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没看过的倡议先看上一篇，原本打算讲讲 linux 内核，也看了一些书籍，可是 c 放了太久了，看代码切实头疼，就先放弃了，写写业务也没必要卷这么深吧。就讲到调用底层 api 为止我感觉刚刚好。不太善于将源码联合讲故事，所以整片略显干燥，将就看下吧～～
demo
public class ServerConnect
{public static void main(String[] args)
{selector();
}
public static void handleAccept(SelectionKey key) throws IOException{ServerSocketChannel ssChannel = (ServerSocketChannel)key.channel();
SocketChannel sc = ssChannel.accept();
sc.configureBlocking(false);
sc.register(key.selector(), SelectionKey.OP_READ,ByteBuffer.allocateDirect(1024));
}
public static void handleRead(SelectionKey key) throws IOException{SocketChannel sc = (SocketChannel)key.channel();
ByteBuffer buf = (ByteBuffer)key.attachment();
long bytesRead = sc.read(buf);
while(bytesRead>0){buf.flip();
while(buf.hasRemaining()){System.out.print((char)buf.get());
}
buf.clear();
bytesRead = sc.read(buf);
}
if(bytesRead == -1){sc.close();
}
}
public static void handleWrite(SelectionKey key) throws IOException{ByteBuffer buf = (ByteBuffer)key.attachment();
buf.flip();
SocketChannel sc = (SocketChannel) key.channel();
while(buf.hasRemaining()){sc.write(buf);
}
buf.compact();}
public static void selector() {
Selector selector = null;
ServerSocketChannel ssc = null;
try{selector = Selector.open();
ssc= ServerSocketChannel.open();
ssc.socket().bind(new InetSocketAddress(8080));
ssc.configureBlocking(false);
ssc.register(selector, SelectionKey.OP_ACCEPT);
while(true){if(selector.select(3000) == 0){continue;}
Iterator<SelectionKey> iter = selector.selectedKeys().iterator();
while(iter.hasNext()){SelectionKey key = iter.next();
if(key.isAcceptable()){handleAccept(key);
}
if(key.isReadable()){handleRead(key);
}
if(key.isWritable() && key.isValid()){handleWrite(key);
}
if(key.isConnectable()){System.out.println("isConnectable = true");
}
iter.remove();}
}
}catch(IOException e){e.printStackTrace();
}finally{
try{if(selector!=null){selector.close();
}
if(ssc!=null){ssc.close();
}
}catch(IOException e){e.printStackTrace();
}
}
}
}源码剖析
Selector.open()
此处会有 SelectorProvider 是个模板办法，不必零碎的实现不同，这就很蛋疼，没有EPollSelectorProvider，莫的方法，只能去 github 找了一份源码迁徙到 gitee，jdk8 感兴趣的能够自行下载，想看其余版本的同学就要自行寻找了。
EPollSelectorImpl(SelectorProvider sp) throws IOException {super(sp);
long pipeFds = IOUtil.makePipe(false);
fd0 = (int) (pipeFds >>> 32);
fd1 = (int) pipeFds;
pollWrapper = new EPollArrayWrapper();
pollWrapper.initInterrupt(fd0, fd1);
fdToKey = new HashMap<>();}IOUtil.makePipe(false)
IOUtil.makePipe(false);是一个 JNI 办法对应的门路为/jdk8u_jdk/src/solaris/native/sun/nio/ch/IOUtil.c
- 底层会调用
int pipe(int pipefd[2]); -
函数 pipe()会建设管道，并将文件形容词由参数 pipefd 数组返回。
- pipefd[0]为管道里的读取端
- pipefd[1]则为管道的写入端
JNIEXPORT jlong JNICALL
Java_sun_nio_ch_IOUtil_makePipe(JNIEnv *env, jobject this, jboolean blocking)
{int fd[2];
// 调用 pipe 函数
if (pipe(fd) < 0) {JNU_ThrowIOExceptionWithLastError(env, "Pipe failed");
return 0;
}
