Clangd: Let users limit the worker thread count

This is particularly interesting for indexing, where users might prefer
a slower-building index with less CPU load.

Change-Id: Id44c58e9041df2857cd0772e71345673b14623f3
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangcodemodel/clangdclient.cpp

@@ -387,6 +387,8 @@ static BaseClientInterface *clientInterface(const Utils::FilePath &jsonDbDir)
         indexingOption += "=0";
     Utils::CommandLine cmd{CppTools::ClangdSettings::clangdFilePath(),
                            {indexingOption, "--limit-results=0"}};
+    if (CppTools::ClangdSettings::workerThreadLimit() != 0)
+        cmd.addArg("-j=" + QString::number(CppTools::ClangdSettings::workerThreadLimit()));
     if (!jsonDbDir.isEmpty())
         cmd.addArg("--compile-commands-dir=" + jsonDbDir.toString());
     if (clangdLog().isDebugEnabled())

src/plugins/cpptools/cppcodemodelsettings.cpp

@@ -66,6 +66,7 @@ static QString indexerFileSizeLimitKey()
 static QString useClangdKey() { return QLatin1String("UseClangd"); }
 static QString clangdPathKey() { return QLatin1String("ClangdPath"); }
 static QString clangdIndexingKey() { return QLatin1String("ClangdIndexing"); }
+static QString clangdThreadLimitKey() { return QLatin1String("ClangdThreadLimit"); }
 
 static FilePath g_defaultClangdFilePath;
 static FilePath fallbackClangdFilePath()
@@ -303,6 +304,7 @@ static bool operator==(const ClangdSettings::Data &s1, const ClangdSettings::Dat
 {
     return s1.useClangd == s2.useClangd
             && s1.executableFilePath == s2.executableFilePath
+            && s1.workerThreadLimit == s2.workerThreadLimit
             && s1.enableIndexing == s2.enableIndexing;
 }
 static bool operator!=(const ClangdSettings::Data &s1, const ClangdSettings::Data &s2)
@@ -342,6 +344,7 @@ void ClangdSettings::loadSettings()
     m_data.useClangd = s->value(useClangdKey(), false).toBool();
     m_data.executableFilePath = FilePath::fromString(s->value(clangdPathKey()).toString());
     m_data.enableIndexing = s->value(clangdIndexingKey(), true).toBool();
+    m_data.workerThreadLimit = s->value(clangdThreadLimitKey(), 0).toInt();
 }
 
 void ClangdSettings::saveSettings()
@@ -350,6 +353,7 @@ void ClangdSettings::saveSettings()
     s->setValue(useClangdKey(), useClangd());
     s->setValue(clangdPathKey(), m_data.executableFilePath.toString());
     s->setValue(clangdIndexingKey(), m_data.enableIndexing);
+    s->setValue(clangdThreadLimitKey(), m_data.workerThreadLimit);
 }
 
 #ifdef WITH_TESTS

src/plugins/cpptools/cppcodemodelsettings.h

@@ -102,9 +102,10 @@ public:
     class Data
     {
     public:
+        Utils::FilePath executableFilePath;
+        int workerThreadLimit = 0;
         bool useClangd = false;
         bool enableIndexing = true;
-        Utils::FilePath executableFilePath;
     };
 
     static bool useClangd() { return instance().m_data.useClangd; }
@@ -112,6 +113,7 @@ public:
     static void setDefaultClangdPath(const Utils::FilePath &filePath);
     static Utils::FilePath clangdFilePath();
     static bool indexingEnabled() { return instance().m_data.enableIndexing; }
+    static int workerThreadLimit() { return instance().m_data.workerThreadLimit; }
 
     static void setData(const Data &data);
     static Data data() { return instance().m_data; }

src/plugins/cpptools/cppcodemodelsettingspage.cpp

@@ -36,6 +36,7 @@
 #include <utils/pathchooser.h>
 
 #include <QFormLayout>
+#include <QSpinBox>
 #include <QTextStream>
 
 namespace CppTools {
@@ -210,6 +211,10 @@ public:
                 "If background indexing is enabled, global symbol searches will yield\n"
                 "more accurate results, at the cost of additional CPU load when\n"
                 "the project is first opened."));
+        m_threadLimitCheckBox.setText(tr("Set worker thread count limit"));
+        m_threadLimitCheckBox.setChecked(ClangdSettings::workerThreadLimit() != 0);
+        m_threadLimitSpinBox.setMinimum(1);
+        m_threadLimitSpinBox.setValue(ClangdSettings::workerThreadLimit());
 
         const auto layout = new QVBoxLayout(this);
         layout->addWidget(&m_useClangdCheckBox);
@@ -218,6 +223,10 @@ public:
         formLayout->addRow(chooserLabel, &m_clangdChooser);
         const auto indexingLabel = new QLabel(tr("Enable background indexing:"));
         formLayout->addRow(indexingLabel, &m_indexingCheckBox);
+        const auto threadLimitLayout = new QHBoxLayout;
+        threadLimitLayout->addWidget(&m_threadLimitSpinBox);
+        threadLimitLayout->addStretch(1);
+        formLayout->addRow(&m_threadLimitCheckBox, threadLimitLayout);
         layout->addLayout(formLayout);
         layout->addStretch(1);
 
@@ -226,9 +235,15 @@ public:
             m_clangdChooser.setEnabled(checked);
             indexingLabel->setEnabled(checked);
             m_indexingCheckBox.setEnabled(checked);
+            m_threadLimitCheckBox.setEnabled(checked);
+            m_threadLimitSpinBox.setEnabled(checked && m_threadLimitCheckBox.isChecked());
         };
         connect(&m_useClangdCheckBox, &QCheckBox::toggled, toggleEnabled);
+        connect(&m_threadLimitCheckBox, &QCheckBox::toggled,
+                &m_threadLimitSpinBox, &QSpinBox::setEnabled);
         toggleEnabled(m_useClangdCheckBox.isChecked());
+        m_threadLimitSpinBox.setEnabled(m_useClangdCheckBox.isChecked()
+                                        && m_threadLimitCheckBox.isChecked());
     }
 
 private:
@@ -238,11 +253,15 @@ private:
         data.useClangd = m_useClangdCheckBox.isChecked();
         data.executableFilePath = m_clangdChooser.filePath();
         data.enableIndexing = m_indexingCheckBox.isChecked();
+        data.workerThreadLimit = m_threadLimitCheckBox.isChecked()
+                ? m_threadLimitSpinBox.value() : 0;
         ClangdSettings::setData(data);
     }
 
     QCheckBox m_useClangdCheckBox;
     QCheckBox m_indexingCheckBox;
+    QCheckBox m_threadLimitCheckBox;
+    QSpinBox m_threadLimitSpinBox;
     Utils::PathChooser m_clangdChooser;
 };
 
@@ -254,7 +273,5 @@ ClangdSettingsPage::ClangdSettingsPage()
     setWidgetCreator([] { return new ClangdSettingsWidget; });
 }
 
-
-
 } // Internal
 } // CppTools