Merge pull request #8882 from xclaesse/msubprojects-parallel

msubprojects: Run action on all subprojects in parallel

3 files changed, 440 insertions, 338 deletions

diff --git a/docs/markdown/Commands.md b/docs/markdown/Commands.md
index aa538b1..3f3cf9f 100644
--- a/docs/markdown/Commands.md
+++ b/docs/markdown/Commands.md
@@ -228,7 +228,9 @@ meson setup builddir
 
 {{ subprojects_usage.inc }}
 
-Manages subprojects of the Meson project.
+Manages subprojects of the Meson project. *Since 0.59.0* commands are run on
+multiple subprojects in parallel by default, use `--num-processes=1` if it is
+not desired.
 
 {{ subprojects_arguments.inc }}
 
diff --git a/docs/markdown/snippets/subprojects_command_parallel.md b/docs/markdown/snippets/subprojects_command_parallel.md
new file mode 100644
index 0000000..4d992e7
--- /dev/null
+++ b/docs/markdown/snippets/subprojects_command_parallel.md
@@ -0,0 +1,7 @@
+## Parallelized `meson subprojects` commands
+
+All `meson subprojects` commands are now run on each subproject in parallel by
+default. The number of processes can be controlled with `--num-processes`
+argument.
+
+This speeds up considerably IO-bound operations such as downloads and git fetch.
diff --git a/mesonbuild/msubprojects.py b/mesonbuild/msubprojects.py
index 7b608c5..63ea98a 100755
--- a/mesonbuild/msubprojects.py
+++ b/mesonbuild/msubprojects.py
@@ -1,380 +1,460 @@
 import os, subprocess
 import argparse
+import asyncio
+import threading
+import copy
+import shutil
+from concurrent.futures.thread import ThreadPoolExecutor
 from pathlib import Path
+import typing as T
 
 from . import mlog
-from .mesonlib import quiet_git, verbose_git, GitException, Popen_safe, MesonException, windows_proof_rmtree
+from .mesonlib import quiet_git, GitException, Popen_safe, MesonException, windows_proof_rmtree
 from .wrap.wrap import PackageDefinition, Resolver, WrapException, ALL_TYPES
 from .wrap import wraptool
 
 ALL_TYPES_STRING = ', '.join(ALL_TYPES)
 
