communication Message Passing Many possible naming schemes. One is direct naming: send(process_id, message)receive(process_id, buffer) Example process P1: process P2: declare x integer declare y integer . . send(P2, x) receive(P1, y) . .end process end process Effect of this communication is y := x | \ local var local var of P2 of P1 CSE 380

  8. Buffering • A buffer, with bounded-buffer synchronization, can be associated with each pair of communicating processes. • A “zero-capacity” buffer means processes must “handshake” in order to communicate. • A buffer can reside in memory of receiving process or in OS addres space. Examples: • no buffer needed P1: send(P2, x) P2: receive(P1, x) receive(P2, y) send(P1, y) • buffer needed P1: send(P2, x) P2: send(P1, x) receive(P2, y) receive(P1, y) CSE 380

  9. Mailboxes • Also known as message queues, ports • The explicit and symmetric naming of processes in direct naming • Þ Limited modularity since changing the name of a process requires changes elsewhere, i.e., in definitions of other processes P mbox R Q P or Q call send(mbox-id, message) R calls receive(mbox-id, message) CSE 380

  10. Mailbox Issues • communication is no longer “point-to-point”; e.g., a message received by R may be from P or Q • “fair merge” property --- do not starve Q from queuing messages by allowing continual queuing of messages only from P • natural extension to multiple receivers. Possible semantics: • Multicast to all in the group gets the same message • The first receiver removes it • Bulletin board: each receiver decides CSE 380

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