SocketChannelImpl 解析二(发送数据后续): http://donald-draper.iteye.com/blog/2372548
引言:
前一篇文章我们看了一下SocketChannelImpl发送多个字节序列的过程,先来回顾一下:
SocketChannelImpl写ByteBuffer数组方法,首先同步写锁,确保通道,输出流打开,连接建立委托给IOUtil,将ByteBuffer数组写到输出流中,这一过程为获取存放i个字节缓冲区的IOVecWrapper,遍历ByteBuffer数组m,将字节缓冲区添加到iovecwrapper的字节缓冲区数组中,如果ByteBuffer非Direct类型,委托Util从当前线程的缓冲区获取容量为j2临时DirectByteBuffer,并将ByteBuffer写到DirectByteBuffer,并将DirectByteBuffer添加到iovecwrapper的字节缓冲区(Shadow-Direct)数组中,将字节缓冲区的起始地址写到iovecwrapper,字节缓冲区的实际容量写到iovecwrapper;遍历iovecwrapper的字节缓冲区(Shadow-Direct)数组,将Shadow数组中的DirectByteBuffer通过Util添加到本地线程的缓存区中,并清除DirectByteBuffer在iovecwrapper的相应数组中的信息;最后通过
SocketDispatcher,将iovecwrapper的缓冲区数据,写到filedescriptor对应的输出流中。
今天我们来看一下接受数据
再来看SocketChannelImpl的读操作
public int read(ByteBuffer bytebuffer) throws IOException { if(bytebuffer == null) throw new NullPointerException(); Object obj = readLock;//获取读锁 JVM INSTR monitorenter ;//进入同步,try if(!ensureReadOpen())//确保通道,输入流打开,通道连接建立 return -1; int i = 0; begin(); int k; Object obj3; Exception exception; synchronized(stateLock) { if(isOpen()) break MISSING_BLOCK_LABEL_146; k = 0; } //清除读线程 readerCleanup(); end(i > 0 || i == -2); obj3 = stateLock; JVM INSTR monitorenter ; if(i > 0 || isInputOpen) goto _L2; else goto _L1 _L1: -1; obj; JVM INSTR monitorexit ; return; _L2: obj3; JVM INSTR monitorexit ; goto _L3 exception; obj3; JVM INSTR monitorexit ; throw exception; _L3: if(!$assertionsDisabled && !IOStatus.check(i)) throw new AssertionError(); obj; JVM INSTR monitorexit ; return k; //初始化本地读线程 readerThread = NativeThread.current(); obj1; JVM INSTR monitorexit ; int j; do //委托IOUtil从输入流读取字节序列,写到bytebuffer i = IOUtil.read(fd, bytebuffer, -1L, nd, readLock); while(i == -3 && isOpen()); ... }
从输入流读取字节序列,写到buffer,有几点要关注
1.
if(!ensureReadOpen())//确保通道,输入流打开,通道连接建立 return -1;
2.
//清除读线程 readerCleanup();
3.
do //委托IOUtil从输入流读取字节序列,写到bytebuffer i = IOUtil.read(fd, bytebuffer, -1L, nd, readLock); while(i == -3 && isOpen());
下面我们分别来看这几点:
1.
if(!ensureReadOpen())//确保通道,输入流打开,通道连接建立 return -1;
//确保通道,输入流打开,通道连接建立
private boolean ensureReadOpen() throws ClosedChannelException { Object obj = stateLock; JVM INSTR monitorenter ; if(!isOpen())//通道打开 throw new ClosedChannelException(); if(!isConnected())//连接建立 throw new NotYetConnectedException(); if(!isInputOpen)//输入流打开 return false; true; obj; JVM INSTR monitorexit ; return; Exception exception; exception; throw exception; }
2.
