1. Implementing Remote Procedure Calls Andrew Birrell and Bruce Nelson Presented by Phil Howard

2. Why?

3. Consider #include int main() { printf("hello world!\n"); return 0; }

4. What Happens main printfglibc main kernel IOkernel update_window X update_display kernel IOkernel

5. But what if X Server Console Window main Linux Box X Client Laptop

6. What Happens main printf glibc main kernel IOkernel update_windowX update_display Linux Box X Client update_display X kernel IO kernel Laptop

7. How do you do this? Fork/Join SendMessage/AwaitReply Remote Procedure Call

8. What's Involved in RPC Remote Procedure Call should look and feel like local call Remote Procedure Call should be independent of where it executes Remote Procedure Call should be "efficient"

9. Issues Finding the callee Passing data Implementation Exceptions Optimizations

10. Finding the Callee (Binding) Where  Server has known static address  Client broadcasts request  Central database of interfaces What  Servers export named interfaces  Clients request a particular interface  Need Globally Unique Identifiers for interfaces

11. Passing Data Can't use the stack Can't use shared memory Generally use message passing

12. Passing Data #include int main() { union { unsigned long stuff1; unsigned char stuff2[4]; } my_var; my_var.stuff1 = 0x12345678; printf("%X %X %X %X\n", my_var.stuff2[0], my_var.stuff2[1], my_var.stuff2[2], my_var.stuff2[3]); return 0; }

13. Passing Data What's the output? 12 34 56 78 or 78 56 34 12

14. Passing data Build a message that includes: Who and what's being called Identity of the caller Data values in known byte order

15. Issues Finding the callee Passing data Implementation Exceptions Optimizations

16. Implementation foo(a,&b) foo(int a, int *b) return;

17. Implementation foo(int a; int *b) { build_msg(a,b); send_msg(); wait_for_reply(); get_from_msg(&b); } do_foo(msg_t msg) { int a,b; get_from_msg(&a,&b); foo(a,&b); build_msg(b); send_reply(); }

18. Implementation Function prototype is (almost) all that's needed to build the client stub –Also need binding information Function prototype is (almost) all that's needed to build server stuf –Also need method to wait for message

19. Implementation Clients Threaded Servers Event Driven

20. Issues Finding the callee Passing data Implementation Exceptions Optimizations

21. Exceptions What can happen in "normal" procedures? Procedure generates an exception Procedure infinite loops Procedure generates wrong results

22. Exceptions What can happen in "remote" procedures? Client stub generates exception Transmission failure  knowable failure  unknowable failure Remote procedure generates an exception Remote procedure infinite loops Remote procedure generates wrong results

23. Optimizations Servers maintain no state on clients –No penalty for a large number of clients Messages must be ack'd –for short calls, result serves as ack –for frequent calls, next call ack's last result –for long requests, only last request msg gets ack'd –for long results, only last result msg gets ack'd Bound to "closest" server –Minimum transmission delay

24. Conclusion Remote Procedure Call should look and feel like local call Remote Procedure Call should be independent of where it executes Remote Procedure Call should be "efficient"