Add function to get the actual PID from QProcess

It was not possible to get the actual process ID (in a cross-platform
manner) from QProcess, as the user would need to handle the returned
typedef (Q_PID) differently on Unix and Windows.

On Unix Q_PID is the actual process ID, but on Windows it's a pointer
to a PROCESS_INFORMATION structure, which among other fields contains
the process ID. Instead of returning a pointer on Windows,
QProcess::processId() will return the actual process ID on both Windows
and Unix.

[ChangeLog][QtCore][QProcess] Added processId() to QProcess. This
function will, unlike pid(), return the actual process identifier on
both Window and Unix.

Task-number: QTBUG-26136
Change-Id: I853ab721297e2dd9cda006666144179a9e25b73d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qprocess.cpp

@@ -1545,16 +1545,40 @@ void QProcess::setWorkingDirectory(const QString &dir)
     d->workingDirectory = dir;
 }
 
+
 /*!
+    \deprecated
+    Use processId() instead.
+
     Returns the native process identifier for the running process, if
-    available.  If no process is currently running, 0 is returned.
+    available.  If no process is currently running, \c 0 is returned.
+
+    \note Unlike \l processId(), pid() returns an integer on Unix and a pointer on Windows.
+
+    \sa Q_PID, processId()
 */
-Q_PID QProcess::pid() const
+Q_PID QProcess::pid() const // ### Qt 6 remove or rename this method to processInformation()
 {
     Q_D(const QProcess);
     return d->pid;
 }
 
+/*!
+    \since 5.3
+
+    Returns the native process identifier for the running process, if
+    available. If no process is currently running, \c 0 is returned.
+ */
+qint64 QProcess::processId() const
+{
+    Q_D(const QProcess);
+#ifdef Q_OS_WIN
+    return d->pid ? d->pid->dwProcessId : 0;
+#else
+    return d->pid;
+#endif
+}
+
 /*! \reimp
 
     This function operates on the current read channel.

src/corelib/io/qprocess.h

@@ -187,6 +187,7 @@ public:
 
     // #### Qt 5: Q_PID is a pointer on Windows and a value on Unix
     Q_PID pid() const;
+    qint64 processId() const;
 
     bool waitForStarted(int msecs = 30000);
     bool waitForReadyRead(int msecs = 30000);

tests/auto/corelib/io/qprocess/tst_qprocess.cpp

@@ -943,7 +943,7 @@ void tst_QProcess::hardExit()
 void tst_QProcess::softExit()
 {
     QProcess proc;
-
+    QCOMPARE(proc.processId(), 0);
     proc.start("testSoftExit/testSoftExit");
 
     QVERIFY(proc.waitForStarted(10000));
@@ -951,6 +951,8 @@ void tst_QProcess::softExit()
     QVERIFY(proc.waitForReadyRead(10000));
 #endif
 
+    QVERIFY(proc.processId() > 0);
+
     proc.terminate();
 
     QVERIFY(proc.waitForFinished(10000));