RFR 8021820: Number of opened files used in select() is limited to 1024 [macosx]

Stuart Marks stuart.marks at oracle.com
Tue Aug 6 01:14:01 UTC 2013

Hi Aleksej,

Thanks for the update. I took a look at the revised test, and there are still 
some issues. (I didn't look at the build changes.)

1) System-specific resource limits.

I think the biggest issue is resource limits on the number of open files per 
process that might vary from system to system. On my Ubuntu system, the hard 
limit on the number of open files is 1,024. The test opens 1,023 files and then 
one more for the socket. Unfortunately the JVM and jtreg have several files 
open already, and the test crashes before the openFiles() method completes.

(Oddly it crashes with a NoClassDefFoundError from the main thread's uncaught 
exception handler, and then the test reports that it passed! Placing a 
try/catch of Throwable in main() or openFiles() doesn't catch this error. I 
have no explanation for this. When run standalone -- i.e., not from jtreg -- 
the test throws FileNotFoundException (too many open files) from openFiles(), 
which is expected.)

On my Mac (10.7.5) the soft limit is 256 files, but the hard limit is 
unlimited. The test succeeds in opening all its files but fails because of the 
select() bug you're fixing. (This is expected; I didn't rebuild my JDK with 
your patch.) I guess the soft limit doesn't do anything on Mac.

Amazingly, the test passed fine on both Windows XP and Windows 8.

I'm not entirely sure what to do about resource limits. Since the test is able 
to open >1024 files on Mac, Windows, and possibly other Linuxes, it seems 
reasonable to continue with this approach. If it's possible to catch the error 
that occurs if the test cannot open its initial 1,024 files, perhaps it should 
do this, log a message indicating what happened, and consider the test to have 
passed. I'm mystified by the uncaught/uncatchable NoClassDefFoundError though.

2) Closing files.

If an exception is thrown while opening the initial set of files, or sometime 
during the closing process, the test can still leak files.

One approach would be to keep a data structure representing the current set of 
open files, and close them all in a finally-block around all the test logic, 
and making sure that exceptions from the close() call are caught and do not 
prevent the rest of the files from being closed.

This seems like a lot of work. Perhaps a more effective approach would be to 
run the test in "othervm" mode, as follows:

     @run main/othervm SelectFdsLimit

This will cause the test to run in a dedicated JVM, so all files will be closed 
automatically when it exits. (It would be good to add a comment explaining the 
need for othervm, if you do this.)

3) Port number for sockets.

It's fairly common for tests to fail occasionally because they use some 
constant port number that sometimes happens to be in use at the same time by 
another process on the system. I have to say, 8080 is a pretty common port 
number. :-)

For purposes of this test, you can let the system assign a port. Just use:

     new ServerSocket(0)

4) Style.

It's probably possible to use the same File object for the test file, instead 
of creating new File objects repeatedly.

It might be nice to add a comment explaining the logic of the test, that 
SocketTimeoutException is expected, and that failure will be indicated if the 
accept() throws SocketException caused by the underlying mishandling of large 
fds by select().



On 8/5/13 4:47 AM, Aleksej Efimov wrote:
> Alan, Tim,
> I have addressed your comments and as a result - new webrev:
> http://cr.openjdk.java.net/~aefimov/8021820/webrev.01
> The list of changes:
> 1. The connection to Oracle site is removed (it's not internal, but anyway it's
> better not to rely on availability of external resource in test). In current
> version a server socket is created and accept() method is used for bug disclosure.
> 2. The cleanup method is added for closing file streams. The JTREG successfully
> cleaned-up on windows after this modification.
> 3. common/autoconf/toolchain.m4 untouched, but 'bash
> common/autoconf/autogen.sh' was executed to update generated-configure.sh.
> Aleksej
> On 07/31/2013 06:35 PM, Tim Bell wrote:
>> Aleksej, Alan
>> The change in common/autoconf/toolchain.m4 looks correct to me, and I think
>> that is a good place to have it.  Remember to run 'bash
>> common/autoconf/autogen.sh' and check in the generated-configure.sh files as
>> part of the changeset.
>> I didn't look at the test case, but I think Alan has some good points.
>> Tim
>> On 07/31/13 06:45 AM, Alan Bateman wrote:
>>> On 31/07/2013 05:18, Aleksej Efimov wrote:
>>>> Hi,
>>>> Can I have a review for the following problem:
>>>> The MACOSX JDK (more precisely - the java.net classes) uses the select()
>>>> system call to wait for different events on sockets fds. And the default
>>>> behaviour for select() on Darwin is to fail when fdset contains the fd with
>>>> id greater than FDSET_SIZE(=1024). Test case in webrev illustrates this
>>>> behavior.
>>>> There is at least one solution for it: use -D_DARWIN_UNLIMITED_SELECT
>>>> compilation flag for all macosx sources: this won't affect other parts of
>>>> JDK because they are not using select().
>>>> Currently, I have added this compilation flag to
>>>> common/autoconf/generated-configure.sh and
>>>> common/autoconf/generated-configure.sh. I wonder, if there is a better
>>>> place where I can put this flag?
>>>> The webrev: http://cr.openjdk.java.net/~aefimov/8021820/webrev.00/
>>>> BUG: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8021820
>>> Thanks for looking into this one. The build changes look okay to me but it's
>>> probably best that someone on build-dev agree to those.
>>> Michael McMahon can probably explain why the net code is using select for
>>> timed read/accept (I have a vague recollection of there being an issue with
>>> poll due to the way that it is implemented on kqueue with the result that it
>>> had to be changed to use select).
>>> I think the test needs re-work. It looks to me that the it attempts to
>>> connect to an Oracle internal site so that's not going to work everywhere.
>>> In general we don't want the tests to be dependent on hosts that may or may
>>> not exist (we had tests that used to this in the past but they caused a lot
>>> of grief). It also looks like the test doesn't close the 1023 files that it
>>> opens at the start and so I assume this test will always fail on Windows
>>> when jtreg tries to clean-up.
>>> -Alan.

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