Add non-static QProcess::startDetached

The three static QProcess::startDetached overloads support a limited number of
features: program, arguments and working directory. To support more features of
QProcess (without adding a plethora of overloads) we add a non-static method
startDetached that can be used as follows:

QProcess p;
p.setProgram("cat");
p.setArguments("meow");
p.setWorkingDirectory("/tmp");
if (!p.startDetached())
    qWarning("Cannot start process.");

We plan to add support for nativeArguments, processEnvironment,
standard{Output|Error}File and maybe more in subsequent commits.

[ChangeLog][QtCore][QProcess] Added non-static QProcess::startDetached
to support more features for detached processes.

Task-number: QTBUG-2058
Task-number: QTBUG-2284
Task-number: QTBUG-37656
Task-number: QTBUG-52405
Task-number: QTBUG-57687
Change-Id: If6fdd57ecb28cd13aa5fff566216a4177f81d339
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>

src/corelib/io/qprocess.cpp

@@ -2111,6 +2111,46 @@ void QProcess::start(OpenMode mode)
     d->start(mode);
 }
 
+/*!
+    \since 5.10
+
+    Starts the program set by setProgram() with arguments set by setArguments()
+    in a new process, and detaches from it. Returns \c true on success;
+    otherwise returns \c false. If the calling process exits, the
+    detached process will continue to run unaffected.
+
+    \b{Unix:} The started process will run in its own session and act
+    like a daemon.
+
+    The process will be started in the directory set by setWorkingDirectory().
+    If workingDirectory() is empty, the working directory is inherited
+    from the calling process.
+
+    \note On QNX, this may cause all application threads to
+    temporarily freeze.
+
+    If the function is successful then *\a pid is set to the process
+    identifier of the started process.
+
+    \sa start()
+    \sa startDetached(const QString &program, const QStringList &arguments,
+                      const QString &workingDirectory, qint64 *pid)
+    \sa startDetached(const QString &command)
+*/
+bool QProcess::startDetached(qint64 *pid)
+{
+    Q_D(QProcess);
+    if (d->processState != NotRunning) {
+        qWarning("QProcess::startDetached: Process is already running");
+        return false;
+    }
+    if (d->program.isEmpty()) {
+        d->setErrorAndEmit(QProcess::FailedToStart, tr("No program defined"));
+        return false;
+    }
+    return d->startDetached(pid);
+}
+
 /*!
     Starts the program set by setProgram() with arguments set by setArguments().
     The OpenMode is set to \a mode.
@@ -2445,6 +2485,8 @@ int QProcess::execute(const QString &command)
 }
 
 /*!
+    \overload startDetached()
+
     Starts the program \a program with the arguments \a arguments in a
     new process, and detaches from it. Returns \c true on success;
     otherwise returns \c false. If the calling process exits, the
@@ -2452,16 +2494,10 @@ int QProcess::execute(const QString &command)
 
     Argument handling is identical to the respective start() overload.
 
-    \b{Unix:} The started process will run in its own session and act
-    like a daemon.
-
     The process will be started in the directory \a workingDirectory.
     If \a workingDirectory is empty, the working directory is inherited
     from the calling process.
 
-    \note On QNX, this may cause all application threads to
-    temporarily freeze.
-
     If the function is successful then *\a pid is set to the process
     identifier of the started process.
 
@@ -2472,10 +2508,11 @@ bool QProcess::startDetached(const QString &program,
                              const QString &workingDirectory,
                              qint64 *pid)
 {
-    return QProcessPrivate::startDetached(program,
-                                          arguments,
-                                          workingDirectory,
-                                          pid);
+    QProcess process;
+    process.setProgram(program);
+    process.setArguments(arguments);
+    process.setWorkingDirectory(workingDirectory);
+    return process.startDetached(pid);
 }
 
 /*!
@@ -2484,11 +2521,14 @@ bool QProcess::startDetached(const QString &program,
 bool QProcess::startDetached(const QString &program,
                              const QStringList &arguments)
 {
-    return QProcessPrivate::startDetached(program, arguments);
+    QProcess process;
+    process.setProgram(program);
+    process.setArguments(arguments);
+    return process.startDetached();
 }
 
 /*!
-    \overload
+    \overload startDetached()
 
     Starts the command \a command in a new process, and detaches from it.
     Returns \c true on success; otherwise returns \c false.
@@ -2506,9 +2546,10 @@ bool QProcess::startDetached(const QString &command)
     if (args.isEmpty())
         return false;
 
-    const QString prog = args.takeFirst();
-
-    return QProcessPrivate::startDetached(prog, args);
+    QProcess process;
+    process.setProgram(args.takeFirst());
+    process.setArguments(args);
+    return process.startDetached();
 }
 
 QT_BEGIN_INCLUDE_NAMESPACE

src/corelib/io/qprocess.h

@@ -163,6 +163,7 @@ public:
     void start(const QString &command, OpenMode mode = ReadWrite);
 #endif
     void start(OpenMode mode = ReadWrite);
+    bool startDetached(qint64 *pid = nullptr);
     bool open(OpenMode mode = ReadWrite) Q_DECL_OVERRIDE;
 
     QString program() const;

src/corelib/io/qprocess_p.h

@@ -368,8 +368,7 @@ public:
     qint64 pipeWriterBytesToWrite() const;
 #endif
 
-    static bool startDetached(const QString &program, const QStringList &arguments, const QString &workingDirectory = QString(),
-                              qint64 *pid = 0);
+    bool startDetached(qint64 *pPid);
 
     int exitCode;
     QProcess::ExitStatus exitStatus;

src/corelib/io/qprocess_unix.cpp

@@ -925,7 +925,7 @@ bool QProcessPrivate::waitForDeadChild()
     return true;
 }
 
-bool QProcessPrivate::startDetached(const QString &program, const QStringList &arguments, const QString &workingDirectory, qint64 *pid)
+bool QProcessPrivate::startDetached(qint64 *pid)
 {
     QByteArray encodedWorkingDirectory = QFile::encodeName(workingDirectory);
 

src/corelib/io/qprocess_win.cpp

@@ -859,7 +859,7 @@ static bool startDetachedUacPrompt(const QString &programIn, const QStringList &
     return true;
 }
 
-bool QProcessPrivate::startDetached(const QString &program, const QStringList &arguments, const QString &workingDir, qint64 *pid)
+bool QProcessPrivate::startDetached(qint64 *pid)
 {
     static const DWORD errorElevationRequired = 740;
 
@@ -876,7 +876,7 @@ bool QProcessPrivate::startDetached(const QString &program, const QStringList &a
                                };
     success = CreateProcess(0, (wchar_t*)args.utf16(),
                             0, 0, FALSE, dwCreationFlags, 0,
-                            workingDir.isEmpty() ? 0 : (wchar_t*)workingDir.utf16(),
+                            workingDirectory.isEmpty() ? 0 : (wchar_t*)workingDirectory.utf16(),
                             &startupInfo, &pinfo);
 
     if (success) {
@@ -885,7 +885,7 @@ bool QProcessPrivate::startDetached(const QString &program, const QStringList &a
         if (pid)
             *pid = pinfo.dwProcessId;
     } else if (GetLastError() == errorElevationRequired) {
-        success = startDetachedUacPrompt(program, arguments, workingDir, pid);
+        success = startDetachedUacPrompt(program, arguments, workingDirectory, pid);
     }
 
     return success;