Use forkfd in QProcess

Replace the existing code in QProcess that dealt with signaling of child
processes exiting with forkfd and spawnfd. The previous code was
convoluted and hard to maintain, having shown its age in the last
year. I've been running it for a year and a half and the new
implementation is definitely an improvement.

This change replaces support for the QNX Neutrino spawn() call with the
POSIX version. We lose the ability to do setsid(), but we gain quite a
few ioctls() that were done to fill in the file descriptor mapping
structure. That's also the only OS for which we have the ability to
thread-safely chdir() before the call to spawnfd().

Another advantage is that forkfd does not require a dedicated thread
running to handle child processes exiting.

Change-Id: I5eb76821dfdb6a8ed2989d7f53b3c31e515c3174
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>

7 files changed, 161 insertions, 399 deletions

diff --git a/src/corelib/io/io.pri b/src/corelib/io/io.pri
index 184ceb34be..78349fbc49 100644
--- a/src/corelib/io/io.pri
+++ b/src/corelib/io/io.pri
@@ -140,6 +140,7 @@ win32 {
                 io/forkfd_qt.cpp
         HEADERS += \
                 ../3rdparty/forkfd/forkfd.h
+        INCLUDEPATH += ../3rdparty/forkfd
 
         !nacl:mac: {
             SOURCES += io/qsettings_mac.cpp
diff --git a/src/corelib/io/qprocess.cpp b/src/corelib/io/qprocess.cpp
index a234050777..976d8503f3 100644
--- a/src/corelib/io/qprocess.cpp
+++ b/src/corelib/io/qprocess.cpp
@@ -89,6 +89,8 @@ QT_END_NAMESPACE
 
 #ifdef Q_OS_WIN
 #include <qwineventnotifier.h>
+#else
+#include <private/qcore_unix_p.h>
 #endif
 
 #ifndef QT_NO_PROCESS
@@ -810,8 +812,7 @@ QProcessPrivate::QProcessPrivate()
     deathNotifier = 0;
     childStartedPipe[0] = INVALID_Q_PIPE;
     childStartedPipe[1] = INVALID_Q_PIPE;
-    deathPipe[0] = INVALID_Q_PIPE;
-    deathPipe[1] = INVALID_Q_PIPE;
+    forkfd = -1;
     exitCode = 0;
     crashed = false;
     dying = false;
@@ -821,9 +822,6 @@ QProcessPrivate::QProcessPrivate()
     notifier = 0;
     processFinishedNotifier = 0;
 #endif // Q_OS_WIN
-#ifdef Q_OS_UNIX
-    serial = 0;
-#endif
 }
 
 /*!
@@ -890,9 +888,10 @@ void QProcessPrivate::cleanup()
     closeChannel(&stderrChannel);
     closeChannel(&stdinChannel);
     destroyPipe(childStartedPipe);
-    destroyPipe(deathPipe);
 #ifdef Q_OS_UNIX
-    serial = 0;
+    if (forkfd != -1)
+        qt_safe_close(forkfd);
+    forkfd = -1;
 #endif
 }
 
diff --git a/src/corelib/io/qprocess_p.h b/src/corelib/io/qprocess_p.h
index 8c5987aa05..3f86960c74 100644
--- a/src/corelib/io/qprocess_p.h
+++ b/src/corelib/io/qprocess_p.h
@@ -62,6 +62,9 @@ typedef HANDLE Q_PIPE;
 #else
 typedef int Q_PIPE;
 #define INVALID_Q_PIPE -1
+#  ifdef Q_OS_QNX
+#    define QPROCESS_USE_SPAWN
+#  endif
 #endif
 
 #ifndef QT_NO_PROCESS
@@ -331,12 +334,13 @@ public:
     QProcessEnvironment environment;
 
     Q_PIPE childStartedPipe[2];
-    Q_PIPE deathPipe[2];
     void destroyPipe(Q_PIPE pipe[2]);
 
     QSocketNotifier *startupSocketNotifier;
     QSocketNotifier *deathNotifier;
 
+    int forkfd;
+
 #ifdef Q_OS_WIN
     // the wonderful windows notifier
     QTimer *notifier;
@@ -345,10 +349,10 @@ public:
 
     void start(QIODevice::OpenMode mode);
     void startProcess();
-#if defined(Q_OS_UNIX) && !defined(Q_OS_QNX)
+#if defined(Q_OS_UNIX) && !defined(QPROCESS_USE_SPAWN)
     void execChild(const char *workingDirectory, char **path, char **argv, char **envp);
-#elif defined(Q_OS_QNX)
-    pid_t spawnChild(const char *workingDirectory, char **argv, char **envp);
+#elif defined(QPROCESS_USE_SPAWN)
+    pid_t spawnChild(pid_t *ppid, const char *workingDirectory, char **argv, char **envp);
 #endif
     bool processStarted();
     void terminateProcess();
@@ -369,9 +373,6 @@ public:
     int exitCode;
     QProcess::ExitStatus exitStatus;
     bool crashed;
-#ifdef Q_OS_UNIX
-    int serial;
-#endif
 
     bool waitForStarted(int msecs = 30000);
     bool waitForReadyRead(int msecs = 30000);
@@ -389,9 +390,6 @@ public:
     QList<QSocketNotifier *> defaultNotifiers() const;
 #endif // Q_OS_BLACKBERRY
 