-def update_wrapdb_file(wrap):
-    try:
-        patch_url = wrap.get('patch_url')
-        branch, revision = wraptool.parse_patch_url(patch_url)
-    except WrapException:
-        return
-    new_branch, new_revision = wraptool.get_latest_version(wrap.name)
-    if new_branch != branch or new_revision != revision:
-        wraptool.update_wrap_file(wrap.filename, wrap.name, new_branch, new_revision)
-        mlog.log('  -> New wrap file downloaded.')
-
-def update_file(r, wrap, repo_dir, options):
-    update_wrapdb_file(wrap)
-    if not os.path.isdir(repo_dir):
-        # The subproject is not needed, or it is a tarball extracted in
-        # 'libfoo-1.0' directory and the version has been bumped and the new
-        # directory is 'libfoo-2.0'. In that case forcing a meson
-        # reconfigure will download and use the new tarball.
-        mlog.log('  -> Not used.')
-        return True
-    elif options.reset:
-        # Delete existing directory and redownload. It is possible that nothing
-        # changed but we have no way to know. Hopefully tarballs are still
-        # cached.
-        windows_proof_rmtree(repo_dir)
+class Logger:
+    def __init__(self, total_tasks: int) -> None:
+        self.lock = threading.Lock()
+        self.total_tasks = total_tasks
+        self.completed_tasks = 0
+        self.running_tasks = set()
+        self.should_erase_line = ''
+
+    def flush(self) -> None:
+        if self.should_erase_line:
+            print(self.should_erase_line, end='\r')
+            self.should_erase_line = ''
+
+    def print_progress(self) -> None:
+        line = f'Progress: {self.completed_tasks} / {self.total_tasks}'
+        max_len = shutil.get_terminal_size().columns - len(line)
+        running = ', '.join(self.running_tasks)
+        if len(running) + 3 > max_len:
+            running = running[:max_len - 6] + '...'
+        line = line + f' ({running})'
+        print(self.should_erase_line, line, sep='', end='\r')
+        self.should_erase_line = '\x1b[K'
+
+    def start(self, wrap_name: str) -> None:
+        with self.lock:
+            self.running_tasks.add(wrap_name)
+            self.print_progress()
+
+    def done(self, wrap_name: str, log_queue: T.List[T.Tuple[mlog.TV_LoggableList, T.Any]]) -> None:
+        with self.lock:
+            self.flush()
+            for args, kwargs in log_queue:
+                mlog.log(*args, **kwargs)
+            self.running_tasks.remove(wrap_name)
+            self.completed_tasks += 1
+            self.print_progress()
+
+
+class Runner:
+    def __init__(self, logger: Logger, r: Resolver, wrap: PackageDefinition, repo_dir: str, options: argparse.Namespace) -> None:
+        # FIXME: Do a copy because Resolver.resolve() is stateful method that
+        # cannot be called from multiple threads.
+        self.wrap_resolver = copy.copy(r)
+        self.wrap = wrap
+        self.repo_dir = repo_dir
+        self.options = options
+        self.run_method = options.subprojects_func.__get__(self)
+        self.log_queue = []
+        self.logger = logger
+
+    def log(self, *args, **kwargs):
+        self.log_queue.append((args, kwargs))
+
+    def run(self):
+        self.logger.start(self.wrap.name)
+        result = self.run_method()
+        self.logger.done(self.wrap.name, self.log_queue)
+        return result
+
+    def update_wrapdb_file(self):
         try:
-            r.resolve(wrap.name, 'meson')
-            mlog.log('  -> New version extracted')
+            patch_url = self.wrap.get('patch_url')
+            branch, revision = wraptool.parse_patch_url(patch_url)
+        except WrapException:
+            return
+        new_branch, new_revision = wraptool.get_latest_version(self.wrap.name)
+        if new_branch != branch or new_revision != revision:
+            wraptool.update_wrap_file(self.wrap.filename, self.wrap.name, new_branch, new_revision)
+            self.log('  -> New wrap file downloaded.')
+
+    def update_file(self):
+        self.update_wrapdb_file()
+        if not os.path.isdir(self.repo_dir):
+            # The subproject is not needed, or it is a tarball extracted in
+            # 'libfoo-1.0' directory and the version has been bumped and the new
+            # directory is 'libfoo-2.0'. In that case forcing a meson
+            # reconfigure will download and use the new tarball.
+            self.log('  -> Not used.')
             return True
-        except WrapException as e:
-            mlog.log('  ->', mlog.red(str(e)))
-            return False
-    else:
-        # The subproject has not changed, or the new source and/or patch
-        # tarballs should be extracted in the same directory than previous
-        # version.
-        mlog.log('  -> Subproject has not changed, or the new source/patch needs to be extracted on the same location.')
-        mlog.log('     Pass --reset option to delete directory and redownload.')
-        return False
-
-def git_output(cmd, workingdir):
-    return quiet_git(cmd, workingdir, check=True)[1]
-
-def git_stash(workingdir):
-    # That git command return 1 (failure) when there is something to stash.
-    # We don't want to stash when there is nothing to stash because that would
-    # print spurious "No local changes to save".
-    if not quiet_git(['diff', '--quiet', 'HEAD'], workingdir)[0]:
-        # Don't pipe stdout here because we want the user to see their changes have
-        # been saved.
-        verbose_git(['stash'], workingdir, check=True)
-
-def git_show(repo_dir):
-    commit_message = git_output(['show', '--quiet', '--pretty=format:%h%n%d%n%s%n[%an]'], repo_dir)
-    parts = [s.strip() for s in commit_message.split('\n')]
-    mlog.log('  ->', mlog.yellow(parts[0]), mlog.red(parts[1]), parts[2], mlog.blue(parts[3]))
-
-def git_rebase(repo_dir, revision):
-    try:
-        git_output(['-c', 'rebase.autoStash=true', 'rebase', 'FETCH_HEAD'], repo_dir)
-    except GitException as e:
-        mlog.log('  -> Could not rebase', mlog.bold(repo_dir), 'onto', mlog.bold(revision))
-        mlog.log(mlog.red(e.output))
-        mlog.log(mlog.red(str(e)))
-        return False
-    return True
-
-def git_reset(repo_dir, revision):
-    try:
-        # Stash local changes, commits can always be found back in reflog, to
-        # avoid any data lost by mistake.
-        git_stash(repo_dir)
-        git_output(['reset', '--hard', 'FETCH_HEAD'], repo_dir)
-    except GitException as e:
-        mlog.log('  -> Could not reset', mlog.bold(repo_dir), 'to', mlog.bold(revision))
-        mlog.log(mlog.red(e.output))
-        mlog.log(mlog.red(str(e)))
-        return False
-    return True
-
-def git_checkout(repo_dir, revision, create=False):
-    cmd = ['checkout', '--ignore-other-worktrees', revision, '--']
-    if create:
-        cmd.insert('-b', 1)
-    try:
-        # Stash local changes, commits can always be found back in reflog, to
