Druid-代码段-1-3

所属文章：池化技术（一）Druid是如何管理数据库连接的？

本代码段对应流程1.2，真正获取连接的执行：

private DruidPooledConnection getConnectionInternal(long maxWait) throws SQLException {
        //可用性判断
        if (closed) {
            connectErrorCountUpdater.incrementAndGet(this);
            throw new DataSourceClosedException("dataSource already closed at " + new Date(closeTimeMillis));
        }

        if (!enable) {
            connectErrorCountUpdater.incrementAndGet(this);
            throw new DataSourceDisableException();
        }

        final long nanos = TimeUnit.MILLISECONDS.toNanos(maxWait); //纳秒
        final int maxWaitThreadCount = this.maxWaitThreadCount; //目前因为拿不到连接而发生阻塞的业务线程数

        DruidConnectionHolder holder;

        for (boolean createDirect = false;;) {
            if (createDirect) { //模式未启用，恒等false，下面的逻辑不会触发，所以为了方便阅读，隐藏这部分代码
                //代码隐藏
            }

            try {
                lock.lockInterruptibly(); //锁获取
            } catch (InterruptedException e) {
                connectErrorCountUpdater.incrementAndGet(this);
                throw new SQLException("interrupt", e);
            }

            try {
                if (maxWaitThreadCount > 0
                        && notEmptyWaitThreadCount >= maxWaitThreadCount) { //如果因为拿不到连接而阻塞的业务线程数达到阈值，则直接抛异常
                    connectErrorCountUpdater.incrementAndGet(this);
                    throw new SQLException("maxWaitThreadCount " + maxWaitThreadCount + ", current wait Thread count "
                            + lock.getQueueLength());
                }

                if (onFatalError
                        && onFatalErrorMaxActive > 0
                        && activeCount >= onFatalErrorMaxActive) {
                    connectErrorCountUpdater.incrementAndGet(this);

                    StringBuilder errorMsg = new StringBuilder();
                    errorMsg.append("onFatalError, activeCount ")
                            .append(activeCount)
                            .append(", onFatalErrorMaxActive ")
                            .append(onFatalErrorMaxActive);

                    if (lastFatalErrorTimeMillis > 0) {
                        errorMsg.append(", time '")
                                .append(StringUtils.formatDateTime19(
                                        lastFatalErrorTimeMillis, TimeZone.getDefault()))
                                .append("'");
                    }

                    if (lastFatalErrorSql != null) {
                        errorMsg.append(", sql \n")
                                .append(lastFatalErrorSql);
                    }

                    throw new SQLException(
                            errorMsg.toString(), lastFatalError);
                }

                connectCount++; //连接数累加

                if (createScheduler != null
                        && poolingCount == 0
                        && activeCount < maxActive
                        && creatingCountUpdater.get(this) == 0
                        && createScheduler instanceof ScheduledThreadPoolExecutor) {
                    ScheduledThreadPoolExecutor executor = (ScheduledThreadPoolExecutor) createScheduler;
                    if (executor.getQueue().size() > 0) {
                        createDirect = true; //createScheduler这种异步添加模式不开启（默认不开启，本文也不是基于该模式的），createDirect永远不等于true，所以上面createDirect==true的代码不会被触发
                        continue;
                    }
                }

                if (maxWait > 0) {
                    holder = pollLast(nanos); //尝试从池子里获取连接
                } else {
                    holder = takeLast();
                }

                if (holder != null) {
                    activeCount++; //拿到连接，activeCount累加
                    if (activeCount > activePeak) {
                        activePeak = activeCount;
                        activePeakTime = System.currentTimeMillis();
                    }
                }
            } catch (InterruptedException e) {
                connectErrorCountUpdater.incrementAndGet(this);
                throw new SQLException(e.getMessage(), e);
            } catch (SQLException e) {
                connectErrorCountUpdater.incrementAndGet(this);
                throw e;
            } finally {
                lock.unlock();
            }

            break;
        }

        if (holder == null) { //没有获取到连接，整理错误信息，抛出错误
            long waitNanos = waitNanosLocal.get();

