Clang: Add Process Generator

So far we only compiled the precompiled headers only sequentially. The
process generator is creating, managing a queue of processes to compile
the PCHs parallel.

Change-Id: I8075def4ef9e6b0191bbd51b3631d1c51ec7b361
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/tools/clangpchmanagerbackend/clangpchmanagerbackendmain.cpp

@@ -27,6 +27,7 @@
 #include <connectionserver.h>
 #include <environment.h>
 #include <pchcreator.h>
+#include <pchgenerator.h>
 #include <pchmanagerserver.h>
 #include <pchmanagerclientproxy.h>
 #include <projectparts.h>
@@ -36,12 +37,16 @@
 #include <QCoreApplication>
 #include <QFileSystemWatcher>
 #include <QLoggingCategory>
+#include <QProcess>
 #include <QTemporaryDir>
 #include <QTimer>
 
+#include <thread>
+
 using ClangBackEnd::ClangPathWatcher;
 using ClangBackEnd::ConnectionServer;
 using ClangBackEnd::PchCreator;
+using ClangBackEnd::PchGenerator;
 using ClangBackEnd::PchManagerClientProxy;
 using ClangBackEnd::PchManagerServer;
 using ClangBackEnd::ProjectParts;
@@ -60,6 +65,11 @@ public:
         return QString(CLANG_COMPILER_PATH);
     }
 
+    uint hardwareConcurrency() const
+    {
+        return std::thread::hardware_concurrency();
+    }
+
 private:
     QTemporaryDir temporaryDirectory;
 };
@@ -96,13 +106,17 @@ int main(int argc, char *argv[])
     StringCache<Utils::SmallString> filePathCache;
     ClangPathWatcher<QFileSystemWatcher, QTimer> includeWatcher(filePathCache);
     ApplicationEnvironment environment;
+    PchGenerator<QProcess> pchGenerator(environment);
     PchCreator pchCreator(environment, filePathCache);
+    pchCreator.setGenerator(&pchGenerator);
     ProjectParts projectParts;
     PchManagerServer clangPchManagerServer(filePathCache,
                                            includeWatcher,
                                            pchCreator,
                                            projectParts);
     includeWatcher.setNotifier(&clangPchManagerServer);
+    pchGenerator.setNotifier(&clangPchManagerServer);
+
     ConnectionServer<PchManagerServer, PchManagerClientProxy> connectionServer(connection);
     connectionServer.start();
     connectionServer.setServer(&clangPchManagerServer);