Split QProcessPrivate::_q_processDied()

The completion of the child process can take place asynchronously or in
one of the waitFor...() functions. In both cases, we used the same
handler (_q_processDied()), which caused several problems:

  a. technically, waitForReadyRead() should have taken into account the
     result of the calls to _q_canRead...() slots inside the
     _q_processDied() function:

       - the user calls waitForReadyRead();
       - forkfd descriptor becomes signaled, while a grandchild
         process is still alive;
       - as readyRead() signal has not been emitted, _q_processDied()
         is called;
       - the grandchild process writes to stdout pipe;
       - now data arrives, and _q_processDied() will collect it, but
         won't report it.

  b. we had a bug with recursions on Unix:

       - death notification comes asynchronously;
       - waitForDeadChild() closes forkfd;
       - _q_canRead...() emits readyRead();
       - a slot connected to readyRead() calls waitForFinished();
       - waitForFinished() hangs (forkfd == -1).

   c. for blocking functions, drainOutputPipes() was called twice on
      Windows.

By introducing a new processFinished() function, we leave the read
operations in the _q_processDied() slot, while the process completion
code is guaranteed to run only once.

Change-Id: I5f9d09bc68a058169de4d9e490b48fc0b35e94cd
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

1 files changed, 6 insertions, 5 deletions

diff --git a/src/corelib/io/qprocess_unix.cpp b/src/corelib/io/qprocess_unix.cpp
index 1ca4a0d65e..17a1425d3f 100644
--- a/src/corelib/io/qprocess_unix.cpp
+++ b/src/corelib/io/qprocess_unix.cpp
@@ -754,8 +754,10 @@ bool QProcessPrivate::waitForReadyRead(const QDeadlineTimer &deadline)
         if (processState == QProcess::NotRunning)
             return false;
 
+        // We do this after checking the pipes, so we cannot reach it as long
+        // as there is any data left to be read from an already dead process.
         if (qt_pollfd_check(poller.forkfd(), POLLIN)) {
-            _q_processDied();
+            processFinished();
             return false;
         }
     }
@@ -796,7 +798,7 @@ bool QProcessPrivate::waitForBytesWritten(const QDeadlineTimer &deadline)
             return false;
 
         if (qt_pollfd_check(poller.forkfd(), POLLIN)) {
-            _q_processDied();
+            processFinished();
             return false;
         }
     }
@@ -837,7 +839,7 @@ bool QProcessPrivate::waitForFinished(const QDeadlineTimer &deadline)
             return true;
 
         if (qt_pollfd_check(poller.forkfd(), POLLIN)) {
-            _q_processDied();
+            processFinished();
             return true;
         }
     }
@@ -850,8 +852,7 @@ void QProcessPrivate::findExitCode()
 
 void QProcessPrivate::waitForDeadChild()
 {
-    if (forkfd == -1)
-        return; // child has already been reaped
+    Q_ASSERT(forkfd != -1);
 
     // read the process information from our fd
     forkfd_info info;