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diff --git a/include/VBox/com/MultiResult.h b/include/VBox/com/MultiResult.h
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+/* $Id: MultiResult.h $ */
+/** @file
+ * MS COM / XPCOM Abstraction Layer - MultiResult class declarations.
+ */
+
+/*
+ * Copyright (C) 2008-2019 Oracle Corporation
+ *
+ * This file is part of VirtualBox Open Source Edition (OSE), as
+ * available from http://www.virtualbox.org. This file is free software;
+ * you can redistribute it and/or modify it under the terms of the GNU
+ * General Public License (GPL) as published by the Free Software
+ * Foundation, in version 2 as it comes in the "COPYING" file of the
+ * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
+ * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
+ *
+ * The contents of this file may alternatively be used under the terms
+ * of the Common Development and Distribution License Version 1.0
+ * (CDDL) only, as it comes in the "COPYING.CDDL" file of the
+ * VirtualBox OSE distribution, in which case the provisions of the
+ * CDDL are applicable instead of those of the GPL.
+ *
+ * You may elect to license modified versions of this file under the
+ * terms and conditions of either the GPL or the CDDL or both.
+ */
+
+#ifndef VBOX_INCLUDED_com_MultiResult_h
+#define VBOX_INCLUDED_com_MultiResult_h
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+#include "VBox/com/defs.h"
+#include "VBox/com/string.h"
+
+#include <stdarg.h>
+
+/** @defgroup grp_com_mr    MultiResult Classes
+ * @ingroup grp_com
+ * @{
+ */
+
+namespace com
+{
+
+/**
+ * "First worst" result type.
+ *
+ * Variables of this class are used instead of HRESULT variables when it is
+ * desirable to memorize the "first worst" result code instead of the last
+ * assigned one. In other words, an assignment operation to a variable of this
+ * class will succeed only if the result code to assign has worse severity. The
+ * following table demonstrate this (the first column lists the previous result
+ * code stored in the variable, the first row lists the new result code being
+ * assigned, 'A' means the assignment will take place, '> S_OK' means a warning
+ * result code):
+ *
+ * {{{
+ *             FAILED    > S_OK    S_OK
+ * FAILED        -         -         -
+ * > S_OK        A         -         -
+ * S_OK          A         A         -
+ *
+ * }}}
+ *
+ * In practice, you will need to use a FWResult variable when you call some COM
+ * method B after another COM method A fails and want to return the result code
+ * of A even if B also fails, but want to return the failed result code of B if
+ * A issues a warning or succeeds.
+ */
+class FWResult
+{
+
+public:
+
+    /**
+     * Constructs a new variable. Note that by default this constructor sets the
+     * result code to E_FAIL to make sure a failure is returned to the caller if
+     * the variable is never assigned another value (which is considered as the
+     * improper use of this class).
+     */
+    FWResult (HRESULT aRC = E_FAIL) : mRC (aRC) {}
+
+    FWResult &operator= (HRESULT aRC)
+    {
+        if ((FAILED (aRC) && !FAILED (mRC)) ||
+            (mRC == S_OK && aRC != S_OK))
+            mRC = aRC;
+
+        return *this;
+    }
+
+    operator HRESULT() const { return mRC; }
+
+    HRESULT *operator&() { return &mRC; }
+
+private:
+
+    HRESULT mRC;
+};
+
+/**
+ * The MultiResult class is a com::FWResult enhancement that also acts as a
+ * switch to turn on multi-error mode for VirtualBoxBase::setError() and
+ * VirtualBoxBase::setWarning() calls.
+ *
+ * When an instance of this class is created, multi-error mode is turned on
+ * for the current thread and the turn-on counter is increased by one. In
+ * multi-error mode, a call to setError() or setWarning() does not
+ * overwrite the current error or warning info object possibly set on the
+ * current thread by other method calls, but instead it stores this old
+ * object in the IVirtualBoxErrorInfo::next attribute of the new error
+ * object being set.
+ *
+ * This way, error/warning objects are stacked together and form a chain of
+ * errors where the most recent error is the first one retrieved by the
+ * calling party, the preceding error is what the
+ * IVirtualBoxErrorInfo::next attribute of the first error points to, and so
+ * on, up to the first error or warning occurred which is the last in the
+ * chain. See IVirtualBoxErrorInfo documentation for more info.