-        # avoid any data lost by mistake.
-        git_stash(repo_dir)
-        git_output(cmd, repo_dir)
-    except GitException as e:
-        mlog.log('  -> Could not checkout', mlog.bold(revision), 'in', mlog.bold(repo_dir))
-        mlog.log(mlog.red(e.output))
-        mlog.log(mlog.red(str(e)))
-        return False
-    return True
-
-def git_checkout_and_reset(repo_dir, revision):
-    # revision could be a branch that already exists but is outdated, so we still
-    # have to reset after the checkout.
-    success = git_checkout(repo_dir, revision)
-    if success:
-        success = git_reset(repo_dir, revision)
-    return success
-
-def git_checkout_and_rebase(repo_dir, revision):
-    # revision could be a branch that already exists but is outdated, so we still
-    # have to rebase after the checkout.
-    success = git_checkout(repo_dir, revision)
-    if success:
-        success = git_rebase(repo_dir, revision)
-    return success
-
-def update_git(r, wrap, repo_dir, options):
-    if not os.path.isdir(repo_dir):
-        mlog.log('  -> Not used.')
-        return True
-    if not os.path.exists(os.path.join(repo_dir, '.git')):
-        if options.reset:
-            # Delete existing directory and redownload
-            windows_proof_rmtree(repo_dir)
+        elif self.options.reset:
+            # Delete existing directory and redownload. It is possible that nothing
+            # changed but we have no way to know. Hopefully tarballs are still
+            # cached.
+            windows_proof_rmtree(self.repo_dir)
             try:
-                r.resolve(wrap.name, 'meson')
-                update_git_done(repo_dir)
+                self.wrap_resolver.resolve(self.wrap.name, 'meson')
+                self.log('  -> New version extracted')
                 return True
             except WrapException as e:
-                mlog.log('  ->', mlog.red(str(e)))
+                self.log('  ->', mlog.red(str(e)))
                 return False
         else:
-            mlog.log('  -> Not a git repository.')
-            mlog.log('Pass --reset option to delete directory and redownload.')
+            # The subproject has not changed, or the new source and/or patch
+            # tarballs should be extracted in the same directory than previous
+            # version.
+            self.log('  -> Subproject has not changed, or the new source/patch needs to be extracted on the same location.')
+            self.log('     Pass --reset option to delete directory and redownload.')
+            return False
+
+    def git_output(self, cmd):
+        return quiet_git(cmd, self.repo_dir, check=True)[1]
+
+    def git_verbose(self, cmd):
+        self.log(self.git_output(cmd))
+
+    def git_stash(self):
+        # That git command return 1 (failure) when there is something to stash.
+        # We don't want to stash when there is nothing to stash because that would
+        # print spurious "No local changes to save".
+        if not quiet_git(['diff', '--quiet', 'HEAD'], self.repo_dir)[0]:
+            # Don't pipe stdout here because we want the user to see their changes have
+            # been saved.
+            self.git_verbose(['stash'])
+
+    def git_show(self):
+        commit_message = self.git_output(['show', '--quiet', '--pretty=format:%h%n%d%n%s%n[%an]'])
+        parts = [s.strip() for s in commit_message.split('\n')]
+        self.log('  ->', mlog.yellow(parts[0]), mlog.red(parts[1]), parts[2], mlog.blue(parts[3]))
+
+    def git_rebase(self, revision):
+        try:
+            self.git_output(['-c', 'rebase.autoStash=true', 'rebase', 'FETCH_HEAD'])
+        except GitException as e:
+            self.log('  -> Could not rebase', mlog.bold(self.repo_dir), 'onto', mlog.bold(revision))
+            self.log(mlog.red(e.output))
+            self.log(mlog.red(str(e)))
             return False
-    revision = wrap.values.get('revision')
-    url = wrap.values.get('url')
-    push_url = wrap.values.get('push-url')
-    if not revision or not url:
-        # It could be a detached git submodule for example.
-        mlog.log('  -> No revision or URL specified.')
         return True
-    try:
-        origin_url = git_output(['remote', 'get-url', 'origin'], repo_dir).strip()
-    except GitException as e:
-        mlog.log('  -> Failed to determine current origin URL in', mlog.bold(repo_dir))
-        mlog.log(mlog.red(e.output))
-        mlog.log(mlog.red(str(e)))
-        return False
-    if options.reset:
+
+    def git_reset(self, revision):
         try:
-            git_output(['remote', 'set-url', 'origin', url], repo_dir)
-            if push_url:
-                git_output(['remote', 'set-url', '--push', 'origin', push_url], repo_dir)
+            # Stash local changes, commits can always be found back in reflog, to
+            # avoid any data lost by mistake.
+            self.git_stash()
+            self.git_output(['reset', '--hard', 'FETCH_HEAD'])
         except GitException as e:
-            mlog.log('  -> Failed to reset origin URL in', mlog.bold(repo_dir))
-            mlog.log(mlog.red(e.output))
-            mlog.log(mlog.red(str(e)))
+            self.log('  -> Could not reset', mlog.bold(repo_dir), 'to', mlog.bold(revision))
+            self.log(mlog.red(e.output))
+            self.log(mlog.red(str(e)))
             return False
-    elif url != origin_url:
-        mlog.log(f'  -> URL changed from {origin_url!r} to {url!r}')
-        return False
-    try:
-        # Same as `git branch --show-current` but compatible with older git version
-        branch = git_output(['rev-parse', '--abbrev-ref', 'HEAD'], repo_dir).strip()
-        branch = branch if branch != 'HEAD' else ''
-    except GitException as e:
-        mlog.log('  -> Failed to determine current branch in', mlog.bold(repo_dir))
-        mlog.log(mlog.red(e.output))
-        mlog.log(mlog.red(str(e)))
-        return False
-    try:
-        # Fetch only the revision we need, this avoids fetching useless branches.
-        # revision can be either a branch, tag or commit id. In all cases we want
-        # FETCH_HEAD to be set to the desired commit and "git checkout <revision>"
-        # to to either switch to existing/new branch, or detach to tag/commit.
-        # It is more complicated than it first appear, see discussion there:
-        # https://github.com/mesonbuild/meson/pull/7723#discussion_r488816189.
-        heads_refmap = '+refs/heads/*:refs/remotes/origin/*'
-        tags_refmap = '+refs/tags/*:refs/tags/*'
-        git_output(['fetch', '--refmap', heads_refmap, '--refmap', tags_refmap, 'origin', revision], repo_dir)
-    except GitException as e:
-        mlog.log('  -> Could not fetch revision', mlog.bold(revision), 'in', mlog.bold(repo_dir))
-        mlog.log(mlog.red(e.output))
-        mlog.log(mlog.red(str(e)))
-        return False
+        return True
 
