Monitors

• High-level synchronization construct that allows the safe sharing of an abstract data type among concurrent processes.

                      monitor monitor-name

                      { 

                      shared variable declarations

                      procedure body P1 (…) {

                      . . .

                      }

                      procedure body P2 (…) {

                      . . .

                     }

                     procedure body Pn (…) {

                     . . .

                    }  

                    {

                    initialization code

                    }

                    }

• To allow a process to wait within the monitor, a condition variable must be declared, as

  condition x, y;

• Condition variable can only be used with the operations wait and signal.

1. The operation

  x.wait();
means that the process invoking this operation is suspended until another process invokes

  x.signal();

1. The x.signal operation resumes exactly one suspended process.  If no process is suspended, then the signal operation has no effect.