tomcat源碼解讀四 tomcat中的processer

     Processor是一個接口，針對於不同協議下具有不同的具體實現類，其實現類的具體功能是處理http請求,主要是對協議進行解析，狀態處理以及響應。然後起一箇中間作用轉發到 Adater,下面是其類的關係圖

     其實現類中我們常用的http協議，所以一般是左邊的部分,用紅線標註

1.1 循環隊列

protected static class RecycledProcessors<P extends Processor<S>, S> extends SynchronizedStack<Processor<S>> {

        private final transient AbstractConnectionHandler<S,P> handler;
        protected final AtomicInteger size = new AtomicInteger(0);

        public RecycledProcessors(AbstractConnectionHandler<S,P> handler) {
            this.handler = handler;
        }

        @SuppressWarnings("sync-override") // Size may exceed cache size a bit
        @Override
        public boolean push(Processor<S> processor) {
            //獲取Processor能夠緩存的大小
            int cacheSize = handler.getProtocol().getProcessorCache();
            boolean offer = cacheSize == -1 ? true : size.get() < cacheSize;
            //向棧中壓入當前processor
            boolean result = false;
            if (offer) {
                result = super.push(processor);
                if (result) {
                    size.incrementAndGet();
                }
            }
            //取消當前processor實例的JMX
            if (!result) handler.unregister(processor);
            return result;
        }

        @SuppressWarnings("sync-override") // OK if size is too big briefly
        @Override
        public Processor<S> pop() {
            Processor<S> result = super.pop();
            if (result != null) {
                size.decrementAndGet();
            }
            return result;
        }

        @Override
        public synchronized void clear() {
            Processor<S> next = pop();
            while (next != null) {
                handler.unregister(next);
                next = pop();
            }
            super.clear();
            size.set(0);
        }
    }

     在講述Processor的獲取以及處理過程之前先看一個類,姑且命名爲循環隊列, 它主要是繼承了SynchronizedStack這個棧（tomcat自己實現）裏面實現了進棧出棧兩種方法。

1.1 Processor的創建

     根據棧中執行的流程可以看出調用的是協議句柄的抽象類中的process方法，所以針對於四種模式其實現過程大致相同，具體代碼如下：

 public SocketState process(SocketWrapper<S> wrapper,
                SocketStatus status) {
            //如果socketWrapper爲空則證明不存在socket則直接將狀態設置爲CLOSED
            if (wrapper == null) {
                return SocketState.CLOSED;
            }
            //獲取當前SocketWrapper實例對應的NIO通道
            S socket = wrapper.getSocket();
            if (socket == null) {
                //什麼也不做 socket已經關閉
                return SocketState.CLOSED;
            }
            /**
             * 從connections中根據socket獲取Processor，如果沒有則在下面創建 connections句柄類型Map<S,Processor<S>>
             * 在以下情況下connections中存在值
             * 1.websocket中
             * 2.異步servlet
             * 3.發送文件
             * */
            Processor<S> processor = connections.get(socket);

            if (status == SocketStatus.DISCONNECT && processor == null) {
                // Nothing to do. Endpoint requested a close and there is no
                // longer a processor associated with this socket.
                return SocketState.CLOSED;
            }

            wrapper.setAsync(false);
            //標記當前線程是否是容器線程 set則是容器線程
            ContainerThreadMarker.set();
            /**
             *
             * 創建一個Http11NioProcessor 實例裏面構造了request 和response成員變量
             * 各封裝了一個InternalNioInputBuffer實例
             * 其中request中封裝了成員屬性名inputBuffer
             *    response中封裝了成員屬性名outputBuffer
             * */
            try {
                if (processor == null) {
                    processor = recycledProcessors.pop();
                }
                if (processor == null) {
                    processor = createProcessor();
                }

                initSsl(wrapper, processor);

                SocketState state = SocketState.CLOSED;