//清除读线程 readerCleanup();
private void readerCleanup() throws IOException { //同步通道状态锁,清除读线程,如果通道关闭则,执行清除工作 synchronized(stateLock) { readerThread = 0L; if(state == 3) kill();//这个后面再讲 } }
3.
do //委托IOUtil从输入流读取字节序列,写到bytebuffer i = IOUtil.read(fd, bytebuffer, -1L, nd, readLock); while(i == -3 && isOpen());
这里循环的原因,线程读输入流,有可能因为某种原因被中断,中断位消除,继续读取输入流,写到buffer
//IOUtil
static int read(FileDescriptor filedescriptor, ByteBuffer bytebuffer, long l, NativeDispatcher nativedispatcher, Object obj) throws IOException { ByteBuffer bytebuffer1; //如果buffer为只读,则抛出IllegalArgumentException if(bytebuffer.isReadOnly()) throw new IllegalArgumentException("Read-only buffer"); //如果buffer为DirectBuffer,则委托给readIntoNativeBuffer if(bytebuffer instanceof DirectBuffer) return readIntoNativeBuffer(filedescriptor, bytebuffer, l, nativedispatcher, obj); //从当前线程缓存区获取临时的DirectByteBuffer bytebuffer1 = Util.getTemporaryDirectBuffer(bytebuffer.remaining()); int j; //委托readIntoNativeBuffer方法,读取输入流数据,到临时DirectByteBuffer int i = readIntoNativeBuffer(filedescriptor, bytebuffer1, l, nativedispatcher, obj); //读写模式切换 bytebuffer1.flip(); if(i > 0) //如果有数据被读取,则放到byteBuffer中 bytebuffer.put(bytebuffer1); j = i;//记录读取的字节数 //添加临时DirectByteBuffer到当前线程的缓冲区,以便重用, //因为重新DirectByteBuffer为直接操作物理内存,频繁分配物理内存,将耗费过多的资源。 Util.offerFirstTemporaryDirectBuffer(bytebuffer1); return j; Exception exception; exception; Util.offerFirstTemporaryDirectBuffer(bytebuffer1); throw exception; }
来看readIntoNativeBuffer方法
private static int readIntoNativeBuffer(FileDescriptor filedescriptor, ByteBuffer bytebuffer, long l, NativeDispatcher nativedispatcher, Object obj) throws IOException { int i = bytebuffer.position(); int j = bytebuffer.limit(); //如果断言开启,buffer的position大于limit,则抛出断言错误 if(!$assertionsDisabled && i > j) throw new AssertionError(); //获取需要读的字节数 int k = i > j ? 0 : j - i; if(k == 0) return 0; int i1 = 0; //从输入流读取k个字节到buffer if(l != -1L) i1 = nativedispatcher.pread(filedescriptor, ((DirectBuffer)bytebuffer).address() + (long)i, k, l, obj); else i1 = nativedispatcher.read(filedescriptor, ((DirectBuffer)bytebuffer).address() + (long)i, k); //重新定位buffer的position if(i1 > 0) bytebuffer.position(i + i1); return i1; }
readIntoNativeBuffer方法中一点我们需要关注:
//从输入流读取k个字节到buffer
if(l != -1L) i1 = nativedispatcher.pread(filedescriptor, ((DirectBuffer)bytebuffer).address() + (long)i, k, l, obj); else i1 = nativedispatcher.read(filedescriptor, ((DirectBuffer)bytebuffer).address() + (long)i, k);
//NativeDispatcher
int pread(FileDescriptor filedescriptor, long l, int i, long l1, Object obj) throws IOException { throw new IOException("Operation Unsupported"); }
从NativeDispatcher的pread方法可以看出,当前JDK版本,还不支持pread操作,我的JDK版本为1.7.0.17。
//SocketDispatcher
int read(FileDescriptor filedescriptor, long l, int i) throws IOException { return read0(filedescriptor, l, i); } static native int read0(FileDescriptor filedescriptor, long l, int i) throws IOException;
