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>

23 files changed, 885 insertions, 96 deletions

diff --git a/src/tools/clangpchmanagerbackend/clangpchmanagerbackendmain.cpp b/src/tools/clangpchmanagerbackend/clangpchmanagerbackendmain.cpp
index 45ddec5bd6..c189e148ec 100644
--- a/src/tools/clangpchmanagerbackend/clangpchmanagerbackendmain.cpp
+++ b/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);
diff --git a/src/tools/clangpchmanagerbackend/source/clangpchmanagerbackend-source.pri b/src/tools/clangpchmanagerbackend/source/clangpchmanagerbackend-source.pri
index b6c36b3945..ec5714df5e 100644
--- a/src/tools/clangpchmanagerbackend/source/clangpchmanagerbackend-source.pri
+++ b/src/tools/clangpchmanagerbackend/source/clangpchmanagerbackend-source.pri
@@ -10,7 +10,9 @@ SOURCES += \
     $$PWD/pchcreatorinterface.cpp \
     $$PWD/clangpathwatcherinterface.cpp \
     $$PWD/projectpartsinterface.cpp \
-    $$PWD/clangpathwatchernotifier.cpp
+    $$PWD/clangpathwatchernotifier.cpp \
+    $$PWD/pchgeneratornotifierinterface.cpp \
+    $$PWD/pchgeneratorinterface.cpp
 
 HEADERS += \
     $$PWD/clangpchmanagerbackend_global.h \
@@ -30,4 +32,7 @@ HEADERS += \
     $$PWD/clangpathwatcherinterface.h \
     $$PWD/projectpartsinterface.h \
     $$PWD/clangpathwatchernotifier.h \
-    $$PWD/changedfilepathcompressor.h
+    $$PWD/changedfilepathcompressor.h \
+    $$PWD/pchgenerator.h \
+    $$PWD/pchgeneratornotifierinterface.h \
+    $$PWD/pchgeneratorinterface.h
diff --git a/src/tools/clangpchmanagerbackend/source/collectincludespreprocessorcallbacks.h b/src/tools/clangpchmanagerbackend/source/collectincludespreprocessorcallbacks.h
index 4dbf0d9758..7be403006b 100644
--- a/src/tools/clangpchmanagerbackend/source/collectincludespreprocessorcallbacks.h
+++ b/src/tools/clangpchmanagerbackend/source/collectincludespreprocessorcallbacks.h
@@ -64,16 +64,18 @@ public:
                             llvm::StringRef /*relativePath*/,
                             const clang::Module */*imported*/) override
     {
-        auto fileUID = file->getUID();
-
-        flagIncludeAlreadyRead(file);
-
-        if (isNotInExcludedIncludeUID(fileUID)) {
-            auto notAlreadyIncluded = isNotAlreadyIncluded(fileUID);
-            if (notAlreadyIncluded.first) {
-                m_alreadyIncludedFileUIDs.insert(notAlreadyIncluded.second, fileUID);
-                uint includeId = m_filePathCache.stringId({fileName.data(), fileName.size()});
-                m_includeIds.emplace_back(includeId);
+        if (file) {
+            auto fileUID = file->getUID();
+
+            flagIncludeAlreadyRead(file);
+
+            if (isNotInExcludedIncludeUID(fileUID)) {
+                auto notAlreadyIncluded = isNotAlreadyIncluded(fileUID);
+                if (notAlreadyIncluded.first) {
+                    m_alreadyIncludedFileUIDs.insert(notAlreadyIncluded.second, fileUID);
+                    uint includeId = m_filePathCache.stringId({fileName.data(), fileName.size()});
+                    m_includeIds.emplace_back(includeId);
+                }
             }
         }
     }
diff --git a/src/tools/clangpchmanagerbackend/source/environment.h b/src/tools/clangpchmanagerbackend/source/environment.h
index 4fe7442c17..879065093b 100644
--- a/src/tools/clangpchmanagerbackend/source/environment.h
+++ b/src/tools/clangpchmanagerbackend/source/environment.h
@@ -34,6 +34,7 @@ class Environment
 public:
     virtual QString pchBuildDirectory() const = 0;
     virtual QString clangCompilerPath() const = 0;
+    virtual uint hardwareConcurrency() const = 0;
 };
 
 } // namespace ClangBackEnd
diff --git a/src/tools/clangpchmanagerbackend/source/pchcreator.cpp b/src/tools/clangpchmanagerbackend/source/pchcreator.cpp
index 560e6a2bb5..0b2d1c67ae 100644
--- a/src/tools/clangpchmanagerbackend/source/pchcreator.cpp
+++ b/src/tools/clangpchmanagerbackend/source/pchcreator.cpp
@@ -33,7 +33,6 @@
 
 #include <QCryptographicHash>
 #include <QFile>
-#include <QProcess>
 
 namespace ClangBackEnd {
 
@@ -45,10 +44,12 @@ PchCreator::PchCreator(Environment &environment, StringCache<Utils::SmallString>
 
 PchCreator::PchCreator(V2::ProjectPartContainers &&projectsParts,
                        Environment &environment,
-                       StringCache<Utils::SmallString> &filePathCache)
+                       StringCache<Utils::SmallString> &filePathCache,
+                       PchGeneratorInterface *pchGenerator)
     : m_projectParts(std::move(projectsParts)),
       m_environment(environment),
-      m_filePathCache(filePathCache)
+      m_filePathCache(filePathCache),
+      m_pchGenerator(pchGenerator)
 {
 }
 
@@ -258,23 +259,17 @@ std::unique_ptr<QFile> PchCreator::generateGlobalPchHeaderFile()
                                  generateGlobalPchHeaderFileContent());
 }
 
