Jimmy, Jing Lv wrote:
Archie Cobbs wrote:
Paulex Yang wrote:
Seems Thread's implementation must be aware of what operation it is
blocking on. So I propose the following solution:
I don't think the VM or java.lang.Thread needs to be involved.
First of all, the code performing the blocking operation knows
what kind of operation it is, so when it wakes up abnormally it
can take the appropriate action. This code doesn't necessarily
reside in java.lang.Thread.
In Classpath the java.nio stuff is all implemented in native
libraries without the VM or java.lang.Thread being specially
"aware" of anything. However, classlib's design may be different
enough to need it (I haven't studied it as much as you guys).
E.g., the java.nio native code does invoke Thread.interrupt() and
Thread.interrupted(), but these are normal, API-specified methods.
Might be worth taking a look for some design ideas.
Thanks Archie, it sounds interesting :).
As I study few about Classpath, I still have a question here. As we
know, there are three states of "blocking" on a thread. One is wait(),
sleep() and so forth, thread class handle them itself, it is easy to
interrupt; and one is blocking on I/O, invoke Thread.interrupt() may
be not enough as it is blocked on a system call, e.g., call read on
socket may not return until it receive something or it is closed. In
this way, the Thread.interrupt should know how to close the socket to
perform the real interruption. The question is: how can the thread
know if it is blocked on wait() or I/O operation currently? I think
this is the reason why Paulex require Thread to be involved. So I'm
very interested in what does Classpath do here to stop I/O operation
without get involved?
Actually Thread.interrupt() is required to handle four different scenario:
1. wait(), join(), etc, throw InterruptException
2. blocking I/O, close the channel, and throw ClosedByInterruptException
3. blocking select, wake up the selector
4. none of above, just set the thread's interrupt status
So if we don't involve Thread and want to implment scenario 2 and 3, we
may find the situation is:
a. If Thread cannot judge scenario 2/3, so it may think they are both
scenario 4, so Thread.interrupt() just set the interrupt status and do
nothing else, the I/O operation is still blocking there, we cannot get
it actually interrupted.
b. If Thread can find the thread is blocking somewhere, and it considers
all blocking as scenario 1, so the InterruptException is thrown, but
considering scenario 3, Selector.select() should be waked up without
exception, while our selector only has the end() executed in finally
block like below, how does end() catch the thrown InterruptException and
handle it silently?
try {
begin();
// Perform blocking I/O operation here
...
} finally {
end();
}
c. If Thread can magically find the thread is blocking on I/O or select,
it may need to set the interrupt status, and make the blocked Java
method return with some error, so that the end() can check them.
Further, the Thread needs to know if this blocking I/O is
"interruptible" in Java, for example, the ServerSocket.accept() and
ServerSocketChannel.accept() probably uses same system call, but Thread
should know ServerSocket cannot be interrupted while ServerSocketChannel
can...I have no any idea how Thread can do this without interaction with
NIO channels.
So, Archie, I'm very interested in how Classpath handle this problem.
Would you please help to give more details for it (if no legal concern)?
Here is the spec about Thread.interrupt():
"
...
If this thread is blocked in an invocation of the wait(), wait(long),
or wait(long, int) methods of the Object class, or of the join(),
join(long), join(long, int), sleep(long), or sleep(long, int), methods
of this class, then its interrupt status will be cleared and it will
receive an InterruptedException.
If this thread is blocked in an I/O operation upon an interruptible
channel then the channel will be closed, the thread's interrupt status
will be set, and the thread will receive a ClosedByInterruptException.
...
"
-Archie
__________________________________________________________________________
Archie Cobbs * CTO, Awarix *
http://www.awarix.com
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Paulex Yang
China Software Development Lab
IBM
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