至此读输入流到buffer,已经看完,首先同步读写,确保通道,输入流打开,通道连接建立,
清除原始读线程,获取新的本地读线程,委托IOUtil读输入流到buffer;IOUtil读输入流到buffer,首先确保buffer是可写的,否则抛出IllegalArgumentException,然后判断buffer是否为Direct类型,是则委托给readIntoNativeBuffer,否则通过Util从当前线程缓冲区获取一个临时的DirectByteBuffer,然后通过readIntoNativeBuffer读输入流数据到临时的DirectByteBuffer,这一个过程是通过SocketDispatcher的read方法实现,读写数据到DirectByteBuffer中后,将DirectByteBuffer中数据,写到原始buffer中,并将
DirectByteBuffer添加到添加临时DirectByteBuffer到当前线程的缓冲区,以便重用,
因为重新DirectByteBuffer为直接操作物理内存,频繁分配物理内存,将耗费过多的资源。
在来看从输入流读取数据,写到多个buffer:
public long read(ByteBuffer abytebuffer[], int i, int j) throws IOException { //校验参数 if(i < 0 || j < 0 || i > abytebuffer.length - j) throw new IndexOutOfBoundsException(); Object obj = readLock;//获取读锁 JVM INSTR monitorenter ;//进入同步,try if(!ensureReadOpen())//确保通道打开,连接建立,输入流打开 return -1L; long l = 0L; begin();//与end协同,记录中断器,处理读操作过程中的中断问题 long l2; Object obj3; Exception exception; synchronized(stateLock) { if(isOpen()) break MISSING_BLOCK_LABEL_177; l2 = 0L; } //清除原始读线程 readerCleanup(); end(l > 0L || l == -2L); obj3 = stateLock; JVM INSTR monitorenter ; if(l > 0L || isInputOpen) goto _L2; else goto _L1 _L1: -1L; obj; JVM INSTR monitorexit ; return; _L2: obj3; JVM INSTR monitorexit ; goto _L3 exception; obj3; JVM INSTR monitorexit ; throw exception; _L3: if(!$assertionsDisabled && !IOStatus.check(l)) throw new AssertionError(); obj; JVM INSTR monitorexit ; return l2; //获取本地读线程 readerThread = NativeThread.current(); obj1; JVM INSTR monitorexit ; long l1; do //委托给IOUtil,从输入流读取数据,写到多个buffer l = IOUtil.read(fd, abytebuffer, i, j, nd); while(l == -3L && isOpen()); l1 = IOStatus.normalize(l); }
从输入流读取数据,写到多个buffer,我们只需要关注下面这点
do //委托给IOUtil,从输入流读取数据,写到多个buffer l = IOUtil.read(fd, abytebuffer, i, j, nd); while(l == -3L && isOpen());
这里循环的原因,线程读输入流,有可能因为某种原因被中断,中断位消除,继续读取输入流,写到buffer;
//IOUtil
static long read(FileDescriptor filedescriptor, ByteBuffer abytebuffer[], int i, int j, NativeDispatcher nativedispatcher) throws IOException { IOVecWrapper iovecwrapper; boolean flag; int k; //获取存放i个byteBuffer的IOVecWrapper iovecwrapper = IOVecWrapper.get(j); flag = false; k = 0; long l1; int l = i + j; for(int i1 = i; i1 < l && k < IOV_MAX; i1++) { ByteBuffer bytebuffer = abytebuffer[i1]; if(bytebuffer.isReadOnly()) throw new IllegalArgumentException("Read-only buffer"); int j1 = bytebuffer.position(); int k1 = bytebuffer.limit(); if(!$assertionsDisabled && j1 > k1) throw new AssertionError(); int j2 = j1 > k1 ? 0 : k1 - j1; if(j2 <= 0) continue; //将buffer添加到iovecwrapper的字节缓冲区数组中 iovecwrapper.setBuffer(k, bytebuffer, j1, j2); if(!