            StringBuilder buf = new StringBuilder(128);
            buf.append("wait millis ")//
                    .append(waitNanos / (1000 * 1000))//
                    .append(", active ").append(activeCount)//
                    .append(", maxActive ").append(maxActive)//
                    .append(", creating ").append(creatingCount)//
            ;
            if (creatingCount > 0 && createStartNanos > 0) {
                long createElapseMillis = (System.nanoTime() - createStartNanos) / (1000 * 1000);
                if (createElapseMillis > 0) {
                    buf.append(", createElapseMillis ").append(createElapseMillis);
                }
            }

            if (createErrorCount > 0) {
                buf.append(", createErrorCount ").append(createErrorCount);
            }

            List sqlList = this.getDataSourceStat().getRuningSqlList();
            for (int i = 0; i < sqlList.size(); ++i) {
                if (i != 0) {
                    buf.append('\n');
                } else {
                    buf.append(", ");
                }
                JdbcSqlStatValue sql = sqlList.get(i);
                buf.append("runningSqlCount ").append(sql.getRunningCount());
                buf.append(" : ");
                buf.append(sql.getSql());
            }

            String errorMessage = buf.toString();

            if (this.createError != null) {
                throw new GetConnectionTimeoutException(errorMessage, createError);
            } else {
                throw new GetConnectionTimeoutException(errorMessage);
            }
        }

        holder.incrementUseCount();

        DruidPooledConnection poolalbeConnection = new DruidPooledConnection(holder); //包装成目标对象
        return poolalbeConnection; //返回
    }

    //尝试从池子里获取连接
    private DruidConnectionHolder pollLast(long nanos) throws InterruptedException, SQLException {
        long estimate = nanos;

        for (;;) {
            if (poolingCount == 0) { //池子里的空闲连接为0，说明需要通知主流程3新增连接了
                emptySignal(); // empty.signal，唤起主流程3新增连接

                if (failFast && isFailContinuous()) { //如果置为快速结束，则不阻塞业务线程，直接抛出异常
                    throw new DataSourceNotAvailableException(createError);
                }

                if (estimate <= 0) {
                    waitNanosLocal.set(nanos - estimate);
                    return null;
                }

                notEmptyWaitThreadCount++; //因为获取不到连接而陷入阻塞状态的业务线程数+1
                if (notEmptyWaitThreadCount > notEmptyWaitThreadPeak) {
                    notEmptyWaitThreadPeak = notEmptyWaitThreadCount;
                }

                try {
                    long startEstimate = estimate;
                    estimate = notEmpty.awaitNanos(estimate); // 阻塞（挂起）estimate这么长的世界，期间如果被唤醒，则estimate就会被刷新成剩余等待时间
                    // recycle or
                    // creator
                    notEmptyWaitCount++;
                    notEmptyWaitNanos += (startEstimate - estimate);

                    if (!enable) {
                        connectErrorCountUpdater.incrementAndGet(this);
                        throw new DataSourceDisableException();
                    }
                } catch (InterruptedException ie) {
                    notEmpty.signal(); // 期间线程被中断，则唤起一次其他处于阻塞状态的业务线程
                    notEmptySignalCount++;
                    throw ie;
                } finally {
                    notEmptyWaitThreadCount--;
                }

                if (poolingCount == 0) { //依然没有竞争到
                    if (estimate > 0) { //如果目标阻塞时间（maxWait）还没有用完，则继续尝试获取
                        continue;
                    }

                    waitNanosLocal.set(nanos - estimate);
                    return null;
                }
            }

            decrementPoolingCount(); //poolingCount--
            DruidConnectionHolder last = connections[poolingCount]; //直接获取
            connections[poolingCount] = null; //获取后意味着连接已被借出，原有位置置空

            long waitNanos = nanos - estimate; //标记这次获取连接花了多长时间，连接够用时便为0
            last.setLastNotEmptyWaitNanos(waitNanos);

            return last; //返回
        }
    }