Fix raise condition in RPCZ

[sashafrey]

There is a critical bug in RPCZ which causes a crash in certain scenarios. Given that it is intermittent it' hard for me provide a reprosteps, but the problem is quite straightforward. To explain, I need three pieces of code.

// Any stub method, generated by RPCZ compiler. void XXXStub::XXXMethod(...) { ::rpcz::rpc rpc; channel_->call_method(..., &rpc, ...); // (1) rpc.wait(); // (3) }

// File rpcz\rpc_channel_impl.cc void rpc_channel_impl::handle_client_response(...) { responsecontext.rpc->set_status(status::OK); // (2) responsecontext.rpc->syncevent->signal(); // (4) }

Assume that the threads were scheduled so that the sequence was as follows:

1. channel_->call_method(..., &rpc, ...);
2. responsecontext.rpc->set_status(status::OK);
3. rpc.wait();
4. responsecontext.rpc->syncevent->signal();

Now, the last piece of code --- rpc.wait() method: int rpc::wait() { status_code status = get_status(); CHECK_NE(status, status::INACTIVE) << "Request must be sent before calling wait()"; if (status != status::ACTIVE) return get_status(); // THIS LINE SHOULD BE REMOVED syncevent->wait(); return 0; }

If threads was scheduled as I described, the status of rpc will be OK, and the rpc::wait() will exit immediately. Therefore, by the moment when handle_client_response() reaches the syncevent->signal() the sync_event might be disposed, and we get a crash.

I believe the fix is just to remove the following line in rpc::wait() method: if (status != status::ACTIVE) return get_status();

[sashafrey]

Resolved in alfrey_rpcz branch

[sashafrey]

This has been reported to RPCZ: https://code.google.com/p/rpcz/issues/detail?id=10