if (blocking == JNI_FALSE) {if ((configureBlocking(fd[0], JNI_FALSE) < 0)
|| (configureBlocking(fd[1], JNI_FALSE) < 0)) {JNU_ThrowIOExceptionWithLastError(env, "Configure blocking failed");
close(fd[0]);
close(fd[1]);
return 0;
}
}
// 2 个地址合并成 long 返回
return ((jlong) fd[0] << 32) | (jlong) fd[1];
}
new EPollArrayWrapper()
这个类呢，类正文写的很分明了，这里剪短的概述下，这个类就是操作 epoll 相干的构造体的，所以啦，外面也基本上都是 JNI 办法
EPollArrayWrapper() throws IOException {
// creates the epoll file descriptor
epfd = epollCreate();
// the epoll_event array passed to epoll_wait
int allocationSize = NUM_EPOLLEVENTS * SIZE_EPOLLEVENT;
pollArray = new AllocatedNativeObject(allocationSize, true);
pollArrayAddress = pollArray.address();
// eventHigh needed when using file descriptors > 64k
if (OPEN_MAX > MAX_UPDATE_ARRAY_SIZE)
eventsHigh = new HashMap<>();}JNIEXPORT jint JNICALL
Java_sun_nio_ch_EPollArrayWrapper_epollCreate(JNIEnv *env, jobject this)
{
/*
* epoll_create expects a size as a hint to the kernel about how to
* dimension internal structures. We can't predict the size in advance.
*/
// 创立 epoll 构造体
int epfd = epoll_create(256);
if (epfd < 0) {JNU_ThrowIOExceptionWithLastError(env, "epoll_create failed");
}
return epfd;
}new AllocatedNativeObject(allocationSize, true);
上面pollArray = new AllocatedNativeObject(allocationSize, true);
pollArray 正文为：来自 epoll_wait 的后果的 epoll_event 数组，然而看源码吧，也算不上数组，就开拓了一个内存块。
protected NativeObject(int var1, boolean var2) {
// 略
if (!var2) {this.allocationAddress = unsafe.allocateMemory((long)var1);
this.address = this.allocationAddress;
} else {
// 获取内存页数
int var3 = pageSize();
// 开拓内存空间，返回地址
long var4 = unsafe.allocateMemory((long)(var1 + var3));
this.allocationAddress = var4;
this.address = var4 + (long)var3 - (var4 & (long)(var3 - 1));
}
}pollWrapper.initInterrupt(fd0, fd1)
fd0: 后面 pipe 申请的读取端的文件描述符
上一篇咱们介绍了 epoll_ctl() 函数，
这里咱们重温下。epollCtl (epfd, EPOLL_CTL_ADD, fd0, EPOLLIN);
向 epfd 增加 fd0 且fd0可读，over～～
void initInterrupt(int fd0, int fd1) {
outgoingInterruptFD = fd1;
incomingInterruptFD = fd0;
epollCtl (epfd, EPOLL_CTL_ADD, fd0, EPOLLIN);
}JNIEXPORT void JNICALL
Java_sun_nio_ch_EPollArrayWrapper_epollCtl(JNIEnv *env, jobject this, jint epfd,
jint opcode, jint fd, jint events)
{
struct epoll_event event;
int res;
event.events = events;
event.data.fd = fd;
RESTARTABLE(epoll_ctl(epfd, (int)opcode, (int)fd, &event), res);
/*
* A channel may be registered with several Selectors. When each Selector
* is polled a EPOLL_CTL_DEL op will be inserted into its pending update
* list to remove the file descriptor from epoll. The "last" Selector will
* close the file descriptor which automatically unregisters it from each
* epoll descriptor. To avoid costly synchronization between Selectors we
* allow pending updates to be processed, ignoring errors. The errors are
* harmless as the last update for the file descriptor is guaranteed to
* be EPOLL_CTL_DEL.
