1 files changed, 103 insertions, 0 deletions
diff --git a/src/ui/widget/canvas/synchronizer.cpp b/src/ui/widget/canvas/synchronizer.cpp
new file mode 100644
index 0000000..331057b
--- /dev/null
+++ b/src/ui/widget/canvas/synchronizer.cpp
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include "synchronizer.h"
+#include <cassert>
+
+namespace Inkscape::UI::Widget {
+
+Synchronizer::Synchronizer()
+{
+    dispatcher.connect([this] { on_dispatcher(); });
+}
+
+void Synchronizer::signalExit() const
+{
+    auto lock = std::unique_lock(mutables);
+    awaken();
+    assert(slots.empty());
+    exitposted = true;
+}
+
+void Synchronizer::runInMain(std::function<void()> const &f) const
+{
+    auto lock = std::unique_lock(mutables);
+    awaken();
+    auto s = Slot{ &f };
+    slots.emplace_back(&s);
+    assert(!exitposted);
+    slots_cond.wait(lock, [&] { return !s.func; });
+}
+
+void Synchronizer::waitForExit() const
+{
+    auto lock = std::unique_lock(mutables);
+    main_blocked = true;
+    while (true) {
+        if (!slots.empty()) {
+            process_slots(lock);
+        } else if (exitposted) {
+            exitposted = false;
+            break;
+        }
+        main_cond.wait(lock);
+    }
+    main_blocked = false;
+}
+
+sigc::connection Synchronizer::connectExit(sigc::slot<void()> const &slot)
+{
+    return signal_exit.connect(slot);
+}
+
+void Synchronizer::awaken() const
+{
+    if (exitposted || !slots.empty()) {
+        return;
+    }
+
+    if (main_blocked) {
+        main_cond.notify_all();
+    } else {
+        const_cast<Glib::Dispatcher&>(dispatcher).emit(); // Glib::Dispatcher is const-incorrect.
+    }
+}
+
+void Synchronizer::on_dispatcher() const
+{
+    auto lock = std::unique_lock(mutables);
+    if (!slots.empty()) {
+        process_slots(lock);
+    } else if (exitposted) {
+        exitposted = false;
+        lock.unlock();
+        signal_exit.emit();
+    }
+}
+
+void Synchronizer::process_slots(std::unique_lock<std::mutex> &lock) const
+{
+    while (!slots.empty()) {
+        auto slots_grabbed = std::move(slots);
+        lock.unlock();
+        for (auto &s : slots_grabbed) {
+            (*s->func)();
+        }
+        lock.lock();
+        for (auto &s : slots_grabbed) {
+            s->func = nullptr;
+        }
+        slots_cond.notify_all();
+    }
+}
+
+} // namespace Inkscape::UI::Widget
+
+/*
+  Local Variables:
+  mode:c++
+  c-file-style:"stroustrup"
+  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+  indent-tabs-mode:nil
+  fill-column:99
+  End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4 :