Re: [capnproto] Build error on Raspbian, "undefined reference to `__atomic_load_8'"

['Kenton Varda' via Cap'n Proto]

Hi Jens,

I answered on your github issue:
https://github.com/capnproto/capnproto/issues/1448#issuecomment-1093275165

-Kenton

On Fri, Apr 8, 2022 at 2:30 PM Jens Alfke  wrote:

> I'm building CapnP 0.9.1 from source on a new Raspberry Pi 4 running
> Raspbian (because apt only has version 0.7.)
>
> curl -O https://capnproto.org/capnproto-c++-0.9.1.tar.gz
> tar zxf capnproto-c++-0.9.1.tar.gz
> cd capnproto-c++-0.9.1
> ./configure
> make -j6 check
> sudo make install
>
>
> Everything went fine until the final "sudo make install" step:
>
> ...
> libtool: link: g++ -I./src -I./src -DKJ_HEADER_WARNINGS
> -DCAPNP_HEADER_WARNINGS -DCAPNP_INCLUDE_DIR=\"/usr/local/include\" -pthread
> -O2 -DNDEBUG -pthread -DKJ_HAS_ZLIB -pthread -o .libs/capnp
> src/capnp/compiler/module-loader.o
> src/capnp/compiler/capnp.o  ./.libs/libcapnpc.so ./.libs/libcapnp-json.so
> ./.libs/libcapnp.so ./.libs/libkj.so -lpthread -pthread
> /usr/bin/ld: ./.libs/libcapnp.so: undefined reference to `__atomic_load_8'
> /usr/bin/ld: ./.libs/libcapnp.so: undefined reference to `__atomic_store_8’
>
> I’m guessing the missing symbols are CPU intrinsics for 64-bit atomic
> operations. Could this have something to do with the fact that Raspbian is
> still running in 32-bit on a 64-bit CPU?
>
> —Jens
>
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[capnproto] Build error on Raspbian, "undefined reference to `__atomic_load_8'"

[Jens Alfke]

I'm building CapnP 0.9.1 from source on a new Raspberry Pi 4 running Raspbian 
(because apt only has version 0.7.) 

curl -O https://capnproto.org/capnproto-c++-0.9.1.tar.gz
tar zxf capnproto-c++-0.9.1.tar.gz
cd capnproto-c++-0.9.1
./configure
make -j6 check
sudo make install

Everything went fine until the final "sudo make install" step:

...
libtool: link: g++ -I./src -I./src -DKJ_HEADER_WARNINGS -DCAPNP_HEADER_WARNINGS 
-DCAPNP_INCLUDE_DIR=\"/usr/local/include\" -pthread -O2 -DNDEBUG -pthread 
-DKJ_HAS_ZLIB -pthread -o .libs/capnp src/capnp/compiler/module-loader.o 
src/capnp/compiler/capnp.o  ./.libs/libcapnpc.so ./.libs/libcapnp-json.so 
./.libs/libcapnp.so ./.libs/libkj.so -lpthread -pthread
/usr/bin/ld: ./.libs/libcapnp.so: undefined reference to `__atomic_load_8'
/usr/bin/ld: ./.libs/libcapnp.so: undefined reference to `__atomic_store_8’

I’m guessing the missing symbols are CPU intrinsics for 64-bit atomic 
operations. Could this have something to do with the fact that Raspbian is 
still running in 32-bit on a 64-bit CPU?

—Jens

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[capnproto] Allow async client connections in pub/sub server

[Dan WIllans]

Hi all,

I've been having fun playing around with Cap'n Proto and attempting to 
create simple subscriber/publisher classes using Cap'n Proto RPC and KJ.

I've created simple server/client pub/sub applications that use 
TwoPartyServer and TwoPartyClient classes. I've attempted to wrap the 
server app I made into it's own class using the constructor to setup the 
connection/listening logic. My current method has been to copy the 
implementation of the TwoPartyServer code and modify where needed.

The issue I'm facing is keeping the `listen()` promise alive to accept new 
incoming connections whilst I continue to do other work in the rest of the 
application.

Code for my normal working application:
```
kj::UnixEventPort::captureSignal(SIGINT);
auto io_context = kj::setupAsyncIo();
auto addrPromise = 
io_context.provider->getNetwork().parseAddress("unix:/tmp/capnp-server-example");
auto addr = addrPromise.wait(io_context.waitScope);
auto addrListen = addr->listen();
capnp::TwoPartyServer server(kj::heap>(sub_map));
auto server_listen = server.listen(*addrListen);
auto& timer = io_context.provider->getTimer();
auto pub = publishLoop(timer, 1);
io_context.unixEventPort.onSignal(SIGINT).wait(io_context.waitScope);
std::cout << "Shutting down Publisher\n";
```

Code for my wrapped class application constructor (the rest of the class is 
effectively the TwoPartyServer code):
```
template 
Publisher::Publisher(const std::string& connection_address, 
kj::AsyncIoContext& io_context)
: tasks_(*this), connection_address_(connection_address), 
io_context_(io_context) {
auto listener = 
io_context_.provider->getNetwork().parseAddress(connection_address);
auto addr = listener.wait(io_context.waitScope);
auto addrListen = addr->listen();
addTask(listen(*addrListen));
}
```

This builds fine but I get an exception when I run the server.
```
error: exception = kj/async.c++:2714: failed: PromiseFulfiller was 
destroyed without fulfilling the promise.
```

I'm assuming the normal main application works because the `listen()` 
promise remains in scope but when I attempt to add the `kj::Promise` 
to the member variable kj::TaskSet something isn't quite right.

My ideal situation would be this.
```
int main(int argc, const char** argv) {
// setup event loop etc.
auto io_context = kj::setupAsyncIO();
// Instantiate a publisher that accepts incoming connections 
asynchronously.
auto pub = Publisher("unix:/tmp/capnp-server-example", 
io_context);
// Start publishing at a specific frequency. Implementation involves a 
kj::Timer with afterDelay().
pub.publishAtFrequency("Hello Subscribers", 1);
// Spin on this publisher. It should continue to accept new subscribers 
whilst publishing.
pub.spin()
}
```

I hope I've given enough context and information. Please let me know if you 
need more information and thank you for this awesome library!

Dan


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