併發程式設計與高併發解決方案學習(常見類執行緒安全性研究)
阿新 • • 發佈:2019-01-28
StringBuilder 非執行緒安全
import com.mmall.concurrency.annoations.NotThreadSafe; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; @Slf4j @NotThreadSafe public class StringExample1 { // 請求總數 public static int clientTotal = 5000; // 同時併發執行的執行緒數 public static int threadTotal = 200; public static StringBuilder stringBuilder = new StringBuilder(); public static void main(String[] args) throws Exception { ExecutorService executorService = Executors.newCachedThreadPool(); final Semaphore semaphore = new Semaphore(threadTotal); final CountDownLatch countDownLatch = new CountDownLatch(clientTotal); for (int i = 0; i < clientTotal ; i++) { executorService.execute(() -> { try { semaphore.acquire(); update(); semaphore.release(); } catch (Exception e) { log.error("exception", e); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("size:{}", stringBuilder.length()); } private static void update() { stringBuilder.append("1"); } }
StringBuffer通過synchronized實現執行緒安全,效能有損耗,有好多程式碼都是在一個方法內部,可以判斷如果不會發生執行緒安全問題,就直接使用StringBuilder來拼接,效率會提升很多。
import com.mmall.concurrency.annoations.ThreadSafe; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; @Slf4j @ThreadSafe public class StringExample2 { // 請求總數 public static int clientTotal = 5000; // 同時併發執行的執行緒數 public static int threadTotal = 200; public static StringBuffer stringBuffer = new StringBuffer(); public static void main(String[] args) throws Exception { ExecutorService executorService = Executors.newCachedThreadPool(); final Semaphore semaphore = new Semaphore(threadTotal); final CountDownLatch countDownLatch = new CountDownLatch(clientTotal); for (int i = 0; i < clientTotal ; i++) { executorService.execute(() -> { try { semaphore.acquire(); update(); semaphore.release(); } catch (Exception e) { log.error("exception", e); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("size:{}", stringBuffer.length()); } private static void update() { stringBuffer.append("1"); } }
SimpleDateFormat非執行緒安全(錯誤寫法)
import com.mmall.concurrency.annoations.NotThreadSafe; import lombok.extern.slf4j.Slf4j; import java.text.SimpleDateFormat; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; @Slf4j @NotThreadSafe public class DateFormatExample1 { private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd"); // 請求總數 public static int clientTotal = 5000; // 同時併發執行的執行緒數 public static int threadTotal = 200; public static void main(String[] args) throws Exception { ExecutorService executorService = Executors.newCachedThreadPool(); final Semaphore semaphore = new Semaphore(threadTotal); final CountDownLatch countDownLatch = new CountDownLatch(clientTotal); for (int i = 0; i < clientTotal ; i++) { executorService.execute(() -> { try { semaphore.acquire(); update(); semaphore.release(); } catch (Exception e) { log.error("exception", e); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); } private static void update() { try { simpleDateFormat.parse("20180208"); } catch (Exception e) { log.error("parse exception", e); } } }
SimpleDateFormat (修改後)
import com.mmall.concurrency.annoations.ThreadSafe;
import lombok.extern.slf4j.Slf4j;
import java.text.SimpleDateFormat;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
@Slf4j
@ThreadSafe
public class DateFormatExample2 {
// 請求總數
public static int clientTotal = 5000;
// 同時併發執行的執行緒數
public static int threadTotal = 200;
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
for (int i = 0; i < clientTotal ; i++) {
executorService.execute(() -> {
try {
semaphore.acquire();
update();
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
}
private static void update() {
try {
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd");
simpleDateFormat.parse("20180208");
} catch (Exception e) {
log.error("parse exception", e);
}
}
}
HashSet非執行緒安全
import com.mmall.concurrency.annoations.NotThreadSafe;
import lombok.extern.slf4j.Slf4j;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
@Slf4j
@NotThreadSafe
public class HashSetExample {
// 請求總數
public static int clientTotal = 5000;
// 同時併發執行的執行緒數
public static int threadTotal = 200;
private static Set<Integer> set = new HashSet<>();
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
for (int i = 0; i < clientTotal; i++) {
final int count = i;
executorService.execute(() -> {
try {
semaphore.acquire();
update(count);
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
log.info("size:{}", set.size());
}
private static void update(int i) {
set.add(i);
}
}
HashMap非執行緒安全
import com.mmall.concurrency.annoations.NotThreadSafe;
import lombok.extern.slf4j.Slf4j;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
@Slf4j
@NotThreadSafe
public class HashMapExample {
// 請求總數
public static int clientTotal = 5000;
// 同時併發執行的執行緒數
public static int threadTotal = 200;
private static Map<Integer, Integer> map = new HashMap<>();
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
for (int i = 0; i < clientTotal; i++) {
final int count = i;
executorService.execute(() -> {
try {
semaphore.acquire();
update(count);
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
log.info("size:{}", map.size());
}
private static void update(int i) {
map.put(i, i);
}
}
ArrayList非執行緒安全
import com.mmall.concurrency.annoations.NotThreadSafe;
import lombok.extern.slf4j.Slf4j;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
@Slf4j
@NotThreadSafe
public class ArrayListExample {
// 請求總數
public static int clientTotal = 5000;
// 同時併發執行的執行緒數
public static int threadTotal = 200;
private static List<Integer> list = new ArrayList<>();
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
for (int i = 0; i < clientTotal; i++) {
final int count = i;
executorService.execute(() -> {
try {
semaphore.acquire();
update(count);
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
log.info("size:{}", list.size());
}
private static void update(int i) {
list.add(i);
}
}