1. Obtain a single license
The semaphore is set to 3, and one license is obtained each time, so you can obtain three licenses in succession.
As the following semaphore Demo
@Slf4j
public class SemaphoreExample1 {
private static int threadCount = 20;
public static void main(String[] args) throws InterruptedException {
ExecutorService exec = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(3);
for(int i = 0; i < threadCount; i++){
final int threadNum = i;
exec.execute(()->{
try {
semaphore.acquire();//获得一个许可
test(threadNum);
semaphore.release();//释放一个许可
} catch (InterruptedException e) {
e.printStackTrace();
}
});
}
exec.shutdown();
}
private static void test(int threadNum) throws InterruptedException {
log.info("{}", threadNum);
Thread.sleep(1000);
}
}
The print result is as follows. The semaphore is set to 3. 3 data are printed almost every 1 second.
2. Obtain multiple licenses
The number of threads is 20, the semaphore is 3, and 3 licenses are obtained each time. Equivalent to single thread.
@ Slf4j
public class SemaphoreExample2 {
private static int threadCount = 20;
public static void main (String [] args) throws InterruptedException {
ExecutorService exec = Executors.newCachedThreadPool ();
final Semaphore semaphore = new Semaphore (3);
for (int i = 0; i <threadCount; i ++) {
final int threadNum = i;
exec.execute (()-> {
try {
semaphore.acquire (3); // Obtain 3 licenses, the semaphore is 3, equivalent to single thread execution
test (threadNum);
semaphore.release (3); // Release 3 licenses
} catch (InterruptedException e) {
e.printStackTrace ();
}
});
}
exec.shutdown();
}
private static void test(int threadNum) throws InterruptedException {
log.info("{}", threadNum);
Thread.sleep(1000);
}
}
Print results: print results almost every 1 second
21:58:55.766 [pool-1-thread-1] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 0 21:58:56.771 [pool-1-thread-2] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 1 21:58:57.771 [pool-1-thread-3] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 2 21:58:58.772 [pool-1-thread-4] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 3 21:58:59.773 [pool-1-thread-5] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 4 21:59:00.774 [pool-1-thread-6] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 5 21:59:01.774 [pool-1-thread-8] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 7 21:59:02.775 [pool-1-thread-7] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 6 21:59:03.776 [pool-1-thread-9] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 8 21:59:04.776 [pool-1-thread-10] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 9 21:59:05.777 [pool-1-thread-11] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 10 21:59:06.778 [pool-1-thread-12] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 11 21:59:07.779 [pool-1-thread-13] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 12 21:59:08.780 [pool-1-thread-14] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 13 21:59:09.780 [pool-1-thread-16] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 15 21:59:10.781 [pool-1-thread-15] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 14 21:59:11.782 [pool-1-thread-17] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 16 21:59:12.783 [pool-1-thread-18] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 17 21:59:13.784 [pool-1-thread-19] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 18 21:59:14.784 [pool-1-thread-20] INFO com.bingfa.concurrency.example.aqs.SemaphoreExample2 - 19
3. Try to wait for a license
@Slf4j
public class SemaphoreExample3 {
private static int threadCount = 20;
public static void main(String[] args) throws InterruptedException {
ExecutorService exec = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(3);
for(int i = 0; i < threadCount; i++){
final int threadNum = i;
exec.execute(()->{
try {
if(semaphore.tryAcquire(3, TimeUnit.SECONDS)) {//尝试获得一个许可
test(threadNum);
semaphore.release();//释放一个许可
}
} catch (InterruptedException e) {
e.printStackTrace();
}
});
}
exec.shutdown();
}
private static void test(int threadNum) throws InterruptedException {
log.info("{}", threadNum);
Thread.sleep(1000);
}
}
Print result: Only the first 9 threads are executed
