Title: Synchronization Classes

(see uvm_ref_sync.gif)

The UVM provides event and barrier synchronization classes
for managing concurrent processes. 

- <uvm_event> - UVM's event class augments the SystemVerilog
event datatype with such services as setting callbacks and data delivery.

- <uvm_barrier> - A barrier is used to prevent a pre-configured number of
processes from continuing until all have reached a certain point in simulation. 

- uvm_event_pool and uvm_barrier_pool -
The event and barrier pool classes are specializations of <uvm_object_string_pool #(T)>
used to store collections of <uvm_events> and <uvm_barriers>, respectively,
indexed by string name.  Each pool class contains a static, "global" pool instance 
for sharing across all processes.

- <uvm_event_callback> - The event callback is used to create callback objects
that may be attached to <uvm_event>s.