build: depends makes libmultiprocess by default

Except for Windows and OpenBSD.

ci/test/00_setup_env_i686_no_multiprocess.sh

@@ -11,7 +11,7 @@ export CONTAINER_NAME=ci_i686_no_multiprocess
 export CI_IMAGE_NAME_TAG="mirror.gcr.io/ubuntu:24.04"
 export CI_IMAGE_PLATFORM="linux/amd64"
 export PACKAGES="llvm clang g++-multilib"
-export DEP_OPTS="DEBUG=1"
+export DEP_OPTS="DEBUG=1 NO_MULTIPROCESS=1"
 export GOAL="install"
 export TEST_RUNNER_EXTRA="--v2transport"
 export BITCOIN_CONFIG="\

depends/Makefile

@@ -41,7 +41,10 @@ NO_SQLITE ?=
 NO_WALLET ?=
 NO_ZMQ ?=
 NO_USDT ?=
-MULTIPROCESS ?=
+# Default NO_MULTIPROCESS value is 1 on unsupported host platforms:
+# - Windows
+# - OpenBSD: https://github.com/capnproto/capnproto/pull/1907
+NO_MULTIPROCESS ?= $(if $(findstring mingw32,$(HOST))$(findstring openbsd,$(HOST)),1,)
 LTO ?=
 NO_HARDEN ?=
 FALLBACK_DOWNLOAD_PATH ?= https://bitcoincore.org/depends-sources
@@ -165,7 +168,7 @@ sqlite_packages_$(NO_SQLITE) = $(sqlite_packages)
 wallet_packages_$(NO_WALLET) = $(bdb_packages_) $(sqlite_packages_)
 
 zmq_packages_$(NO_ZMQ) = $(zmq_packages)
-multiprocess_packages_$(MULTIPROCESS) = $(multiprocess_packages)
+multiprocess_packages_$(NO_MULTIPROCESS) = $(multiprocess_packages)
 usdt_packages_$(NO_USDT) = $(usdt_$(host_os)_packages)
 
 packages += $($(host_arch)_$(host_os)_packages) $($(host_os)_packages) $(boost_packages_) $(libevent_packages_) $(qt_packages_) $(wallet_packages_) $(usdt_packages_)
@@ -175,7 +178,7 @@ ifneq ($(zmq_packages_),)
 packages += $(zmq_packages)
 endif
 
-ifeq ($(multiprocess_packages_),)
+ifneq ($(multiprocess_packages_),)
 packages += $(multiprocess_packages)
 native_packages += $(multiprocess_native_packages)
 endif
@@ -237,7 +240,7 @@ $(host_prefix)/toolchain.cmake : toolchain.cmake.in $(host_prefix)/.stamp_$(fina
             -e 's|@sqlite_packages@|$(sqlite_packages_)|' \
             -e 's|@usdt_packages@|$(usdt_packages_)|' \
             -e 's|@no_harden@|$(NO_HARDEN)|' \
-            -e 's|@multiprocess@|$(MULTIPROCESS)|' \
+            -e 's|@multiprocess_packages@|$(multiprocess_packages_)|' \
             $< > $@
 	touch $@
 

depends/README.md

@@ -119,7 +119,7 @@ The following can be set when running make: `make FOO=bar`
 - `NO_BDB`: Don't download/build/cache BerkeleyDB
 - `NO_SQLITE`: Don't download/build/cache SQLite
 - `NO_USDT`: Don't download/build/cache packages needed for enabling USDT tracepoints
-- `MULTIPROCESS`: Build libmultiprocess (experimental)
+- `NO_MULTIPROCESS`: Don't build experimental libmultiprocess (default on Windows and OpenBSD)
 - `DEBUG`: Disable some optimizations and enable more runtime checking
 - `HOST_ID_SALT`: Optional salt to use when generating host package ids
 - `BUILD_ID_SALT`: Optional salt to use when generating build package ids

depends/toolchain.cmake.in

@@ -152,11 +152,12 @@ else()
   set(ENABLE_HARDENING ON CACHE BOOL "")
 endif()
 
-if("@multiprocess@" STREQUAL "1")
+set(multiprocess_packages @multiprocess_packages@)
+if("${multiprocess_packages}" STREQUAL "")
+  set(ENABLE_IPC OFF CACHE BOOL "")
+else()
   set(ENABLE_IPC ON CACHE BOOL "")
   set(MPGEN_EXECUTABLE "${CMAKE_CURRENT_LIST_DIR}/native/bin/mpgen" CACHE FILEPATH "")
   set(CAPNP_EXECUTABLE "${CMAKE_CURRENT_LIST_DIR}/native/bin/capnp" CACHE FILEPATH "")
   set(CAPNPC_CXX_EXECUTABLE "${CMAKE_CURRENT_LIST_DIR}/native/bin/capnpc-c++" CACHE FILEPATH "")
-else()
-  set(ENABLE_IPC OFF CACHE BOOL "")
 endif()

doc/multiprocess.md

@@ -16,11 +16,11 @@ Specifying `-DENABLE_IPC=ON` requires [Cap'n Proto](https://capnproto.org/) to b
 
 ### Depends installation
 
-Alternately the [depends system](../depends) can be used to avoid need to install local dependencies. A simple way to get started is to pass the `MULTIPROCESS=1` [dependency option](../depends#dependency-options) to make:
+Alternatively the [depends system](../depends) can be used to avoid needing to local install dependencies:
 
 ```
 cd <BITCOIN_SOURCE_DIRECTORY>
-make -C depends NO_QT=1 MULTIPROCESS=1
+make -C depends NO_QT=1
 # Set host platform to output of gcc -dumpmachine or clang -dumpmachine or check the depends/ directory for the generated subdirectory name
 HOST_PLATFORM="x86_64-pc-linux-gnu"
 cmake -B build --toolchain=depends/$HOST_PLATFORM/toolchain.cmake
@@ -29,7 +29,7 @@ build/src/bitcoin-node -regtest -printtoconsole -debug=ipc
 BITCOIND=$(pwd)/build/src/bitcoin-node build/test/functional/test_runner.py
 ```
 
-The `cmake` build will pick up settings and library locations from the depends directory, so there is no need to pass `-DENABLE_IPC=ON` as a separate flag when using the depends system (it's controlled by the `MULTIPROCESS=1` option).
+The `cmake` build will pick up settings and library locations from the depends directory, so there is no need to pass `-DENABLE_IPC=ON` as a separate flag when using the depends system (it's controlled by the `NO_MULTIPROCESS=1` option).
 
 ### Cross-compiling