-void PchCreator::generatePch(const Utils::SmallStringVector &clangCompilerArguments)
+void PchCreator::generatePch(Utils::SmallStringVector &&compilerArguments,
+                             ProjectPartPch &&projectPartPch)
 {
-    QProcess process;
-    process.setProcessChannelMode(QProcess::ForwardedChannels);
-
-    process.start(m_environment.clangCompilerPath(),
-                  convertToQStringList(clangCompilerArguments));
-    process.waitForFinished(100000);
-
-    checkIfProcessHasError(process);
+    m_pchGenerator->startTask(std::move(compilerArguments), std::move(projectPartPch));
 }
 
 void PchCreator::generateGlobalPch()
 {
     generateGlobalPchHeaderFile();
 
-    generatePch(generateGlobalClangCompilerArguments());
+    generatePch(generateGlobalClangCompilerArguments(), ProjectPartPch());
 }
 
 QStringList PchCreator::convertToQStringList(const Utils::SmallStringVector &compilerArguments)
@@ -310,14 +305,6 @@ QByteArray PchCreator::globalProjectHash() const
     return result.toBase64(QByteArray::Base64UrlEncoding | QByteArray::OmitTrailingEquals);
 }
 
-void PchCreator::checkIfProcessHasError(const QProcess &process)
-{
-    if (process.exitCode()) {
-        const std::string errorString = process.errorString().toStdString();
-        throw PchNotCreatedError(errorString);
-    }
-}
-
 Utils::SmallString PchCreator::generateGlobalPchFilePathWithoutExtension() const
 {
     QByteArray fileName = m_environment.pchBuildDirectory().toUtf8();
@@ -449,27 +436,25 @@ Utils::SmallStringVector PchCreator::generateProjectPartClangCompilerArguments(
     return compilerArguments;
 }
 
-std::pair<ProjectPartPch, IdPaths> PchCreator::generateProjectPartPch(
-        const V2::ProjectPartContainer &projectPart)
+IdPaths PchCreator::generateProjectPartPch(const V2::ProjectPartContainer &projectPart)
 {
     auto includes = generateProjectPartPchIncludes(projectPart);
     auto content = generatePchIncludeFileContent(includes);
     auto pchIncludeFilePath = generateProjectPathPchHeaderFilePath(projectPart);
     auto pchFilePath = generateProjectPartPchFilePath(projectPart);
-    auto file = generatePchHeaderFile(pchIncludeFilePath, content);
+    generatePchHeaderFile(pchIncludeFilePath, content);
 
-    generatePch(generateProjectPartClangCompilerArguments(projectPart));
+    generatePch(generateProjectPartClangCompilerArguments(projectPart),
+                {projectPart.projectPartId().clone(), std::move(pchFilePath)});
 
-    return {{projectPart.projectPartId().clone(), std::move(pchFilePath)},
-            {projectPart.projectPartId().clone(), includes}};
+    return {projectPart.projectPartId().clone(), std::move(includes)};
 }
 
 void PchCreator::generatePchs()
 {
     for (const V2::ProjectPartContainer &projectPart : m_projectParts) {
-        auto projectInfos = generateProjectPartPch(projectPart);
-        m_projectPartPchs.push_back(projectInfos.first);
-        m_projectsIncludeIds.push_back(projectInfos.second);
+        auto includePaths = generateProjectPartPch(projectPart);
+        m_projectsIncludeIds.push_back(std::move(includePaths));
     }
 }
 
@@ -480,14 +465,14 @@ void PchCreator::generatePchs(V2::ProjectPartContainers &&projectsParts)
     generatePchs();
 }
 
-std::vector<ProjectPartPch> PchCreator::takeProjectPartPchs()
+std::vector<IdPaths> PchCreator::takeProjectsIncludes()
 {
-    return std::move(m_projectPartPchs);
+    return std::move(m_projectsIncludeIds);
 }
 
-std::vector<IdPaths> PchCreator::takeProjectsIncludes()
+void PchCreator::setGenerator(PchGeneratorInterface *pchGenerator)
 {
-    return std::move(m_projectsIncludeIds);
+    m_pchGenerator = pchGenerator;
 }
 
 std::unique_ptr<QFile> PchCreator::generatePchHeaderFile(
diff --git a/src/tools/clangpchmanagerbackend/source/pchcreator.h b/src/tools/clangpchmanagerbackend/source/pchcreator.h
index 5bc38cb58b..7affe82f6c 100644
--- a/src/tools/clangpchmanagerbackend/source/pchcreator.h
+++ b/src/tools/clangpchmanagerbackend/source/pchcreator.h
@@ -27,6 +27,7 @@
 
 #include "pchcreatorinterface.h"
 
+#include "pchgeneratorinterface.h"
 #include "stringcache.h"
 #include "idpaths.h"
 
@@ -50,12 +51,14 @@ public:
                StringCache<Utils::SmallString> &filePathCache);
     PchCreator(V2::ProjectPartContainers &&projectsParts,
                Environment &environment,
-               StringCache<Utils::SmallString> &filePathCache);
+               StringCache<Utils::SmallString> &filePathCache,
+               PchGeneratorInterface *pchGenerator);
 
     void generatePchs(V2::ProjectPartContainers &&projectsParts) override;
-    std::vector<ProjectPartPch> takeProjectPartPchs() override;
     std::vector<IdPaths> takeProjectsIncludes() override;
 
+    void setGenerator(PchGeneratorInterface *pchGenerator);
+
 unitttest_public:
     Utils::SmallStringVector generateGlobalHeaderPaths() const;
     Utils::SmallStringVector generateGlobalSourcePaths() const;
@@ -70,7 +73,8 @@ unitttest_public:
     Utils::SmallString generatePchIncludeFileContent(const std::vector<uint> &includeIds) const;
     Utils::SmallString generateGlobalPchHeaderFileContent() const;
     std::unique_ptr<QFile> generateGlobalPchHeaderFile();
-    void generatePch(const Utils::SmallStringVector &commandLineArguments);
+    void generatePch(Utils::SmallStringVector &&commandLineArguments,
+                     ProjectPartPch &&projectPartPch);
     void generateGlobalPch();
 
