Utility Classes TimeUnit and ThreadLocalRandom – Concurrency: Part II
23.1 Utility Classes TimeUnit and ThreadLocalRandom
This section can be skipped on the first reading, and can be read if and when the need arises while working through this chapter.
Before diving into high-level concurrency support provided by the java.util.concurrent package, we begin by providing an overview of two utility classes whose methods are used in many of the examples presented in this chapter.
The TimeUnit Enum Type
The enum type java.util.concurrent.TimeUnit represents time units at different levels of granularity, from nanoseconds to days, as shown in Table 23.1.
A TimeUnit can be used to indicate the time unit in which a numerical value should be interpreted as a time duration. Many time-based methods interpret their timing parameter according to the time unit specified by this enum type. In the code below, the numerical value 2 will be interpreted by the awaitTermination() method as two seconds.
boolean allTerminated = executor.awaitTermination(2, TimeUnit.SECONDS);
Note that a TimeUnit enum constant does not maintain any time information, like date or time of day.
Table 23.1 Constants Defined by the java.util.concurrent.TimeUnit Enum Type
The enum type TimeUnit also provides convenience methods that call the methods Thread.sleep(), Thread.join(), and Object.wait(), allowing the timeout for these methods to be specified in different time units. For example, the following method calls are equivalent:
TimeUnit.SECONDS.sleep(1); // 1 second.
TimeUnit.MILLISECONDS.sleep(1000); // 1000 milliseconds.
Thread.sleep(1000); // 1000 milliseconds.
Following convenience methods are defined in the TimeUnit enum type:
void sleep(long timeout) throws InterruptedException
void timedJoin(Thread thread, long timeout) throws InterruptedException
void timedWait(Object obj, long timeout) throws InterruptedException
Call the Thread.sleep(long millis) method, the Thread.join(long millis) method, and the Object.wait(long millis) method, respectively, where the specified timeout is converted to milliseconds using this time unit.