-#ifdef Q_OS_UNIX
-    static void initializeProcessManager();
-#endif
 };
 
 QT_END_NAMESPACE
diff --git a/src/corelib/io/qprocess_unix.cpp b/src/corelib/io/qprocess_unix.cpp
index cfee5f1d46..d626607dfa 100644
--- a/src/corelib/io/qprocess_unix.cpp
+++ b/src/corelib/io/qprocess_unix.cpp
@@ -95,15 +95,14 @@ QT_END_NAMESPACE
 #include <qthread.h>
 #include <qelapsedtimer.h>
 
+#ifdef Q_OS_QNX
+#  include <sys/neutrino.h>
+#endif
+
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>
-#ifdef Q_OS_QNX
-#include "qvarlengtharray.h"
-
-#include <spawn.h>
-#include <sys/neutrino.h>
-#endif
+#include <forkfd.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -111,38 +110,6 @@ QT_BEGIN_NAMESPACE
 // so we will use 512
 static const int errorBufferMax = 512;
 
-static int qt_qprocess_deadChild_pipe[2];
-static struct sigaction qt_sa_old_sigchld_handler;
-static void qt_sa_sigchld_sigaction(int signum, siginfo_t *info, void *context)
-{
-    // *Never* use the info or contect variables in this function
-    // (except for passing them to the next signal in the chain).
-    // We cannot be sure if another library or if the application
-    // installed a signal handler for SIGCHLD without SA_SIGINFO
-    // and fails to pass the arguments to us. If they do that,
-    // these arguments contain garbage and we'd most likely crash.
-
-    qt_safe_write(qt_qprocess_deadChild_pipe[1], "", 1);
-#if defined (QPROCESS_DEBUG)
-    fprintf(stderr, "*** SIGCHLD\n");
-#endif
-
-    // load as volatile
-    volatile struct sigaction *vsa = &qt_sa_old_sigchld_handler;
-
-    if (qt_sa_old_sigchld_handler.sa_flags & SA_SIGINFO) {
-        void (*oldAction)(int, siginfo_t *, void *) = vsa->sa_sigaction;
-
-        if (oldAction)
-            oldAction(signum, info, context);
-    } else {
-        void (*oldAction)(int) = vsa->sa_handler;
-
-        if (oldAction && oldAction != SIG_IGN)
-            oldAction(signum);
-    }
-}
-
 static inline void add_fd(int &nfds, int fd, fd_set *fdset)
 {
     FD_SET(fd, fdset);
@@ -150,199 +117,6 @@ static inline void add_fd(int &nfds, int fd, fd_set *fdset)
         nfds = fd;
 }
 