     Utils::SmallString globalPchContent() const;
@@ -97,7 +101,7 @@ unitttest_public:
             const V2::ProjectPartContainer &projectPart) const;
     Utils::SmallStringVector generateProjectPartClangCompilerArguments(
              const V2::ProjectPartContainer &projectPart) const;
-    std::pair<ProjectPartPch, IdPaths> generateProjectPartPch(
+    IdPaths generateProjectPartPch(
             const V2::ProjectPartContainer &projectPart);
     static std::unique_ptr<QFile> generatePchHeaderFile(
             const Utils::SmallString &filePath,
@@ -108,7 +112,6 @@ unitttest_public:
 private:
     static QByteArray projectPartHash(const V2::ProjectPartContainer &projectPart);
     QByteArray globalProjectHash() const;
-    static void checkIfProcessHasError(const QProcess &process);
 
 private:
     V2::ProjectPartContainers m_projectParts;
@@ -116,6 +119,7 @@ private:
     std::vector<IdPaths> m_projectsIncludeIds;
     Environment &m_environment;
     StringCache<Utils::SmallString> &m_filePathCache;
+    PchGeneratorInterface *m_pchGenerator = nullptr;
 };
 
 } // namespace ClangBackEnd
diff --git a/src/tools/clangpchmanagerbackend/source/pchcreatorinterface.h b/src/tools/clangpchmanagerbackend/source/pchcreatorinterface.h
index 89aac39bd5..f2e6f0f6a2 100644
--- a/src/tools/clangpchmanagerbackend/source/pchcreatorinterface.h
+++ b/src/tools/clangpchmanagerbackend/source/pchcreatorinterface.h
@@ -38,7 +38,6 @@ public:
     virtual ~PchCreatorInterface();
 
     virtual void generatePchs(V2::ProjectPartContainers &&projectsParts) = 0;
-    virtual std::vector<ProjectPartPch> takeProjectPartPchs() = 0;
     virtual std::vector<IdPaths> takeProjectsIncludes() = 0;
 };
 