-    if branch == '':
-        # We are currently in detached mode
-        if options.reset:
-            success = git_checkout_and_reset(repo_dir, revision)
-        else:
-            success = git_checkout_and_rebase(repo_dir, revision)
-    elif branch == revision:
-        # We are in the same branch. A reset could still be needed in the case
-        # a force push happened on remote repository.
-        if options.reset:
-            success = git_reset(repo_dir, revision)
+    def git_checkout(self, revision, create=False):
+        cmd = ['checkout', '--ignore-other-worktrees', revision, '--']
+        if create:
+            cmd.insert('-b', 1)
+        try:
+            # Stash local changes, commits can always be found back in reflog, to
+            # avoid any data lost by mistake.
+            self.git_stash()
+            self.git_output(cmd)
+        except GitException as e:
+            self.log('  -> Could not checkout', mlog.bold(revision), 'in', mlog.bold(self.repo_dir))
+            self.log(mlog.red(e.output))
+            self.log(mlog.red(str(e)))
+            return False
+        return True
+
+    def git_checkout_and_reset(self, revision):
+        # revision could be a branch that already exists but is outdated, so we still
+        # have to reset after the checkout.
+        success = self.git_checkout(revision)
+        if success:
+            success = self.git_reset(revision)
+        return success
+
+    def git_checkout_and_rebase(self, revision):
+        # revision could be a branch that already exists but is outdated, so we still
+        # have to rebase after the checkout.
+        success = self.git_checkout(revision)
+        if success:
+            success = self.git_rebase(revision)
+        return success
+
+    def update_git(self):
+        if not os.path.isdir(self.repo_dir):
+            self.log('  -> Not used.')
+            return True
+        if not os.path.exists(os.path.join(self.repo_dir, '.git')):
+            if self.options.reset:
+                # Delete existing directory and redownload
+                windows_proof_rmtree(self.repo_dir)
+                try:
+                    self.wrap_resolver.resolve(self.wrap.name, 'meson')
+                    self.update_git_done()
+                    return True
+                except WrapException as e:
+                    self.log('  ->', mlog.red(str(e)))
+                    return False
+            else:
+                self.log('  -> Not a git repository.')
+                self.log('Pass --reset option to delete directory and redownload.')
+                return False
+        revision = self.wrap.values.get('revision')
+        url = self.wrap.values.get('url')
+        push_url = self.wrap.values.get('push-url')
+        if not revision or not url:
+            # It could be a detached git submodule for example.
+            self.log('  -> No revision or URL specified.')
+            return True
+        try:
+            origin_url = self.git_output(['remote', 'get-url', 'origin']).strip()
+        except GitException as e:
+            self.log('  -> Failed to determine current origin URL in', mlog.bold(self.repo_dir))
+            self.log(mlog.red(e.output))
+            self.log(mlog.red(str(e)))
+            return False
+        if self.options.reset:
+            try:
+                self.git_output(['remote', 'set-url', 'origin', url])
+                if push_url:
+                    self.git_output(['remote', 'set-url', '--push', 'origin', push_url])
+            except GitException as e:
+                self.log('  -> Failed to reset origin URL in', mlog.bold(self.repo_dir))
+                self.log(mlog.red(e.output))
+                self.log(mlog.red(str(e)))
+                return False
+        elif url != origin_url:
+            self.log(f'  -> URL changed from {origin_url!r} to {url!r}')
+            return False
+        try:
+            # Same as `git branch --show-current` but compatible with older git version
+            branch = self.git_output(['rev-parse', '--abbrev-ref', 'HEAD']).strip()
+            branch = branch if branch != 'HEAD' else ''
+        except GitException as e:
+            self.log('  -> Failed to determine current branch in', mlog.bold(self.repo_dir))
+            self.log(mlog.red(e.output))
+            self.log(mlog.red(str(e)))
+            return False
+        try:
+            # Fetch only the revision we need, this avoids fetching useless branches.
+            # revision can be either a branch, tag or commit id. In all cases we want
+            # FETCH_HEAD to be set to the desired commit and "git checkout <revision>"
+            # to to either switch to existing/new branch, or detach to tag/commit.
+            # It is more complicated than it first appear, see discussion there:
+            # https://github.com/mesonbuild/meson/pull/7723#discussion_r488816189.
