remove non-single-threaded option

Single-threaded is the build-default, and seems to work well enough for
1.12.7, so remove the option to turn it off.

This is because build-options that influence such low-level/core
behavior are a pain to maintain.

NEWS.org

@@ -15,11 +15,8 @@
 
   - many small mu4e bugs fixed, usually very old ones
 
-  - with 1.12.7, ~mu~ indexing is single-threaded again (by default), to avoid
+  - with 1.12.7, ~mu~ indexing is single-threaded again, to avoid cases of
-    cases of database-corruption that have appeared.
+    database-corruption that have appeared.
-
-  There's the ~-Dxapian-single-threaded=false~ flag to Meson to retain the old
-  behavior.
 
 * 1.12 (released on February 24, 2024)
 

lib/mu-indexer.cc

@@ -106,7 +106,6 @@ struct Indexer::Private {
 
 	void maybe_start_worker();
 
-	void item_worker();
 	void scan_worker();
 
 	bool add_message(const std::string& path);
@@ -123,8 +122,6 @@ struct Indexer::Private {
 	const size_t    max_message_size_;
 
 	::time_t                 dirstamp_{};
-	std::size_t              max_workers_;
-	std::vector<std::thread> workers_;
 	std::thread              scanner_worker_;
 
 	struct WorkItem {
@@ -138,8 +135,6 @@ struct Indexer::Private {
 
 	void handle_item(WorkItem&& item);
 
-	AsyncQueue<WorkItem> todos_;
-
 	Progress   progress_{};
 	IndexState state_{};
 	std::mutex lock_, w_lock_;
@@ -198,11 +193,7 @@ Indexer::Private::handler(const std::string& fullpath, struct stat* statbuf,
 		return true;
 	}
 	case Scanner::HandleType::LeaveDir: {
-#ifdef XAPIAN_SINGLE_THREADED
 		handle_item({fullpath, WorkItem::Type::Dir});
-#else
-		todos_.push({fullpath, WorkItem::Type::Dir});
-#endif /*XAPIAN_SINGLE_THREADED*/
 		return true;
 	}
 
@@ -223,13 +214,7 @@ Indexer::Private::handler(const std::string& fullpath, struct stat* statbuf,
 		if (statbuf->st_ctime <= dirstamp_ && store_.contains_message(fullpath))
 			return false;
 
-#ifdef XAPIAN_SINGLE_THREADED
 		handle_item({fullpath, WorkItem::Type::File});
-#else
-		// push the remaining messages to our "todo" queue for
-		// (re)parsing and adding/updating to the database.
-		todos_.push({fullpath, WorkItem::Type::File});
-#endif
 		return true;
 	}
 	default:
@@ -238,17 +223,6 @@ Indexer::Private::handler(const std::string& fullpath, struct stat* statbuf,
 	}
 }
 
-void
-Indexer::Private::maybe_start_worker()
-{
-	std::lock_guard lock{w_lock_};
-
-	if (todos_.size() > workers_.size() && workers_.size() < max_workers_) {
-		workers_.emplace_back(std::thread([this] { item_worker(); }));
-		mu_debug("added worker {}", workers_.size());
-	}
-}
-
 bool
 Indexer::Private::add_message(const std::string& path)
 {
@@ -299,26 +273,6 @@ Indexer::Private::handle_item(WorkItem&& item)
 	}
 }
 
-
-
-void
-Indexer::Private::item_worker()
-{
-	WorkItem item;
-
-	mu_debug("started worker");
-
-	while (state_ == IndexState::Scanning) {
-		if (!todos_.pop(item, 250ms))
-			continue;
-
-		handle_item(std::move(item));
-
-		maybe_start_worker();
-		std::this_thread::yield();
-	}
-}
-
 bool
 Indexer::Private::cleanup()
 {
@@ -359,28 +313,11 @@ Indexer::Private::scan_worker()
 			state_.change_to(IndexState::Idle);
 			return;
 		}
-		mu_debug("scanner finished with {} file(s) in queue", todos_.size());
+		mu_debug("scanner finished");
 	}
 
-	// now there may still be messages in the work queue...
-	// finish those; this is a bit ugly; perhaps we should
-	// handle SIGTERM etc.
-
-	if (!todos_.empty()) {
-		const auto workers_size = std::invoke([this] {
-			std::lock_guard lock{w_lock_};
-			return workers_.size();
-		});
-		mu_debug("process {} remaining message(s) with {} worker(s)",
-			todos_.size(), workers_size);
-		while (!todos_.empty())
-			std::this_thread::sleep_for(100ms);
-	}
 	// and let the worker finish their work.
 	state_.change_to(IndexState::Finishing);
-	for (auto&& w : workers_)
-		if (w.joinable())
-			w.join();
 
 	if (conf_.cleanup) {
 		mu_debug("starting cleanup");
@@ -402,21 +339,13 @@ Indexer::Private::start(const Indexer::Config& conf, bool block)
 	stop();
 
 	conf_ = conf;
-	if (conf_.max_threads == 0) {
-		/* benchmarking suggests that ~4 threads is the fastest (the
-		 * real bottleneck is the database, so adding more threads just
-		 * slows things down)
-		 */
-		max_workers_ = std::min(4U, std::thread::hardware_concurrency());
-	} else
-		max_workers_ = conf.max_threads;
 
 	if (store_.empty() && conf_.lazy_check) {
 		mu_debug("turn off lazy check since we have an empty store");
 		conf_.lazy_check = false;
 	}
 
