sessiond: ust: conditionally enable the underscore prefix variant quirk

[lttng-tools.git] / src / common / scope-exit.hpp

diff --git a/src/common/scope-exit.hpp b/src/common/scope-exit.hpp
new file mode 100644 (file)
index 0000000..46479bc
--- /dev/null
+++ b/src/common/scope-exit.hpp
@@ -0,0 +1,89 @@
+/*
+ * Copyright (C) 2022 Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * SPDX-License-Identifier: LGPL-2.1-only
+ *
+ */
+
+#ifndef LTTNG_SCOPE_EXIT_H
+#define LTTNG_SCOPE_EXIT_H
+
+#include <utility>
+
+namespace lttng {
+
+namespace details {
+/* Is operator() of InvocableType is marked as noexcept? */
+template <typename InvocableType>
+struct is_invocation_noexcept
+       : std::integral_constant<bool, noexcept((std::declval<InvocableType>())())> {
+};
+} /* namespace details. */
+
+/*
+ * Generic utility to run a lambda (or any other invocable object) when leaving
+ * a scope.
+ *
+ * Notably, this makes it easy to specify an action (e.g. restore a context)
+ * that must occur at the end of a function or roll-back operations in an
+ * exception-safe way.
+ */
+template <typename ScopeExitInvocableType>
+class scope_exit {
+public:
+       /*
+        * Since ScopeExitInvocableType will be invoked in the destructor, it
+        * must be `noexcept` lest we anger the undefined behaviour gods.
+        */
+       static_assert(details::is_invocation_noexcept<ScopeExitInvocableType>::value,
+                       "scope_exit requires a noexcept invocable type");
+
+       explicit scope_exit(ScopeExitInvocableType&& scope_exit_callable) :
+               _on_scope_exit{std::forward<ScopeExitInvocableType>(scope_exit_callable)}
+       {
+       }
+
+       scope_exit(scope_exit&& rhs) :
+               _on_scope_exit{std::move(rhs._on_scope_exit)}, _armed{rhs._armed}
+       {
+               /* Don't invoke ScopeExitInvocableType for the moved-from copy. */
+               rhs.disarm();
+       }
+
+       /*
+        * The copy constructor is disabled to prevent the action from being
+        * executed twice should a copy be performed accidentaly.
+        *
+        * The move-constructor is present to enable make_scope_exit() but to
+        * also propagate the scope_exit to another scope, should it be needed.
+        */
+       scope_exit(const scope_exit&) = delete;
+       scope_exit() = delete;
+
+       void disarm() noexcept
+       {
+               _armed = false;
+       }
+
+       ~scope_exit()
+       {
+               if (_armed) {
+                       _on_scope_exit();
+               }
+       }
+
+private:
+       ScopeExitInvocableType _on_scope_exit;
+       bool _armed = true;
+};
+
+template <typename ScopeExitInvocableType>
+scope_exit<ScopeExitInvocableType> make_scope_exit(ScopeExitInvocableType&& scope_exit_callable)
+{
+       return scope_exit<ScopeExitInvocableType>(
+                       std::forward<ScopeExitInvocableType>(scope_exit_callable));
+}
+
+} /* namespace lttng */
+
+#endif /* LTTNG_SCOPE_EXIT_H */