Squashed 'src/ipc/libmultiprocess/' changes from a4f92969649..1fc65008f7d

1fc65008f7d Merge bitcoin-core/libmultiprocess#237: Made SpawnProcess() behavior safe post fork()
5205a87cd90 test: check SpawnProcess post-fork safety
69652f0edfa Precompute argv before fork in SpawnProcess
30a8681de62 SpawnProcess: avoid fd leak on close failure
d0fc1081d09 Merge bitcoin-core/libmultiprocess#196: ci: Add NetBSD job
7b171f45bfc Merge bitcoin-core/libmultiprocess#234: doc: Fix typos and grammar in documentation and comments
861da39cae9 ci: Add NetBSD job
458745e3940 Fix various typos, spelling mistakes, and grammatical errors in design.md and source code comments.
585decc8561 Merge bitcoin-core/libmultiprocess#236: ci: Install binary package `capnproto` on OpenBSD instead of building it
14e926a3ff3 refactor: extract MakeArgv helper
1ee909393f4 ci: Install binary package `capnproto` on OpenBSD instead of building it
470fc518d4b Merge bitcoin-core/libmultiprocess#230: cmake: add ONLY_CAPNP target_capnp_sources option
2d8886f26c4 Merge bitcoin-core/libmultiprocess#228: Add versions.md and version.h files describing version branches and tags
c1838be565d Merge bitcoin-core/libmultiprocess#225: Improve and document act support
a173f1704ce Merge bitcoin-core/libmultiprocess#223: ci: Replace nix-shell with equivalent nix develop command
625eaca42fb Merge bitcoin-core/libmultiprocess#229: Design Documentation Update
cc234be73a6 Design doc update
81c652687b8 cmake: add ONLY_CAPNP target_capnp_sources option
6e01d2d766e Add versions.md and version.h files describing version branches and tags
4e3f8fa0d2c doc: add instructions for using act
81712ff6bbf ci: disable KVM and sandbox inside act containers
18a2237a8ef ci: Replace nix-shell with equivalent nix develop command

git-subtree-dir: src/ipc/libmultiprocess
git-subtree-split: 1fc65008f7d64161e84c08cbd93109a23dd6a1e9

include/mp/proxy-io.h

@@ -317,12 +317,12 @@ public:
     void* m_context;
 };
 
-//! Single element task queue used to handle recursive capnp calls. (If server
-//! makes an callback into the client in the middle of a request, while client
+//! Single element task queue used to handle recursive capnp calls. (If the
+//! server makes a callback into the client in the middle of a request, while the client
 //! thread is blocked waiting for server response, this is what allows the
-//! client to run the request in the same thread, the same way code would run in
-//! single process, with the callback sharing same thread stack as the original
-//! call.
+//! client to run the request in the same thread, the same way code would run in a
+//! single process, with the callback sharing the same thread stack as the original
+//! call.)
 struct Waiter
 {
     Waiter() = default;

include/mp/proxy-types.h

@@ -87,7 +87,7 @@ struct StructField
 // actually construct the read destination object. For example, if a std::string
 // is being read, the ReadField call will call the custom emplace_fn with char*
 // and size_t arguments, and the emplace function can decide whether to call the
-// constructor via the operator or make_shared or emplace or just return a
+// constructor via the operator, make_shared, emplace or just return a
 // temporary string that is moved from.
 template <typename LocalType, typename EmplaceFn>
 struct ReadDestEmplace
@@ -205,11 +205,11 @@ void BuildField(TypeList<LocalTypes...>, Context& context, Output&& output, Valu
     }
 }
 
-// Adapter to let BuildField overloads methods work set & init list elements as
-// if they were fields of a struct. If BuildField is changed to use some kind of
-// accessor class instead of calling method pointers, then then maybe this could
-// go away or be simplified, because would no longer be a need to return
-// ListOutput method pointers emulating capnp struct method pointers..
+// Adapter that allows BuildField overloads to work with, set, and initialize list
+// elements as if they were fields of a struct. If BuildField is changed to use some
+// kind of accessor class instead of calling method pointers, then maybe this could
+// go away or be simplified, because there would no longer be a need to return
+// ListOutput method pointers emulating capnp struct method pointers.
 template <typename ListType>
 struct ListOutput;
 

include/mp/util.h

@@ -221,13 +221,16 @@ using FdToArgsFn = std::function<std::vector<std::string>(int fd)>;
 
 //! Spawn a new process that communicates with the current process over a socket
 //! pair. Returns pid through an output argument, and file descriptor for the
-//! local side of the socket. Invokes fd_to_args callback with the remote file
-//! descriptor number which returns the command line arguments that should be
-//! used to execute the process, and which should have the remote file
-//! descriptor embedded in whatever format the child process expects.
+//! local side of the socket.
+//! The fd_to_args callback is invoked in the parent process before fork().
+//! It must not rely on child pid/state, and must return the command line
+//! arguments that should be used to execute the process. Embed the remote file
+//! descriptor number in whatever format the child process expects.
 int SpawnProcess(int& pid, FdToArgsFn&& fd_to_args);
 
 //! Call execvp with vector args.
+//! Not safe to call in a post-fork child of a multi-threaded process.
+//! Currently only used by mpgen at build time.
 void ExecProcess(const std::vector<std::string>& args);
 
 //! Wait for a process to exit and return its exit code.

include/mp/version.h

@@ -0,0 +1,26 @@
+// Copyright (c) The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef MP_VERSION_H
+#define MP_VERSION_H
+
+//! Major version number. Should be incremented in the master branch before
+//! changes that introduce major new features or break API compatibility, if
+//! there are clients relying on the previous API. (If an API changes multiple
+//! times and nothing uses the intermediate changes, it is sufficient to
+//! increment this only once before the first change.)
+//!
+//! Each time this is incremented, a new stable branch should be created. E.g.
+//! when this is incremented to 8, a "v7" stable branch should be created
+//! pointing at the prior merge commit. The /doc/versions.md file should also be
+//! updated, noting any significant or incompatible changes made since the
+//! previous version, and backported to the stable branch before it is tagged.
+#define MP_MAJOR_VERSION 7
+
+//! Minor version number. Should be incremented in stable branches after
+//! backporting changes. The /doc/versions.md file in the master and stable
+//! branches should also be updated to list the new minor version.
+#define MP_MINOR_VERSION 0
+
+#endif // MP_VERSION_H