diff --git a/src/tools/clangpchmanagerbackend/source/pchgenerator.h b/src/tools/clangpchmanagerbackend/source/pchgenerator.h
new file mode 100644
index 0000000000..7c5b50f13b
--- /dev/null
+++ b/src/tools/clangpchmanagerbackend/source/pchgenerator.h
@@ -0,0 +1,165 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include "environment.h"
+#include "pchgeneratorinterface.h"
+#include "pchgeneratornotifierinterface.h"
+
+#include <projectpartpch.h>
+
+#include <QProcess>
+
+#include <queue>
+
+namespace ClangBackEnd {
+
+template <typename Process>
+class PchGenerator final : public PchGeneratorInterface
+{
+public:
+    PchGenerator(Environment &environment,
+                 PchGeneratorNotifierInterface *notifier=nullptr)
+        : m_environment(environment),
+          m_notifier(notifier)
+    {
+    }
+
+    ~PchGenerator()
+    {
+        cleanupAllProcesses();
+    }
+
+    void startTask(Utils::SmallStringVector &&compilerArguments, ProjectPartPch &&projectPartPch) override
+    {
+        addTask(std::move(compilerArguments), std::move(projectPartPch));
+    }
+
+    void setNotifier(PchGeneratorNotifierInterface *notifier)
+    {
+        m_notifier = notifier;
+    }
+
+unitttest_public:
+    Process *addTask(Utils::SmallStringVector &&compilerArguments, ProjectPartPch &&projectPartPch)
+    {
+        auto process = std::make_unique<Process>();
+        Process *processPointer = process.get();
+
+        process->setProcessChannelMode(QProcess::ForwardedChannels);
+        process->setArguments(compilerArguments);
+        process->setProgram(m_environment.clangCompilerPath());
+
+        connectProcess(processPointer, std::move(projectPartPch));
+
+        if (!deferProcess())
+            startProcess(std::move(process));
+        else
+            m_deferredProcesses.push(std::move(process));
+
+        return processPointer;
+    }
+
+    void connectProcess(Process *process, ProjectPartPch &&projectPartPch)
+    {
+        auto finishedCallback = [=,projectPartPch=std::move(projectPartPch)] (int exitCode, QProcess::ExitStatus exitStatus) {
+            deleteProcess(process);
+            activateNextDeferredProcess();
+            m_notifier->taskFinished(generateTaskFinishStatus(exitCode, exitStatus), projectPartPch);
+        };
+
+        QObject::connect(process,
+                         static_cast<void (Process::*)(int, QProcess::ExitStatus)>(&Process::finished),
+                         std::move(finishedCallback));
+    }
+
+    void startProcess(std::unique_ptr<Process> &&process)
+    {
+        process->start();
+        m_runningProcesses.push_back(std::move(process));
+    }
+
+    const std::vector<std::unique_ptr<Process>> &runningProcesses() const
+    {
+        return m_runningProcesses;
+    }
+
+    const std::queue<std::unique_ptr<Process>> &deferredProcesses() const
+    {
+        return m_deferredProcesses;
+    }
+
+    void deleteProcess(Process *process)
+    {
+        auto found = std::find_if(m_runningProcesses.begin(),
+                     m_runningProcesses.end(),
+                     [=] (const std::unique_ptr<Process> &entry) {
+            return entry.get() == process;
+        });
+
+        if (found != m_runningProcesses.end()) {
+            std::unique_ptr<Process> avoidDoubleDeletedProcess = std::move(*found);
+            m_runningProcesses.erase(found);
+        }
+    }
+
+    void cleanupAllProcesses()
+    {
+        std::vector<std::unique_ptr<Process>> runningProcesses = std::move(m_runningProcesses);
+        std::queue<std::unique_ptr<Process>> deferredProcesses = std::move(m_deferredProcesses);
+    }
+
+    static TaskFinishStatus generateTaskFinishStatus(int exitCode, QProcess::ExitStatus exitStatus)
+    {
+        if (exitCode != 0 || exitStatus != QProcess::NormalExit)
+            return TaskFinishStatus::Unsuccessfully;
+         else
+            return TaskFinishStatus::Successfully;
+    }
+
+    bool deferProcess() const
+    {
+        return m_environment.hardwareConcurrency() <= m_runningProcesses.size();
+    }
+
+    void activateNextDeferredProcess()
+    {
+        if (!m_deferredProcesses.empty()) {
+            std::unique_ptr<Process> process = std::move(m_deferredProcesses.front());
+            m_deferredProcesses.pop();
+
+            startProcess(std::move(process));
+        }
+    }
+
+private:
+    std::vector<std::unique_ptr<Process>> m_runningProcesses;
+    std::queue<std::unique_ptr<Process>> m_deferredProcesses;
+    Environment &m_environment;
+    PchGeneratorNotifierInterface *m_notifier=nullptr;
+};
+
+} // namespace ClangBackEnd
diff --git a/src/tools/clangpchmanagerbackend/source/pchgeneratorinterface.cpp b/src/tools/clangpchmanagerbackend/source/pchgeneratorinterface.cpp
new file mode 100644
index 0000000000..7653ed71b2
--- /dev/null
+++ b/src/tools/clangpchmanagerbackend/source/pchgeneratorinterface.cpp
@@ -0,0 +1,31 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#include "pchgeneratorinterface.h"
+
+ClangBackEnd::PchGeneratorInterface::~PchGeneratorInterface()
+{
+
+}
diff --git a/src/tools/clangpchmanagerbackend/source/pchgeneratorinterface.h b/src/tools/clangpchmanagerbackend/source/pchgeneratorinterface.h
new file mode 100644
index 0000000000..9e942a3a06
--- /dev/null
+++ b/src/tools/clangpchmanagerbackend/source/pchgeneratorinterface.h
@@ -0,0 +1,45 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include <utils/smallstringvector.h>
+
+namespace ClangBackEnd {
+
+class ProjectPartPch;
+
+class PchGeneratorInterface
+{
+public:
+    virtual ~PchGeneratorInterface();
+
+    virtual void startTask(Utils::SmallStringVector &&compilerArguments,
+                           ProjectPartPch &&projectPartPch) = 0;
+
+};
+
+} // namespace ClangBackEnd
+
diff --git a/src/tools/clangpchmanagerbackend/source/pchgeneratornotifierinterface.cpp b/src/tools/clangpchmanagerbackend/source/pchgeneratornotifierinterface.cpp
new file mode 100644
index 0000000000..d37446d3a9
--- /dev/null
+++ b/src/tools/clangpchmanagerbackend/source/pchgeneratornotifierinterface.cpp
@@ -0,0 +1,53 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#include "pchgeneratornotifierinterface.h"
+
+#include <ostream>
+
+namespace ClangBackEnd {
+
+PchGeneratorNotifierInterface::~PchGeneratorNotifierInterface()
+{
+
+}
+
+std::ostream &operator<<(std::ostream &out, TaskFinishStatus status)
+{
+    enum class TaskFinishStatus
+    {
+        Successfully,
+        Unsuccessfully
+    };
+
+    if (status == ClangBackEnd::TaskFinishStatus::Successfully)
+        out << "Successfully";
+    else
+        out << "Unsuccessfully";
+
+    return out;
+}
+
+} // namespace ClangBackEnd
diff --git a/src/tools/clangpchmanagerbackend/source/pchgeneratornotifierinterface.h b/src/tools/clangpchmanagerbackend/source/pchgeneratornotifierinterface.h
new file mode 100644
index 0000000000..32611750ad
--- /dev/null
+++ b/src/tools/clangpchmanagerbackend/source/pchgeneratornotifierinterface.h
@@ -0,0 +1,50 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include <iosfwd>
+
+namespace ClangBackEnd {
+
+class ProjectPartPch;
+
+enum class TaskFinishStatus
+{
+    Successfully,
+    Unsuccessfully
+};
+
+class PchGeneratorNotifierInterface
+{
+public:
+    virtual ~PchGeneratorNotifierInterface();
+
+    virtual void taskFinished(TaskFinishStatus status, const ProjectPartPch &projectPartPch) = 0;
+};
+
+std::ostream &operator<<(std::ostream &out, TaskFinishStatus status);
+
+} // namespace ClangBackEnd
diff --git a/src/tools/clangpchmanagerbackend/source/pchmanagerserver.cpp b/src/tools/clangpchmanagerbackend/source/pchmanagerserver.cpp
index 71ec82e45c..271412bf36 100644
--- a/src/tools/clangpchmanagerbackend/source/pchmanagerserver.cpp
+++ b/src/tools/clangpchmanagerbackend/source/pchmanagerserver.cpp
@@ -58,8 +58,6 @@ void PchManagerServer::updatePchProjectParts(UpdatePchProjectPartsMessage &&mess
 {
     m_pchCreator.generatePchs(m_projectParts.update(message.takeProjectsParts()));
 
-    client()->precompiledHeadersUpdated(PrecompiledHeadersUpdatedMessage(m_pchCreator.takeProjectPartPchs()));
-
     m_fileSystemWatcher.updateIdPaths(m_pchCreator.takeProjectsIncludes());
 }
 
@@ -74,9 +72,13 @@ void PchManagerServer::pathsWithIdsChanged(const Utils::SmallStringVector &ids)
 {
     m_pchCreator.generatePchs(m_projectParts.projects(ids));
 
-    client()->precompiledHeadersUpdated(PrecompiledHeadersUpdatedMessage(m_pchCreator.takeProjectPartPchs()));
-
     m_fileSystemWatcher.updateIdPaths(m_pchCreator.takeProjectsIncludes());
 }
 
