3 files changed, 35 insertions, 2 deletions
diff --git a/src/corelib/io/qlockfile_unix.cpp b/src/corelib/io/qlockfile_unix.cpp
index d1ef9c1770..cd4cf3a50d 100644
--- a/src/corelib/io/qlockfile_unix.cpp
+++ b/src/corelib/io/qlockfile_unix.cpp
@@ -206,7 +206,10 @@ void QLockFile::unlock()
         return;
     close(d->fileHandle);
     d->fileHandle = -1;
-    QFile::remove(d->fileName);
+    if (!QFile::remove(d->fileName)) {
+        qWarning() << "Could not remove our own lock file" << d->fileName << "maybe permissions changed meanwhile?";
+        // This is bad because other users of this lock file will now have to wait for the stale-lock-timeout...
+    }
     d->lockError = QLockFile::NoError;
     d->isLocked = false;
 }
diff --git a/src/corelib/io/qlockfile_win.cpp b/src/corelib/io/qlockfile_win.cpp
index 00c8a85bcc..5f82270706 100644
--- a/src/corelib/io/qlockfile_win.cpp
+++ b/src/corelib/io/qlockfile_win.cpp
@@ -47,6 +47,7 @@
 #include "QtCore/qfileinfo.h"
 #include "QtCore/qdatetime.h"
 #include "QtCore/qdebug.h"
+#include "QtCore/qthread.h"
 
 QT_BEGIN_NAMESPACE
 
@@ -149,7 +150,16 @@ void QLockFile::unlock()
      if (!d->isLocked)
         return;
      CloseHandle(d->fileHandle);
-     QFile::remove(d->fileName);
+     int attempts = 0;
+     static const int maxAttempts = 500; // 500ms
+     while (!QFile::remove(d->fileName) && ++attempts < maxAttempts) {
+         // Someone is reading the lock file right now (on Windows this prevents deleting it).
+         QThread::msleep(1);
+     }
+     if (attempts == maxAttempts) {
+        qWarning() << "Could not remove our own lock file" << d->fileName << ". Either other users of the lock file are reading it constantly for 500 ms, or we (no longer) have permissions to delete the file";
+        // This is bad because other users of this lock file will now have to wait for the stale-lock-timeout...
+     }
      d->lockError = QLockFile::NoError;
      d->isLocked = false;
 }
diff --git a/tests/auto/corelib/io/qlockfile/tst_qlockfile.cpp b/tests/auto/corelib/io/qlockfile/tst_qlockfile.cpp
index bd9e28beb5..de5d641c57 100644
--- a/tests/auto/corelib/io/qlockfile/tst_qlockfile.cpp
+++ b/tests/auto/corelib/io/qlockfile/tst_qlockfile.cpp
@@ -57,6 +57,7 @@ private slots:
     void lockUnlock();
     void lockOutOtherProcess();
     void lockOutOtherThread();
+    void raceWithOtherThread();
     void waitForLock_data();
     void waitForLock();
     void staleLockFromCrashedProcess_data();
@@ -165,6 +166,25 @@ void tst_QLockFile::lockOutOtherThread()
     QCOMPARE(ret2.result(), QLockFile::NoError);
 }
 
+static QLockFile::LockError lockFromThread(const QString &fileName)
+{
+    QLockFile lockInThread(fileName);
+    lockInThread.lock();
+    return lockInThread.error();
+}
+
+// QTBUG-38853, best way to trigger it was to add a QThread::sleep(1) in QLockFilePrivate::getLockInfo() after the first readLine.
+// Then (on Windows), the QFile::remove() in unlock() (called by the first thread who got the lock, in the destructor)
+// would fail due to the existing reader on the file. Fixed by checking the return value of QFile::remove() in unlock().
+void tst_QLockFile::raceWithOtherThread()
+{
+    const QString fileName = dir.path() + "/raceWithOtherThread";
+    QFuture<QLockFile::LockError> ret = QtConcurrent::run<QLockFile::LockError>(lockFromThread, fileName);
+    QFuture<QLockFile::LockError> ret2 = QtConcurrent::run<QLockFile::LockError>(lockFromThread, fileName);
+    QCOMPARE(ret.result(), QLockFile::NoError);
+    QCOMPARE(ret2.result(), QLockFile::NoError);
+}
+
 static bool lockFromThread(const QString &fileName, int sleepMs, QSemaphore *semThreadReady, QSemaphore *semMainThreadDone)
 {
     QLockFile lockFile(fileName);