Lower priority on build

This should prevent slowdown of the IDE (and the rest of the system) while
building with all the CPU cores.

Fixes: QTCREATORBUG-5155
Change-Id: Icaadc53958f2d8e918035463e3c9344c91235615
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/process_ctrlc_stub.cpp

@@ -45,6 +45,7 @@
 
 const wchar_t szTitle[] = L"qtcctrlcstub";
 const wchar_t szWindowClass[] = L"wcqtcctrlcstub";
+const wchar_t szNice[] = L"-nice ";
 UINT uiShutDownWindowMessage;
 UINT uiInterruptMessage;
 HWND hwndMain = nullptr;
@@ -53,7 +54,7 @@ LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
 BOOL WINAPI shutdownHandler(DWORD dwCtrlType);
 BOOL WINAPI interruptHandler(DWORD dwCtrlType);
 bool isSpaceOrTab(const wchar_t c);
-bool startProcess(wchar_t pCommandLine[]);
+bool startProcess(wchar_t pCommandLine[], bool lowerPriority);
 
 int main(int argc, char **)
 {
@@ -93,7 +94,14 @@ int main(int argc, char **)
         ++pos;
     }
 
-    bool bSuccess = startProcess(strCommandLine + pos);
+    const size_t niceLen = wcslen(szNice);
+    bool lowerPriority = !wcsncmp(strCommandLine + pos, szNice, niceLen);
+    if (lowerPriority) {
+        pos += niceLen - 1; // reach the space, then the following line skips all spaces.
+        while (isSpaceOrTab(strCommandLine[++pos]))
+            ;
+    }
+    bool bSuccess = startProcess(strCommandLine + pos, lowerPriority);
     free(strCommandLine);
 
     if (!bSuccess)
@@ -166,7 +174,7 @@ DWORD WINAPI processWatcherThread(LPVOID lpParameter)
     return 0;
 }
 
-bool startProcess(wchar_t *pCommandLine)
+bool startProcess(wchar_t *pCommandLine, bool lowerPriority)
 {
     SECURITY_ATTRIBUTES sa = {0};
     sa.nLength = sizeof(sa);
@@ -176,7 +184,7 @@ bool startProcess(wchar_t *pCommandLine)
     si.cb = sizeof(si);
 
     PROCESS_INFORMATION pi;
-    DWORD dwCreationFlags = 0;
+    DWORD dwCreationFlags = lowerPriority ? BELOW_NORMAL_PRIORITY_CLASS : 0;
     BOOL bSuccess = CreateProcess(NULL, pCommandLine, &sa, &sa, TRUE, dwCreationFlags, NULL, NULL, &si, &pi);
     if (!bSuccess) {
         fwprintf(stderr, L"qtcreator_ctrlc_stub: Command line failed: %s\n", pCommandLine);

src/libs/utils/qtcprocess.cpp

@@ -37,6 +37,9 @@
 
 #ifdef Q_OS_WIN
 #include <qt_windows.h>
+#else
+#include <errno.h>
+#include <unistd.h>
 #endif
 
 
@@ -712,9 +715,17 @@ void QtcProcess::start()
     if (osType == OsTypeWindows) {
         QString args;
         if (m_useCtrlCStub) {
-            args = QtcProcess::quoteArg(QDir::toNativeSeparators(command));
+            if (m_lowPriority)
+                addArg(&args, "-nice");
+            addArg(&args, QDir::toNativeSeparators(command));
             command = QCoreApplication::applicationDirPath()
                     + QLatin1String("/qtcreator_ctrlc_stub.exe");
+        } else if (m_lowPriority) {
+#ifdef Q_OS_WIN
+            setCreateProcessArgumentsModifier([](CreateProcessArguments *args) {
+                args->flags |= BELOW_NORMAL_PRIORITY_CLASS;
+            });
+#endif
         }
         QtcProcess::addArgs(&args, arguments.toWindowsArgs());
 #ifdef Q_OS_WIN
@@ -1208,6 +1219,19 @@ QString QtcProcess::expandMacros(const QString &str, AbstractMacroExpander *mx,
     return ret;
 }
 