+void PchManagerServer::taskFinished(TaskFinishStatus status, const ProjectPartPch &projectPartPch)
+{
+    if (status == TaskFinishStatus::Successfully)
+        client()->precompiledHeadersUpdated(PrecompiledHeadersUpdatedMessage({projectPartPch.clone()}));
+}
+
 } // namespace ClangBackEnd
diff --git a/src/tools/clangpchmanagerbackend/source/pchmanagerserver.h b/src/tools/clangpchmanagerbackend/source/pchmanagerserver.h
index b12ffeca7f..2e504dfe8e 100644
--- a/src/tools/clangpchmanagerbackend/source/pchmanagerserver.h
+++ b/src/tools/clangpchmanagerbackend/source/pchmanagerserver.h
@@ -28,6 +28,7 @@
 #include "clangpathwatcherinterface.h"
 #include "clangpathwatchernotifier.h"
 #include "pchcreatorinterface.h"
+#include "pchgeneratornotifierinterface.h"
 #include "pchmanagerserverinterface.h"
 #include "projectpartsinterface.h"
 #include "stringcache.h"
@@ -36,7 +37,9 @@ namespace ClangBackEnd {
 
 class SourceRangesAndDiagnosticsForQueryMessage;
 
-class PchManagerServer : public PchManagerServerInterface, public ClangPathWatcherNotifier
+class PchManagerServer : public PchManagerServerInterface,
+                         public ClangPathWatcherNotifier,
+                         public PchGeneratorNotifierInterface
 {
 public:
     PchManagerServer(StringCache<Utils::SmallString> &filePathCache,
@@ -50,6 +53,7 @@ public:
     void removePchProjectParts(RemovePchProjectPartsMessage &&message) override;
 
     void pathsWithIdsChanged(const Utils::SmallStringVector &ids) override;
+    void taskFinished(TaskFinishStatus status, const ProjectPartPch &projectPartPch) override;
 
 private:
     StringCache<Utils::SmallString> &m_filePathCache;
diff --git a/tests/unit/unittest/fakeprocess.cpp b/tests/unit/unittest/fakeprocess.cpp
new file mode 100644
index 0000000000..e4eb8592e6
--- /dev/null
+++ b/tests/unit/unittest/fakeprocess.cpp
@@ -0,0 +1,88 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#include "fakeprocess.h"
+
+FakeProcess::FakeProcess()
+{
+}
+
+FakeProcess::~FakeProcess()
+{
+    if (m_isStarted && !m_isFinished)
+        emit finished(0, QProcess::NormalExit);
+}
+
+void FakeProcess::finishUnsuccessfully()
+{
+    m_isFinished = true;
+    emit finished(1, QProcess::NormalExit);
+}
+
+void FakeProcess::finishByCrash()
+{
+    m_isFinished = true;
+    emit finished(0, QProcess::CrashExit);
+}
+
+void FakeProcess::finish()
+{
+    m_isFinished = true;
+    emit finished(0, QProcess::NormalExit);
+}
+
+void FakeProcess::setArguments(const QStringList &arguments)
+{
+    m_arguments = arguments;
+}
+
+void FakeProcess::setProgram(const QString &program)
+{
+    m_applicationPath = program;
+}
+
+void FakeProcess::setProcessChannelMode(QProcess::ProcessChannelMode)
+{
+}
+
+void FakeProcess::start()
+{
+    m_isStarted = true;
+}
+
+bool FakeProcess::isStarted() const
+{
+    return m_isStarted;
+}
+
+const QStringList &FakeProcess::arguments() const
+{
+    return m_arguments;
+}
+
+const QString &FakeProcess::applicationPath() const
+{
+    return m_applicationPath;
+}
diff --git a/tests/unit/unittest/fakeprocess.h b/tests/unit/unittest/fakeprocess.h
new file mode 100644
index 0000000000..88642b303d
--- /dev/null
+++ b/tests/unit/unittest/fakeprocess.h
@@ -0,0 +1,62 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include <QProcess>
+
+class FakeProcess : public QObject
+{
+    Q_OBJECT
+
+public:
+    FakeProcess();
+    ~FakeProcess();
+
+    void finishUnsuccessfully();
+    void finishByCrash();
+    void finish();
+
+    void start();
+    void setArguments(const QStringList &arguments);
+    void setProgram(const QString &program);
+
+    void setProcessChannelMode(QProcess::ProcessChannelMode mode);
+
+
+    bool isStarted() const;
+
+    const QStringList &arguments() const;
+    const QString &applicationPath() const;
+
+signals:
+    void finished(int exitCode, QProcess::ExitStatus exitStatus);
+
+private:
+    QStringList m_arguments;
+    QString m_applicationPath;
+    bool m_isFinished = false;
+    bool m_isStarted = false;
+};
diff --git a/tests/unit/unittest/mockpchcreator.h b/tests/unit/unittest/mockpchcreator.h
index d4cbd62793..761c10b316 100644
--- a/tests/unit/unittest/mockpchcreator.h
+++ b/tests/unit/unittest/mockpchcreator.h
@@ -36,8 +36,6 @@ class MockPchCreator : public ClangBackEnd::PchCreatorInterface
 public:
     MOCK_METHOD1(generatePchs,
                  void(const std::vector<ClangBackEnd::V2::ProjectPartContainer> &projectParts));
-    MOCK_METHOD0(takeProjectPartPchs,
-                 std::vector<ClangBackEnd::ProjectPartPch>());
     MOCK_METHOD0(takeProjectsIncludes,
                  std::vector<ClangBackEnd::IdPaths>());
 
diff --git a/tests/unit/unittest/mockpchgeneratornotifier.h b/tests/unit/unittest/mockpchgeneratornotifier.h
new file mode 100644
index 0000000000..fe5b8b2af4
--- /dev/null
+++ b/tests/unit/unittest/mockpchgeneratornotifier.h
@@ -0,0 +1,38 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include "googletest.h"
+
+#include <pchgeneratornotifierinterface.h>
+
+class MockPchGeneratorNotifier : public ClangBackEnd::PchGeneratorNotifierInterface
+{
+public:
+    MOCK_METHOD2(taskFinished,
+                 void (ClangBackEnd::TaskFinishStatus status,
+                       const ClangBackEnd::ProjectPartPch &projectPartPch));
+};
diff --git a/tests/unit/unittest/pchcreator-test.cpp b/tests/unit/unittest/pchcreator-test.cpp
index d57c2b7fe2..bf44fbdbb9 100644
--- a/tests/unit/unittest/pchcreator-test.cpp
+++ b/tests/unit/unittest/pchcreator-test.cpp
@@ -25,9 +25,12 @@
 