+ *
+ * When the instance of the MultiResult class goes out of scope and gets
+ * destroyed, it automatically decreases the turn-on counter by one. If
+ * the counter drops to zero, multi-error mode for the current thread is
+ * turned off and the thread switches back to single-error mode where every
+ * next error or warning object overwrites the previous one.
+ *
+ * Note that the caller of a COM method uses a non-S_OK result code to
+ * decide if the method has returned an error (negative codes) or a warning
+ * (positive non-zero codes) and will query extended error info only in
+ * these two cases. However, since multi-error mode implies that the method
+ * doesn't return control return to the caller immediately after the first
+ * error or warning but continues its execution, the functionality provided
+ * by the base com::FWResult class becomes very useful because it allows to
+ * preserve the error or the warning result code even if it is later assigned
+ * a S_OK value multiple times. See com::FWResult for details.
+ *
+ * Here is the typical usage pattern:
+ * @code
+    HRESULT Bar::method()
+    {
+        // assume multi-errors are turned off here...
+
+        if (something)
+        {
+            // Turn on multi-error mode and make sure severity is preserved
+            MultiResult rc = foo->method1();
+
+            // return on fatal error, but continue on warning or on success
+            CheckComRCReturnRC (rc);
+
+            rc = foo->method2();
+            // no matter what result, stack it and continue
+
+            // ...
+
+            // return the last worst result code (it will be preserved even if
+            // foo->method2() returns S_OK.
+            return rc;
+        }
+
+        // multi-errors are turned off here again...
+
+        return S_OK;
+    }
+ * @endcode
+ *
+ * @note This class is intended to be instantiated on the stack, therefore
+ *       You cannot create them using new(). Although it is possible to copy
+ *       instances of MultiResult or return them by value, please never do
+ *       that as it is breaks the class semantics (and will assert);
+ */
+class MultiResult : public FWResult
+{
+public:
+
+    /**
+     * @copydoc FWResult::FWResult()
+     */
+    MultiResult (HRESULT aRC = E_FAIL) : FWResult (aRC) { incCounter(); }
+
+    MultiResult (const MultiResult &aThat) : FWResult (aThat)
+    {
+        /* We need this copy constructor only for GCC that wants to have
+         * it in case of expressions like |MultiResult rc = E_FAIL;|. But
+         * we assert since the optimizer should actually avoid the
+         * temporary and call the other constructor directly instead. */
+        AssertFailed();
+    }
+
+    ~MultiResult() { decCounter(); }
+
+    MultiResult &operator= (HRESULT aRC)
+    {
+        FWResult::operator= (aRC);
+        return *this;
+    }
+
+    MultiResult &operator= (const MultiResult & /* aThat */)
+    {
+        /* We need this copy constructor only for GCC that wants to have
+         * it in case of expressions like |MultiResult rc = E_FAIL;|. But
+         * we assert since the optimizer should actually avoid the
+         * temporary and call the other constructor directly instead. */
+        AssertFailed();
+        return *this;
+    }
+
+    /**
+     * Returns true if multi-mode is enabled for the current thread (i.e. at
+     * least one MultiResult instance exists on the stack somewhere).
+     * @return
+     */
+    static bool isMultiEnabled();
+
+private:
+
+    DECLARE_CLS_NEW_DELETE_NOOP(MultiResult);
+
+    static void incCounter();
+    static void decCounter();
+
+    static RTTLS sCounter;
+
+    friend class MultiResultRef;
+};
+
+/**
+ * The MultiResultRef class is equivalent to MultiResult except that it takes
+ * a reference to the existing HRESULT variable instead of maintaining its own
+ * one.
+ */
+class MultiResultRef
+{
+public:
+
+    MultiResultRef (HRESULT &aRC) : mRC (aRC) { MultiResult::incCounter(); }
+
+    ~MultiResultRef() { MultiResult::decCounter(); }
+
+    MultiResultRef &operator= (HRESULT aRC)
+    {
+        /* Copied from FWResult */
+        if ((FAILED (aRC) && !FAILED (mRC)) ||
+            (mRC == S_OK && aRC != S_OK))
+            mRC = aRC;
+
+        return *this;
+    }
+
+    operator HRESULT() const { return mRC; }
+
+    HRESULT *operator&() { return &mRC; }
+
+private:
+
+    DECLARE_CLS_NEW_DELETE_NOOP(MultiResultRef);
+
+    HRESULT &mRC;
+};
+
+
+} /* namespace com */
+
+/** @} */
+
+#endif /* !VBOX_INCLUDED_com_MultiResult_h */
+