Re-revert "Delay creation of the process manager"

This reverts commit daba2c507ad42c66dafa6a29cffa94e9641e0c58,
re-applying commit d9c06bf25210b3d0b31ee6126e57bcb82c292da1, because
the change was accidentally brought back in commit
eae8fb8599.

There's a potential deadlock when a QProcess is created while a
QCoreApplication is instantiated but never executed, or if the main
thread waits() for the child thread.

Task-number: QTBUG-27260
Change-Id: I9e0fdc0341b3063de90979377bac35f2a827b260
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

src/corelib/io/qprocess_unix.cpp

@@ -177,7 +177,7 @@ static QProcessManager *processManager()
     QMutexLocker locker(&processManagerGlobalMutex);
 
     if (!processManagerInstance)
-        QProcessPrivate::initializeProcessManager();
+        new QProcessManager;
 
     Q_ASSERT(processManagerInstance);
     return processManagerInstance;
@@ -185,9 +185,6 @@ static QProcessManager *processManager()
 
 QProcessManager::QProcessManager()
 {
-    // can only be called from main thread
-    Q_ASSERT(!qApp || qApp->thread() == QThread::currentThread());
-
 #if defined (QPROCESS_DEBUG)
     qDebug() << "QProcessManager::QProcessManager()";
 #endif
@@ -1434,15 +1431,7 @@ bool QProcessPrivate::startDetached(const QString &program, const QStringList &a
 
 void QProcessPrivate::initializeProcessManager()
 {
-    if (qApp && qApp->thread() != QThread::currentThread()) {
-        // The process manager must be initialized in the main thread
-        // Note: The call below will re-enter this function, but in the right thread,
-        // so the else statement below will be executed.
-        QMetaObject::invokeMethod(qApp, "_q_initializeProcessManager", Qt::BlockingQueuedConnection);
-    } else {
-        static QProcessManager processManager;
-        Q_UNUSED(processManager);
-    }
+    (void) processManager();
 }
 
 QT_END_NAMESPACE

src/corelib/kernel/qcoreapplication.cpp

@@ -392,16 +392,6 @@ void QCoreApplicationPrivate::createEventDispatcher()
 #endif
 }
 
-void QCoreApplicationPrivate::_q_initializeProcessManager()
-{
-#ifndef QT_NO_PROCESS
-#  ifdef Q_OS_UNIX
-    QProcessPrivate::initializeProcessManager();
-#  endif
-#endif
-}
-
-
 QThread *QCoreApplicationPrivate::theMainThread = 0;
 QThread *QCoreApplicationPrivate::mainThread()
 {
@@ -625,6 +615,12 @@ void QCoreApplication::init()
         d->appendApplicationPathToLibraryPaths();
 #endif
 
+#if defined(Q_OS_UNIX) && !(defined(QT_NO_PROCESS))
+    // Make sure the process manager thread object is created in the main
+    // thread.
+    QProcessPrivate::initializeProcessManager();
+#endif
+
 #ifdef QT_EVAL
     extern void qt_core_eval_init(uint);
     qt_core_eval_init(d->application_type);
@@ -2364,5 +2360,3 @@ void QCoreApplication::setEventDispatcher(QAbstractEventDispatcher *eventDispatc
 */
 
 QT_END_NAMESPACE
-
-#include "moc_qcoreapplication.cpp"

src/corelib/kernel/qcoreapplication.h

@@ -178,7 +178,6 @@ protected:
     QCoreApplication(QCoreApplicationPrivate &p);
 
 private:
-    Q_PRIVATE_SLOT(d_func(), void _q_initializeProcessManager())
     static bool sendSpontaneousEvent(QObject *receiver, QEvent *event);
     bool notifyInternal(QObject *receiver, QEvent *event);
 

src/corelib/kernel/qcoreapplication_p.h

@@ -76,8 +76,6 @@ public:
     bool sendThroughObjectEventFilters(QObject *, QEvent *);
     bool notify_helper(QObject *, QEvent *);
 
-    void _q_initializeProcessManager();
-
     QString appName() const;
     virtual void createEventDispatcher();
     static void removePostedEvent(QEvent *);

tests/auto/corelib/io/io.pro

@@ -16,6 +16,7 @@ SUBDIRS=\
     qipaddress \
     qnodebug \
     qprocess \
+    qprocess-noapplication \
     qprocessenvironment \
     qresourceengine \
     qsettings \

tests/auto/corelib/io/qprocess-noapplication/qprocess-noapplication.pro

@@ -0,0 +1,5 @@
+CONFIG += testcase
+CONFIG += parallel_test
+CONFIG -= app_bundle debug_and_release_target
+QT = core testlib
+SOURCES = tst_qprocessnoapplication.cpp

tests/auto/corelib/io/qprocess-noapplication/tst_qprocessnoapplication.cpp

@@ -0,0 +1,84 @@
+/****************************************************************************
+**
+** Copyright (C) 2012 Intel Corporation.
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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 Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtCore/QCoreApplication>
+#include <QtCore/QProcess>
+#include <QtCore/QThread>
+#include <QtTest>
+
+class tst_QProcessNoApplication : public QObject
+{
+    Q_OBJECT
+
+private Q_SLOTS:
+    void initializationDeadlock();
+};
+
+void tst_QProcessNoApplication::initializationDeadlock()
+{
+    // see QTBUG-27260
+    // QProcess on Unix uses (or used to, at the time of the writing of this test)
+    // a global class called QProcessManager.
+    // This class is instantiated (or was) only in the main thread, which meant that
+    // blocking the main thread while waiting for QProcess could mean a deadlock.
+
+    struct MyThread : public QThread
+    {
+        void run()
+        {
+            // what we execute does not matter, as long as we try to
+            // and that the process exits
+            QProcess::execute("true");
+        }
+    };
+
+    static char argv0[] = "tst_QProcessNoApplication";
+    char *argv[] = { argv0, 0 };
+    int argc = 1;
+    QCoreApplication app(argc, argv);
+    MyThread thread;
+    thread.start();
+    QVERIFY(thread.wait(10000));
+}
+
+QTEST_APPLESS_MAIN(tst_QProcessNoApplication)
+
+#include "tst_qprocessnoapplication.moc"