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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/multiprocess.md | 39 |
1 files changed, 38 insertions, 1 deletions
diff --git a/doc/multiprocess.md b/doc/multiprocess.md index 7a42fdd734..e3f389a6d3 100644 --- a/doc/multiprocess.md +++ b/doc/multiprocess.md @@ -15,7 +15,7 @@ Specific next steps after [#10102](https://github.com/bitcoin/bitcoin/pull/10102 ## Debugging -After [#10102](https://github.com/bitcoin/bitcoin/pull/10102), the `-debug=ipc` command line option can be used to see requests and responses between processes. +The `-debug=ipc` command line option can be used to see requests and responses between processes. ## Installation @@ -33,3 +33,40 @@ BITCOIND=bitcoin-node test/functional/test_runner.py The configure script will pick up settings and library locations from the depends directory, so there is no need to pass `--enable-multiprocess` as a separate flag when using the depends system (it's controlled by the `MULTIPROCESS=1` option). Alternately, you can install [Cap'n Proto](https://capnproto.org/) and [libmultiprocess](https://github.com/chaincodelabs/libmultiprocess) packages on your system, and just run `./configure --enable-multiprocess` without using the depends system. The configure script will be able to locate the installed packages via [pkg-config](https://www.freedesktop.org/wiki/Software/pkg-config/). See [Installation](https://github.com/chaincodelabs/libmultiprocess#installation) section of the libmultiprocess readme for install steps. See [build-unix.md](build-unix.md) and [build-osx.md](build-osx.md) for information about installing dependencies in general. + +## IPC implementation details + +Cross process Node, Wallet, and Chain interfaces are defined in +[`src/interfaces/`](../src/interfaces/). These are C++ classes which follow +[conventions](developer-notes.md#internal-interface-guidelines), like passing +serializable arguments so they can be called from different processes, and +making methods pure virtual so they can have proxy implementations that forward +calls between processes. + +When Wallet, Node, and Chain code is running in the same process, calling any +interface method invokes the implementation directly. When code is running in +different processes, calling an interface method invokes a proxy interface +implementation that communicates with a remote process and invokes the real +implementation in the remote process. The +[libmultiprocess](https://github.com/chaincodelabs/libmultiprocess) code +generation tool internally generates proxy client classes and proxy server +classes for this purpose that are thin wrappers around Cap'n Proto +[client](https://capnproto.org/cxxrpc.html#clients) and +[server](https://capnproto.org/cxxrpc.html#servers) classes, which handle the +actual serialization and socket communication. + +As much as possible, calls between processes are meant to work the same as +calls within a single process without adding limitations or requiring extra +implementation effort. Processes communicate with each other by calling regular +[C++ interface methods](../src/interfaces/README.md). Method arguments and +return values are automatically serialized and sent between processes. Object +references and `std::function` arguments are automatically tracked and mapped +to allow invoked code to call back into invoking code at any time, and there is +a 1:1 threading model where any thread invoking a method in another process has +a corresponding thread in the invoked process responsible for executing all +method calls from the source thread, without blocking I/O or holding up another +call, and using the same thread local variables, locks, and callbacks between +calls. The forwarding, tracking, and threading is implemented inside the +[libmultiprocess](https://github.com/chaincodelabs/libmultiprocess) library +which has the design goal of making calls between processes look like calls in +the same process to the extent possible. |