1. Mark Stanovich Operating Systems COP 4610

2. Primitives to Build Distributed Applications send and receive Used to synchronize cooperating processes running on different machines Communicate through mailboxes (ports) Temporary holding areas for messages Atomic operations send/receive the entire message or nothing

3. More on send and receive To put a message to the network send(message, destination_mbox) receive(buffer, mbox) Waits until a message arrives Copies the message into a given buffer

4. Remote Procedure Call (RPC) Allows you to invoke a procedure on either a local or remote machine Client RemoteMachine  Say(“Meow”); Server Machine  Say(“Meow”); Implemented on top of two-way messaging

5. RPC Illustrated Server (callee)Client (caller) OS or Network Server stub Client stub callreplycallreply

6. Procedure Stubs Provide the invocation interface programmers e.g. foo(int a) Client stub Build messages (a.k.a. marshalling) Send messages Wait for response Unpack reply Return result

7. Server Stub Create N threads to wait for requests Loop Wait for command Decode and unpack request parameters (unmarshalling) Call procedure Build replay message with results Send reply

8. RPC vs. Procedure Call From the programmer’s viewpoint Similar semantics Pointers are instantiated before transmission Data structures pointed by the pointer are copied Processes running on the remote machine is in a different address space

9. Implementation Issues Stubs are automatically generated Need to have a well-known port to talk to servers Server can upgrade the implementation without recompiling client applications

10. Interprocess Communication RPC is just another way to communicate between processes Example uses Microkernel operating systems Portions of an OS are implemented at the user level to minimize the kernel-level code Object linking and embedding (OLE) Mix-and-match applications

11. Using RPC for IPC + Fault isolation: bugs are unlikely to propagate across different address spaces + Modularity: independent component upgrades + Location transparency: a service can be provided from local or remote machines

12. Using RPC for IPC - Poor performance - Increased number of failure modes Network failure Machine failure - More outcomes for procedure execution No execution Partial execution...