Use app::Task instead of raw threads on FilterPreview

We can use a thread pool (avoid creating/destroying threads) and we
can continue the same task running when the filter restart (there is
no need to stop/wait and restart, because the filter task keeps
calling the applyStep() function anyway).

laf

@@ -1 +1 @@
-Subproject commit 41476b78d001b82a72cc6556164bc20954d75636
+Subproject commit 41822911e4091503bf22071a5ce579c2e03d52eb

src/app/commands/filters/filter_preview.cpp

@@ -21,8 +21,6 @@
 #include "ui/message.h"
 #include "ui/widget.h"
 
-#include <thread>
-
 namespace app {
 
 using namespace ui;
@@ -32,8 +30,6 @@ FilterPreview::FilterPreview(FilterManagerImpl* filterMgr)
   : Widget(kGenericWidget)
   , m_filterMgr(filterMgr)
   , m_timer(1, this)
-  , m_filterThread(nullptr)
-  , m_filterIsDone(false)
 {
   setVisible(false);
 }
@@ -67,27 +63,32 @@ void FilterPreview::stop()
       ASSERT(m_filterMgr);
       m_filterMgr->end();
     }
+    m_timer.stop();
   }
-
+  if (m_filterTask.running()) {
-  m_timer.stop();
+    m_filterTask.cancel();
-
+    m_filterTask.wait();
-  if (m_filterThread) {
-    m_filterThread->join();
-    m_filterThread.reset();
   }
 }
 
 void FilterPreview::restartPreview()
 {
-  stop();
-
   std::scoped_lock lock(m_filterMgrMutex);
 
+  // Restart filter, timer, and task if needed (there is no need to
+  // restart the task if it's already running)
+  if (m_timer.isRunning()) {
+    ASSERT(m_filterMgr);
+    m_filterMgr->end();
+  }
   m_filterMgr->beginForPreview();
-  m_filterIsDone = false;
   m_timer.start();
-  m_filterThread.reset(
+
-    new std::thread([this]{ onFilterThread(); }));
+  if (!m_filterTask.running()) {
+    m_filterTask.run([this](base::task_token& token){
+      onFilterTask(token);
+    });
+  }
 }
 
 bool FilterPreview::onProcessMessage(Message* msg)
@@ -112,7 +113,7 @@ bool FilterPreview::onProcessMessage(Message* msg)
       std::scoped_lock lock(m_filterMgrMutex);
       if (m_filterMgr) {
         m_filterMgr->flush();
-        if (m_filterIsDone)
+        if (m_filterTask.completed())
           m_timer.stop();
       }
       break;
@@ -123,14 +124,13 @@ bool FilterPreview::onProcessMessage(Message* msg)
 }
 
 // This is executed in other thread.
-void FilterPreview::onFilterThread()
+void FilterPreview::onFilterTask(base::task_token& token)
 {
-  bool running = true;
+  while (!token.canceled()) {
-  while (running) {
     {
       std::scoped_lock lock(m_filterMgrMutex);
-      m_filterIsDone = !m_filterMgr->applyStep();
+      if (!m_filterMgr->applyStep())
-      running = (!m_filterIsDone && m_timer.isRunning());
+        token.cancel();
     }
     base::this_thread::yield();
   }

src/app/commands/filters/filter_preview.h

@@ -9,11 +9,11 @@
 #define APP_COMMANDS_FILTERS_FILTER_PREVIEW_H_INCLUDED
 #pragma once
 
+#include "app/task.h"
 #include "ui/timer.h"
 #include "ui/widget.h"
 
 #include <mutex>
-#include <thread>
 
 namespace app {
 
@@ -34,12 +34,12 @@ namespace app {
     bool onProcessMessage(ui::Message* msg) override;
 
   private:
-    void onFilterThread();
+    void onFilterTask(base::task_token& token);
 
     FilterManagerImpl* m_filterMgr;
     ui::Timer m_timer;
     std::mutex m_filterMgrMutex;
-    std::unique_ptr<std::thread> m_filterThread;
+    app::Task m_filterTask;
     bool m_filterIsDone;
   };