                Iterator<DispatchType> dispatches = null;
                do {
                    if (dispatches != null) {
                        // Associate the processor with the connection as
                        // these calls may result in a nested call to process()
                        connections.put(socket, processor);
                        DispatchType nextDispatch = dispatches.next();
                        if (processor.isUpgrade()) {
                            state = processor.upgradeDispatch(
                                    nextDispatch.getSocketStatus());
                        } else {
                            state = processor.asyncDispatch(
                                    nextDispatch.getSocketStatus());
                        }
                    } else if (processor.isComet()) {
                        state = processor.event(status);
                    } else if (processor.isUpgrade()) {
                        state = processor.upgradeDispatch(status);
                    } else if (status == SocketStatus.DISCONNECT) {
                        // Comet and upgrade need to see DISCONNECT but the
                        // others don't. NO-OP and let socket close.
                    } else if (processor.isAsync() || state == SocketState.ASYNC_END) {
                        state = processor.asyncDispatch(status);
                        if (state == SocketState.OPEN) {
                            // release() won't get called so in case this request
                            // takes a long time to process, remove the socket from
                            // the waiting requests now else the async timeout will
                            // fire
                            getProtocol().endpoint.removeWaitingRequest(wrapper);
                            // There may be pipe-lined data to read. If the data
                            // isn't processed now, execution will exit this
                            // loop and call release() which will recycle the
                            // processor (and input buffer) deleting any
                            // pipe-lined data. To avoid this, process it now.
                            state = processor.process(wrapper);
                        }
                    } else if (status == SocketStatus.OPEN_WRITE) {
                        // Extra write event likely after async, ignore
                        state = SocketState.LONG;
                    } else {
                        //這個是在第一次請求的時候執行
                        state = processor.process(wrapper);
                    }

                    //根據異步asyncStateMachine的狀態設置Socket的狀態
                    if (state != SocketState.CLOSED && processor.isAsync()) {
                        state = processor.asyncPostProcess();
                    }

                    if (state == SocketState.UPGRADING) {
                        // Get the HTTP upgrade handler
                        UpgradeToken upgradeToken = processor.getUpgradeToken();
                        HttpUpgradeHandler httpUpgradeHandler = upgradeToken.getHttpUpgradeHandler();
                        // Retrieve leftover input
                        ByteBuffer leftoverInput = processor.getLeftoverInput();
                        // Release the Http11 processor to be re-used
                        release(wrapper, processor, false, false);
                        // Create the upgrade processor
                        processor = createUpgradeProcessor(
                                wrapper, leftoverInput, upgradeToken);
                        // Mark the connection as upgraded
                        wrapper.setUpgraded(true);
                        // Associate with the processor with the connection
                        connections.put(socket, processor);
                        // Initialise the upgrade handler (which may trigger
                        // some IO using the new protocol which is why the lines
                        // above are necessary)
                        // This cast should be safe. If it fails the error
                        // handling for the surrounding try/catch will deal with
                        // it.
                        if (upgradeToken.getInstanceManager() == null) {
                            httpUpgradeHandler.init((WebConnection) processor);
                        } else {
                            ClassLoader oldCL = upgradeToken.getContextBind().bind(false, null);
                            try {
                                httpUpgradeHandler.init((WebConnection) processor);
                            } finally {
                                upgradeToken.getContextBind().unbind(false, oldCL);
                            }
                        }
                    }
                    if (getLog().isDebugEnabled()) {
                        getLog().debug("Socket: [" + wrapper +
                                "], Status in: [" + status +
                                "], State out: [" + state + "]");
                    }
                    if (dispatches == null || !dispatches.hasNext()) {
                        // Only returns non-null iterator if there are
                        // dispatches to process.
                        dispatches = wrapper.getIteratorAndClearDispatches();
                    }
                } while (state == SocketState.ASYNC_END ||
                        state == SocketState.UPGRADING ||
                        dispatches != null && state != SocketState.CLOSED);