*/
if (res < 0 && errno != EBADF && errno != ENOENT && errno != EPERM) {JNU_ThrowIOExceptionWithLastError(env, "epoll_ctl failed");
}
}ServerSocketChannel.open()
上面就来到了 channel，外部调用为sun.nio.ch.ServerSocketChannelImpl#ServerSocketChannelImpl(java.nio.channels.spi.SelectorProvider)
ServerSocketChannelImpl(SelectorProvider var1) throws IOException {super(var1);
this.fd = Net.serverSocket(true);
this.fdVal = IOUtil.fdVal(this.fd);
this.state = 0;
}Net.serverSocket(true)
这里看个办法名就大略晓得这是创立 socket 套接字的中央，各种协定规定之类的就跳过了，感兴趣的能够钻研下。
static FileDescriptor serverSocket(boolean var0) {return IOUtil.newFD(socket0(isIPv6Available(), var0, true, fastLoopback));
}JNIEXPORT int JNICALL
Java_sun_nio_ch_Net_socket0(JNIEnv *env, jclass cl, jboolean preferIPv6,
jboolean stream, jboolean reuse, jboolean ignored)
{
int fd;
int type = (stream ? SOCK_STREAM : SOCK_DGRAM);
#ifdef AF_INET6
int domain = (ipv6_available() && preferIPv6) ? AF_INET6 : AF_INET;
#else
int domain = AF_INET;
#endif
// 创立套接字
fd = socket(domain, type, 0);
if (fd < 0) {return handleSocketError(env, errno);
}
#ifdef AF_INET6
/* Disable IPV6_V6ONLY to ensure dual-socket support */
if (domain == AF_INET6) {
int arg = 0;
if (setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, (char*)&arg,
sizeof(int)) < 0) {
JNU_ThrowByNameWithLastError(env,
JNU_JAVANETPKG "SocketException",
"Unable to set IPV6_V6ONLY");
close(fd);
return -1;
}
}
#endif
if (reuse) {
int arg = 1;
if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, (char*)&arg,
sizeof(arg)) < 0) {
JNU_ThrowByNameWithLastError(env,
JNU_JAVANETPKG "SocketException",
"Unable to set SO_REUSEADDR");
close(fd);
return -1;
}
}
#if defined(__linux__)
if (type == SOCK_DGRAM) {
int arg = 0;
int level = (domain == AF_INET6) ? IPPROTO_IPV6 : IPPROTO_IP;
if ((setsockopt(fd, level, IP_MULTICAST_ALL, (char*)&arg, sizeof(arg)) < 0) &&
(errno != ENOPROTOOPT)) {
JNU_ThrowByNameWithLastError(env,
JNU_JAVANETPKG "SocketException",
"Unable to set IP_MULTICAST_ALL");
close(fd);
return -1;
}
}
#endif
#if defined(__linux__) && defined(AF_INET6)
/* By default, Linux uses the route default */
if (domain == AF_INET6 && type == SOCK_DGRAM) {
int arg = 1;
if (setsockopt(fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &arg,
sizeof(arg)) < 0) {
JNU_ThrowByNameWithLastError(env,
JNU_JAVANETPKG "SocketException",
"Unable to set IPV6_MULTICAST_HOPS");
close(fd);
return -1;
}
}
#endif
return fd;
}这里 newFD，就是创立一个对应的 java 对象，setfdVal()就是把文件描述符地址，放入到 java 对象中
public static FileDescriptor newFD(int var0) {FileDescriptor var1 = new FileDescriptor();
setfdVal(var1, var0);
return var1;
}JNIEXPORT void JNICALL
Java_sun_nio_ch_IOUtil_setfdVal(JNIEnv *env, jclass clazz, jobject fdo, jint val)
{(*env)->SetIntField(env, fdo, fd_fdID, val);
}ssc.socket().bind()
无聊的省略了，最初会到sun.nio.ch.ServerSocketChannelImpl#bind
public ServerSocketChannel bind(SocketAddress var1, int var2) throws IOException {synchronized(this.lock) {if (!this.isOpen()) {throw new ClosedChannelException();