 #include "googletest.h"
 
+#include "fakeprocess.h"
+#include "mockpchgeneratornotifier.h"
 #include "testenvironment.h"
 
 #include <pchcreator.h>
+#include <pchgenerator.h>
 #include <stringcache.h>
 
 #include <QFileInfo>
@@ -70,9 +73,12 @@ protected:
                                       {header2Path.clone()},
                                       {main2Path.clone()}};
     TestEnvironment environment;
+    NiceMock<MockPchGeneratorNotifier> mockPchGeneratorNotifier;
+    ClangBackEnd::PchGenerator<FakeProcess> generator{environment, &mockPchGeneratorNotifier};
     ClangBackEnd::PchCreator creator{{projectPart1.clone(),projectPart2.clone()},
                                      environment,
-                                     filePathCache};
+                                     filePathCache,
+                                     &generator};
 };
 
 using PchCreatorSlowTest = PchCreator;
@@ -116,7 +122,7 @@ TEST_F(PchCreator, CreateGlobalCommandLine)
     ASSERT_THAT(arguments, ElementsAre(environment.clangCompilerPath(), "-I", TESTDATA_DIR, "-Wno-pragma-once-outside-header", "-I", TESTDATA_DIR, "-x" , "c++-header", "-Wno-pragma-once-outside-header"));
 }
 
-TEST_F(PchCreator, CreateGlobalPchIncludes)
+TEST_F(PchCreatorVerySlowTest, CreateGlobalPchIncludes)
 {
     auto includeIds = creator.generateGlobalPchIncludeIds();
 
@@ -167,13 +173,6 @@ TEST_F(PchCreator, CreateGlobalClangCompilerArguments)
                                  Not(Contains(environment.clangCompilerPath()))));
 }
 
-TEST_F(PchCreatorVerySlowTest, CreateGlobalPch)
-{
-    creator.generateGlobalPch();
-
-    ASSERT_TRUE(QFileInfo::exists(creator.generateGlobalPchFilePath()));
-}
-
 TEST_F(PchCreator, CreateProjectPartCommandLine)
 {
     auto commandLine = creator.generateProjectPartCommandLine(projectPart1);
@@ -258,23 +257,34 @@ TEST_F(PchCreatorVerySlowTest, CreatePartPchs)
 {
     creator.generateGlobalPch();
 
-    auto projectPartPchAndIdPath = creator.generateProjectPartPch(projectPart1);
+    auto includePaths = creator.generateProjectPartPch(projectPart1);
 
-    ASSERT_THAT(projectPartPchAndIdPath.first.id(), projectPart1.projectPartId());
-    ASSERT_THAT(projectPartPchAndIdPath.first.path(), creator.generateProjectPartPchFilePath(projectPart1));
-    ASSERT_THAT(projectPartPchAndIdPath.second.id, projectPart1.projectPartId());
-    ASSERT_THAT(projectPartPchAndIdPath.second.paths, UnorderedElementsAre(1, 2, 3));
+    ASSERT_THAT(includePaths.id, projectPart1.projectPartId());
+    ASSERT_THAT(includePaths.paths, UnorderedElementsAre(1, 2, 3));
 }
 
-TEST_F(PchCreatorVerySlowTest, ProjectPartPchsForCreatePchsForProjectParts)
+TEST_F(PchCreatorVerySlowTest, IncludesForCreatePchsForProjectParts)
 {
     creator.generatePchs();
 
-    ASSERT_THAT(creator.takeProjectPartPchs(),
-                ElementsAre(Property(&ProjectPartPch::id, "project1"),
-                            Property(&ProjectPartPch::id, "project2")));
+    ASSERT_THAT(creator.takeProjectsIncludes(),
+                ElementsAre(Field(&IdPaths::id, "project1"),
+                            Field(&IdPaths::id, "project2")));
+}
+
+TEST_F(PchCreatorVerySlowTest, ProjectPartPchsForCreatePchsForProjectParts)
+{
+    EXPECT_CALL(mockPchGeneratorNotifier,
+                taskFinished(ClangBackEnd::TaskFinishStatus::Successfully,
+                             Property(&ProjectPartPch::id, "project1")));
+    EXPECT_CALL(mockPchGeneratorNotifier,
+                taskFinished(ClangBackEnd::TaskFinishStatus::Successfully,
+                             Property(&ProjectPartPch::id, "project2")));
+
+    creator.generatePchs();
 }
 
