java - 在实例对象上同步

Question

我有一个服务方法，基本上是将一条记录插入数据库。我想要实现的是基于对象或其变量来阻止一段代码。

我需要根据此 id 阻止其他线程:rcvTransactionRequest.getPoDistributionId()我不想阻止进入此方法的所有线程。最后，我试图验证不应超过的应收数量，如果多个线程进入临界区，则可能会发生这种情况。

    PoDistPayload poDistPayload = poDistService.getPoDist(rcvTransactionRequest.getPoDistributionId());
    synchronized (poDistPayload) {
        if (!poDistService.isReceivable(poDistPayload, rcvTransactionRequest.getQuantity()))
            throw ebsExceptionFactory.build(1036L, rcvTransactionRequest.getQuantity(), poDistPayload.getReceivableQuantity());

        PoDistRcv poDistRcv = PoDistRcv.of(rcvTransactionRequest);
        poDistRcv.setStatus(Status.TRANSACTION_STARTED);
        poDistRcv = poDistRcvRepository.save(poDistRcv);
        return new BaseTransactionResponse(poDistRcv.getTransactionId(), serialCountPerRequest, poDistRcv.getStatus());
    }

Answer 1

您可以使用 ConcurrentMap 来实现简单的锁定方案:

Object newLock=new Object();
Object existingLock;
// Wait until this thread can acquire lock
synchronized(newLock) {
  do {
    existingLock=cMap.putIfAbsent(distributionId,newLock);
    if(existingLock!=null) {
        // Locked by another thread. You can fail immediately, or wait until the lock is released
        synchronized(existingLock) {
          // Need timeout here because lock holder may notify before we wait
          existingLock.wait(timeout);
       }
    }
  } while(existingLock!=null);
  // You have the lock
  // Do work
  // Unlock and notify
  cMap.remove(distributionId,newLock);
  newLock.notify();
}