} else if (this.isBound()) {throw new AlreadyBoundException();
} else {
// 端口
InetSocketAddress var4 = var1 == null ? new InetSocketAddress(0) : Net.checkAddress(var1);
SecurityManager var5 = System.getSecurityManager();
if (var5 != null) {var5.checkListen(var4.getPort());
}
NetHooks.beforeTcpBind(this.fd, var4.getAddress(), var4.getPort());
// 最终会调用 bind 和 listen
Net.bind(this.fd, var4.getAddress(), var4.getPort());
Net.listen(this.fd, var2 < 1 ? 50 : var2);
synchronized(this.stateLock) {this.localAddress = Net.localAddress(this.fd);
}
return this;
}
}
}bind()
能够看到，channel 外面封装的 fd(Socket 文件描述符)，后续也是把这个绑定端口。
public static void bind(FileDescriptor var0, InetAddress var1, int var2) throws IOException {bind(UNSPEC, var0, var1, var2);
}
static void bind(ProtocolFamily var0, FileDescriptor var1, InetAddress var2, int var3) throws IOException {boolean var4 = isIPv6Available() && var0 != StandardProtocolFamily.INET;
bind0(var1, var4, exclusiveBind, var2, var3);
}JNIEXPORT void JNICALL
Java_sun_nio_ch_Net_bind0(JNIEnv *env, jclass clazz, jobject fdo, jboolean preferIPv6,
jboolean useExclBind, jobject iao, int port)
{
SOCKADDR sa;
int sa_len = SOCKADDR_LEN;
int rv = 0;
if (NET_InetAddressToSockaddr(env, iao, port, (struct sockaddr *)&sa, &sa_len, preferIPv6) != 0) {return;}
//
rv = NET_Bind(fdval(env, fdo), (struct sockaddr *)&sa, sa_len);
if (rv != 0) {handleSocketError(env, errno);
}
}
int
NET_Bind(int fd, struct sockaddr *him, int len)
{
// 略
rv = bind(fd, him, len);
// 略
return rv;
}listen()
listen()就很直白了，就相当于间接调用本地办法。
static native void listen(FileDescriptor var0, int var1) throws IOException;JNIEXPORT void JNICALL
Java_sun_nio_ch_Net_listen(JNIEnv *env, jclass cl, jobject fdo, jint backlog)
{if (listen(fdval(env, fdo), backlog) < 0)
handleSocketError(env, errno);
}ssc.configureBlocking(false)
将文件描述符设置为 NIO，简略形容下略过啦
configureBlocking(int fd, jboolean blocking)
{int flags = fcntl(fd, F_GETFL);
int newflags = blocking ? (flags & ~O_NONBLOCK) : (flags | O_NONBLOCK);
return (flags == newflags) ? 0 : fcntl(fd, F_SETFL, newflags);
}ssc.register(selector, SelectionKey.OP_ACCEPT);
在此之前先梳理下，
selector：就相当于 epoll 构造体，增加了pipe()创立的读取端文件描述符channel：封装了创立的socket, 记录了套接字文件描述符，并且绑定了本地端口，并且开始监听申请
public final SelectionKey register(Selector sel, int ops,
Object att)
throws ClosedChannelException
{synchronized (regLock) {
// 略
if (k == null) {
// New registration
synchronized (keyLock) {if (!isOpen())
throw new ClosedChannelException();
//att :null 这里先疏忽
k = ((AbstractSelector)sel).register(this, ops, att);
addKey(k);
}
}
return k;
}
}protected final SelectionKey register(AbstractSelectableChannel var1, int var2, Object var3) {if (!(var1 instanceof SelChImpl)) {throw new IllegalSelectorException();
} else {SelectionKeyImpl var4 = new SelectionKeyImpl((SelChImpl)var1, this);
var4.attach(var3);
synchronized(this.publicKeys) {
// 对应不同零碎的实现
this.implRegister(var4);
}
var4.interestOps(var2);
return var4;
