In a destructor, how to detect if an exception is currently in flight?

Subject says it all. I want to make a small "ScopeGuard" library for exception-safe transactions, like the following: $scope = new ScopeGuard; $scope->onSucces(function() { logTransactionOne(); }); $scope->onFailure(function() { rollbackTransationOne(); }); doTransactionOne(); $scope->onSuccess(function() { logTransactionTwo(); }); $scope->onFailure(function() { rollbackTransactionTwo(); }); $scope->onFailure(function() { logFailureOfTransactionTwo(); }); doTransactionTwo(); // ... Three Four etc... So if an exception is thrown the attached onFailure callbacks will be executed, if the scope is exited through a return however the success callbacks will be executed. This requires me to know in ScopeGuard::__destruct() if the scope was left normally or due to an exception. The code in https://github.com/php/php-src/blob/master/Zend/zend_objects.c#L135 (line 135) seems to prevent me from knowing that information, because the exception is temporarily removed from the globals and put in a local variable. Is there any way to detect if an exception is currently in flight? (I've asked this same question on SO last week: http://stackoverflow.com/questions/33199997/in-destruct-how-can-you-see-if-an-exception-is-currently-in-flight)