scope_guard.hpp

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#pragma once
 
/// @file userver/utils/scope_guard.hpp
/// @brief @copybrief utils::ScopeGuard
 
#include <exception>
#include <functional>
 
#include <userver/logging/log.hpp>
#include <userver/utils/assert.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils {
 
/// @ingroup userver_universal userver_containers
///
/// @brief a helper class to perform actions on scope exit
///
/// Usage example:
/// @snippet universal/src/utils/scope_guard_test.cpp  ScopeGuard usage example
///
/// @note exception handling is done in such way that std::terminate will not be
/// called: in the normal path of execution, exception from handler will
/// propagate into client code, but if we leave scope because of an exception,
/// handler's exception, if thrown, will be silenced and written into log to
/// avoid std::terminate
class ScopeGuard final {
public:
    using Callback = std::function<void()>;
 
    explicit ScopeGuard(Callback callback)
        : callback_(std::move(callback)),
          exceptions_on_enter_(std::uncaught_exceptions())
    {}
 
    ScopeGuard(const ScopeGuard&) = delete;
    ScopeGuard(ScopeGuard&&) = delete;
 
    ScopeGuard& operator=(const ScopeGuard&) = delete;
    ScopeGuard& operator=(ScopeGuard&&) = delete;
 
    ~ScopeGuard() noexcept(false) {
        if (!callback_) {
            return;
        }
 
        if (std::uncaught_exceptions() != exceptions_on_enter_) {
            // keep all exceptions inside the destructor to avoid std::terminate
            try {
                callback_();
            } catch (const std::exception& e) {
                UASSERT_MSG(false, "exception is thrown during stack unwinding");
                LOG_ERROR() << "Exception is thrown during stack unwinding - ignoring: " << e;
            }
        } else {
            // safe to throw
            callback_();
        }
    }
 
    void Release() noexcept { callback_ = {}; }
 
private:
    Callback callback_;
    const int exceptions_on_enter_;
};
 
}  // namespace utils
 
USERVER_NAMESPACE_END