The TimeUnit Enumeration

The TimeUnit Enumeration

The concurrent API defines several methods that take an argument of type TimeUnit, which indicates a time-out period. TimeUnit is an enumeration that is used to specify the granularity (or resolution) of the timing. TimeUnit is defined within java.util.concurrent. It can be one of the following values:

DAYS

HOURS

MINUTES

SECONDS

MICROSECONDS

MILLISECONDS

NANOSECONDS

Although TimeUnit lets you specify any of these values in calls to methods that take a timing argument, there is no guarantee that the system is capable of the specified resolution.

Here is an example that uses TimeUnit. The CallableDemo class, shown in the previous section, is modified as shown next to use the second form of get( ) that takes a TimeUnit argument.

try {

System.out.println(f.get(10, TimeUnit.MILLISECONDS)); System.out.println(f2.get(10, TimeUnit.MILLISECONDS)); System.out.println(f3.get(10, TimeUnit.MILLISECONDS));

} catch (InterruptedException exc) { System.out.println(exc);

}

catch (ExecutionException exc) { System.out.println(exc);

} catch (TimeoutException exc) { System.out.println(exc);

}

In this version, no call to get( ) will wait more than 10 milliseconds.

The TimeUnit enumeration defines various methods that convert between units. These are shown here:

long convert(long tval, TimeUnit tu) long toMicros(long tval)

long toMillis(long tval) long toNanos(long tval)

long toSeconds(long tval) long toDays(long tval) long toHours(long tval) long toMinutes(long tval)

The convert( ) method converts tval into the specified unit and returns the result. The to methods perform the indicated conversion and return the result.

TimeUnit also defines the following timing methods:

void sleep(long delay) throws InterruptedExecution

void timedJoin(Thread thrd, long delay) throws InterruptedExecution void timedWait(Object obj, long delay) throws InterruptedExecution

Here, sleep( ) pauses execution for the specified delay period, which is specified in terms of the invoking enumeration constant. It translates into a call to Thread.sleep( ). The timedJoin( ) method is a specialized version of Thread.join( ) in which thrd pauses for the time period specified by delay, which is described in terms of the invoking time unit. The timedWait( ) method is a specialized version of Object.wait( ) in which obj is waited on for the period of time specified by delay, which is described in terms of the invoking time unit.

The Concurrent Collections

As explained, the concurrent API defines several collection classes that have been engineered for concurrent operation. They include:

ArrayBlockingQueue

ConcurrentHashMap ConcurrentLinkedDeque ConcurrentLinkedQueue ConcurrentSkipListMap ConcurrentSkipListSet CopyOnWriteArrayList CopyOnWriteArraySet DelayQueue LinkedBlockingDeque LinkedBlockingQueue LinkedTransferQueue PriorityBlockingQueue SynchronousQueue

These offer concurrent alternatives to their related classes defined by the Collections Framework. These collections work much like the other collections except that they provide concurrency support. Programmers familiar with the Collections Framework will have no trouble using these concurrent collections.