                if (state == SocketState.LONG) {
                    // In the middle of processing a request/response. Keep the
                    // socket associated with the processor. Exact requirements
                    // depend on type of long poll
                    //異步在第一次處理的時候會將其設置到當前connections中去
                    connections.put(socket, processor);
                    longPoll(wrapper, processor);
                } else if (state == SocketState.OPEN) {
                    // In keep-alive but between requests. OK to recycle
                    // processor. Continue to poll for the next request.
                    connections.remove(socket);
                    release(wrapper, processor, false, true);
                } else if (state == SocketState.SENDFILE) {
                    // Sendfile in progress. If it fails, the socket will be
                    // closed. If it works, the socket either be added to the
                    // poller (or equivalent) to await more data or processed
                    // if there are any pipe-lined requests remaining.
                    connections.put(socket, processor);
                } else if (state == SocketState.UPGRADED) {
                    // Don't add sockets back to the poller if this was a
                    // non-blocking write otherwise the poller may trigger
                    // multiple read events which may lead to thread starvation
                    // in the connector. The write() method will add this socket
                    // to the poller if necessary.
                    if (status != SocketStatus.OPEN_WRITE) {
                        longPoll(wrapper, processor);
                    }
                } else {
                    // Connection closed. OK to recycle the processor. Upgrade
                    // processors are not recycled.
                    connections.remove(socket);
                    if (processor.isUpgrade()) {
                        UpgradeToken upgradeToken = processor.getUpgradeToken();
                        HttpUpgradeHandler httpUpgradeHandler = upgradeToken.getHttpUpgradeHandler();
                        InstanceManager instanceManager = upgradeToken.getInstanceManager();
                        if (instanceManager == null) {
                            httpUpgradeHandler.destroy();
                        } else {
                            ClassLoader oldCL = upgradeToken.getContextBind().bind(false, null);
                            try {
                                httpUpgradeHandler.destroy();
                            } finally {
                                try {
                                    instanceManager.destroyInstance(httpUpgradeHandler);
                                } catch (Throwable e) {
                                    ExceptionUtils.handleThrowable(e);
                                    getLog().error(sm.getString("abstractConnectionHandler.error"), e);
                                }
                                upgradeToken.getContextBind().unbind(false, oldCL);
                            }
                        }
                    } else {
                        release(wrapper, processor, true, false);
                    }
                }
                return state;
            } catch(java.net.SocketException e) {
                // SocketExceptions are normal
                getLog().debug(sm.getString(
                        "abstractConnectionHandler.socketexception.debug"), e);
            } catch (java.io.IOException e) {
                // IOExceptions are normal
                getLog().debug(sm.getString(
                        "abstractConnectionHandler.ioexception.debug"), e);
            }
            // Future developers: if you discover any other
            // rare-but-nonfatal exceptions, catch them here, and log as
            // above.
            catch (Throwable e) {
                ExceptionUtils.handleThrowable(e);
                // any other exception or error is odd. Here we log it
                // with "ERROR" level, so it will show up even on
                // less-than-verbose logs.
                getLog().error(
                        sm.getString("abstractConnectionHandler.error"), e);
            } finally {
                ContainerThreadMarker.clear();
            }

            // Make sure socket/processor is removed from the list of current
            // connections
            connections.remove(socket);
            // Don't try to add upgrade processors back into the pool
            if (processor !=null && !processor.isUpgrade()) {
                release(wrapper, processor, true, false);
            }
            return SocketState.CLOSED;
        }

     從代碼中可以看出獲取Processor共經過三種途徑，首先在connections這個map根據socket找到對應的Processor實例，也許你會有疑惑socket爲什麼會相同,目前我知道的有基於長連接和Upgrade來實現的socket,這樣就有效的保留其中的協議狀態，以及部分請求數據。如果從其中並沒有獲取則在循環隊列中獲取（下文講述循環隊列），這相當於從棧中獲取元素，這是因爲當一個實例化後的Processor處理完之後，並不會回收，而是釋放存入棧中供下次來可以直接進行使用，如果棧中不存在則自己再實例化一個。由這種方式可以看出其實例化跟瀏覽器的請求沒有多大關係，在一次會話中可能使用不同的，在不同會話中也可能使用相同的Processor

1.3 Processor的釋放

     在當前socket處理完之後，會將Processor給釋放,在這裏將其部分句柄給重置之後,然後就壓入循環隊列供下次使用，其具體處理過程在BIO NIO 和AIO中有所出入

 protected abstract void release(SocketWrapper<S> socket,
                Processor<S> processor, boolean socketClosing,
                boolean addToPoller);