[英]How do I achieve a performant object isolation solution in concurrent transactions
我正在创建此方法issueTransfer以实现从一个帐户到另一个帐户的转移。
我的解决方案是:
public void issueTransfer(final int amount, final Account src,
final Account dst) {
/*
* TODO implement issueTransfer using object-based isolation instead of
* global isolation, based on the reference code provided in
* BankTransactionsUsingGlobalIsolation. Keep in mind that isolation
* must be applied to both src and dst.
*/
isolated(src, dst, () -> {
if (src.withdraw(amount)) {
dst.deposit(amount);
}
});
}
全局隔离的解决方案是:
public void issueTransfer(final int amount, final Account src,
final Account dst) {
isolated(() -> {
src.performTransfer(amount, dst);
});
}
全局和对象隔离方法的定义如下:
public static void isolated(Runnable runnable) {
isolatedManager.acquireAllLocks();
try {
runnable.run();
} finally {
isolatedManager.releaseAllLocks();
}
}
public static void isolated(Object obj1, Object obj2, Runnable runnable) {
Object[] objArr = new Object[]{obj1, obj2};
isolatedManager.acquireLocksFor(objArr);
try {
runnable.run();
} finally {
isolatedManager.releaseLocksFor(objArr);
}
}
辅助方法(获取和释放)是:
public void acquireAllLocks() {
for(int i = 0; i < this.locks.length; ++i) {
this.locks[i].lock();
}
}
public void releaseAllLocks() {
for(int i = this.locks.length - 1; i >= 0; --i) {
this.locks[i].unlock();
}
}
public void acquireLocksFor(Object[] objects) {
TreeSet<Object> sorted = this.createSortedObjects(objects);
Iterator var3 = sorted.iterator();
while(var3.hasNext()) {
Object obj = var3.next();
int lockIndex = this.lockIndexFor(obj);
this.locks[lockIndex].lock();
}
}
public void releaseLocksFor(Object[] objects) {
TreeSet<Object> sorted = this.createSortedObjects(objects);
Iterator var3 = sorted.iterator();
while(var3.hasNext()) {
Object obj = var3.next();
int lockIndex = this.lockIndexFor(obj);
this.locks[lockIndex].unlock();
}
}
private int lockIndexFor(Object obj) {
return Math.abs(obj.hashCode()) % 64;
}
private TreeSet<Object> createSortedObjects(Object[] objects) {
TreeSet<Object> sorted = new TreeSet(new Comparator<Object>() {
public int compare(Object o1, Object o2) {
return IsolatedManager.this.lockIndexFor(o1) - IsolatedManager.this.lockIndexFor(o2);
}
});
Object[] var3 = objects;
int var4 = objects.length;
for(int var5 = 0; var5 < var4; ++var5) {
Object obj = var3[var5];
sorted.add(obj);
}
return sorted;
}
如您所见,我应该按照文档中的要求应用第二种方法(对象隔离)。 测试顺利通过:
public void testObjectIsolation() {
testDriver(new BankTransactionsUsingGlobalIsolation());
final long globalTime = testDriver(
new BankTransactionsUsingGlobalIsolation());
testDriver(new BankTransactionsUsingObjectIsolation());
final long objectTime = testDriver(
new BankTransactionsUsingObjectIsolation());
final double improvement = (double)globalTime / (double)objectTime;
final int ncores = getNCores();
final double expected = (double)ncores * 0.75;
final String msg = String.format("Expected an improvement of at " +
"least %fx with object-based isolation, but saw %fx", expected,
improvement);
assertTrue(msg, improvement >= expected);
}
但是,用于评估的平台说我没有通过2核或4核的测试。 根据执行时间的不同,有时我会通过其中一项测试(我假设是2核心测试。
从我通过的测试中可以看出,我的对象隔离解决方案比全局隔离要快(每个内核的比率为1:0.75)。 是平台故障还是我的代码可以改进? 我曾尝试使用锁定,解锁和trylock,但是我的解决方案似乎运行得更快,但还不够。
您可以尝试使用Brian Goetz和Tim Pierels的“ Java Concurrency in Practice”一书中的这种方法。
您可以将Taooka分布式锁管理器与某些SQL数据库一起使用,以编写如下代码:
if taooka.Lock(srcUser.ID, time.Minute) {
if srcUser.Balance < transferSum {
taooka.Unlock(srcUser.ID)
return "Not enough money"
}
if taooka.Lock(dstUser.ID, time.Minute) {
srcSQLServer = GetSQLServerFor(srcUser)
dstSQLServer = GetSQLServerFor(dstUser)
transferID = journalSQLServer.do("INSERT INTO money_transfer SET start_time=NOW()")
srcSQLServer.do("INSERT INTO money_log SET transfer_id=", transferID, ", user_id=", srcUser.ID, ", sum=", -transferSum)
dstSQLServer.do("INSERT INTO money_log SET transfer_id=", transferID, ", user_id=", dstUser.ID, ", sum=", transferSum)
journalSQLServer.do("DELETE FROM money_transfer WHERE id=", transferID)
taooka.Unlock(dstUser.ID)
taooka.Unlock(srcUser.ID)
return "Ok"
}
taooka.Unlock(srcUser.ID)
return "wait please..."
}
else {
return "wait please..."
}
并在后台运行此代码:
for {
partialTransferID = journalSQLServer.do("SELECT id FROM money_transfer WHERE start_time < DATE_SUB(NOW(), INTERVAL 1 MINUTE) LIMIT 1")
if partialTransferID > 0 {
foreach sql in SQLServers {
sql.do("DELETE FROM money_log WHERE transfer_id=", partialTransferID)
}
journalSQLServer.do("DELETE FROM money_transfer WHERE id=", partialTransferID)
continue
}
Sleep(time.Second)
}
但是不幸的是Taooka仍然没有Java绑定。
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