浅析Tomcat之AprEndpoint

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APR是Apache可移植运行库(Apache portable Run-time libraries)的简称,这是一个可以跨越多操作系统平台使用的底层支持接口库.在Tomcat的实现中就有使用该库的地方,AprEndpoint就是将Socket方面的操作直接用JNI替代而非Java元素的API.这使得其有较高的性能要求.同样AprEndpoint也是继承了AbstractEndpoint在实现的具体细节有点差别而已.只是另一种JIoEndpoint.提供了Acceptor线程,Socket轮询线程,Worker线程池和文件发送线程.
先看看Acceptor的实现.于JIoEndpoint有着极其相似的代码结构.

public void run() {
int errorDelay = 0;
// Loop until we receive a shutdown command
while (running) {
// Loop if endpoint is paused
while (paused && running) {
state = AcceptorState.PAUSED;
try {
Thread.sleep(50);
} catch (InterruptedException e) {
// Ignore
}
}
if (!running) {
break;
}
state = AcceptorState.RUNNING;
try {
//if we have reached max connections, wait
countUpOrAwaitConnection();
long socket = 0;
try {
// Accept the next incoming connection from the server
// socket
socket = Socket.accept(serverSock);
} catch (Exception e) {
//we didn't get a socket
countDownConnection();
// Introduce delay if necessary
errorDelay = handleExceptionWithDelay(errorDelay);
// re-throw
throw e;
}
// Successful accept, reset the error delay
errorDelay = 0;
if (running && !paused) {
// Hand this socket off to an appropriate processor
if (!processSocketWithOptions(socket)) {
// Close socket and pool right away
destroySocket(socket);
}
} else {
// Close socket and pool right away
destroySocket(socket);
}
} catch (Throwable t) {
....
}
// The processor will recycle itself when it finishes
}
state = AcceptorState.ENDED;
}

   其中的socket = Socket.accept(serverSocket)就是使用的JNI,也就是APR库.而这个类的所有Socket的实现也是使用该库的.至于其他线程也是使用了该库.看下生命周期的bind方法的部分代码,里面用了更多的APR的函数.大体的内容也是一致的.只是在Socket实现的API不一样而已.至于NIoEndpoint也是类似的实现.只不过实现方式是ServerSockeChannel,SockeChannel和Selector的就绪选择.
 
 
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