-struct QProcessInfo {
-    QProcess *process;
-    int deathPipe;
-    int exitResult;
-    pid_t pid;
-    int serialNumber;
-};
-
-class QProcessManager : public QThread
-{
-    Q_OBJECT
-public:
-    QProcessManager();
-    ~QProcessManager();
-
-    void run() Q_DECL_OVERRIDE;
-    void catchDeadChildren();
-    void add(pid_t pid, QProcess *process);
-    void remove(QProcess *process);
-    void lock();
-    void unlock();
-
-private:
-    QMutex mutex;
-    QHash<int, QProcessInfo *> children;
-};
-
-
-static QProcessManager *processManagerInstance = 0;
-
-static QProcessManager *processManager()
-{
-    // The constructor of QProcessManager should be called only once
-    // so we cannot use Q_GLOBAL_STATIC directly for QProcessManager
-    static QBasicMutex processManagerGlobalMutex;
-    QMutexLocker locker(&processManagerGlobalMutex);
-
-    if (!processManagerInstance)
-        new QProcessManager;
-
-    Q_ASSERT(processManagerInstance);
-    return processManagerInstance;
-}
-
-QProcessManager::QProcessManager()
-{
-#if defined (QPROCESS_DEBUG)
-    qDebug() << "QProcessManager::QProcessManager()";
-#endif
-    // initialize the dead child pipe and make it non-blocking. in the
-    // extremely unlikely event that the pipe fills up, we do not under any
-    // circumstances want to block.
-    qt_safe_pipe(qt_qprocess_deadChild_pipe, O_NONBLOCK);
-
-    // set up the SIGCHLD handler, which writes a single byte to the dead
-    // child pipe every time a child dies.
-
-    struct sigaction action;
-    // use the old handler as template, i.e., preserve the signal mask
-    // otherwise the original signal handler might be interrupted although it
-    // was marked to never be interrupted
-    ::sigaction(SIGCHLD, NULL, &action);
-    action.sa_sigaction = qt_sa_sigchld_sigaction;
-    // set the SA_SIGINFO flag such that we can use the three argument handler
-    // function
-    action.sa_flags = SA_NOCLDSTOP | SA_SIGINFO;
-    ::sigaction(SIGCHLD, &action, &qt_sa_old_sigchld_handler);
-
-    processManagerInstance = this;
-}
-
-QProcessManager::~QProcessManager()
-{
-    // notify the thread that we're shutting down.
-    qt_safe_write(qt_qprocess_deadChild_pipe[1], "@", 1);
-    qt_safe_close(qt_qprocess_deadChild_pipe[1]);
-    wait();
-
-    // on certain unixes, closing the reading end of the pipe will cause
-    // select in run() to block forever, rather than return with EBADF.
-    qt_safe_close(qt_qprocess_deadChild_pipe[0]);
-
-    qt_qprocess_deadChild_pipe[0] = -1;
-    qt_qprocess_deadChild_pipe[1] = -1;
-
-    qDeleteAll(children.values());
-    children.clear();
-
-    struct sigaction currentAction;
-    ::sigaction(SIGCHLD, 0, &currentAction);
-    if (currentAction.sa_sigaction == qt_sa_sigchld_sigaction) {
-        ::sigaction(SIGCHLD, &qt_sa_old_sigchld_handler, 0);
-    }
-
-    processManagerInstance = 0;
-}
-
-void QProcessManager::run()
-{
-    forever {
-        fd_set readset;
-        FD_ZERO(&readset);
-        FD_SET(qt_qprocess_deadChild_pipe[0], &readset);
-
-#if defined (QPROCESS_DEBUG)
-        qDebug() << "QProcessManager::run() waiting for children to die";
-#endif
-
-        // block forever, or until activity is detected on the dead child
-        // pipe. the only other peers are the SIGCHLD signal handler, and the
-        // QProcessManager destructor.
-        int nselect = select(qt_qprocess_deadChild_pipe[0] + 1, &readset, 0, 0, 0);
-        if (nselect < 0) {
-            if (errno == EINTR)
-                continue;
-            break;
-        }
-
-        // empty only one byte from the pipe, even though several SIGCHLD
-        // signals may have been delivered in the meantime, to avoid race
-        // conditions.
-        char c;
-        if (qt_safe_read(qt_qprocess_deadChild_pipe[0], &c, 1) < 0 || c == '@')
-            break;
-
-        // catch any and all children that we can.
-        catchDeadChildren();
-    }
-}
-
-void QProcessManager::catchDeadChildren()
-{
-    QMutexLocker locker(&mutex);
-
-    // try to catch all children whose pid we have registered, and whose
-    // deathPipe is still valid (i.e, we have not already notified it).
-    QHash<int, QProcessInfo *>::Iterator it = children.begin();
-    while (it != children.end()) {
-        // notify all children that they may have died. they need to run
-        // waitpid() in their own thread.
-        QProcessInfo *info = it.value();
-        qt_safe_write(info->deathPipe, "", 1);
-
-#if defined (QPROCESS_DEBUG)
-        qDebug() << "QProcessManager::run() sending death notice to" << info->process;
-#endif
-        ++it;
-    }
-}
-
-static QBasicAtomicInt idCounter = Q_BASIC_ATOMIC_INITIALIZER(1);
-
-void QProcessManager::add(pid_t pid, QProcess *process)
-{
-#if defined (QPROCESS_DEBUG)
-    qDebug() << "QProcessManager::add() adding pid" << pid << "process" << process;
-#endif
-
-    // insert a new info structure for this process
-    QProcessInfo *info = new QProcessInfo;
-    info->process = process;
-    info->deathPipe = process->d_func()->deathPipe[1];
-    info->exitResult = 0;
-    info->pid = pid;
-
-    int serial = idCounter.fetchAndAddRelaxed(1);
-    process->d_func()->serial = serial;
-    children.insert(serial, info);
-}
-
-void QProcessManager::remove(QProcess *process)
-{
-    QMutexLocker locker(&mutex);
-
-    int serial = process->d_func()->serial;
-    QProcessInfo *info = children.take(serial);
-#if defined (QPROCESS_DEBUG)
-    if (info)
-        qDebug() << "QProcessManager::remove() removing pid" << info->pid << "process" << info->process;
-#endif
-    delete info;
-}
-
-void QProcessManager::lock()
-{
-    mutex.lock();
-}
-
-void QProcessManager::unlock()
-{
-    mutex.unlock();
-}
-
 static int qt_create_pipe(int *pipe)
 {
     if (pipe[0] != -1)
@@ -562,14 +336,11 @@ void QProcessPrivate::startProcess()
     qDebug("QProcessPrivate::startProcess()");
 #endif
 
-    processManager()->start();
-
     // Initialize pipes
     if (!openChannel(stdinChannel) ||
         !openChannel(stdoutChannel) ||
         !openChannel(stderrChannel) ||
-        qt_create_pipe(childStartedPipe) != 0 ||
-        qt_create_pipe(deathPipe) != 0) {
+        qt_create_pipe(childStartedPipe) != 0) {
         processError = QProcess::FailedToStart;
         q->setErrorString(qt_error_string(errno));
         emit q->error(processError);
@@ -582,11 +353,6 @@ void QProcessPrivate::startProcess()
                                                     QSocketNotifier::Read, q);
         QObject::connect(startupSocketNotifier, SIGNAL(activated(int)),
                          q, SLOT(_q_startupNotification()));
-
-        deathNotifier = new QSocketNotifier(deathPipe[0],
-                                            QSocketNotifier::Read, q);
-        QObject::connect(deathNotifier, SIGNAL(activated(int)),
-                         q, SLOT(_q_processDied()));
     }
 
