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++ // Copyright (C) 2026 The Qt Company Ltd.
++ // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
++
++ #ifndef QTRACECALLBACK_P_H
++ #define QTRACECALLBACK_P_H
++
++ //
++ // W A R N I N G
++ // -------------
++ //
++ // This file is not part of the Qt API. It exists purely as an
++ // implementation detail. This header file may change from version to
++ // version without notice, or even be removed.
++ //
++ // We mean it.
++ //
++
++ #include <QtCore/private/qglobal_p.h>
++
++ QT_REQUIRE_CONFIG(tracecallback);
++
++ QT_BEGIN_NAMESPACE
++
++ // The "callback" tracegen backend turns every Q_TRACE point into a call to a
++ // single process-wide hook, passing a pointer to a static descriptor of the
++ // firing point and the arguments as varargs. The callback is supposed to figure
++ // out what to do with the arguments using the tracepoint name/provider. It is
++ // meant for in-process profilers (e.g. benchmarks) that need to attribute time
++ // to the tracepoint that is currently executing. As such, the use cases are
++ // specialized for a finite collection of trace points of which we can
++ // statically know the argument types.
++ struct QTraceCallbackTracepoint
++ {
++ const char *provider;
++ const char *name;
++ // Scratch space owned by the installed callback. The generated code initialises it
++ // to -1; the callback may cache whatever it resolves the descriptor to (e.g. a
++ // category id, or entry/exit kind) so that repeated firings of a hot tracepoint do
++ // not re-parse the name. Each descriptor is a unique, stable object, so its address
++ // doubles as an identity key.
++ qint64 cookie;
++ };
++
++ using QTraceCallbackFunction = void (*)(QTraceCallbackTracepoint *...);
++
++ // Read on every tracepoint firing by the generated wrappers; set via qSetTraceCallback().
++ // Plain pointer on purpose: it is expected to be installed once before a measured region
++ // and left untouched while tracing, so the hot-path read needs no synchronisation.
++ Q_CORE_EXPORT extern QTraceCallbackFunction qtTraceCallbackFunction;
++
++ // Installs (or clears, with nullptr) the trace callback and returns the previous one.
++ Q_CORE_EXPORT QTraceCallbackFunction qSetTraceCallback(QTraceCallbackFunction callback);
++
++ QT_END_NAMESPACE
++
++ #endif // QTRACECALLBACK_P_H