+            heads_refmap = '+refs/heads/*:refs/remotes/origin/*'
+            tags_refmap = '+refs/tags/*:refs/tags/*'
+            self.git_output(['fetch', '--refmap', heads_refmap, '--refmap', tags_refmap, 'origin', revision])
+        except GitException as e:
+            self.log('  -> Could not fetch revision', mlog.bold(revision), 'in', mlog.bold(self.repo_dir))
+            self.log(mlog.red(e.output))
+            self.log(mlog.red(str(e)))
+            return False
+
+        if branch == '':
+            # We are currently in detached mode
+            if self.options.reset:
+                success = self.git_checkout_and_reset(revision)
+            else:
+                success = self.git_checkout_and_rebase(revision)
+        elif branch == revision:
+            # We are in the same branch. A reset could still be needed in the case
+            # a force push happened on remote repository.
+            if self.options.reset:
+                success = self.git_reset(revision)
+            else:
+                success = self.git_rebase(revision)
         else:
-            success = git_rebase(repo_dir, revision)
-    else:
-        # We are in another branch, either the user created their own branch and
-        # we should rebase it, or revision changed in the wrap file and we need
-        # to checkout the new branch.
-        if options.reset:
-            success = git_checkout_and_reset(repo_dir, revision)
+            # We are in another branch, either the user created their own branch and
+            # we should rebase it, or revision changed in the wrap file and we need
+            # to checkout the new branch.
+            if self.options.reset:
+                success = self.git_checkout_and_reset(revision)
+            else:
+                success = self.git_rebase(revision)
+        if success:
+            self.update_git_done()
+        return success
+
+    def update_git_done(self):
+        self.git_output(['submodule', 'update', '--checkout', '--recursive'])
+        self.git_show()
+
+    def update_hg(self):
+        if not os.path.isdir(self.repo_dir):
+            self.log('  -> Not used.')
+            return True
+        revno = self.wrap.get('revision')
+        if revno.lower() == 'tip':
+            # Failure to do pull is not a fatal error,
+            # because otherwise you can't develop without
+            # a working net connection.
+            subprocess.call(['hg', 'pull'], cwd=self.repo_dir)
         else:
-            success = git_rebase(repo_dir, revision)
-    if success:
-        update_git_done(repo_dir)
-    return success
-
-def update_git_done(repo_dir):
-    git_output(['submodule', 'update', '--checkout', '--recursive'], repo_dir)
-    git_show(repo_dir)
-
-def update_hg(r, wrap, repo_dir, options):
-    if not os.path.isdir(repo_dir):
-        mlog.log('  -> Not used.')
+            if subprocess.call(['hg', 'checkout', revno], cwd=self.repo_dir) != 0:
+                subprocess.check_call(['hg', 'pull'], cwd=self.repo_dir)
+                subprocess.check_call(['hg', 'checkout', revno], cwd=self.repo_dir)
         return True
-    revno = wrap.get('revision')
-    if revno.lower() == 'tip':
-        # Failure to do pull is not a fatal error,
-        # because otherwise you can't develop without
-        # a working net connection.
-        subprocess.call(['hg', 'pull'], cwd=repo_dir)
-    else:
-        if subprocess.call(['hg', 'checkout', revno], cwd=repo_dir) != 0:
-            subprocess.check_call(['hg', 'pull'], cwd=repo_dir)
-            subprocess.check_call(['hg', 'checkout', revno], cwd=repo_dir)
-    return True
-
-def update_svn(r, wrap, repo_dir, options):
-    if not os.path.isdir(repo_dir):
-        mlog.log('  -> Not used.')
-        return True
-    revno = wrap.get('revision')
-    p, out, _ = Popen_safe(['svn', 'info', '--show-item', 'revision', repo_dir])
-    current_revno = out
-    if current_revno == revno:
-        return True
-    if revno.lower() == 'head':
-        # Failure to do pull is not a fatal error,
-        # because otherwise you can't develop without
-        # a working net connection.
-        subprocess.call(['svn', 'update'], cwd=repo_dir)
-    else:
-        subprocess.check_call(['svn', 'update', '-r', revno], cwd=repo_dir)
-    return True
-
-def update(r, wrap, repo_dir, options):
-    mlog.log(f'Updating {wrap.name}...')
-    if wrap.type == 'file':
-        return update_file(r, wrap, repo_dir, options)
-    elif wrap.type == 'git':
-        return update_git(r, wrap, repo_dir, options)
-    elif wrap.type == 'hg':
-        return update_hg(r, wrap, repo_dir, options)
-    elif wrap.type == 'svn':
-        return update_svn(r, wrap, repo_dir, options)
-    elif wrap.type is None:
-        mlog.log('  -> Cannot update subproject with no wrap file')
-    else:
-        mlog.log('  -> Cannot update', wrap.type, 'subproject')
-    return True
 
