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ryanofskyryanofsky
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Add standalone example with 3 processes
Added build instructions to README, but could use some more documentation and CMakeLists.txt file could be made less repetitive maybe introducing a mp_generate_cpp function that works like the capnp_generate_cpp function.
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‎CMakeLists.txt

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@@ -91,4 +91,5 @@ install(FILES "include/mpgen.mk" DESTINATION "include")
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install(EXPORT Multiprocess DESTINATION lib/cmake/Multiprocess)
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add_subdirectory(example EXCLUDE_FROM_ALL)
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add_subdirectory(test EXCLUDE_FROM_ALL)

‎README.md

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@@ -27,6 +27,13 @@ basis in this library to construct the event-loop necessary to service IPC reque
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A simple interface description can be found at [test/mp/test/foo.capnp](test/mp/test/foo.capnp), implementation in [test/mp/test/foo.h](test/mp/test/foo.h), and usage in [test/mp/test/test.cpp](test/mp/test/test.cpp).
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A more complete example can be found in [example](example/) and run with:
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```sh
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make -C build example
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build/example/mpexample
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```
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## Future directions
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_libmultiprocess_ uses the [Cap'n Proto](https://capnproto.org) interface description language and protocol, but it could be extended or changed to use a different IDL/protocol like [gRPC](https://grpc.io). The nice thing about _Cap'n Proto_ compared to _gRPC_ and most other lower level protocols is that it allows interface pointers (_Services_ in gRPC parlance) to be passed as method arguments and return values, so object references and bidirectional requests work out of the box. Supporting a lower-level protocol would require writing adding maps and tracking code to proxy objects.