+void QtcProcess::setupChildProcess()
+{
+#if defined Q_OS_UNIX
+    // nice value range is -20 to +19 where -20 is highest, 0 default and +19 is lowest
+    if (m_lowPriority) {
+        errno = 0;
+        if (::nice(5) == -1 && errno != 0)
+            qWarning("Failed to set nice value. Error: %d", errno);
+    }
+#endif
+    QProcess::setupChildProcess();
+}
+
 bool QtcProcess::ArgIterator::next()
 {
     // We delay the setting of m_prev so we can still delete the last argument

src/libs/utils/qtcprocess.h

@@ -45,6 +45,7 @@ public:
     void start();
     void terminate();
     void interrupt();
+    void setLowPriority() { m_lowPriority = true; }
 
     class QTCREATOR_UTILS_EXPORT Arguments
     {
@@ -141,10 +142,13 @@ public:
     };
 
 private:
+    void setupChildProcess() override;
+
     CommandLine m_commandLine;
     Environment m_environment;
     bool m_haveEnv = false;
     bool m_useCtrlCStub = false;
+    bool m_lowPriority = false;
 };
 
 } // namespace Utils

src/plugins/cmakeprojectmanager/cmakebuildstep.cpp

@@ -87,6 +87,8 @@ CMakeBuildStep::CMakeBuildStep(BuildStepList *bsl) :
     if (m_buildTarget.isEmpty())
         setBuildTarget(defaultBuildTarget());
 
+    setLowPriority();
+
     connect(target(), &Target::kitChanged, this, &CMakeBuildStep::cmakeCommandChanged);
     connect(project(), &Project::parsingFinished,
             this, &CMakeBuildStep::handleBuildTargetChanges);

src/plugins/projectexplorer/abstractprocessstep.cpp

@@ -109,6 +109,7 @@ public:
     QByteArray deferredText;
     bool m_ignoreReturnValue = false;
     bool m_skipFlush = false;
+    bool m_lowPriority = false;
 
     void readData(void (AbstractProcessStep::*func)(const QString &), bool isUtf8 = false);
     void processLine(const QByteArray &data,
@@ -227,6 +228,8 @@ void AbstractProcessStep::doRun()
     d->m_process->setWorkingDirectory(wd.absolutePath());
     d->m_process->setEnvironment(d->m_param.environment());
     d->m_process->setCommand(effectiveCommand);
+    if (d->m_lowPriority)
+        d->m_process->setLowPriority();
 
     connect(d->m_process.get(), &QProcess::readyReadStandardOutput,
             this, &AbstractProcessStep::processReadyReadStdOutput);
@@ -246,6 +249,11 @@ void AbstractProcessStep::doRun()
     processStarted();
 }
 
+void AbstractProcessStep::setLowPriority()
+{
+    d->m_lowPriority = true;
+}
+
 void AbstractProcessStep::doCancel()
 {
     Core::Reaper::reap(d->m_process.release());

src/plugins/projectexplorer/abstractprocessstep.h

@@ -57,6 +57,7 @@ protected:
     ~AbstractProcessStep() override;
     bool init() override;
     void doRun() override;
+    void setLowPriority();
     virtual void finish(bool success);
 
     virtual void processStarted();

src/plugins/projectexplorer/makestep.cpp

@@ -65,6 +65,7 @@ MakeStep::MakeStep(BuildStepList *parent, Core::Id id)
       m_userJobCount(defaultJobCount())
 {
     setDefaultDisplayName(defaultDisplayName());
+    setLowPriority();
 }
 
 void MakeStep::setBuildTarget(const QString &buildTarget)

src/plugins/qmakeprojectmanager/qmakestep.cpp

@@ -76,6 +76,7 @@ QMakeStep::QMakeStep(BuildStepList *bsl) : AbstractProcessStep(bsl, Constants::Q
 {
     //: QMakeStep default display name
     setDefaultDisplayName(tr("qmake"));
+    setLowPriority();
 }
 
 QmakeBuildConfiguration *QMakeStep::qmakeBuildConfiguration() const