private long read0(ByteBuffer[] bufs) throws IOException {
if (bufs == null) throw new NullPointerException();
synchronized (readLock) {
if (!ensureReadOpen()) return -1;
long n = 0;
try {
begin();
synchronized (stateLock) {
if (!isOpen()) return 0;
readerThread = NativeThread.current();
}
for (; ; ) {
n = Net.read(fd, bufs);
if ((n == IOStatus.INTERRUPTED) && isOpen()) continue;
return IOStatus.normalize(n);
}
} finally {
readerCleanup();
end(n > 0 || (n == IOStatus.UNAVAILABLE));
synchronized (stateLock) {
if ((n <= 0) && (!isInputOpen)) return IOStatus.EOF;
}
assert IOStatus.check(n);
}
}
}
public int read(ByteBuffer buf) throws IOException {
if (buf == null) throw new NullPointerException();
synchronized (readLock) {
if (!ensureReadOpen()) return -1;
int n = 0;
try {
// Set up the interruption machinery; see
// AbstractInterruptibleChannel for details
//
begin();
synchronized (stateLock) {
if (!isOpen()) {
// Either the current thread is already interrupted, so
// begin() closed the channel, or another thread closed the
// channel since we checked it a few bytecodes ago. In
// either case the value returned here is irrelevant since
// the invocation of end() in the finally block will throw
// an appropriate exception.
//
return 0;
}
// Save this thread so that it can be signalled on those
// platforms that require it
//
readerThread = NativeThread.current();
}
// Between the previous test of isOpen() and the return of the
// IOUtil.read invocation below, this channel might be closed
// or this thread might be interrupted. We rely upon the
// implicit synchronization point in the kernel read() call to
// make sure that the right thing happens. In either case the
// implCloseSelectableChannel method is ultimately invoked in
// some other thread, so there are three possibilities:
//
// - implCloseSelectableChannel() invokes nd.preClose()
// before this thread invokes read(), in which case the
// read returns immediately with either EOF or an error,
// the latter of which will cause an IOException to be
// thrown.
//
// - implCloseSelectableChannel() invokes nd.preClose() after
// this thread is blocked in read(). On some operating
// systems (e.g., Solaris and Windows) this causes the read
// to return immediately with either EOF or an error
// indication.
//
// - implCloseSelectableChannel() invokes nd.preClose() after
// this thread is blocked in read() but the operating
// system (e.g., Linux) doesn't support preemptive close,
// so implCloseSelectableChannel() proceeds to signal this
// thread, thereby causing the read to return immediately
// with IOStatus.INTERRUPTED.
//
// In all three cases the invocation of end() in the finally
// clause will notice that the channel has been closed and
// throw an appropriate exception (AsynchronousCloseException
// or ClosedByInterruptException) if necessary.
//
// *There is A fourth possibility. implCloseSelectableChannel()
// invokes nd.preClose(), signals reader/writer thred and quickly
// moves on to nd.close() in kill(), which does a real close.
// Then a third thread accepts a new connection, opens file or
// whatever that causes the released "fd" to be recycled. All
// above happens just between our last isOpen() check and the
// next kernel read reached, with the recycled "fd". The solution
// is to postpone the real kill() if there is a reader or/and
// writer thread(s) over there "waiting", leave the cleanup/kill
// to the reader or writer thread. (the preClose() still happens
// so the connection gets cut off as usual).
//
// For socket channels there is the additional wrinkle that
// asynchronous shutdown works much like asynchronous close,
// except that the channel is shutdown rather than completely
// closed. This is analogous to the first two cases above,
// except that the shutdown operation plays the role of
// nd.preClose().
for (; ; ) {
n = Net.read(fd, buf);
if ((n == IOStatus.INTERRUPTED) && isOpen()) {
// The system call was interrupted but the channel
// is still open, so retry
continue;
}
return IOStatus.normalize(n);
}
} finally {
readerCleanup(); // Clear reader thread
// The end method, which is defined in our superclass
// AbstractInterruptibleChannel, resets the interruption
// machinery. If its argument is true then it returns
// normally; otherwise it checks the interrupt and open state
// of this channel and throws an appropriate exception if
// necessary.
//
// So, if we actually managed to do any I/O in the above try
// block then we pass true to the end method. We also pass
// true if the channel was in non-blocking mode when the I/O
// operation was initiated but no data could be transferred;
// this prevents spurious exceptions from being thrown in the
// rare event that a channel is closed or a thread is
// interrupted at the exact moment that a non-blocking I/O
// request is made.
//
end(n > 0 || (n == IOStatus.UNAVAILABLE));
// Extra case for socket channels: Asynchronous shutdown
//
synchronized (stateLock) {
if ((n <= 0) && (!isInputOpen)) return IOStatus.EOF;
}
assert IOStatus.check(n);
}
}
}