‎example/CMakeLists.txt

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# Copyright (c) 2021 The Bitcoin Core developers
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# Distributed under the MIT software license, see the accompanying
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# file COPYING or http://www.opensource.org/licenses/mit-license.php.
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add_custom_command(
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OUTPUT
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init.capnp.h
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init.capnp.c++
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init.capnp.proxy.h
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init.capnp.proxy-server.c++
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init.capnp.proxy-client.c++
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init.capnp.proxy-types.c++
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init.capnp.proxy-types.h
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COMMAND mpgen "${CMAKE_CURRENT_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}/init.capnp" "${CMAKE_SOURCE_DIR}/include" "${capnp_PREFIX}/include"
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DEPENDS init.capnp mpgen
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)
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add_custom_command(
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OUTPUT
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calculator.capnp.h
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calculator.capnp.c++
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calculator.capnp.proxy.h
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calculator.capnp.proxy-server.c++
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calculator.capnp.proxy-client.c++
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calculator.capnp.proxy-types.c++
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calculator.capnp.proxy-types.h
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COMMAND mpgen "${CMAKE_CURRENT_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}/calculator.capnp" "${CMAKE_SOURCE_DIR}/include" "${capnp_PREFIX}/include"
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DEPENDS calculator.capnp mpgen
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)
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add_executable(mpcalculator
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calculator.capnp.h
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calculator.capnp.c++
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calculator.capnp.proxy.h
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calculator.capnp.proxy-server.c++
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calculator.capnp.proxy-client.c++
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calculator.capnp.proxy-types.c++
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calculator.capnp.proxy-types.h
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calculator.cpp
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init.capnp.h
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init.capnp.c++
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init.capnp.proxy.h
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init.capnp.proxy-server.c++
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init.capnp.proxy-client.c++
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init.capnp.proxy-types.c++
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init.capnp.proxy-types.h
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printer.capnp.h
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printer.capnp.c++
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printer.capnp.proxy.h
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printer.capnp.proxy-server.c++
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printer.capnp.proxy-client.c++
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printer.capnp.proxy-types.c++
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printer.capnp.proxy-types.h
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)
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target_include_directories(mpcalculator PUBLIC
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${CAPNP_INCLUDE_DIRECTORY}
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${CMAKE_CURRENT_SOURCE_DIR}
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${CMAKE_CURRENT_BINARY_DIR}
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)
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target_link_libraries(mpcalculator PRIVATE CapnProto::capnp)
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target_link_libraries(mpcalculator PRIVATE CapnProto::capnp-rpc)
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target_link_libraries(mpcalculator PRIVATE CapnProto::kj)
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target_link_libraries(mpcalculator PRIVATE CapnProto::kj-async)
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target_link_libraries(mpcalculator PRIVATE Threads::Threads)
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target_link_libraries(mpcalculator PRIVATE multiprocess)
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set_target_properties(mpcalculator PROPERTIES
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CXX_STANDARD 17
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CXX_STANDARD_REQUIRED YES)
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add_custom_command(
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OUTPUT
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printer.capnp.h
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printer.capnp.c++
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printer.capnp.proxy.h
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printer.capnp.proxy-server.c++
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printer.capnp.proxy-client.c++
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printer.capnp.proxy-types.c++
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printer.capnp.proxy-types.h
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COMMAND mpgen "${CMAKE_CURRENT_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}/printer.capnp" "${CMAKE_SOURCE_DIR}/include" "${capnp_PREFIX}/include"
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DEPENDS printer.capnp mpgen
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)
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add_executable(mpprinter
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calculator.capnp.c++
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calculator.capnp.h
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calculator.capnp.proxy-client.c++
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calculator.capnp.proxy-server.c++
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calculator.capnp.proxy-types.c++
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calculator.capnp.proxy-types.h
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calculator.capnp.proxy.h
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init.capnp.h
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init.capnp.c++
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init.capnp.proxy.h
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init.capnp.proxy-server.c++
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init.capnp.proxy-client.c++
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init.capnp.proxy-types.c++
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init.capnp.proxy-types.h
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printer.capnp.h
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printer.capnp.c++
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printer.capnp.proxy.h
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printer.capnp.proxy-server.c++
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printer.capnp.proxy-client.c++
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printer.capnp.proxy-types.c++
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printer.capnp.proxy-types.h
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printer.cpp
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)
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target_include_directories(mpprinter PUBLIC
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${CAPNP_INCLUDE_DIRECTORY}
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${CMAKE_CURRENT_SOURCE_DIR}
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${CMAKE_CURRENT_BINARY_DIR}
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)
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target_link_libraries(mpprinter PRIVATE CapnProto::capnp)
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target_link_libraries(mpprinter PRIVATE CapnProto::capnp-rpc)
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target_link_libraries(mpprinter PRIVATE CapnProto::kj)
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target_link_libraries(mpprinter PRIVATE CapnProto::kj-async)
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target_link_libraries(mpprinter PRIVATE Threads::Threads)
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target_link_libraries(mpprinter PRIVATE multiprocess)
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set_target_properties(mpprinter PROPERTIES
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CXX_STANDARD 17
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CXX_STANDARD_REQUIRED YES)
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add_executable(mpexample
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calculator.capnp.c++
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calculator.capnp.h
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calculator.capnp.proxy-client.c++
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calculator.capnp.proxy-server.c++
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calculator.capnp.proxy-types.c++
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calculator.capnp.proxy-types.h
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calculator.capnp.proxy.h
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init.capnp.c++
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init.capnp.h
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init.capnp.proxy-client.c++
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init.capnp.proxy-server.c++
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init.capnp.proxy-types.c++
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init.capnp.proxy-types.h
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init.capnp.proxy.h
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printer.capnp.h
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printer.capnp.c++
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printer.capnp.proxy.h
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printer.capnp.proxy-server.c++
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printer.capnp.proxy-client.c++
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printer.capnp.proxy-types.c++
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printer.capnp.proxy-types.h
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printer.h
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calculator.h
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example.cpp
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)
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target_include_directories(mpexample PUBLIC
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${CAPNP_INCLUDE_DIRECTORY}
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${CMAKE_CURRENT_SOURCE_DIR}
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${CMAKE_CURRENT_BINARY_DIR}
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)
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target_link_libraries(mpexample PRIVATE CapnProto::capnp)
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target_link_libraries(mpexample PRIVATE CapnProto::capnp-rpc)
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target_link_libraries(mpexample PRIVATE CapnProto::kj)
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target_link_libraries(mpexample PRIVATE CapnProto::kj-async)
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target_link_libraries(mpexample PRIVATE Threads::Threads)
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target_link_libraries(mpexample PRIVATE multiprocess)
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target_link_libraries(mpexample PRIVATE stdc++fs)
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set_target_properties(mpexample PROPERTIES
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CXX_STANDARD 17
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CXX_STANDARD_REQUIRED YES)
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add_custom_target(example DEPENDS mpexample mpcalculator mpprinter)

