@@ -42,4 +42,4 @@ When an event dispatcher passes a task to a worker thread, the user code probabl
Flow controls in asynchronous programming are even difficult for experts. Any suspending operation such as sleeping for a while or waiting for something to finish, implies that users have to save states explicitly and restore states in callbacks. Asynchronous code is often written as state machines. A few suspensions are troublesome, but still handleable. The problem is that once the suspension occurs inside a condition, loop or sub-function, it's almost impossible to write such a state machine being understood and maintained by many people, although the scenario is quite common in distributed systems where a node often needs to interact with multiple nodes simultaneously. In addition, if the wakeup can be triggered by more than one events (such as either fd has data or timeout is reached), the suspension and resuming are prone to race conditions, which require good multi-threaded programming skills to solve. Syntactic sugars(such as lambda) just make coding less troublesome rather than reducing difficulty.
Shared pointers are commonly in asynchronous programming , which seems convenient, but also makes ownerships of memory elusive. If the memory is leaked, it's difficult to locate the code that forgot to release; if segment fault happens, where the double-free occurs is also unknown. Code with a lot of referential countings is hard to remain good-quality and may waste a lot of time on debugging memory related issues. If references are even counted manually, keeping quality of the code is harder and the maintainers are less willing to modify the code. [RAII](http://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization) cannot be used in many scenarios in asynchronous programming, sometimes resources need to be locked before a callback and unlocked inside the callback, which is very error-prone in practice.
Shared pointers are common in asynchronous programming, which seems convenient, but also makes ownerships of memory elusive. If the memory is leaked, it's difficult to locate the code that forgot to release; if segment fault happens, where the double-free occurs is also unknown. Code with a lot of referential countings is hard to remain good-quality and may waste a lot of time on debugging memory related issues. If references are even counted manually, keeping quality of the code is harder and the maintainers are less willing to modify the code. [RAII](http://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization) cannot be used in many scenarios in asynchronous programming, sometimes resources need to be locked before a callback and unlocked inside the callback, which is very error-prone in practice.