     // Start the process (platform dependent)
@@ -669,14 +435,17 @@ void QProcessPrivate::startProcess()
     }
 
     // Start the process manager, and fork off the child process.
-    processManager()->lock();
-#if defined(Q_OS_QNX)
-    pid_t childPid = spawnChild(workingDirPtr, argv, envp);
+#if defined(QPROCESS_USE_SPAWN)
+    pid_t childPid;
+    forkfd = spawnChild(&childPid, workingDirPtr, argv, envp);
+    Q_ASSUME(forkfd != FFD_CHILD_PROCESS);
 #else
-    pid_t childPid = fork();
-    int lastForkErrno = errno;
+    pid_t childPid;
+    forkfd = ::forkfd(FFD_CLOEXEC, &childPid);
 #endif
-    if (childPid != 0) {
+    int lastForkErrno = errno;
+    if (forkfd != FFD_CHILD_PROCESS) {
+        // Parent process.
         // Clean up duplicated memory.
         free(dupProgramName);
         for (int i = 1; i <= arguments.count(); ++i)
@@ -690,23 +459,15 @@ void QProcessPrivate::startProcess()
         delete [] path;
     }
 
-    // This is not a valid check under QNX, because the semantics are
-    // different. While under other platforms where fork() may succeed and exec() can still fail,
-    // causing the childPid to hold a valid value (and thus evaluating the
-    // following if to false), and then signaling the error via
-    // childStartedPipe, under QNX on the other hand, spawn() return value will be assigned
-    // to childPid (which will be -1 in case of failure). This will force
-    // QProcess to cleanup, instead of signaling the error via
-    // childStartedPipe. Since it will invalidade the pipes, functions like
-    // QProcess::waitForStarted() will fail, for childStartedPipe will be
-    // '-1' and mess with the select() calls.
-#if !defined(Q_OS_QNX)
-    if (childPid < 0) {
+    // On QNX, if spawnChild failed, childPid will be -1 but forkfd is still 0.
+    // This is intentional because we only want to handle failure to fork()
+    // here, which is a rare occurrence. Handling of the failure to start is
+    // done elsewhere.
+    if (forkfd == -1) {
         // Cleanup, report error and return
 #if defined (QPROCESS_DEBUG)
         qDebug("fork failed: %s", qPrintable(qt_error_string(lastForkErrno)));
 #endif
-        processManager()->unlock();
         q->setProcessState(QProcess::NotRunning);
         processError = QProcess::FailedToStart;
         q->setErrorString(QProcess::tr("Resource error (fork failure): %1").arg(qt_error_string(lastForkErrno)));
@@ -716,21 +477,17 @@ void QProcessPrivate::startProcess()
     }
 
     // Start the child.
-    if (childPid == 0) {
+#if !defined(QPROCESS_USE_SPAWN)
+    if (forkfd == FFD_CHILD_PROCESS) {
         execChild(workingDirPtr, path, argv, envp);
         ::_exit(-1);
     }
 #endif
 
-    // Register the child. In the mean time, we can get a SIGCHLD, so we need
-    // to keep the lock held to avoid a race to catch the child.
-    processManager()->add(childPid, q);
     pid = Q_PID(childPid);
-    processManager()->unlock();
 
     // parent
     // close the ends we don't use and make all pipes non-blocking
-    ::fcntl(deathPipe[0], F_SETFL, ::fcntl(deathPipe[0], F_GETFL) | O_NONBLOCK);
     qt_safe_close(childStartedPipe[1]);
     childStartedPipe[1] = -1;
 
@@ -756,110 +513,117 @@ void QProcessPrivate::startProcess()
     }
     if (stderrChannel.pipe[0] != -1)
         ::fcntl(stderrChannel.pipe[0], F_SETFL, ::fcntl(stderrChannel.pipe[0], F_GETFL) | O_NONBLOCK);
+
+    if (threadData->eventDispatcher) {
+        deathNotifier = new QSocketNotifier(forkfd, QSocketNotifier::Read, q);
+        QObject::connect(deathNotifier, SIGNAL(activated(int)),
+                         q, SLOT(_q_processDied()));
+    }
 }
 