‎example/calculator.capnp

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# Copyright (c) 2021 The Bitcoin Core developers
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# Distributed under the MIT software license, see the accompanying
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# file COPYING or http://www.opensource.org/licenses/mit-license.php.
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@0xb67dbf34061180a9;
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using Cxx = import "/capnp/c++.capnp";
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using Proxy = import "/mp/proxy.capnp";
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$Proxy.include("calculator.h");
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interface CalculatorInterface $Proxy.wrap("Calculator") {
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destroy @0 (context :Proxy.Context) -> ();
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solveEquation @1 (context :Proxy.Context, eqn: Text) -> ();
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}

‎example/calculator.cpp

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// Copyright (c) 2021 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include <calculator.h>
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#include <fstream>
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#include <init.capnp.h>
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#include <init.capnp.proxy-types.h>
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#include <init.h>
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#include <iostream>
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#include <memory>
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#include <mp/proxy-io.h>
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#include <printer.h>
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#include <stdexcept>
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class CalculatorImpl : public Calculator
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{
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public:
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CalculatorImpl(std::unique_ptr<Printer> printer) : m_printer(std::move(printer)) {}
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void solveEquation(const std::string& eqn) override { m_printer->print("Wow " + eqn + ", that's a tough one.\n"); }
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std::unique_ptr<Printer> m_printer;
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};
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class InitImpl : public Init
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{
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public:
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std::unique_ptr<Calculator> makeCalculator(std::unique_ptr<Printer> printer) override
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{
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return std::make_unique<CalculatorImpl>(std::move(printer));
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}
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};
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void LogPrint(bool raise, std::string message)
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{
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if (raise) throw std::runtime_error(std::move(message));
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std::ofstream("debug.log", std::ios_base::app) << message << std::endl;
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}
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int main(int argc, char** argv)
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{
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if (argc != 2) {
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std::cout << "Usage: mpcalculator <fd>\n";
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return 1;
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}
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mp::EventLoop loop("mpcalculator", LogPrint);
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int fd = std::stoi(argv[1]);
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std::unique_ptr<Init> init = std::make_unique<InitImpl>();
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mp::ServeStream<InitInterface>(loop, fd, *init);
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loop.loop();
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return 0;
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}

‎example/calculator.h

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// Copyright (c) 2021 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#ifndef EXAMPLE_CALCULATOR_H
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#define EXAMPLE_CALCULATOR_H
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#include <string>
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class Calculator
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{
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public:
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virtual ~Calculator() = default;
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virtual void solveEquation(const std::string& eqn) = 0;
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};
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#endif // EXAMPLE_CALCULATOR_H

