meson: Pass -j option to sphinx

Save a bit of build time by passing the number of jobs option to
sphinx.

We cannot use  the -j option from make because  meson does not support
setting build time parameters for custom targets. Use nproc instead or
the equivalent sphinx option "-j  auto", if that is available (version
>=1.7.0).

Also make sure our plugins support parallelism and report it properly
to sphinx. Particularly, implement the merge_domaindata method in
DBusDomain that is used to merge in data from other subprocesses.

Tested-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <20230503203947.3417-2-farosas@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/docs/meson.build b/docs/meson.build
index f220800e3e..6d0986579e 100644
--- a/docs/meson.build
+++ b/docs/meson.build
@@ -10,6 +10,18 @@ if sphinx_build.found()
     SPHINX_ARGS += [ '-W', '-Dkerneldoc_werror=1' ]
   endif
 
+  sphinx_version = run_command(SPHINX_ARGS + ['--version'],
+                               check: true).stdout().split()[1]
+  if sphinx_version.version_compare('>=1.7.0')
+    SPHINX_ARGS += ['-j', 'auto']
+  else
+    nproc = find_program('nproc')
+    if nproc.found()
+      jobs = run_command(nproc, check: true).stdout()
+      SPHINX_ARGS += ['-j', jobs]
+    endif
+  endif
+
   # This is a bit awkward but works: create a trivial document and
   # try to run it with our configuration file (which enforces a
   # version requirement). This will fail if sphinx-build is too old.