}
}implRegister()
SelectionKey外部封装了 channel，后面曾经很显著的看到，channel 创立的 Socket(套接字) 和 epoll 构造体之间并没有显示关联，在这里，就是进行关联。上面是 Epoll 的实现
fdToKey是 selector 初始化的时候创立的类型为 Map<Integer,SelectionKeyImpl>，就是将文件描述符和SelectionKey 关联起来, 最终会增加到EpollArrayWrapper::eventsLow, 此时 events=0
protected void implRegister(SelectionKeyImpl ski) {if (closed)
throw new ClosedSelectorException();
SelChImpl ch = ski.channel;
int fd = Integer.valueOf(ch.getFDVal());
fdToKey.put(fd, ski);
pollWrapper.add(fd);
keys.add(ski);
}
//pollWrapper.add(fd); 最终会调用
private void setUpdateEvents(int fd, byte events, boolean force) {if (fd < MAX_UPDATE_ARRAY_SIZE) {if ((eventsLow[fd] != KILLED) || force) {eventsLow[fd] = events;
}
} else {Integer key = Integer.valueOf(fd);
if (!isEventsHighKilled(key) || force) {eventsHigh.put(key, Byte.valueOf(events));
}
}
}在随后的 var4.interestOps(var2); 吧eventsLow数组中 event 从 0 改成 POLLIN，此时还没有调用epollCtl() 增加进 epoll 构造体
selector.select(3000)
间接从 sun.nio.ch.EPollSelectorImpl#doSelect 开始
protected int doSelect(long timeout) throws IOException {if (closed)
throw new ClosedSelectorException();
processDeregisterQueue();
try {begin();
pollWrapper.poll(timeout);
} finally {end();
}
processDeregisterQueue();
int numKeysUpdated = updateSelectedKeys();
if (pollWrapper.interrupted()) {
// Clear the wakeup pipe
pollWrapper.putEventOps(pollWrapper.interruptedIndex(), 0);
synchronized (interruptLock) {pollWrapper.clearInterrupted();
IOUtil.drain(fd0);
interruptTriggered = false;
}
}
return numKeysUpdated;
}poll()
这里就能够很容易的看进去在每次 poll() 的时候会先把未注册的 Socket 套接字，通过调用 epollCtl() 增加进 epoll 构造体中
int poll(long timeout) throws IOException {updateRegistrations();
updated = epollWait(pollArrayAddress, NUM_EPOLLEVENTS, timeout, epfd);
// 这一段我猜想是中断操作，因为就算设置了 true，sun.nio.ch.EPollSelectorImpl#doSelect 中也会批改成 false。如有 dalao 欢送通知我
for (int i=0; i<updated; i++) {if (getDescriptor(i) == incomingInterruptFD) {
interruptedIndex = i;
interrupted = true;
break;
}
}
return updated;
}
private void updateRegistrations() {synchronized (updateLock) {
int j = 0;
while (j < updateCount) {int fd = updateDescriptors[j];
short events = getUpdateEvents(fd);
boolean isRegistered = registered.get(fd);
int opcode = 0;
if (events != KILLED) {if (isRegistered) {opcode = (events != 0) ? EPOLL_CTL_MOD : EPOLL_CTL_DEL;
} else {opcode = (events != 0) ? EPOLL_CTL_ADD : 0;
}
if (opcode != 0) {
// 这里增加进构造体
epollCtl(epfd, opcode, fd, events);
if (opcode == EPOLL_CTL_ADD) {registered.set(fd);
} else if (opcode == EPOLL_CTL_DEL) {registered.clear(fd);
}
}
}
j++;
}
updateCount = 0;
}
}epollWait也就是对应的调用底层办法了，pollArrayAddress后面开拓的内存块，这里也就晓得干什么用了，也就是对应着epoll_event 构造体指针
JNIEXPORT jint JNICALL
Java_sun_nio_ch_EPollArrayWrapper_epollWait(JNIEnv *env, jobject this,
jlong address, jint numfds,
jlong timeout, jint epfd)
{struct epoll_event *events = jlong_to_ptr(address);
int res;
if (timeout <= 0) { /* Indefinite or no wait */
RESTARTABLE(epoll_wait(epfd, events, numfds, timeout), res);