-	mu_debug("starting indexer with <= {} worker thread(s)", max_workers_);
+	mu_debug("starting indexer");
 	mu_debug("indexing: {}; clean-up: {}", conf_.scan ? "yes" : "no",
 		 conf_.cleanup ? "yes" : "no");
 
@@ -425,8 +354,6 @@ Indexer::Private::start(const Indexer::Config& conf, bool block)
 	last_index_ = store_.config().get<Mu::Config::Id::LastIndex>();
 
 	state_.change_to(IndexState::Scanning);
-	/* kick off the first worker, which will spawn more if needed. */
-	workers_.emplace_back(std::thread([this] { item_worker(); }));
 	/* kick the disk-scanner thread */
 	scanner_worker_ = std::thread([this] { scan_worker(); });
 
@@ -446,15 +373,10 @@ Indexer::Private::stop()
 {
 	scanner_.stop();
 
-	todos_.clear();
 	if (scanner_worker_.joinable())
 		scanner_worker_.join();
 
 	state_.change_to(IndexState::Idle);
-	for (auto&& w : workers_)
-		if (w.joinable())
-			w.join();
-	workers_.clear();
 
 	return true;
 }
@@ -562,7 +484,6 @@ test_index_basic()
 	}
 
 	conf.lazy_check	     = true;
-	conf.max_threads     = 1;
 	conf.ignore_noupdate = false;
 
 	{

lib/mu-indexer.hh

@@ -49,8 +49,6 @@ public:
 		/**< scan for new messages */
 		bool cleanup{true};
 		/**< clean messages no longer in the file system */
-		size_t max_threads{};
-		/**< maximum # of threads to use */
 		bool ignore_noupdate{};
 		/**< ignore .noupdate files */
 		bool lazy_check{};

lib/mu-server.cc

@@ -785,23 +785,11 @@ Server::Private::index_handler(const Command& cmd)
 	// ignore .noupdate with an empty store.
 	conf.ignore_noupdate = store().empty();
 
-#ifdef XAPIAN_SINGLE_THREADED
 	// nothing to do
 	if (indexer().is_running()) {
 		throw Error{Error::Code::Xapian, "indexer is already running"};
 	}
 	do_index(conf);
-#else
-	indexer().stop();
-	if (index_thread_.joinable())
-		index_thread_.join();
-
-	// start a background track.
-	index_thread_ = std::thread([this, conf = std::move(conf)] {
-		do_index(conf);
-	});
-#endif /*XAPIAN_SINGLE_THREADED */
-
 }
 
 void
@@ -975,9 +963,6 @@ Server::Private::ping_handler(const Command& cmd)
 				       ":personal-addresses", std::move(addrs),
 				       ":database-path", store().path(),
 				       ":root-maildir", store().root_maildir(),
-#ifdef XAPIAN_SINGLE_THREADED
-				       ":xapian-single-threaded", Sexp::t_sym,
-#endif /*XAPIAN_SINGLE_THREADED*/
 				       ":doccount", storecount)));
 }
 

lib/tests/bench-indexer.cc

@@ -467,7 +467,6 @@ benchmark_indexer(gconstpointer testdata)
 		auto store{Store::make_new(BENCH_STORE, BENCH_MAILDIRS)};
 		g_assert_true(!!store);
 		Indexer::Config conf{};
-		conf.max_threads = tdata->num_threads;
 
 		auto res = store->indexer().start(conf);
 		g_assert_true(res);

meson.build

@@ -133,13 +133,6 @@ add_project_arguments(['-DHAVE_CONFIG_H'], language: 'cpp')
 config_h_dep=declare_dependency(
   include_directories: include_directories(['.']))
 
-#
-# single-threaded Xapian access?
-#
-if get_option('xapian-single-threaded')
-  config_h_data.set('XAPIAN_SINGLE_THREADED', true)
-  message('use Xapian only in a single thread')
-endif
 #
 # d_type, d_ino are not available universally, so let's check
 # (we use them for optimizations in mu-scanner

meson_options.txt

@@ -48,7 +48,6 @@ option('guile-extension-dir',
        type: 'string',
        description: 'custom install path for the guile extension module')
 
-
 #
 # misc
 #
@@ -58,11 +57,6 @@ option('tests',
        value: 'auto',
        description: 'build unit tests')
 
-option('xapian-single-threaded',
-       type : 'boolean',
-       value: true,
-       description: 'only use Xapian from a single thread')
-
 option('readline',
        type: 'feature',
        value: 'auto',

mu4e/meson.build

@@ -1,4 +1,4 @@
-## Copyright (C) 2022 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+## Copyright (C) 2022-2024 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
 ##
 ## This program is free software; you can redistribute it and/or modify
 ## it under the terms of the GNU General Public License as published by
@@ -17,9 +17,6 @@
 
 # generate some build data for use in mu4e
 version_extra=''
-if get_option('xapian-single-threaded')
-  version_extra='-st'
-endif
 
 mu4e_meta = configure_file(
   input: 'mu4e-config.el.in',

mu4e/mu4e-main.el

@@ -299,9 +299,7 @@ Otherwise, do nothing."
          "* "
          (propertize "mu4e" 'face 'mu4e-header-key-face)
          (propertize " - mu for emacs version " 'face 'mu4e-title-face)
-         (propertize  (concat mu4e-mu-version
+         (propertize  mu4e-mu-version 'face 'mu4e-header-key-face)
-                              (if (mu4e--server-xapian-single-threaded-p) "-st" ""))
-                      'face 'mu4e-header-key-face)
          "\n\n"
          (propertize "  Basics\n\n" 'face 'mu4e-title-face)
          (mu4e--main-action