在并发中,事务的范围死锁是指两个或多个事务在同一时间相互等待对方释放资源,导致无法继续执行的情况。下面给出一个代码示例和解决方法来避免并发中的事务范围死锁问题:
示例代码:
public class TransactionExample {
public void transferMoney(Account fromAccount, Account toAccount, int amount) {
synchronized (fromAccount) {
synchronized (toAccount) {
if (fromAccount.getBalance() > amount) {
fromAccount.decreaseBalance(amount);
toAccount.increaseBalance(amount);
}
}
}
}
}
解决方法:
public class TransactionExample {
private static final Object lock = new Object();
public void transferMoney(Account fromAccount, Account toAccount, int amount) {
int fromHash = System.identityHashCode(fromAccount);
int toHash = System.identityHashCode(toAccount);
if (fromHash < toHash) {
synchronized (fromAccount) {
synchronized (toAccount) {
if (fromAccount.getBalance() > amount) {
fromAccount.decreaseBalance(amount);
toAccount.increaseBalance(amount);
}
}
}
} else if (fromHash > toHash) {
synchronized (toAccount) {
synchronized (fromAccount) {
if (fromAccount.getBalance() > amount) {
fromAccount.decreaseBalance(amount);
toAccount.increaseBalance(amount);
}
}
}
} else {
synchronized (lock) {
synchronized (fromAccount) {
synchronized (toAccount) {
if (fromAccount.getBalance() > amount) {
fromAccount.decreaseBalance(amount);
toAccount.increaseBalance(amount);
}
}
}
}
}
}
}
public class TransactionExample {
public void transferMoney(Account fromAccount, Account toAccount, int amount) {
long startTime = System.currentTimeMillis();
long timeout = 5000; // 设置超时时间为5秒
while (true) {
if (System.currentTimeMillis() - startTime > timeout) {
// 超时处理逻辑
break;
}
if (fromAccount.tryLock()) {
try {
if (toAccount.tryLock()) {
try {
if (fromAccount.getBalance() > amount) {
fromAccount.decreaseBalance(amount);
toAccount.increaseBalance(amount);
break;
}
} finally {
toAccount.unlock();
}
}
} finally {
fromAccount.unlock();
}
}
}
}
}
public class TransactionExample {
public void transferMoney(Account fromAccount, Account toAccount, int amount) {
DeadlockDetector detector = new DeadlockDetector();
detector.addResource(fromAccount);
detector.addResource(toAccount);
while (true) {
if (detector.detectDeadlock()) {
detector.resolveDeadlock();
}
synchronized (fromAccount) {
synchronized (toAccount) {
if (fromAccount.getBalance() > amount) {
fromAccount.decreaseBalance(amount);
toAccount.increaseBalance(amount);
break;
}
}
}
}
}
}
这些方法可以帮助避免并发中的事务范围死锁问题,但是请注意,在实际应用中,应该根据具体情况选择适合的解决方法,并综合考虑性能和可靠性。