Critical Regions

• High-level synchronization construct
• A shared variable v of type T, is declared as:

  v: shared T

• Variable v accessed only inside statement

  region v when B do S

where B is a boolean expression.

• While statement S is being executed, no other process can access variable v.
• Regions referring to the same shared variable exclude each other in time.
• When a process tries to execute the region statement, the Boolean expression B is evaluated.  If B is true, statement S is executed.  If it is false, the process is delayed until B becomes true and no other process is in the region associated with v.