The existing concurrency model for Java (or C) requires programmers to design and implement thread-safe classes by explicitly acquiring locks and releasing locks. Such a model is error-prone and is the reason for many concurrency bugs. While there are alternative models like transactional memory, manually writing locks remains prevalent in practice. In this work, we propose AutoLock, which aims to solve the problem by fully automatically generating thread-safe classes. Given a class which is assumed to be correct with sequential clients, AutoLock automatically generates a thread-safe class which is linearizable and does it in a way without requiring a specification of the class. AutoLock takes three steps: (1) infer access annotations (i.e., abstract information on how variables are accessed and aliased), (2) synthesize a locking policy based on the access annotations, and (3) consistently implement the locking policy. AutoLock has been evaluated on a set of benchmark programs and the results show that AutoLock generates thread-safe classes effectively and could have prevented existing concurrency bugs.