<标题>A multithreaded malloc
Your task in this assignment is to implement a multithreaded malloc i.e. we
should be able to use it in a multithreaded application. The basic require-
ment is of course that it is thread safe, that it still works even if two threads
us it at the same time. This is of course very easy to solve by having one
central lock that protects any data structures that are used by the module.
It is a bit harder to allow multiple threads to actually use the malloc module