Synchronization constructs of four categories

Simple blocking methods

These wait for another thread to finish or for a period of time to elapse.  Sleep,  Join, and  Task.Wait are simple blocking methods.

Locking constructs

These limit the number of threads that can perform some activity or execute a section of code at a time. Exclusive locking constructs are most common — these allow just one thread in at a time, and allow competing threads to access common data without interfering with each other. The standard exclusive locking constructs are  lock ( Monitor.Enter/ Monitor.Exit),  Mutex, and  SpinLock. The nonexclusive locking constructs are Semaphore,  SemaphoreSlim, and the  reader/writer locks.

Signaling constructs

These allow a thread to pause until receiving a notification from another, avoiding the need for inefficient polling. There are two commonly used signaling devices:  event wait handles and  Monitor’s  Wait/Pulse methods. Framework 4.0 introduces the  CountdownEvent and  Barrier classes.

Nonblocking synchronization constructs

These protect access to a common field by calling upon processor primitives. The CLR and C# provide the following nonblocking constructs:  Thread.MemoryBarrier, Thread.VolatileRead, Thread.VolatileWrite, the volatile keyword, and the  Interlocked class.

Blocking is essential to all but the last category.