Report the error as being AlreadyExists if this is why it fails

On Windows it would never report this error, and on Unix it would
report a different error ulimately instead as it tried to obtain the
semaphore a second time which could cause a different error to what
should be reported.

Task-number: QTBUG-9610
Reviewed-by: Frans Englich

3 files changed, 32 insertions, 3 deletions

diff --git a/src/corelib/kernel/qsystemsemaphore_unix.cpp b/src/corelib/kernel/qsystemsemaphore_unix.cpp
index 07e3618..d6c6c37 100644
--- a/src/corelib/kernel/qsystemsemaphore_unix.cpp
+++ b/src/corelib/kernel/qsystemsemaphore_unix.cpp
@@ -145,10 +145,10 @@ key_t QSystemSemaphorePrivate::handle(QSystemSemaphore::AccessMode mode)
     // Get semaphore
     semaphore = semget(unix_key, 1, 0666 | IPC_CREAT | IPC_EXCL);
     if (-1 == semaphore) {
+        setErrorString(QLatin1String("QSystemSemaphore::handle"));
         if (errno == EEXIST)
             semaphore = semget(unix_key, 1, 0666 | IPC_CREAT);
         if (-1 == semaphore) {
-            setErrorString(QLatin1String("QSystemSemaphore::handle"));
             cleanHandle();
             return -1;
         }
diff --git a/src/corelib/kernel/qsystemsemaphore_win.cpp b/src/corelib/kernel/qsystemsemaphore_win.cpp
index 96a47f5..74f253a 100644
--- a/src/corelib/kernel/qsystemsemaphore_win.cpp
+++ b/src/corelib/kernel/qsystemsemaphore_win.cpp
@@ -69,6 +69,10 @@ void QSystemSemaphorePrivate::setErrorString(const QString &function)
         error = QSystemSemaphore::PermissionDenied;
         errorString = QCoreApplication::translate("QSystemSemaphore", "%1: permission denied").arg(function);
         break;
+    case ERROR_ALREADY_EXISTS:
+        error = QSystemSemaphore::AlreadyExists;
+        errorString = QCoreApplication::translate("QSystemSemaphore", "%1: already exists").arg(function);
+        break;
     default:
         errorString = QCoreApplication::translate("QSystemSemaphore", "%1: unknown error %2").arg(function).arg(windowsError);
         error = QSystemSemaphore::UnknownError;
@@ -88,8 +92,8 @@ HANDLE QSystemSemaphorePrivate::handle(QSystemSemaphore::AccessMode)
     if (semaphore == 0) {
         QString safeName = makeKeyFileName();
         semaphore = CreateSemaphore(0, initialValue, MAXLONG, (wchar_t*)safeName.utf16());
-        if (semaphore == NULL)
-            setErrorString(QLatin1String("QSystemSemaphore::handle"));
+        // If the semaphore exists then the handle is still valid but there is still an error
+        setErrorString(QLatin1String("QSystemSemaphore::handle"));
     }
 
     return semaphore;
diff --git a/tests/auto/qtipc/qsystemsemaphore/tst_qsystemsemaphore.cpp b/tests/auto/qtipc/qsystemsemaphore/tst_qsystemsemaphore.cpp
index eb82fd4..0dc9c99 100644
--- a/tests/auto/qtipc/qsystemsemaphore/tst_qsystemsemaphore.cpp
+++ b/tests/auto/qtipc/qsystemsemaphore/tst_qsystemsemaphore.cpp
@@ -76,6 +76,8 @@ private slots:
     void undo();
     void initialValue();
 
+    void exists();
+
 private:
     QSystemSemaphore *existingLock;
 
@@ -297,6 +299,29 @@ void tst_QSystemSemaphore::initialValue()
     release.waitForFinished(LACKYWAITTIME);
     QVERIFY(acquire.state()== QProcess::NotRunning);
 }
+
+void tst_QSystemSemaphore::exists()
+{
+    QSystemSemaphore sem("store", 1, QSystemSemaphore::Create);
+    QVERIFY(sem.error() == QSystemSemaphore::NoError);
+    QVERIFY(sem.acquire());
+    QVERIFY(sem.error() == QSystemSemaphore::NoError);
+
+    {
+        QSystemSemaphore dupSem("store", 1, QSystemSemaphore::Create);
+        QVERIFY(dupSem.error() == QSystemSemaphore::AlreadyExists);
+    }
+#ifndef Q_OS_UNIX
+    // The rest of the test does not make sense on Unix because open will 
+    // actually succeed anyway (see QSystemSemaphore docs)
+    QSystemSemaphore anotherSem("store", 1, QSystemSemaphore::Open);
+    QVERIFY(anotherSem.error() == QSystemSemaphore::AlreadyExists);
+    QVERIFY(sem.release());
+    QVERIFY(anotherSem.acquire());
+    QVERIFY(anotherSem.release());
+#endif
+}
+
 QTEST_MAIN(tst_QSystemSemaphore)
 #include "tst_qsystemsemaphore.moc"