+
 TEST_F(PchCreatorVerySlowTest, IdPathsForCreatePchsForProjectParts)
 {
     creator.generatePchs();
diff --git a/tests/unit/unittest/pchgenerator-test.cpp b/tests/unit/unittest/pchgenerator-test.cpp
new file mode 100644
index 0000000000..1bb816bb59
--- /dev/null
+++ b/tests/unit/unittest/pchgenerator-test.cpp
@@ -0,0 +1,224 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#include "googletest.h"
+
+#include "fakeprocess.h"
+#include "testenvironment.h"
+#include "mockpchgeneratornotifier.h"
+
+#include <pchgenerator.h>
+
+namespace {
+
+using testing::_;
+using testing::Contains;
+using testing::Eq;
+using testing::NiceMock;
+using testing::Not;
+using testing::PrintToString;
+using ClangBackEnd::TaskFinishStatus;
+
+MATCHER_P(ContainsProcess, process,
+          std::string(negation ? "isn't" : "is")
+          + " process " + PrintToString(process))
+{
+    auto found = std::find_if(arg.begin(),
+                              arg.end(),
+                              [&] (const std::unique_ptr<FakeProcess> &processOwner) {
+        return processOwner.get() == process;
+    });
+
+    return found != arg.end();
+}
+
+class PchGenerator : public testing::Test
+{
+protected:
+    TestEnvironment environment;
+    NiceMock<MockPchGeneratorNotifier> mockNotifier;
+    ClangBackEnd::PchGenerator<FakeProcess> generator{environment, &mockNotifier};
+    Utils::SmallStringVector compilerArguments = {"-DXXXX", "-Ifoo"};
+    ClangBackEnd::ProjectPartPch projectPartPch{"projectPartId", "/path/to/pch"};
+};
+
+bool operator==(const std::unique_ptr<FakeProcess> &first, FakeProcess *const second)
+{
+    return first.get() == second;
+}
+
+TEST_F(PchGenerator, ProcessFinished)
+{
+    EXPECT_CALL(mockNotifier, taskFinished(TaskFinishStatus::Successfully, std::move(projectPartPch)));
+
+    generator.startTask(compilerArguments.clone(), projectPartPch.clone());
+}
+
+TEST_F(PchGenerator, ProcessFinishedForDeferredProcess)
+{
+    auto process = generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+    generator.startTask(compilerArguments.clone(), projectPartPch.clone());
+
+    EXPECT_CALL(mockNotifier, taskFinished(TaskFinishStatus::Successfully, std::move(projectPartPch)))
+            .Times(3);
+
+    generator.startTask(compilerArguments.clone(), projectPartPch.clone());
+    process->finish();
+}
+
+TEST_F(PchGenerator, ProcessSuccessfullyFinished)
+{
+    EXPECT_CALL(mockNotifier, taskFinished(TaskFinishStatus::Unsuccessfully, std::move(projectPartPch)));
+
+    auto process =  generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+    process->finishUnsuccessfully();
+}
+
+TEST_F(PchGenerator, ProcessSuccessfullyFinishedByWrongExitCode)
+{
+    EXPECT_CALL(mockNotifier, taskFinished(TaskFinishStatus::Unsuccessfully, std::move(projectPartPch)));
+
+    auto process =  generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+    process->finishUnsuccessfully();
+}
+
+TEST_F(PchGenerator, AddTaskAddsProcessToProcesses)
+{
+    auto process =  generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    ASSERT_THAT(generator.runningProcesses(), ContainsProcess(process));
+}
+
+TEST_F(PchGenerator, RemoveProcessAfterFinishingProcess)
+{
+    auto process =  generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    process->finish();
+
+    ASSERT_THAT(generator.runningProcesses(), Not(ContainsProcess(process)));
+}
+
+TEST_F(PchGenerator, ProcessSuccessfullyFinishedByCrash)
+{
+    EXPECT_CALL(mockNotifier, taskFinished(TaskFinishStatus::Unsuccessfully, std::move(projectPartPch)));
+
+    auto process =  generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+    process->finishByCrash();
+}
+
+TEST_F(PchGenerator, CreateProcess)
+{
+    auto process = generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    ASSERT_THAT(generator.runningProcesses(), ContainsProcess(process));
+}
+
+TEST_F(PchGenerator, DeleteProcess)
+{
+    auto process = generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    generator.deleteProcess(process);
+
+    ASSERT_THAT(generator.runningProcesses(), Not(ContainsProcess(process)));
+}
+
+TEST_F(PchGenerator, StartProcessApplicationPath)
+{
+    auto process =  generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    ASSERT_THAT(process->applicationPath(), environment.clangCompilerPath());
+
+}
+
+TEST_F(PchGenerator, SetCompilerArguments)
+{
+    auto process =  generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    ASSERT_THAT(process->arguments(), compilerArguments);
+}
+
+TEST_F(PchGenerator, ProcessIsStartedAfterAddingTask)
+{
+    auto process = generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    ASSERT_TRUE(process->isStarted());
+}
+
+TEST_F(PchGenerator, DeferProcess)
+{
+    generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+    generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    auto deferProcess = generator.deferProcess();
+
+    ASSERT_TRUE(deferProcess);
+}
+
+TEST_F(PchGenerator, ThirdTaskIsDeferred)
+{
+    generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+    generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    auto process = generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    ASSERT_THAT(process, generator.deferredProcesses().back().get());
+}
+
+TEST_F(PchGenerator, ThirdTaskIsNotRunning)
+{
+    generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+    generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    auto process = generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    ASSERT_THAT(generator.runningProcesses(), Not(ContainsProcess(process)));
+}
+
+TEST_F(PchGenerator, DoNotDeferProcess)
+{
+    generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    auto deferProcess = generator.deferProcess();
+
+    ASSERT_FALSE(deferProcess);
+}
+
+TEST_F(PchGenerator, DoNotActivateIfNothingIsDeferred)
+{
+    generator.activateNextDeferredProcess();
+}
+
+TEST_F(PchGenerator, AfterActivationProcessIsRunning)
+{
+    generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+    generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+    auto process = generator.addTask(compilerArguments.clone(), projectPartPch.clone());
+
+    generator.activateNextDeferredProcess();
+
+    ASSERT_THAT(generator.runningProcesses(), ContainsProcess(process));
+}
+
+}
diff --git a/tests/unit/unittest/pchmanagerserver-test.cpp b/tests/unit/unittest/pchmanagerserver-test.cpp
index 7c174794c0..b1f6ca8ab0 100644
--- a/tests/unit/unittest/pchmanagerserver-test.cpp
+++ b/tests/unit/unittest/pchmanagerserver-test.cpp
@@ -47,6 +47,7 @@ using testing::IsEmpty;
 
