IPython can interactively manage parallel computing clusters using asynchronous status callbacks and/or MPI. These promise callbacks must be used due to the asynchronous nature of Ajax requests. Program flow using asynchronous XHR callbacks can present difficulty with readability and maintenance. It is commonly seen when checking for null pointers or handling callbacks. This is commonly implemented in C++ as callbacks. Closures are frequently used in JavaScript, due to being used for callbacks. Node.js exits the event loop when there are no further callbacks to be performed. One could simply call the callbacks as regular functions, . The Deinterlacing DDI specifies the callbacks for deinterlacing operations. Webhooks are "user-defined HTTP callbacks". The following C code demonstrates the use of callbacks to display two numbers. This option is always available for customers that already pay the monthly fee for callbacks. "Boston Globe" dismissed it as "riddled with needless callbacks to episodes past". Despite her lack of acting experience, she arranged a meeting following persistent callbacks. She was encouraged by subsequent callbacks, but did not land the role.