QProcess: Handle spurious socket notifications for stdout and stderr

On Unix systems where the GUI event dispatcher uses a notification
system for socket notifiers that is out of band compared to select(),
it's possible for the QSocketNotifier to activate after the pipe has
been read from. When that happened, the ioctl(2) call with FIONREAD
might return 0 bytes available, which we interpreted to mean EOF.

Instead of doing that, always try to read at least one byte and examine
the returned byte count from read(2). If it returns 0, that's a real
EOF; if it returns -1 EWOULDBLOCK, we simply ignore the situation.

That's the case on OS X: the Cocoa event dispatcher uses CFSocket to get
notifications and those use kevent (and, apparently, an auxiliary
thread) instead of an in-thread select() or poll(). That means the event
loop would activate the QSocketNotifier even though there is nothing to
be read.

Task-number: QTBUG-39488
Change-Id: I1a58b5b1db7a47034fb36a78a005ebff96290efb
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

2 files changed, 1 insertions, 2 deletions

diff --git a/tests/auto/corelib/io/qprocess/test/test.pro b/tests/auto/corelib/io/qprocess/test/test.pro
index 79ea53cc6b..90afeddaa0 100644
--- a/tests/auto/corelib/io/qprocess/test/test.pro
+++ b/tests/auto/corelib/io/qprocess/test/test.pro
@@ -2,7 +2,6 @@ CONFIG += testcase
 CONFIG += parallel_test
 CONFIG -= app_bundle debug_and_release_target
 QT = core testlib network
-embedded: QT += gui
 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 b67166272b..82a0f3f832 100644
--- a/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
+++ b/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
@@ -1953,7 +1953,7 @@ void tst_QProcess::setStandardOutputFile2()
     process.start("testProcessEcho2/testProcessEcho2");
     process.write(testdata, sizeof testdata);
     QPROCESS_VERIFY(process,waitForFinished());
-    QVERIFY(!process.bytesAvailable());
+    QCOMPARE(process.bytesAvailable(), Q_INT64_C(0));
 
     QVERIFY(!QFileInfo(QProcess::nullDevice()).isFile());
 }