-#if defined(Q_OS_QNX)
-static pid_t doSpawn(int fd_count, int fd_map[], char **argv, char **envp,
-        const char *workingDir, bool spawn_detached)
+#if defined(QPROCESS_USE_SPAWN)
+static int doSpawn(pid_t *ppid, const posix_spawn_file_actions_t *file_actions,
+                   char **argv, char **envp, const char *workingDir, bool spawn_detached)
 {
-    // A multi threaded QNX Process can't fork so we call spawn() instead.
-
-    struct inheritance inherit;
-    memset(&inherit, 0, sizeof(inherit));
-    inherit.flags |= SPAWN_SETSID;
-    inherit.flags |= SPAWN_CHECK_SCRIPT;
-    if (spawn_detached)
-        inherit.flags |= SPAWN_NOZOMBIE;
-    inherit.flags |= SPAWN_SETSIGDEF;
-    sigaddset(&inherit.sigdefault, SIGPIPE); // reset the signal that we ignored
+    // A multi threaded QNX Process can't fork so we call spawnfd() instead.
+    posix_spawnattr_t attr;
+    posix_spawnattr_init(&attr);
+#  ifdef Q_OS_QNX
+    posix_spawnattr_setxflags(&attr, POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETPGROUP
+                              | (spawn_detached * POSIX_SPAWN_NOZOMBIE));
+#  else
+    posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETPGROUP);
+#  endif
+    posix_spawnattr_setpgroup(&attr, 0);
+
+    sigset_t sigdefault;
+    sigemptyset(&sigdefault);
+    sigaddset(&sigdefault, SIGPIPE); // reset the signal that we ignored
+    posix_spawnattr_setsigdefault(&attr, &sigdefault);
 
     // enter the working directory
     const char *oldWorkingDir = 0;
     char buff[PATH_MAX + 1];
 
     if (workingDir) {
+#  ifdef Q_OS_QNX
         //we need to freeze everyone in order to avoid race conditions with //chdir().
         if (ThreadCtl(_NTO_TCTL_THREADS_HOLD, 0) == -1)
             qWarning("ThreadCtl(): cannot hold threads: %s", qPrintable(qt_error_string(errno)));
+#  endif
 
         oldWorkingDir = QT_GETCWD(buff, PATH_MAX + 1);
         if (QT_CHDIR(workingDir) == -1)
             qWarning("ThreadCtl(): failed to chdir to %s", workingDir);
     }
 
-    pid_t childPid;
-    EINTR_LOOP(childPid, ::spawn(argv[0], fd_count, fd_map, &inherit, argv, envp));
-    if (childPid == -1) {
-        inherit.flags |= SPAWN_SEARCH_PATH;
-        EINTR_LOOP(childPid, ::spawn(argv[0], fd_count, fd_map, &inherit, argv, envp));
+    int fd;
+    if (spawn_detached) {
+        fd = ::posix_spawn(ppid, argv[0], file_actions, &attr, argv, envp);
+        if (fd == -1) {
+            fd = ::posix_spawnp(ppid, argv[0], file_actions, &attr, argv, envp);
+        }
+    } else {
+        // use spawnfd
+        fd = ::spawnfd(FFD_CLOEXEC | FFD_NONBLOCK, ppid, argv[0], file_actions, &attr, argv, envp);
+        if (fd == -1) {
+            fd = ::spawnfd(FFD_CLOEXEC | FFD_NONBLOCK | FFD_SPAWN_SEARCH_PATH, ppid, argv[0], file_actions,
+                           &attr, argv, envp);
+        }
     }
 
     if (oldWorkingDir) {
         if (QT_CHDIR(oldWorkingDir) == -1)
             qWarning("ThreadCtl(): failed to chdir to %s", oldWorkingDir);
 
+#  ifdef Q_OS_QNX
         if (ThreadCtl(_NTO_TCTL_THREADS_CONT, 0) == -1)
             qFatal("ThreadCtl(): cannot resume threads: %s", qPrintable(qt_error_string(errno)));
+#  endif
     }
 
-    return childPid;
+    posix_spawnattr_destroy(&attr);
+    return fd;
 }
 
-pid_t QProcessPrivate::spawnChild(const char *workingDir, char **argv, char **envp)
+pid_t QProcessPrivate::spawnChild(pid_t *ppid, const char *workingDir, char **argv, char **envp)
 {
-    // we need to manually fill in fd_map
-    // to inherit the file descriptors from
-    // the parent
-    const int fd_count = sysconf(_SC_OPEN_MAX);
-    QVarLengthArray<int, 1024> fd_map(fd_count);
-
-    for (int i = 3; i < fd_count; ++i) {
-        // here we rely that fcntl returns -1 and
-        // sets errno to EBADF
-        const int flags = ::fcntl(i, F_GETFD);
-
-        fd_map[i] = ((flags >= 0) && !(flags & FD_CLOEXEC))
-                  ? i : SPAWN_FDCLOSED;
+    // posix_spawn causes all file descriptors with FD_CLOEXEC to be closed automatically;
+    // we only need to add the actions for our own pipes
+    posix_spawn_file_actions_t file_actions;
+    posix_spawn_file_actions_init(&file_actions);
+
+    if (processChannelMode == QProcess::MergedChannels) {
+        // managed stderr == stdout
+        posix_spawn_file_actions_adddup2(&file_actions, stdoutChannel.pipe[1], STDERR_FILENO);
+    } else if (processChannelMode != QProcess::ForwardedChannels && processChannelMode != QProcess::ForwardedErrorChannel) {
+        // managed stderr
+        posix_spawn_file_actions_adddup2(&file_actions, stderrChannel.pipe[1], STDERR_FILENO);
+        posix_spawn_file_actions_addclose(&file_actions, stderrChannel.pipe[1]);
+    }
+
+    if (processChannelMode != QProcess::ForwardedChannels && processChannelMode != QProcess::ForwardedOutputChannel) {
+        // managed stdout
+        posix_spawn_file_actions_adddup2(&file_actions, stdoutChannel.pipe[1], STDOUT_FILENO);
+        posix_spawn_file_actions_addclose(&file_actions, stdoutChannel.pipe[1]);
     }
 
