Capnproto - Make client request in server callback - c++

Question

I need to do some client-requests inside a server-callback and are not sure where to store the created capnp::EzRpcClient and CompareNetwork::Client comparer objects. That's because the clients go out of scope (I think - I just get a SEGFAULT, but that seems to be the reason). It's basically a master who forwards a loading request to it's slaves (slaves can register via a REG-request and their address is stored).
So - where/how should I store the client objects? Is there any "best-practice" with this? I think temporarily storing them in some class member variable is a little dirty, isn't it?
GroupMaster2.cpp:
kj::Promise<void> GroupMaster2::CompareMasterImpl::load(LoadContext context) {
auto loadData = context.getParams().getIds();
slaveListLock.lock();
auto promList = kj::Vector<kj::Promise<std::pair<std::string, CompareNetwork::Status>>>();
for(auto& slave : slaveList) {
try {
capnp::EzRpcClient client(slave.second->address);
CompareNetwork::Client comparer = client.getMain<CompareNetwork>();
auto request = comparer.loadRequest();
std::string addrCopy(slave.first);
request.setIds(loadData);
auto loadPromise = request.send();
promList.add(loadPromise.then([addrCopy](auto response) {
return std::make_pair(addrCopy, response.getStatus());
},
[&, addrCopy](kj::Exception && exception) {
slaveListLock.lock();
slaveList.erase(addrCopy);//something failed, remove this slave!
slaveListLock.unlock();
std::cout << "ErrLoad0: " << std::string(exception.getDescription()) << std::endl;
return std::make_pair(addrCopy, CompareNetwork::Status::ERROR);
}));
}
catch(...) {
std::cout << "Error sending load to: " << slave.first << std::endl;
}
}
slaveListLock.unlock();
auto retProm = kj::joinPromises(promList.releaseAsArray()).then([&, KJ_CPCAP(context)](kj::Array<std::pair<std::string, CompareNetwork::Status>> res) mutable {
bool error = false;
for(auto& loadRes : res) {
switch(loadRes.second) {
case CompareNetwork::Status::OK: {
std::cout << "LOAD OK: " << loadRes.first << std::endl;
break;
}
case CompareNetwork::Status::ERROR: {
std::cout << "LOAD ERROR: " << loadRes.first << std::endl;
error = true;
break;
}
}
}
if(!error)
context.getResults().setStatus(CompareNetwork::Status::OK);
else
context.getResults().setStatus(CompareNetwork::Status::ERROR);
}, [](kj::Exception && exception) {
std::cout << __FILE__ << ":" << __LINE__ << std::string(exception.getDescription()) << std::endl;
}).eagerlyEvaluate([](kj::Exception && exception) {
std::cout << __FILE__ << ":" << __LINE__ << std::string(exception.getDescription()) << std::endl;
});
std::cout << "ReturnedLoad" << std::endl;
return retProm;
}
GroupNetworkData.capnp:
interface CompareNetwork {
compare #0 (jobs :JobPartList) -> (res :JobResList);
load #1 (ids :WIDList) -> (status :Status);
struct JobPartList {
jobParts #0 :List(JobPart);
struct JobPart {
jobs #0 :List(Job);
startID #1 :UInt32;
struct Job {
wid1 #0 :UInt32;
wid2 #1 :UInt32;
}
}
}
struct JobResList {
jobResults #0 :List(JobRes);
struct JobRes {
jobIndex #0 :UInt32;
result #1 :Float64;
}
}
struct WIDList {
ids #0 :List(WID);
struct WID {
id #0 :UInt32;
}
}
enum Status {
ok #0;
error #1;
}
}
interface CompareMaster extends(CompareNetwork) {
reg #0 (data :SlaveData) -> (status :CompareNetwork.Status);
struct SlaveData {
perfInd #0 :Float64;
maxMem #1 :UInt32;
address #2 :Text;
}
}
Thanks in advance!
dvs23

Answer 1

C++14 seems to have the answer:
How to capture a unique_ptr into a lambda expression?
Allocate both objects on heap with kj::heap and move the kj::Own to the callback lambda:
for(auto& slave : slaveList) {
try {
auto client = kj::heap<capnp::EzRpcClient>(slave.second->address);
auto comparer = kj::heap<CompareNetwork::Client>(client->getMain<CompareNetwork>());
auto request = comparer->loadRequest();
std::string addrCopy(slave.first);
request.setIds(loadData);
auto loadPromise = request.send();
promList.add(loadPromise.then([addrCopy, client = std::move(client), comparer = std::move(comparer)](auto response) {
return std::make_pair(addrCopy, response.getStatus());
},
[&, addrCopy](kj::Exception && exception) {
slaveListLock.lock();
slaveList.erase(addrCopy);//something failed, remove this slave!
slaveListLock.unlock();
std::cout << "ErrLoad0: " << std::string(exception.getDescription()) << std::endl;
return std::make_pair(addrCopy, CompareNetwork::Status::ERROR);
}));
}
catch(...) {
std::cout << "Error sending load to: " << slave.first << std::endl;
}
}
Better ideas are welcome, but at the moment it seems to work pretty well :)