java.net.Socket.connect超时的准确性如何？

Question

I was wondering what's the timeout accuracy of the method java.net.Socket.connect(SocketAddress, int timeout) ?

Initially I'd thought that it's built atop java.lang.Object.wait and thus have a 10-15 millisecond error ( source ),

But after examining the source code, it looks like all it does is to delegate the call to java.net.SocketImpl.connect(SocketaAddress, int) .

Does this mean that java.net.Socket.connect(SocketAddress, int) does not use Object.wait and hence is not subject to the 10-15 millisecond error Object.wait has?

Answer 1

Firstly, I would expect that the socket connect timeout is handled directly by the OS/kernel. The C socket API supports connect timeouts, so I expect the JVM native implementation will simply delegate to it.

Secondly, why do you care about accuracy of 10-15ms on a network connect? It sounds like you'll end up with something very brittle.

Answer 2

it looks like all it does is to delegate the call to java.net.SocketImpl.connect(SocketaAddress, int).

which is an abstract method of the SocketImpl class.

The subclass actually implementing it (the system-default SocketImpl implicitly retrieved from SocketImplFactory.createSocketImpl() in the Socket constructor) in turn relies on a native method, so it's not possible to know the inaccuracy in a platform-independent way.

-- EDIT (response to comment)

If not using a Socket subclass that specifies a custom SocketImpl via the protected Socket(SocketImpl impl) constructor, the standard Socket instance created by the Socket() constructor uses a SocksSocketImpl (which in turn extends PlainSocketImpl ).

SocksSocketImpl.connect(SocketAddress address, int timeout)

calls

super.connect(SocketAddress address, int timeout) ( PlainSocketImpl.connect(SocketAddress address, int timeout) ),

which in turn calls

PlainSocketImpl.connectToAddress(InetAddress address, int port, int timeout) ,

which in turn calls

PlainSocketImpl.doConnect(InetAddress address, int port, int timeout) ,

which in turn calls

PlainSocketImpl.socketConnect(InetAddress address, int port, int timeout) ,

which is a private native method, and we don't know what's inside :)

So no, we're not relying upon Object.wait .

--

See http://jcs.mobile-utopia.com/jcs/18846_PlainSocketImpl.java and http://jcs.mobile-utopia.com/jcs/31401_SocksSocketImpl.java for source code