-    if (inputChannelMode == QProcess::ManagedInputChannel)
-        fd_map[0] = stdinChannel.pipe[0];
-    else
-        fd_map[0] = QT_FILENO(stdin);
-
-    switch (processChannelMode) {
-    case QProcess::ForwardedChannels:
-        fd_map[1] = QT_FILENO(stdout);
-        fd_map[2] = QT_FILENO(stderr);
-        break;
-    case QProcess::ForwardedOutputChannel:
-        fd_map[1] = QT_FILENO(stdout);
-        fd_map[2] = stderrChannel.pipe[1];
-        break;
-    case QProcess::ForwardedErrorChannel:
-        fd_map[1] = stdoutChannel.pipe[1];
-        fd_map[2] = QT_FILENO(stderr);
-        break;
-    case QProcess::MergedChannels:
-        fd_map[1] = stdoutChannel.pipe[1];
-        fd_map[2] = stdoutChannel.pipe[1];
-        break;
-    case QProcess::SeparateChannels:
-        fd_map[1] = stdoutChannel.pipe[1];
-        fd_map[2] = stderrChannel.pipe[1];
-        break;
+    if (inputChannelMode == QProcess::ManagedInputChannel) {
+        posix_spawn_file_actions_adddup2(&file_actions, stdinChannel.pipe[0], STDIN_FILENO);
+        posix_spawn_file_actions_addclose(&file_actions, stdinChannel.pipe[0]);
     }
 
-    pid_t childPid = doSpawn(fd_count, fd_map.data(), argv, envp, workingDir, false);
+    int retval = doSpawn(ppid, &file_actions, argv, envp, workingDir, false);
 
-    if (childPid == -1) {
+    if (retval == -1) {
         QString error = qt_error_string(errno);
         qt_safe_write(childStartedPipe[1], error.data(), error.length() * sizeof(QChar));
         qt_safe_close(childStartedPipe[1]);
         childStartedPipe[1] = -1;
     }
 
-    return childPid;
+    posix_spawn_file_actions_destroy(&file_actions);
+    return retval;
 }
 
 #else
@@ -1092,8 +856,8 @@ bool QProcessPrivate::waitForReadyRead(int msecs)
         FD_ZERO(&fdread);
         FD_ZERO(&fdwrite);
 
-        int nfds = deathPipe[0];
-        FD_SET(deathPipe[0], &fdread);
+        int nfds = forkfd;
+        FD_SET(forkfd, &fdread);
 
         if (processState == QProcess::Starting)
             add_fd(nfds, childStartedPipe[0], &fdread);
@@ -1143,7 +907,7 @@ bool QProcessPrivate::waitForReadyRead(int msecs)
         if (stdinChannel.pipe[1] != -1 && FD_ISSET(stdinChannel.pipe[1], &fdwrite))
             _q_canWrite();
 
-        if (deathPipe[0] == -1 || FD_ISSET(deathPipe[0], &fdread)) {
+        if (forkfd == -1 || FD_ISSET(forkfd, &fdread)) {
             if (_q_processDied())
                 return false;
         }
@@ -1172,8 +936,8 @@ bool QProcessPrivate::waitForBytesWritten(int msecs)
         FD_ZERO(&fdread);
         FD_ZERO(&fdwrite);
 
-        int nfds = deathPipe[0];
-        FD_SET(deathPipe[0], &fdread);
+        int nfds = forkfd;
+        FD_SET(forkfd, &fdread);
 
         if (processState == QProcess::Starting)
             add_fd(nfds, childStartedPipe[0], &fdread);
@@ -1217,7 +981,7 @@ bool QProcessPrivate::waitForBytesWritten(int msecs)
         if (stderrChannel.pipe[0] != -1 && FD_ISSET(stderrChannel.pipe[0], &fdread))
             _q_canReadStandardError();
 
-        if (deathPipe[0] == -1 || FD_ISSET(deathPipe[0], &fdread)) {
+        if (forkfd == -1 || FD_ISSET(forkfd, &fdread)) {
             if (_q_processDied())
                 return false;
         }
@@ -1256,8 +1020,8 @@ bool QProcessPrivate::waitForFinished(int msecs)
         if (stderrChannel.pipe[0] != -1)
             add_fd(nfds, stderrChannel.pipe[0], &fdread);
 
-        if (processState == QProcess::Running)
-            add_fd(nfds, deathPipe[0], &fdread);
+        if (processState == QProcess::Running && forkfd != -1)
+            add_fd(nfds, forkfd, &fdread);
 
         if (!stdinChannel.buffer.isEmpty() && stdinChannel.pipe[1] != -1)
             add_fd(nfds, stdinChannel.pipe[1], &fdwrite);
@@ -1290,7 +1054,7 @@ bool QProcessPrivate::waitForFinished(int msecs)
         if (stderrChannel.pipe[0] != -1 && FD_ISSET(stderrChannel.pipe[0], &fdread))
             _q_canReadStandardError();
 
