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Trail: Essential Classes
Lesson: Concurrency
Section: Thread Objects
Concurrency
Processes and Threads
Thread Objects
Defining and Starting a Thread
Pausing Execution with Sleep
Interrupts
Joins
The SimpleThreads Example
Synchronization
Thread Interference
Memory Consistency Errors
Synchronized Methods
Intrinsic Locks and Synchronization
Atomic Access
Liveness
Deadlock
Starvation and Livelock
Guarded Blocks
Immutable Objects
A Synchronized Class Example
A Strategy for Defining Immutable Objects
High Level Concurrency Objects
Lock Objects
Executors
Executor Interfaces
Thread Pools
Concurrent Collections
Atomic Variables
For Further Reading
Questions and Exercises
Home Page > Essential Classes > Concurrency
Pausing Execution with Sleep

> `Thread.sleep` causes the current thread to suspend execution for a specified period. This is an efficient means of making processor time available to the other threads of an application or other applications that might be running on a computer system. The `sleep` method can also be used for pacing, as shown in the example that follows, and waiting for another thread with duties that are understood to have time requirements, as with the `SimpleThreads` example in a later section.

> Two overloaded versions of `sleep` are provided: one that specifies the sleep time to the millisecond and one that specifies the sleep time to the nanosecond. However, these sleep times are not guaranteed to be precise, because they are limited by the facilities provided by the underlying OS. Also, the sleep period can be terminated by interrupts, as we'll see in a later section. In any case, you cannot assume that invoking `sleep` will suspend the thread for precisely the time period specified.

> The ``SleepMessages`` example uses `sleep` to print messages at four-second intervals:

> >     public class SleepMessages {
> >         public static void main(String args[]) throws InterruptedException {
> >             String importantInfo[] = {
> >                 "Mares eat oats",
> >                 "Does eat oats",
> >                 "Little lambs eat ivy",
> >                 "A kid will eat ivy too"
> >             };

> >             for (int i = 0; i < importantInfo.length; i++) {
> >                 //Pause for 4 seconds
> >                 Thread.sleep(4000);
> >                 //Print a message
> >                 System.out.println(importantInfo[i]);
> >             }
> >         }
> >     }

> Notice that `main` declares that it `throws InterruptedException`. This is an exception that `sleep` throws when another thread interrupts the current thread while `sleep` is active. Since this application has not defined another thread to cause the interrupt, it doesn't bother to catch `InterruptedException`.

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