(bytebuffer instanceof DirectBuffer)) { //获取容量为j2临时DirectByteBuffer ByteBuffer bytebuffer2 = Util.getTemporaryDirectBuffer(j2); //添加DirectByteBuffer到iovecwrapper的shadow buffer数组 iovecwrapper.setShadow(k, bytebuffer2); bytebuffer = bytebuffer2; j1 = bytebuffer2.position(); } //将字节缓冲区的起始地址写到iovecwrapper iovecwrapper.putBase(k, ((DirectBuffer)bytebuffer).address() + (long)j1); //将字节缓冲区的实际容量写到iovecwrapper iovecwrapper.putLen(k, j2); k++; } if(k != 0) break MISSING_BLOCK_LABEL_263; l1 = 0L; if(!flag) { for(int i2 = 0; i2 < k; i2++) { //获取iovecwrapper索引i2对应的字节序列副本 ByteBuffer bytebuffer1 = iovecwrapper.getShadow(i2); if(bytebuffer1 != null) //如果字节序列不为空,则添加到当前线程的缓存区中 Util.offerLastTemporaryDirectBuffer(bytebuffer1); //清除索引i2对应的字节序列在iovecwrapper中的字节序列数组,及相应副本数组的信息 iovecwrapper.clearRefs(i2); } } return l1; long l4; //委托给nativedispatcher,从filedescriptor对应的输入流读取数据,写到iovecwrapper的缓冲区中。 long l2 = nativedispatcher.readv(filedescriptor, iovecwrapper.address, k); }
再来看IOUtil写buffer数组的关键点
long l2 = nativedispatcher.readv(filedescriptor, iovecwrapper.address, k);
//SocketDispatcher
long readv(FileDescriptor filedescriptor, long l, int i) throws IOException { return readv0(filedescriptor, l, i); } static native long readv0(FileDescriptor filedescriptor, long l, int i) throws IOException;
至此我们把SocketChannelImpl从输入流读取数据,写到ByteBuffer数组的read方法看完,首先同步写锁,确保通道,连接建立,输入流打开,委托给IOUtil,从输入流读取数据写到ByteBuffer数组中;IOUtil首先获取存放i个字节缓冲区的IOVecWrapper,遍历ByteBuffer数组m,将buffer添加到iovecwrapper的字节缓冲区数组中,如果ByteBuffer非Direct类型,委托Util从当前线程的缓冲区获取容量为j2临时DirectByteBuffer,并将ByteBuffer写到DirectByteBuffer,并将DirectByteBuffer添加到iovecwrapper的字节缓冲区(Shadow-Direct)数组中,将字节缓冲区的起始地址写到iovecwrapper,字节缓冲区的实际容量写到iovecwrapper;遍历iovecwrapper的字节缓冲区(Shadow-Direct)数组,将Shadow数组中的DirectByteBuffer通过Util添加到本地线程的缓存区中,并清除DirectByteBuffer在iovecwrapper的相应数组中的信息;最后通过
SocketDispatcher,从filedescriptor对应的输入流读取数据,写到iovecwrapper的缓冲区中。
总结:
读输入流到buffer,首先同步读写,确保通道,输入流打开,通道连接建立,
清除原始读线程,获取新的本地读线程,委托IOUtil读输入流到buffer;IOUtil读输入流到buffer,首先确保buffer是可写的,否则抛出IllegalArgumentException,然后判断buffer是否为Direct类型,是则委托给readIntoNativeBuffer,否则通过Util从当前线程缓冲区获取一个临时的DirectByteBuffer,然后通过readIntoNativeBuffer读输入流数据到临时的DirectByteBuffer,这一个过程是通过SocketDispatcher的read方法实现,读写数据到DirectByteBuffer中后,将DirectByteBuffer中数据,写到原始buffer中,并将
DirectByteBuffer添加到添加临时DirectByteBuffer到当前线程的缓冲区,以便重用,因为重新DirectByteBuffer为直接操作物理内存,频繁分配物理内存,将耗费过多的资源。
从输入流读取数据,写到ByteBuffer数组的read方法,首先同步写锁,确保通道,连接建立,输入流打开,委托给IOUtil,从输入流读取数据写到ByteBuffer数组中;IOUtil首先获取存放i个字节缓冲区的IOVecWrapper,遍历ByteBuffer数组m,将buffer添加到iovecwrapper的字节缓冲区数组中,如果ByteBuffer非Direct类型,委托Util从当前线程的缓冲区获取容量为j2临时DirectByteBuffer,并将ByteBuffer写到DirectByteBuffer,并将DirectByteBuffer添加到iovecwrapper的字节缓冲区(Shadow-Direct)数组中,将字节缓冲区的起始地址写到iovecwrapper,字节缓冲区的实际容量写到iovecwrapper;遍历iovecwrapper的字节缓冲区(Shadow-Direct)数组,将Shadow数组中的DirectByteBuffer通过Util添加到本地线程的缓存区中,并清除DirectByteBuffer在iovecwrapper的相应数组中的信息;最后通过
SocketDispatcher,从filedescriptor对应的输入流读取数据,写到iovecwrapper的缓冲区中。
SocketChannelImpl 解析四(关闭通道等): http://donald-draper.iteye.com/blog/2372717