-        if (deathPipe[0] == -1 || FD_ISSET(deathPipe[0], &fdread)) {
+        if (forkfd == -1 || FD_ISSET(forkfd, &fdread)) {
             if (_q_processDied())
                 return true;
         }
@@ -1308,46 +1072,41 @@ bool QProcessPrivate::waitForWrite(int msecs)
 
 void QProcessPrivate::findExitCode()
 {
-    Q_Q(QProcess);
-    processManager()->remove(q);
 }
 
 bool QProcessPrivate::waitForDeadChild()
 {
-    Q_Q(QProcess);
+    if (forkfd == -1)
+        return true; // child has already exited
 
-    // read a byte from the death pipe
-    char c;
-    qt_safe_read(deathPipe[0], &c, 1);
+    // read the process information from our fd
+    siginfo_t info;
+    qint64 ret = qt_safe_read(forkfd, &info, sizeof info);
+    Q_ASSERT(ret == sizeof info);
+    Q_UNUSED(ret);
+
+    Q_ASSERT(info.si_pid == pid_t(pid));
+
+    exitCode = info.si_status;
+    crashed = info.si_code != CLD_EXITED;
+
+    qt_safe_close(forkfd);
+    forkfd = -1; // Child is dead, don't try to kill it anymore
 
-    // check if our process is dead
-    int exitStatus;
-    if (qt_safe_waitpid(pid_t(pid), &exitStatus, WNOHANG) > 0) {
-        processManager()->remove(q);
-        crashed = !WIFEXITED(exitStatus);
-        exitCode = WEXITSTATUS(exitStatus);
-#if defined QPROCESS_DEBUG
-        qDebug() << "QProcessPrivate::waitForDeadChild() dead with exitCode"
-                 << exitCode << ", crashed?" << crashed;
-#endif
-        return true;
-    }
 #if defined QPROCESS_DEBUG
-    qDebug() << "QProcessPrivate::waitForDeadChild() not dead!";
+    qDebug() << "QProcessPrivate::waitForDeadChild() dead with exitCode"
+             << exitCode << ", crashed?" << crashed;
 #endif
-    return false;
+    return true;
 }
 
 void QProcessPrivate::_q_notified()
 {
 }
 
-#if defined(Q_OS_QNX)
+#if defined(QPROCESS_USE_SPAWN)
 bool QProcessPrivate::startDetached(const QString &program, const QStringList &arguments, const QString &workingDirectory, qint64 *pid)
 {
-    const int fd_count = 3;
-    int fd_map[fd_count] = { QT_FILENO(stdin), QT_FILENO(stdout), QT_FILENO(stderr) };
-
     QList<QByteArray> enc_args;
     enc_args.append(QFile::encodeName(program));
     for (int i = 0; i < arguments.size(); ++i)
@@ -1369,19 +1128,18 @@ bool QProcessPrivate::startDetached(const QString &program, const QStringList &a
         workingDirPtr = encodedWorkingDirectory.constData();
     }
 
-    pid_t childPid = doSpawn(fd_count, fd_map, raw_argv.data(), envp, workingDirPtr, true);
-    if (pid && childPid != -1)
+    pid_t childPid;
+    int retval = doSpawn(&childPid, NULL, raw_argv.data(), envp, workingDirPtr, true);
+    if (pid && retval != -1)
         *pid = childPid;
 
-    return childPid != -1;
+    return retval != -1;
 }
 
 #else
 
 bool QProcessPrivate::startDetached(const QString &program, const QStringList &arguments, const QString &workingDirectory, qint64 *pid)
 {
-    processManager()->start();
-
     QByteArray encodedWorkingDirectory = QFile::encodeName(workingDirectory);
 
     // To catch the startup of the child
@@ -1496,13 +1254,6 @@ bool QProcessPrivate::startDetached(const QString &program, const QStringList &a
 }
 #endif
 
-void QProcessPrivate::initializeProcessManager()
-{
-    (void) processManager();
-}
-
 QT_END_NAMESPACE
 
-#include "qprocess_unix.moc"
-
 #endif // QT_NO_PROCESS
diff --git a/src/corelib/kernel/qcoreapplication.cpp b/src/corelib/kernel/qcoreapplication.cpp
index 555b5e0263..d082a2739a 100644
--- a/src/corelib/kernel/qcoreapplication.cpp
+++ b/src/corelib/kernel/qcoreapplication.cpp
@@ -48,7 +48,6 @@
 #include <qhash.h>
 #include <qmutex.h>
 #include <private/qloggingregistry_p.h>
-#include <private/qprocess_p.h>
 #include <qstandardpaths.h>
 #include <qtextcodec.h>
 #ifndef QT_NO_QOBJECT
@@ -739,14 +738,6 @@ void QCoreApplication::init()
         d->appendApplicationPathToLibraryPaths();
 #endif
 
