Semaphore使用
摘要：
Semaphore：訊號量通常用於限制執行緒的數量訪問一些(物理或邏輯)資源。個人理解：限流、控制訪問量。
使用場景：競爭僅有的資源、一個車廂最多可容納多少人數，超載則不能上車，或者每條通道一次僅能n個人進入，剩下的需要排隊等等。。
import org....
Semaphore：訊號量通常用於限制執行緒的數量訪問一些(物理或邏輯)資源。個人理解：限流、控制訪問量。
使用場景：競爭僅有的資源、一個車廂最多可容納多少人數，超載則不能上車，或者每條通道一次僅能n個人進入，剩下的需要排隊等等。。
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.concurrent.Semaphore;
/**
* 訊號量
* Semaphore限流、控制訪問量
*/
public class SemaphoreTest {
public static final Logger logger = LoggerFactory.getLogger(SemaphoreTest.class);
public static void main(String[] args) {
/**
* Creates a {@code Semaphore} with the given number of
* permits and nonfair fairness setting.
*
* @param permits the initial number of permits available.
*This value may be negative, in which case releases
*must occur before any acquires will be granted.
*/
// public Semaphore(int permits);
/**
* Creates a {@code Semaphore} with the given number of
* permits and the given fairness setting.
*
* @param permits the initial number of permits available.
*This value may be negative, in which case releases
*must occur before any acquires will be granted.
* @param fair {@code true} if this semaphore will guarantee
*first-in first-out granting of permits under contention,
*else {@code false}
*/
// public Semaphore(int permits, boolean fair);
//初始化2個訊號量,也就是說同時最多隻能有2個請求的訪問
Semaphore semaphore = new Semaphore(2);
//模擬5次呼叫，迴圈5次，開啟5個非同步執行緒
for (int i = 1; i <= 5; i++) {
new Thread(() -> {
try {
//獲得訪問機會
semaphore.acquire();
logger.info(Thread.currentThread().getName() + "獲得訪問機會!");
} catch (InterruptedException e) {
e.printStackTrace();
}
//假設這裡有一個1秒鐘的任務，阻塞一秒
try {
Thread.sleep(1000L);
} catch (InterruptedException e) {
e.printStackTrace();
}
//釋放許可，
logger.info(Thread.currentThread().getName() + "釋放許可，釋放當前執行緒!");
semaphore.release();
logger.info(Thread.currentThread().getName() + "================================================");
}).start();
}
}
}
Semaphore並不能保證程式的順序和安全性。
輸出日誌:
11:59:54.157 [Thread-1] INFO com.test.tenant.SemaphoreTest - Thread-1獲得訪問機會! 11:59:54.157 [Thread-0] INFO com.test.tenant.SemaphoreTest - Thread-0獲得訪問機會! 11:59:55.165 [Thread-0] INFO com.test.tenant.SemaphoreTest - Thread-0釋放許可，釋放當前執行緒! 11:59:55.165 [Thread-1] INFO com.test.tenant.SemaphoreTest - Thread-1釋放許可，釋放當前執行緒! 11:59:55.165 [Thread-0] INFO com.test.tenant.SemaphoreTest - Thread-0================================================ 11:59:55.165 [Thread-1] INFO com.test.tenant.SemaphoreTest - Thread-1================================================ 11:59:55.165 [Thread-2] INFO com.test.tenant.SemaphoreTest - Thread-2獲得訪問機會! 11:59:55.165 [Thread-3] INFO com.test.tenant.SemaphoreTest - Thread-3獲得訪問機會! 11:59:56.167 [Thread-3] INFO com.test.tenant.SemaphoreTest - Thread-3釋放許可，釋放當前執行緒! 11:59:56.167 [Thread-2] INFO com.test.tenant.SemaphoreTest - Thread-2釋放許可，釋放當前執行緒! 11:59:56.168 [Thread-3] INFO com.test.tenant.SemaphoreTest - Thread-3================================================ 11:59:56.168 [Thread-2] INFO com.test.tenant.SemaphoreTest - Thread-2================================================ 11:59:56.168 [Thread-4] INFO com.test.tenant.SemaphoreTest - Thread-4獲得訪問機會! 11:59:57.172 [Thread-4] INFO com.test.tenant.SemaphoreTest - Thread-4釋放許可，釋放當前執行緒! 11:59:57.173 [Thread-4] INFO com.test.tenant.SemaphoreTest - Thread-4================================================