THREADS AND LOCKS

Wait Sets and Notification

17.14

Some other thread invokes the

notify

 method for that object and thread

T

happens to be the one arbitrarily chosen as the one to notify.

Some other thread invokes the

notifyAll

 method for that object.

If the call by thread

T

 to the wait method specified a timeout interval, the

specified amount of real time has elapsed.

The thread

T

 is then removed from the wait set and re enabled for thread schedul 

ing. It then locks the object again (which may involve competing in the usual

manner with other threads); once it has gained control of the lock, it performs

N

  1  additional

lock

 actions and then returns from the invocation of the

wait

method. Thus, on return from the

wait

 method, the state of the object's lock is

exactly as it was when the

wait

 method was invoked.

The

notify

 method should be called for an object only when the current

thread has already locked the object's lock. If the wait set for the object is not

empty, then some arbitrarily chosen thread is removed from the wait set and re 

enabled for thread scheduling. (Of course, that thread will not be able to proceed

until the current thread relinquishes the object's lock.)

The

notifyAll

 method should be called for an object only when the current

thread has already locked the object's lock. Every thread in the wait set for the

object is removed from the wait set and re enabled for thread scheduling. (Of

course, those threads will not be able to proceed until the current thread relin 

quishes the object's lock.)

These pearls of thought in Persian gulfs were bred,

Each softly lucent as a rounded moon;

The diver Omar plucked them from their bed,

Fitzgerald strung them on an English thread.

 James Russell Lowell,

in a copy of Omar Khayyam

417