-#ifndef QT_NO_QOBJECT
-#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
-#endif
-
 #ifdef QT_EVAL
     extern void qt_core_eval_init(QCoreApplicationPrivate::Type);
     qt_core_eval_init(d->application_type);
diff --git a/tests/auto/corelib/io/qprocess/test/test.pro b/tests/auto/corelib/io/qprocess/test/test.pro
index 90afeddaa0..f77dacc87b 100644
--- a/tests/auto/corelib/io/qprocess/test/test.pro
+++ b/tests/auto/corelib/io/qprocess/test/test.pro
@@ -1,7 +1,7 @@
 CONFIG += testcase
 CONFIG += parallel_test
 CONFIG -= app_bundle debug_and_release_target
-QT = core testlib network
+QT = core-private testlib network
 SOURCES = ../tst_qprocess.cpp
 
 TARGET = ../tst_qprocess
diff --git a/tests/auto/corelib/io/qprocess/tst_qprocess.cpp b/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
index c8ba69c0fb..3866dd246b 100644
--- a/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
+++ b/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
@@ -44,6 +44,7 @@
 #include <stdlib.h>
 
 #ifndef QT_NO_PROCESS
+# include <private/qprocess_p.h>    // only so we get QPROCESS_USE_SPAWN
 # if defined(Q_OS_WIN)
 #  include <windows.h>
 # endif
@@ -316,6 +317,9 @@ void tst_QProcess::execute()
 {
     QCOMPARE(QProcess::execute("testProcessNormal/testProcessNormal",
                                QStringList() << "arg1" << "arg2"), 0);
+#ifdef QPROCESS_USE_SPAWN
+    QEXPECT_FAIL("", "QProcess cannot detect failure to start when using posix_spawn()", Continue);
+#endif
     QCOMPARE(QProcess::execute("nonexistingexe"), -2);
 }
 
@@ -325,6 +329,9 @@ void tst_QProcess::startDetached()
     QProcess proc;
     QVERIFY(proc.startDetached("testProcessNormal/testProcessNormal",
                                QStringList() << "arg1" << "arg2"));
+#ifdef QPROCESS_USE_SPAWN
+    QEXPECT_FAIL("", "QProcess cannot detect failure to start when using posix_spawn()", Continue);
+#endif
     QCOMPARE(QProcess::startDetached("nonexistingexe"), false);
 }
 
@@ -713,6 +720,9 @@ void tst_QProcess::waitForFinished()
     QCOMPARE(output.count("\n"), 10*1024);
 
     process.start("blurdybloop");
+#ifdef QPROCESS_USE_SPAWN
+    QEXPECT_FAIL("", "QProcess cannot detect failure to start when using posix_spawn()", Abort);
+#endif
     QVERIFY(!process.waitForFinished());
     QCOMPARE(process.error(), QProcess::FailedToStart);
 }
@@ -1528,6 +1538,9 @@ void tst_QProcess::exitCodeTest()
 //-----------------------------------------------------------------------------
 void tst_QProcess::failToStart()
 {
+#ifdef QPROCESS_USE_SPAWN
+    QSKIP("QProcess cannot detect failure to start when using posix_spawn()");
+#endif
     qRegisterMetaType<QProcess::ProcessError>("QProcess::ProcessError");
     qRegisterMetaType<QProcess::ExitStatus>("QProcess::ExitStatus");
     qRegisterMetaType<QProcess::ProcessState>("QProcess::ProcessState");
@@ -1595,6 +1608,9 @@ void tst_QProcess::failToStart()
 //-----------------------------------------------------------------------------
 void tst_QProcess::failToStartWithWait()
 {
+#ifdef QPROCESS_USE_SPAWN
+    QSKIP("QProcess cannot detect failure to start when using posix_spawn()");
+#endif
     qRegisterMetaType<QProcess::ProcessError>("QProcess::ProcessError");
     qRegisterMetaType<QProcess::ExitStatus>("QProcess::ExitStatus");
 
@@ -1622,6 +1638,9 @@ void tst_QProcess::failToStartWithWait()
 //-----------------------------------------------------------------------------
 void tst_QProcess::failToStartWithEventLoop()
 {
+#ifdef QPROCESS_USE_SPAWN
+    QSKIP("QProcess cannot detect failure to start when using posix_spawn()");
+#endif
     qRegisterMetaType<QProcess::ProcessError>("QProcess::ProcessError");
     qRegisterMetaType<QProcess::ExitStatus>("QProcess::ExitStatus");
 
@@ -1870,6 +1889,9 @@ void tst_QProcess::waitForReadyReadForNonexistantProcess()
     QVERIFY(!process.waitForReadyRead()); // used to crash
     process.start("doesntexist");
     QVERIFY(!process.waitForReadyRead());
+#ifdef QPROCESS_USE_SPAWN
+    QEXPECT_FAIL("", "QProcess cannot detect failure to start when using posix_spawn()", Abort);
+#endif
     QCOMPARE(errorSpy.count(), 1);
     QCOMPARE(errorSpy.at(0).at(0).toInt(), 0);
     QCOMPARE(finishedSpy1.count(), 0);