Cmake: Read the build.ninja file only once

The first getCmakeCXXFlags that reads the build.ninja file
stores the contents in the inout parameter cachedBuildNinja.
Further calls to getCMakeCXXFlags just use this cached value.

This prevents excessive locking of this file while constructing
the code model information.

Change-Id: I81e1431194bed6913c69abb2d954068c999a5c1b
Task-number: QTCREATORBUG-14639
Reviewed-by: Tom Tanner
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

2 files changed, 40 insertions, 27 deletions

diff --git a/src/plugins/cmakeprojectmanager/cmakeproject.cpp b/src/plugins/cmakeprojectmanager/cmakeproject.cpp
index ef10812ffd..8942b98879 100644
--- a/src/plugins/cmakeprojectmanager/cmakeproject.cpp
+++ b/src/plugins/cmakeprojectmanager/cmakeproject.cpp
@@ -177,7 +177,7 @@ void CMakeProject::changeBuildDirectory(CMakeBuildConfiguration *bc, const QStri
     parseCMakeLists();
 }
 
-QStringList CMakeProject::getCXXFlagsFor(const CMakeBuildTarget &buildTarget)
+QStringList CMakeProject::getCXXFlagsFor(const CMakeBuildTarget &buildTarget, QByteArray *cachedBuildNinja)
 {
     QString makeCommand = QDir::fromNativeSeparators(buildTarget.makeCommand);
     int startIndex = makeCommand.indexOf(QLatin1Char('\"'));
@@ -206,32 +206,43 @@ QStringList CMakeProject::getCXXFlagsFor(const CMakeBuildTarget &buildTarget)
     // found
     // Get "all" target's working directory
     if (!buildTargets().empty()) {
-        QString buildNinjaFile = QDir::fromNativeSeparators(buildTargets().at(0).workingDirectory);
-        buildNinjaFile += QLatin1String("/build.ninja");
-        QFile buildNinja(buildNinjaFile);
-        if (buildNinja.exists()) {
-            buildNinja.open(QIODevice::ReadOnly | QIODevice::Text);
-            QTextStream stream(&buildNinja);
-            bool targetFound = false;
-            bool cxxFound = false;
-            QString targetSearchPattern = QString::fromLatin1("target %1").arg(buildTarget.title);
+        if (cachedBuildNinja->isNull()) {
+            QString buildNinjaFile = QDir::fromNativeSeparators(buildTargets().at(0).workingDirectory);
+            buildNinjaFile += QLatin1String("/build.ninja");
+            QFile buildNinja(buildNinjaFile);
+            if (buildNinja.exists()) {
+                buildNinja.open(QIODevice::ReadOnly | QIODevice::Text);
+                *cachedBuildNinja = buildNinja.readAll();
+                buildNinja.close();
+            } else {
+                *cachedBuildNinja = QByteArray();
+            }
+        }
 
-            while (!stream.atEnd()) {
-                // 1. Look for a block that refers to the current target
-                // 2. Look for a build rule which invokes CXX_COMPILER
-                // 3. Return the FLAGS definition
-                QString line = stream.readLine().trimmed();
-                if (line.startsWith(QLatin1String("#"))) {
-                    if (!line.startsWith(QLatin1String("# Object build statements for"))) continue;
-                    targetFound = line.endsWith(targetSearchPattern);
-                } else if (targetFound && line.startsWith(QLatin1String("build"))) {
-                    cxxFound = line.indexOf(QLatin1String("CXX_COMPILER")) != -1;
-                } else if (cxxFound && line.startsWith(QLatin1String("FLAGS ="))) {
-                    // Skip past =
-                    return line.mid(7).trimmed().split(QLatin1Char(' '), QString::SkipEmptyParts);
-                }
+        if (cachedBuildNinja->isEmpty())
+            return QStringList();
+
+        QTextStream stream(cachedBuildNinja);
+        bool targetFound = false;
+        bool cxxFound = false;
+        QString targetSearchPattern = QString::fromLatin1("target %1").arg(buildTarget.title);
+
+        while (!stream.atEnd()) {
+            // 1. Look for a block that refers to the current target
+            // 2. Look for a build rule which invokes CXX_COMPILER
+            // 3. Return the FLAGS definition
+            QString line = stream.readLine().trimmed();
+            if (line.startsWith(QLatin1String("#"))) {
+                if (!line.startsWith(QLatin1String("# Object build statements for"))) continue;
+                targetFound = line.endsWith(targetSearchPattern);
+            } else if (targetFound && line.startsWith(QLatin1String("build"))) {
+                cxxFound = line.indexOf(QLatin1String("CXX_COMPILER")) != -1;
+            } else if (cxxFound && line.startsWith(QLatin1String("FLAGS ="))) {
+                // Skip past =
+                return line.mid(7).trimmed().split(QLatin1Char(' '), QString::SkipEmptyParts);
             }
         }
+
     }
     return QStringList();
 }
@@ -338,13 +349,15 @@ bool CMakeProject::parseCMakeLists()
 
     ppBuilder.setQtVersion(activeQtVersion);
 
+    QByteArray cachedBuildNinja;
     foreach (const CMakeBuildTarget &cbt, m_buildTargets) {
         // This explicitly adds -I. to the include paths
         QStringList includePaths = cbt.includeFiles;
         includePaths += projectDirectory().toString();
         ppBuilder.setIncludePaths(includePaths);
-        ppBuilder.setCFlags(getCXXFlagsFor(cbt));
-        ppBuilder.setCxxFlags(getCXXFlagsFor(cbt));
+        QStringList cxxflags = getCXXFlagsFor(cbt, &cachedBuildNinja);
+        ppBuilder.setCFlags(cxxflags);
+        ppBuilder.setCxxFlags(cxxflags);
         ppBuilder.setDefines(cbt.defines);
         ppBuilder.setDisplayName(cbt.title);
 
diff --git a/src/plugins/cmakeprojectmanager/cmakeproject.h b/src/plugins/cmakeprojectmanager/cmakeproject.h
index db58567df9..ca35b9c7f0 100644
--- a/src/plugins/cmakeprojectmanager/cmakeproject.h
+++ b/src/plugins/cmakeprojectmanager/cmakeproject.h
@@ -139,7 +139,7 @@ private:
     QString uiHeaderFile(const QString &uiFile);
     void updateRunConfigurations(ProjectExplorer::Target *t);
     void updateApplicationAndDeploymentTargets();
-    QStringList getCXXFlagsFor(const CMakeBuildTarget &buildTarget);
+    QStringList getCXXFlagsFor(const CMakeBuildTarget &buildTarget, QByteArray *cachedBuildNinja);
 
     Internal::CMakeManager *m_manager;
     ProjectExplorer::Target *m_activeTarget;