androidPN服务端用的是mina,略去不表，客户端的socket通讯用的是asmack,期间使用xmpp协议通讯，这个xmpp通用是通用了，但用的是xml格式互发，之间不得不加了一堆的xml解析，大部分篇幅都是干这个，对此没多大兴趣，这里只是简单记录一下阅读源码中client与server的阻塞读写，寻找可以借鉴之处。
客户端启动之后，负责管理连接的XMPPConnection初始化：
if (isFirstInitialization) {
packetWriter = new PacketWriter(this);
packetReader = new PacketReader(this);
分别负责读写。然后启动二者：
// Start the packet writer. This will open a XMPP stream to the server
packetWriter.startup();
// Start the packet reader. The startup() method will block until we
// get an opening stream packet back from server.
packetReader.startup();
// Make note of the fact that we're now connected.
connected = true;
先来看packetWriter是如何向服务器发送数据的，它的初始化方法
protected void init() {
this.writer = connection.writer;
done = false;
writerThread = new Thread() {
public void run() {
writePackets(this);
}
};
writerThread.setName("Smack Packet Writer (" + connection.connectionCounterValue + ")");
writerThread.setDaemon(true);
}
开一个守候线程writeThread,跑writePackets(this),该方法主要代码：
// Write out packets from the queue.
while (!done && (writerThread == thisThread)) {
Packet packet = nextPacket();
if (packet != null) {
writer.write(packet.toXML());
if (queue.isEmpty()) {
writer.flush();
}
}
}
其中queue,线程安全:
private final BlockingQueuequeue;
queue中有数据就write到服务器，如果没数据，阻塞在nextPacket()：
private Packet nextPacket() {
Packet packet = null;
// Wait until there's a packet or we're done.
while (!done && (packet = queue.poll()) == null) {
try {
synchronized (queue) {
queue.wait();
}
}
catch (InterruptedException ie) {
// Do nothing
}
}
return packet;
}
看看，queue.wait(),写线程阻塞于此，省电! 既然有wait(),必然有notifyAll():
public void sendPacket(Packet packet) {
if (!done) {
// Invoke interceptors for the new packet that is about to be sent. Interceptors
// may modify the content of the packet.
connection.firePacketInterceptors(packet);
try {
queue.put(packet);
}
catch (InterruptedException ie) {
ie.printStackTrace();
return;
}
synchronized (queue) {
queue.notifyAll();
}
// Process packet writer listeners. Note that we're using the sending
// thread so it's expected that listeners are fast.
connection.firePacketSendingListeners(packet);
}
}
当其他线程把要写的数据put进queue时，writerThread即被唤醒,继续运作，标准的生产消费模式。这个过程还是比较简单的，一目了然，相比之下PacketReader就不那么省心。
PacketReader初始化：
protected void init() {
//...
readerThread = new Thread() {
public void run() {
parsePackets(this);
}
};
//...
resetParser();
}
接着看parsePackets:
private void parsePackets(Thread thread) {
try {
int eventType = parser.getEventType();
do {
if (eventType == XmlPullParser.START_TAG) {
//...
//...很长很长，都在xml纠结
//...
eventType = parser.next();
} while (!done && eventType != XmlPullParser.END_DOCUMENT && thread == readerThread);
}