-def checkout(r, wrap, repo_dir, options):
-    if wrap.type != 'git' or not os.path.isdir(repo_dir):
-        return True
-    branch_name = options.branch_name if options.branch_name else wrap.get('revision')
-    if not branch_name:
-        # It could be a detached git submodule for example.
-        return True
-    mlog.log(f'Checkout {branch_name} in {wrap.name}...')
-    if git_checkout(repo_dir, branch_name, create=options.b):
-        git_show(repo_dir)
+    def update_svn(self):
+        if not os.path.isdir(self.repo_dir):
+            self.log('  -> Not used.')
+            return True
+        revno = self.wrap.get('revision')
+        p, out, _ = Popen_safe(['svn', 'info', '--show-item', 'revision', self.repo_dir])
+        current_revno = out
+        if current_revno == revno:
+            return True
+        if revno.lower() == 'head':
+            # Failure to do pull is not a fatal error,
+            # because otherwise you can't develop without
+            # a working net connection.
+            subprocess.call(['svn', 'update'], cwd=self.repo_dir)
+        else:
+            subprocess.check_call(['svn', 'update', '-r', revno], cwd=self.repo_dir)
         return True
-    return False
 
-def download(r, wrap, repo_dir, options):
-    mlog.log(f'Download {wrap.name}...')
-    if os.path.isdir(repo_dir):
-        mlog.log('  -> Already downloaded')
+    def update(self):
+        self.log(f'Updating {self.wrap.name}...')
+        if self.wrap.type == 'file':
+            return self.update_file()
+        elif self.wrap.type == 'git':
+            return self.update_git()
+        elif self.wrap.type == 'hg':
+            return self.update_hg()
+        elif self.wrap.type == 'svn':
+            return self.update_svn()
+        elif self.wrap.type is None:
+            self.log('  -> Cannot update subproject with no wrap file')
+        else:
+            self.log('  -> Cannot update', self.wrap.type, 'subproject')
         return True
-    try:
-        r.resolve(wrap.name, 'meson')
-        mlog.log('  -> done')
-    except WrapException as e:
-        mlog.log('  ->', mlog.red(str(e)))
+
+    def checkout(self):
+        if self.wrap.type != 'git' or not os.path.isdir(self.repo_dir):
+            return True
+        branch_name = self.options.branch_name if self.options.branch_name else self.wrap.get('revision')
+        if not branch_name:
+            # It could be a detached git submodule for example.
+            return True
+        self.log(f'Checkout {branch_name} in {self.wrap.name}...')
+        if self.git_checkout(branch_name, create=self.options.b):
+            self.git_show()
+            return True
         return False
-    return True
 