} else { /* Bounded wait; bounded restarts */
res = iepoll(epfd, events, numfds, timeout);
}
if (res < 0) {JNU_ThrowIOExceptionWithLastError(env, "epoll_wait failed");
}
return res;
}
static int
iepoll(int epfd, struct epoll_event *events, int numfds, jlong timeout)
{
jlong start, now;
int remaining = timeout;
struct timeval t;
int diff;
gettimeofday(&t, NULL);
start = t.tv_sec * 1000 + t.tv_usec / 1000;
for (;;) {int res = epoll_wait(epfd, events, numfds, remaining);
if (res < 0 && errno == EINTR) {if (remaining >= 0) {gettimeofday(&t, NULL);
now = t.tv_sec * 1000 + t.tv_usec / 1000;
diff = now - start;
remaining -= diff;
if (diff < 0 || remaining <= 0) {return 0;}
start = now;
}
} else {return res;}
}
}// 这一段我猜想是中断操作，因为就算设置了 true，sun.nio.ch.EPollSelectorImpl#doSelect 中也会批改成 false, 临时存疑。如有 dalao 欢送通知我
//sun.nio.ch.EPollArrayWrapper#poll
for (int i=0; i<updated; i++) {if (getDescriptor(i) == incomingInterruptFD) {
interruptedIndex = i;
interrupted = true;
break;
}
}
//sun.nio.ch.EPollSelectorImpl#doSelect
if (pollWrapper.interrupted()) {
// Clear the wakeup pipe
pollWrapper.putEventOps(pollWrapper.interruptedIndex(), 0);
synchronized (interruptLock) {pollWrapper.clearInterrupted();
IOUtil.drain(fd0);
interruptTriggered = false;
}
}updateSelectedKeys()
private int updateSelectedKeys() {
int entries = pollWrapper.updated;
int numKeysUpdated = 0;
for (int i=0; i<entries; i++) {
// 从 pollArrayAddress 找到 epoll_event 构造体
int nextFD = pollWrapper.getDescriptor(i);
// 找到对应的 SelectionKey
SelectionKeyImpl ski = fdToKey.get(Integer.valueOf(nextFD));
// ski is null in the case of an interrupt
if (ski != null) {int rOps = pollWrapper.getEventOps(i);
// 第一次没有
if (selectedKeys.contains(ski)) {if (ski.channel.translateAndSetReadyOps(rOps, ski)) {numKeysUpdated++;}
} else {ski.channel.translateAndSetReadyOps(rOps, ski);
if ((ski.nioReadyOps() & ski.nioInterestOps()) != 0) {
// 增加进 selectedKeys 汇合
selectedKeys.add(ski);
numKeysUpdated++;
}
}
}
}
return numKeysUpdated;
}其余
到这里，整体脉络就很分明了剩下的这些也没必要剖析了，根本和上一篇外面的对应了，各位读者姥爷这么聪慧，就不节约大家工夫了
if(key.isReadable()){handleRead(key);
}
if(key.isWritable() && key.isValid()){handleWrite(key);
}
if(key.isConnectable()){System.out.println("isConnectable = true");
}
// 上面是 c
// 如果是新的连贯, 须要把新的 socket 增加到 efd 中
if (ep[i].data.fd == listenfd )
{connfd = accept(listenfd,(struct sockaddr*)&cliaddr,&clilen);
tep.events = EPOLLIN;
tep.data.fd = connfd;
ret = epoll_ctl(efd,EPOLL_CTL_ADD,connfd,&tep);
}
// 否则, 读取数据
else
{connfd = ep[i].data.fd;
int bytes = read(connfd,buf,MAXLEN);
// 客户端敞开连贯
if (bytes == 0){ret =epoll_ctl(efd,EPOLL_CTL_DEL,connfd,NULL);
close(connfd);
printf("client[%d] closed\n", i);
}
else
{for (int j = 0; j < bytes; ++j)
{buf[j] = toupper(buf[j]);
}
// 向客户端发送数据
write(connfd,buf,bytes);
}
}总结
- Channel：对 socket 的封装
- Selector：对 Epoll&epoll_event2 个构造体的封装
- SelectionKey：关联下面 2 个，有了文件描述符疾速找到对应 Socket
参考文章
epoll:https://zh.wikipedia.org/wiki…
linux 文档:https://man7.org/linux/man-pa…
正文完