 using Utils::SmallString;
 using ClangBackEnd::V2::ProjectPartContainer;
+using ClangBackEnd::TaskFinishStatus;
 
 class PchManagerServer : public ::testing::Test
 {
@@ -76,18 +77,28 @@ protected:
                                       {main2Path.clone()}};
     std::vector<ClangBackEnd::V2::ProjectPartContainer> projectParts{projectPart1, projectPart2};
     ClangBackEnd::UpdatePchProjectPartsMessage updatePchProjectPartsMessage{Utils::clone(projectParts)};
-    std::vector<ClangBackEnd::ProjectPartPch> projectPartPchs{{projectPart1.projectPartId().clone(), "/path1/to/pch"},
-                                                              {projectPart2.projectPartId().clone(), "/path2/to/pch"}};
-    ClangBackEnd::PrecompiledHeadersUpdatedMessage precompiledHeaderUpdatedMessage{Utils::clone(projectPartPchs)};
+    ClangBackEnd::ProjectPartPch projectPartPch1{projectPart1.projectPartId().clone(), "/path1/to/pch"};
+    ClangBackEnd::ProjectPartPch projectPartPch2{projectPart2.projectPartId().clone(), "/path2/to/pch"};
+    std::vector<ClangBackEnd::ProjectPartPch> projectPartPchs{projectPartPch1, projectPartPch2};
+    ClangBackEnd::PrecompiledHeadersUpdatedMessage precompiledHeaderUpdatedMessage1{{projectPartPch1}};
+    ClangBackEnd::PrecompiledHeadersUpdatedMessage precompiledHeaderUpdatedMessage2{{projectPartPch2}};
     ClangBackEnd::RemovePchProjectPartsMessage removePchProjectPartsMessage{{projectPart1.projectPartId().clone(),
                                                                              projectPart2.projectPartId().clone()}};
 };
 
-TEST_F(PchManagerServer, CallPrecompiledHeadersUpdatedInClientForUpdate)
+TEST_F(PchManagerServer, CallPrecompiledHeadersForSuccessfullyFinishedTask)
 {
-    EXPECT_CALL(mockPchManagerClient, precompiledHeadersUpdated(precompiledHeaderUpdatedMessage));
+    EXPECT_CALL(mockPchManagerClient, precompiledHeadersUpdated(precompiledHeaderUpdatedMessage1));
 
-    server.updatePchProjectParts(updatePchProjectPartsMessage.clone());
+    server.taskFinished(TaskFinishStatus::Successfully, projectPartPch1);
+}
+
+TEST_F(PchManagerServer, DoNotCallPrecompiledHeadersForUnsuccessfullyFinishedTask)
+{
+    EXPECT_CALL(mockPchManagerClient, precompiledHeadersUpdated(precompiledHeaderUpdatedMessage1))
+            .Times(0);
+
+    server.taskFinished(TaskFinishStatus::Unsuccessfully, projectPartPch1);
 }
 
 TEST_F(PchManagerServer, CallBuildInPchCreator)
@@ -150,15 +161,6 @@ TEST_F(PchManagerServer, CallGeneratePchsInPchCreatorForIncludeChange)
     server.pathsWithIdsChanged({projectPartId1});
 }
 
-TEST_F(PchManagerServer, CallPrecompiledHeadersUpdatedInClientForIncludeChange)
-{
-    server.updatePchProjectParts(updatePchProjectPartsMessage.clone());
-
-    EXPECT_CALL(mockPchManagerClient, precompiledHeadersUpdated(precompiledHeaderUpdatedMessage));
-
-    server.pathsWithIdsChanged({projectPartId1});
-}
-
 TEST_F(PchManagerServer, CallUpdateIdPathsInFileSystemWatcherForIncludeChange)
 {
     server.updatePchProjectParts(updatePchProjectPartsMessage.clone());
@@ -172,8 +174,6 @@ void PchManagerServer::SetUp()
 {
     server.setClient(&mockPchManagerClient);
 
-    ON_CALL(mockPchCreator, takeProjectPartPchs())
-            .WillByDefault(Return(projectPartPchs));
     ON_CALL(mockProjectParts, update(projectParts))
             .WillByDefault(Return(projectParts));
     ON_CALL(mockProjectParts, projects(Utils::SmallStringVector{{projectPartId1}}))
diff --git a/tests/unit/unittest/testenvironment.h b/tests/unit/unittest/testenvironment.h
index f318116972..a071b45432 100644
--- a/tests/unit/unittest/testenvironment.h
+++ b/tests/unit/unittest/testenvironment.h
@@ -45,6 +45,11 @@ public:
         return QString::fromUtf8(CLANG_COMPILER_PATH);
     }
 
+    uint hardwareConcurrency() const
+    {
+        return 2;
+    }
+
 private:
     QTemporaryDir temporaryDirectory;
 };
diff --git a/tests/unit/unittest/unittest.pro b/tests/unit/unittest/unittest.pro
index fe8b68c68b..0d06c359ae 100644
--- a/tests/unit/unittest/unittest.pro
+++ b/tests/unit/unittest/unittest.pro
@@ -49,7 +49,9 @@ SOURCES += \
     projectparts-test.cpp \
     stringcache-test.cpp \
     changedfilepathcompressor-test.cpp \
-    faketimer.cpp
+    faketimer.cpp \
+    pchgenerator-test.cpp \
+    fakeprocess.cpp
 
 !isEmpty(LIBCLANG_LIBS) {
 SOURCES += \
@@ -148,7 +150,9 @@ HEADERS += \
     mockprojectparts.h \
     mockclangpathwatchernotifier.h \
     mockchangedfilepathcompressor.h \
-    faketimer.h
+    faketimer.h \
+    mockpchgeneratornotifier.h \
+    fakeprocess.h
 
 !isEmpty(LIBCLANG_LIBS) {
 HEADERS += \