-def foreach(r, wrap, repo_dir, options):
-    mlog.log(f'Executing command in {repo_dir}')
-    if not os.path.isdir(repo_dir):
-        mlog.log('  -> Not downloaded yet')
+    def download(self):
+        self.log(f'Download {self.wrap.name}...')
+        if os.path.isdir(self.repo_dir):
+            self.log('  -> Already downloaded')
+            return True
+        try:
+            self.wrap_resolver.resolve(self.wrap.name, 'meson')
+            self.log('  -> done')
+        except WrapException as e:
+            self.log('  ->', mlog.red(str(e)))
+            return False
         return True
-    cmd = [options.command] + options.args
-    p, out, _ = Popen_safe(cmd, stderr=subprocess.STDOUT, cwd=repo_dir)
-    if p.returncode != 0:
-        err_message = "Command '{}' returned non-zero exit status {}.".format(" ".join(cmd), p.returncode)
-        mlog.log('  -> ', mlog.red(err_message))
-        mlog.log(out, end='')
-        return False
 
-    mlog.log(out, end='')
-    return True
+    def foreach(self):
+        self.log(f'Executing command in {self.repo_dir}')
+        if not os.path.isdir(self.repo_dir):
+            self.log('  -> Not downloaded yet')
+            return True
+        cmd = [self.options.command] + self.options.args
+        p, out, _ = Popen_safe(cmd, stderr=subprocess.STDOUT, cwd=self.repo_dir)
+        if p.returncode != 0:
+            err_message = "Command '{}' returned non-zero exit status {}.".format(" ".join(cmd), p.returncode)
+            self.log('  -> ', mlog.red(err_message))
+            self.log(out, end='')
+            return False
 
-def purge(r: Resolver, wrap: PackageDefinition, repo_dir: str, options: argparse.Namespace) -> bool:
-    # if subproject is not wrap-based, then don't remove it
-    if not wrap.type:
+        self.log(out, end='')
         return True
 
-    if wrap.type == 'redirect':
-        redirect_file = Path(wrap.filename).resolve()
-        if options.confirm:
-            redirect_file.unlink()
-        mlog.log(f'Deleting {redirect_file}')
+    def purge(self) -> bool:
+        # if subproject is not wrap-based, then don't remove it
+        if not self.wrap.type:
+            return True
 
-    if options.include_cache:
-        packagecache = Path(r.cachedir).resolve()
-        try:
-            subproject_cache_file = packagecache / wrap.get("source_filename")
-            if subproject_cache_file.is_file():
-                if options.confirm:
-                    subproject_cache_file.unlink()
-                mlog.log(f'Deleting {subproject_cache_file}')
-        except WrapException:
-            pass
+        if self.wrap.type == 'redirect':
+            redirect_file = Path(self.wrap.filename).resolve()
+            if self.options.confirm:
+                redirect_file.unlink()
+            self.log(f'Deleting {redirect_file}')
 
-        try:
-            subproject_patch_file = packagecache / wrap.get("patch_filename")
-            if subproject_patch_file.is_file():
-                if options.confirm:
-                    subproject_patch_file.unlink()
-                mlog.log(f'Deleting {subproject_patch_file}')
-        except WrapException:
-            pass
+        if self.options.include_cache:
+            packagecache = Path(self.wrap_resolver.cachedir).resolve()
+            try:
+                subproject_cache_file = packagecache / self.wrap.get("source_filename")
+                if subproject_cache_file.is_file():
+                    if self.options.confirm:
+                        subproject_cache_file.unlink()
+                    self.log(f'Deleting {subproject_cache_file}')
+            except WrapException:
+                pass
 
-        # Don't log that we will remove an empty directory
-        if packagecache.exists() and not any(packagecache.iterdir()):
-            packagecache.rmdir()
+            try:
+                subproject_patch_file = packagecache / self.wrap.get("patch_filename")
+                if subproject_patch_file.is_file():
+                    if self.options.confirm:
+                        subproject_patch_file.unlink()
+                    self.log(f'Deleting {subproject_patch_file}')
+            except WrapException:
+                pass
+
+            # Don't log that we will remove an empty directory. Since purge is
+            # parallelized, another thread could have deleted it already.
+            try:
+                if not any(packagecache.iterdir()):
+                    packagecache.rmdir()
+            except FileNotFoundError:
+                pass
+
+        subproject_source_dir = Path(self.repo_dir).resolve()
+
+        # Don't follow symlink. This is covered by the next if statement, but why
+        # not be doubly sure.
+        if subproject_source_dir.is_symlink():
+            if self.options.confirm:
+                subproject_source_dir.unlink()
+            self.log(f'Deleting {subproject_source_dir}')
+            return True
+        if not subproject_source_dir.is_dir():
+            return True
 
-    subproject_source_dir = Path(repo_dir).resolve()
+        try:
+            if self.options.confirm:
+                windows_proof_rmtree(str(subproject_source_dir))
+            self.log(f'Deleting {subproject_source_dir}')
+        except OSError as e:
+            mlog.error(f'Unable to remove: {subproject_source_dir}: {e}')
+            return False
 
-    # Don't follow symlink. This is covered by the next if statement, but why
-    # not be doubly sure.
-    if subproject_source_dir.is_symlink():
-        if options.confirm:
-            subproject_source_dir.unlink()
-        mlog.log(f'Deleting {subproject_source_dir}')
-        return True
-    if not subproject_source_dir.is_dir():
         return True
 
