What is a background (daemon) thread?

The so-called background (daemon) thread, also known as the daemon thread, refers to a thread that provides a generic service in the background (for example, a daemon thread GC) while the program is running, and this thread is not part of the program, so when all non-background threads end, The program also terminates, killing all background threads at the same time. Conversely, the program does not terminate as long as there are any non-background threads (for example: the non-daemon thread, main ()). Background threads have the lowest priority.

The Setdaemon (Boolean on) method makes it easy to set the thread's daemon mode, true to daemon mode, and default (FALSE) to user mode. The Setdaemon (Boolean on) method must be called before the thread is started (Start ()), and an exception is generated when threads are running.

The Isdaemon method tests whether the thread is a daemon thread. Note: When you create other threads in a daemon thread, these newly generated threads do not have to set the Daemon property, they will be the daemon thread, and the user thread is the same.　　

The only difference between a daemon thread and a normal thread is that the daemon is the main die, and when main exits, it terminates , and the normal thread stops at the end of the task execution .

Normal Thread Code:

1  PackageCom.mianshi.easy;2  Public classStartruntest {3     /**4 * Background (daemon) threading Experiment5      */6      Public Static voidMain (string[] args) {7Thread thread=NewThreaddemo ();8 9         //1, why did not print out 100 sentences? Because we set the thread thread to Daemon (daemon) thread, it is possible to exit the program only when the daemon thread exists, so only seven sentences are printed out.Ten         //2. When the Java virtual machine has a daemon thread running, the Java virtual opportunity is turned off. When all regular threads have finished running, One         //the virtual machine exits running regardless of where the daemon is running. So it's best that your daemon doesn't write business logic that will affect the program. Otherwise, you can't predict what's going to happen to the program. A         //Thread.setdaemon (true); - Thread.Start (); -     } the      -      Public Static classThreaddemoextendsthread{ - @Override -          Public voidrun () { +              for(inti = 0; I < 100; i++) { -System.out.println ("This is a Thread test" +i); +             } A         } at     } -}

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Results:

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It can be seen that the default normal thread is started in the main thread, then the main thread does not have any execution statements, start waiting for the child threads to execute, after the child threads get CPU execution, start executing the Run () method, after printing 100 sentences, the thread execution completes and terminates, at this time, the main thread will also end. All non-daemon threads in the program are completed and the program ends.

Daemon Thread Code:

1  PackageCom.mianshi.easy;2  Public classStartruntest {3     /**4 * Background (daemon) threading Experiment5      */6      Public Static voidMain (string[] args) {7Thread thread=NewThreaddemo ();8 9         //1, why did not print out 100 sentences? Because we set the thread thread to Daemon (daemon) thread, it is possible to exit the program only when the daemon thread exists, so only seven sentences are printed out.Ten         //2. When the Java virtual machine has a daemon thread running, the Java virtual opportunity is turned off. When all regular threads have finished running, One         //the virtual machine exits running regardless of where the daemon is running. So it's best that your daemon doesn't write business logic that will affect the program. Otherwise, you can't predict what's going to happen to the program. AThread.setdaemon (true); - Thread.Start (); -     } the      -      Public Static classThreaddemoextendsthread{ - @Override -          Public voidrun () { +              for(inti = 0; I < 100; i++) { -System.out.println ("This is a Thread test" +i); +             } A         } at     } -}

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Results:

1       

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At this point, go to the main thread, create a thread, then set it as a background thread, and call the start () method to make the child thread ready, but at this time, there is no non-background thread in the program, so the main thread can end and the program will stop.

What is a background (daemon) thread?