Druid 连接池源码阅读 05

private DruidConnectionHolder pollLast(long nanos) throws InterruptedException, SQLException {        long estimate = nanos;
        for (;;) {            if (poolingCount == 0) {                emptySignal(); // send signal to CreateThread create connection
                if (failFast && isFailContinuous()) {                    throw new DataSourceNotAvailableException(createError);                }
                if (estimate <= 0) {                    waitNanosLocal.set(nanos - estimate);                    return null;                }
                notEmptyWaitThreadCount++;                if (notEmptyWaitThreadCount > notEmptyWaitThreadPeak) {                    notEmptyWaitThreadPeak = notEmptyWaitThreadCount;                }
                try {                    long startEstimate = estimate;                    estimate = notEmpty.awaitNanos(estimate); // signal by                                                              // recycle or                                                              // creator                    notEmptyWaitCount++;                    notEmptyWaitNanos += (startEstimate - estimate);
                    if (!enable) {                        connectErrorCountUpdater.incrementAndGet(this);
                        if (disableException != null) {                            throw disableException;                        }
                        throw new DataSourceDisableException();                    }                } catch (InterruptedException ie) {                    notEmpty.signal(); // propagate to non-interrupted thread                    notEmptySignalCount++;                    throw ie;                } finally {                    notEmptyWaitThreadCount--;                }
                if (poolingCount == 0) {                    if (estimate > 0) {                        continue;                    }
                    waitNanosLocal.set(nanos - estimate);                    return null;                }            }
            decrementPoolingCount();            DruidConnectionHolder last = connections[poolingCount];            connections[poolingCount] = null;
            long waitNanos = nanos - estimate;            last.setLastNotEmptyWaitNanos(waitNanos);
            return last;        }    }