message_service: create object using placement new()
Object reference may point to a unit member that was not properly
created, so assign will not work on it. Use placement new() instead.
It is built on top of seastar rpc infrastructure. I've sorted out all
the message VERBs which Origin use. All of them can be implemented using
this messaging_service.
Each Verb contains a handler. There are two types of handlers, one
will return a message back to sender, the other will not. The former
can be registered using ms.register_handler(), the latter can be
registered using ms.register_handler_oneway().
Usage example:
To use messaging_service to send a message. All you need is:
messaging_service& ms = get_local_messaging_service();
1) To register a message hander:
ms.register_handler(messaging_verb::ECHO, [] (int x, long y) {
print("Server got echo msg = (%d, %ld) \n", x, y);
std::tuple<int, long> ret(x*x, y*y);
return make_ready_future<decltype(ret)>(std::move(ret));
});
ms.register_handler_oneway(messaging_verb::GOSSIP_SHUTDOWN, [] (empty_msg msg) {
print("Server got shutdown msg = %s\n", msg);
return messaging_service::no_wait();
});
2) To send a message:
using RetMsg = std::tuple<int, long>;
return ms.send_message<RetMsg>(messaging_verb::ECHO, id, msg1, msg2).then([] (RetMsg msg) {
print("Client sent echo got reply = (%d , %ld)\n", std::get<0>(msg), std::get<1>(msg));
return sleep(100ms).then([]{
return make_ready_future<>();
});
});
return ms.send_message_oneway<void>(messaging_verb::GOSSIP_SHUTDOWN, std::move(id), std::move(msg)).then([] () {
print("Client sent gossip_shutdown got reply = void\n");
return make_ready_future<>();
});
Tests:
send to cpu 0
$ ./message --server 127.0.0.1 --cpuid 0 --smp 2
send to cpu 1
$ ./message --server 127.0.0.1 --cpuid 1 --smp 2
