Fix QSystemSemaphore handle management issues in Symbian

QSystemSemaphore native RSemaphore handle was unnecessarily created
again on each acquire. The creation logic was also susceptible for
random failures when two or more threads tried simultaneously acquire
the semaphore.

Task-number: QTBUG-16615
Reviewed-by: Janne Koskinen
(cherry picked from commit 570e7b38487455d394b5b74a59edc639f3dc416f)

1 files changed, 16 insertions, 4 deletions

diff --git a/src/corelib/kernel/qsystemsemaphore_symbian.cpp b/src/corelib/kernel/qsystemsemaphore_symbian.cpp
index a25a119..07cfffc 100644
--- a/src/corelib/kernel/qsystemsemaphore_symbian.cpp
+++ b/src/corelib/kernel/qsystemsemaphore_symbian.cpp
@@ -73,6 +73,9 @@ void QSystemSemaphorePrivate::setErrorString(const QString &function, int err)
     case KErrInUse:
         errorString = QCoreApplication::tr("%1: out of resources", "QSystemSemaphore").arg(function);
         error = QSystemSemaphore::OutOfResources;
+    case KErrPermissionDenied:
+        errorString = QCoreApplication::tr("%1: permission denied", "QSystemSemaphore").arg(function);
+        error = QSystemSemaphore::PermissionDenied;
     break;
 default:
     errorString = QCoreApplication::tr("%1: unknown error %2", "QSystemSemaphore").arg(function).arg(err);
@@ -86,15 +89,24 @@ default:
 
 int QSystemSemaphorePrivate::handle(QSystemSemaphore::AccessMode)
 {
+    if (semaphore.Handle()) {
+        return semaphore.Handle();
+    }
+
     // don't allow making handles on empty keys
     if (key.isEmpty())
         return 0;
+
     QString safeName = makeKeyFileName();
     TPtrC name(qt_QString2TPtrC(safeName));
-    int err;
-    err = semaphore.OpenGlobal(name,EOwnerProcess);
-    if (err == KErrNotFound){
-        err = semaphore.CreateGlobal(name,initialValue, EOwnerProcess);
+    int err = KErrAlreadyExists;
+    int tryCount = 10;
+    // Sort out race conditions by retrying several times until existing handle is acquired.
+    // Sometimes opening can fail inexplicably with KErrPermissionDenied many times in a row.
+    while (err != KErrNoMemory && err != KErrNone && tryCount-- >= 0) {
+        err = semaphore.CreateGlobal(name, initialValue, EOwnerProcess);
+        if (err != KErrNoMemory && err != KErrNone)
+            err = semaphore.OpenGlobal(name,EOwnerProcess);
     }
     if (err){
         setErrorString(QLatin1String("QSystemSemaphore::handle"),err);