-    try:
-        if options.confirm:
-            windows_proof_rmtree(str(subproject_source_dir))
-        mlog.log(f'Deleting {subproject_source_dir}')
-    except OSError as e:
-        mlog.error(f'Unable to remove: {subproject_source_dir}: {e}')
-        return False
-
-    return True
+    @staticmethod
+    def post_purge(options):
+        if not options.confirm:
+            mlog.log('')
+            mlog.log('Nothing has been deleted, run again with --confirm to apply.')
 
 def add_common_arguments(p):
     p.add_argument('--sourcedir', default='.',
                    help='Path to source directory')
     p.add_argument('--types', default='',
                    help=f'Comma-separated list of subproject types. Supported types are: {ALL_TYPES_STRING} (default: all)')
+    p.add_argument('--num-processes', default=None, type=int,
+                   help='How many parallel processes to use (Since 0.59.0).')
 
 def add_subprojects_argument(p):
     p.add_argument('subprojects', nargs='*',
@@ -392,7 +472,7 @@ def add_arguments(parser):
                    help='Checkout wrap\'s revision and hard reset to that commit. (git only)')
     add_common_arguments(p)
     add_subprojects_argument(p)
-    p.set_defaults(subprojects_func=update)
+    p.set_defaults(subprojects_func=Runner.update)
 
     p = subparsers.add_parser('checkout', help='Checkout a branch (git only)')
     p.add_argument('-b', default=False, action='store_true',
@@ -401,14 +481,14 @@ def add_arguments(parser):
                    help='Name of the branch to checkout or create (default: revision set in wrap file)')
     add_common_arguments(p)
     add_subprojects_argument(p)
-    p.set_defaults(subprojects_func=checkout)
+    p.set_defaults(subprojects_func=Runner.checkout)
 
     p = subparsers.add_parser('download', help='Ensure subprojects are fetched, even if not in use. ' +
                                                'Already downloaded subprojects are not modified. ' +
                                                'This can be used to pre-fetch all subprojects and avoid downloads during configure.')
     add_common_arguments(p)
     add_subprojects_argument(p)
-    p.set_defaults(subprojects_func=download)
+    p.set_defaults(subprojects_func=Runner.download)
 
     p = subparsers.add_parser('foreach', help='Execute a command in each subproject directory.')
     p.add_argument('command', metavar='command ...',
@@ -417,14 +497,15 @@ def add_arguments(parser):
                    help=argparse.SUPPRESS)
     add_common_arguments(p)
     p.set_defaults(subprojects=[])
-    p.set_defaults(subprojects_func=foreach)
+    p.set_defaults(subprojects_func=Runner.foreach)
 
     p = subparsers.add_parser('purge', help='Remove all wrap-based subproject artifacts')
     add_common_arguments(p)
     add_subprojects_argument(p)
     p.add_argument('--include-cache', action='store_true', default=False, help='Remove the package cache as well')
     p.add_argument('--confirm', action='store_true', default=False, help='Confirm the removal of subproject artifacts')
-    p.set_defaults(subprojects_func=purge)
+    p.set_defaults(subprojects_func=Runner.purge)
+    p.set_defaults(post_func=Runner.post_purge)
 
 def run(options):
     src_dir = os.path.relpath(os.path.realpath(options.sourcedir))
@@ -444,13 +525,25 @@ def run(options):
     for t in types:
         if t not in ALL_TYPES:
             raise MesonException(f'Unknown subproject type {t!r}, supported types are: {ALL_TYPES_STRING}')
-    failures = []
+    tasks = []
+    task_names = []
+    loop = asyncio.get_event_loop()
+    executor = ThreadPoolExecutor(options.num_processes)
+    if types:
+        wraps = [wrap for wrap in wraps if wrap.type in types]
+    logger = Logger(len(wraps))
     for wrap in wraps:
-        if types and wrap.type not in types:
-            continue
         dirname = Path(subprojects_dir, wrap.directory).as_posix()
-        if not options.subprojects_func(r, wrap, dirname, options):
-            failures.append(wrap.name)
+        runner = Runner(logger, r, wrap, dirname, options)
+        task = loop.run_in_executor(executor, runner.run)
+        tasks.append(task)
+        task_names.append(wrap.name)
+    results = loop.run_until_complete(asyncio.gather(*tasks))
+    logger.flush()
+    post_func = getattr(options, 'post_func', None)
+    if post_func:
+        post_func(options)
+    failures = [name for name, success in zip(task_names, results) if not success]
     if failures:
         m = 'Please check logs above as command failed in some subprojects which could have been left in conflict state: '
         m += ', '.join(failures)