Windows support

[promag]

I think this should be referenced here:

Supporting windows, not just unix systems. The existing socket code is already cross-platform, so the only windows-specific code that needs to be written is code spawning a process and passing a socket descriptor. This can be implemented with CreateProcess and WSADuplicateSocket. Example: https://memset.wordpress.com/2010/10/13/win32-api-passing-socket-with-ipc-method/.

From https://github.com/bitcoin/bitcoin/blob/master/doc/multiprocess.md

Is there anything else worth mentioning? I could give it a try.

[ryanofsky]

This is interesting since that I think comment was written before libmultiprocess existed as a separate library.

I think basically the comment is still applicable and can be used to implement windows versions of mp::SpawnProcess and mp::WaitProcess (with the latter calling WaitForSingleObject and GetExitCodeProcess).

Function signatures in mp/util.h should also change slightly to take generic socket and process handles instead of using ints. Maybe should look something like:

#ifdef WIN32
using SocketId = HANDLE;
using ProcessId = HANDLE;
#else 
using SocketId = int;
using ProcessId = int;
#endif

using FdToArgsFn = std::function<std::vector<std::string>(SocketId fd)>;
int SpawnProcess(ProcessId& pid, FdToArgsFn&& fd_to_args);
int WaitProcess(ProcessId pid);

[ryanofsky]

Another part of this is that signatures of mp::ConnectStream and mp::ServeStream should change to accept windows handles:

template <typename InitInterface>
std::unique_ptr<ProxyClient<InitInterface>> ConnectStream(EventLoop& loop, SocketId socket);

template <typename InitInterface, typename InitImpl>
void ServeStream(EventLoop& loop, SocketId socket, InitImpl& init);

I think this should only require replacing the int type with the generic SocketId though.

[ryanofsky]

Also finally some KJ_SYSCALL uses in mp/proxy.cpp might have to be replaced:

libmultiprocess/src/mp/proxy.cpp

Lines 132 to 135 in 805eb73

	int fds[2];
	KJ_SYSCALL(socketpair(AF_UNIX, SOCK_STREAM, 0, fds));
	m_wait_fd = fds[0];
	m_post_fd = fds[1];

libmultiprocess/src/mp/proxy.cpp

Line 183 in 805eb73

KJ_SYSCALL(::close(m_post_fd));

libmultiprocess/src/mp/proxy.cpp

Lines 196 to 197 in 805eb73

	char buffer = 0;
	KJ_SYSCALL(write(m_post_fd, &buffer, 1));

libmultiprocess/src/mp/proxy.cpp

Lines 211 to 212 in 805eb73

	char buffer = 0;
	KJ_SYSCALL(write(m_post_fd, &buffer, 1));

I think there are straightforward replacements for all of these. Replace socketpair with maybe 2
CreatePipe calls, replace close with CloseHandle write with WriteFile.

EDIT: Should only need to replace socketpair with one CreatePipe call not two. I was thinking 2 because socketpair is bidirectional, but this code is only using the socket for signalling just writing to one end, so even on unix I think this could just use plain pipe.

[promag]

I'm having some issues trying to build on windows.

I downloaded and built capnproto-c++-0.8.0 with msvc2017. Then I set CapnProto_DIR and ran cmake. Then building the solution I have the following error:

C:\Users\joao\Projects\libmultiprocess\build>msbuild Libmultiprocess.sln  /property:Configuration=Release /property:Platform=Win32

[...]

CustomBuild:
  Compiling Cap'n Proto schema include/mp/proxy.capnp
  C:\Users\joao\Projects\capnproto-c++-0.8.0\build\src\capnp\Release\capnp.exe compile: -I C:/Users/joao/Projects/include: no such directory
  Try 'C:\Users\joao\Projects\capnproto-c++-0.8.0\build\src\capnp\Release\capnp.exe compile --help' for more information.

Looks like it's using C:/Users/joao/Projects to search for include/mp/proxy.capnp?

[ryanofsky]

Hmm, that custom build rule comes from this line in CMakeLists:

libmultiprocess/CMakeLists.txt

Line 45 in 805eb73

capnp_generate_cpp(MP_PROXY_SRCS MP_PROXY_HDRS include/mp/proxy.capnp)

It's possible prefixing include/mp/proxy.capnp as ${CMAKE_CURRENT_SOURCE_DIR}/include/mp/proxy.capnp could help, but this is a guess, and it would probably be good to see if there's way to get more verbose build output (complete command line) to see what could be happening.

In longer run, I assume the best way to get these various packages working together on windows will be with vcpkg, but I don't have any experience using vcpkg yet. I'm expecting there are more build issues waiting after this one. My previous comments above were about porting library code, and I think porting build code should be simpler and require fewer changes than porting library code, but the problems are probably less predictable and may take more time to debug.

[promag]

Same here, not used to code on windows, I'll try your suggestion just to have it build so I can work on the actual code change.

[promag]

Issue is related to CAPNP_INCLUDE_DIRECTORY , not with include/mp/proxy.capnp. Tomorrow I'll try to see why it's getting that value, otherwise I'll set it manually to the correct one just to move forward.