‎example/example.cpp

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// Copyright (c) 2021 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include <filesystem>
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#include <fstream>
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#include <init.capnp.h>
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#include <init.capnp.proxy-types.h>
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#include <iostream>
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#include <mp/proxy-io.h>
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namespace fs = std::filesystem;
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auto Spawn(mp::EventLoop& loop, const std::string& process_argv0, const std::string& new_exe_name)
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{
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int pid;
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int fd = mp::SpawnProcess(pid, [&](int fd) -> std::vector<std::string> {
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fs::path path = process_argv0;
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path.remove_filename();
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path.append(new_exe_name);
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return {path.string(), std::to_string(fd)};
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});
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return std::make_tuple(mp::ConnectStream<InitInterface>(loop, fd), pid);
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}
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void LogPrint(bool raise, std::string message)
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{
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if (raise) throw std::runtime_error(std::move(message));
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std::ofstream("debug.log", std::ios_base::app) << message << std::endl;
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}
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int main(int argc, char** argv)
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{
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if (argc != 1) {
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std::cout << "Usage: mpexample\n";
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return 1;
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}
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std::promise<mp::EventLoop*> promise;
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std::thread loop_thread([&] {
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mp::EventLoop loop("mpexample", LogPrint);
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{
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std::unique_lock<std::mutex> lock(loop.m_mutex);
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loop.addClient(lock);
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}
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promise.set_value(&loop);
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loop.loop();
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});
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mp::EventLoop* loop = promise.get_future().get();
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auto [printer_init, printer_pid] = Spawn(*loop, argv[0], "mpprinter");
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auto [calc_init, calc_pid] = Spawn(*loop, argv[0], "mpcalculator");
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auto calc = calc_init->makeCalculator(printer_init->makePrinter());
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while (true) {
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std::string eqn;
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std::cout << "Enter the equation: ";
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std::getline(std::cin, eqn);
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calc->solveEquation(eqn);
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}
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calc.reset();
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calc_init.reset();
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mp::WaitProcess(calc_pid);
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printer_init.reset();
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mp::WaitProcess(printer_pid);
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return 0;
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}

‎example/init.capnp

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# Copyright (c) 2021 The Bitcoin Core developers
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# Distributed under the MIT software license, see the accompanying
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# file COPYING or http://www.opensource.org/licenses/mit-license.php.
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@0xba5a7448664901b1;
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using Cxx = import "/capnp/c++.capnp";
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using Proxy = import "/mp/proxy.capnp";
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using Calculator = import "calculator.capnp";
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using Printer = import "printer.capnp";
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$Proxy.include("calculator.h");
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$Proxy.include("init.h");
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$Proxy.include("printer.h");
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$Proxy.includeTypes("calculator.capnp.proxy-types.h");
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$Proxy.includeTypes("printer.capnp.proxy-types.h");
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interface InitInterface $Proxy.wrap("Init") {
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construct @0 (threadMap: Proxy.ThreadMap) -> (threadMap :Proxy.ThreadMap);
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makeCalculator @1 (context :Proxy.Context, print :Printer.PrinterInterface) -> (result :Calculator.CalculatorInterface);
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makePrinter @2 (context :Proxy.Context) -> (result :Printer.PrinterInterface);
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}

‎example/init.h

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// Copyright (c) 2021 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#ifndef EXAMPLE_INIT_H
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#define EXAMPLE_INIT_H
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#include <calculator.h>
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#include <memory>
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#include <printer.h>
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class Init
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{
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public:
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virtual ~Init() = default;
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virtual std::unique_ptr<Printer> makePrinter() { return nullptr; }
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virtual std::unique_ptr<Calculator> makeCalculator(std::unique_ptr<Printer> printer) { return nullptr; }
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};
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#endif // EXAMPLE_INIT_H

‎example/printer.capnp

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# Copyright (c) 2021 The Bitcoin Core developers
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# Distributed under the MIT software license, see the accompanying
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# file COPYING or http://www.opensource.org/licenses/mit-license.php.
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@0x893db95f456ed0e3;
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using Cxx = import "/capnp/c++.capnp";
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using Proxy = import "/mp/proxy.capnp";
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$Proxy.include("printer.h");
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interface PrinterInterface $Proxy.wrap("Printer") {
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destroy @0 (context :Proxy.Context) -> ();
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print @1 (context :Proxy.Context, text: Text) -> ();
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}

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