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From "Andrew Zhang" <zhanghuang...@gmail.com>
Subject [classlib][nio] How to fix read-only problem? (Re: [classlib][io][nio] Sync issue of java.io.FileOutputStream and java.nio.channels.FileChannel)
Date Tue, 03 Oct 2006 06:32:34 GMT
There are two ways to fix this problem:

1. Add a read-only flag in FileDescriptor. The default value is false. Set
the flag to true in FileInputStream and RandomeAccessFile("r").

2. Determine the fd in native code whether the fd is read-only.

Solution 1 judges the fd in java code, but has to remove "native"
from FileDescriptor#sync() signature.  While solution 2 seems nature, and
solves the problem thoroughly, but requires more codes. If we adopt solution
2, we should add a new portable native mehtod like isReadOnly(int fd). Where
should we put the method? in port? or OSFileSystemWin32/Linux?  Any
suggestions and comments?

Thanks!

On 9/19/06, Andrew Zhang <zhanghuangzhu@gmail.com> wrote:
>
> I just found another bug of sync. Harmony throws SyncFailedException when
> fd is read-only while RI returns silently. Spec doesn't explictly describe
> the behaviour in such case[1]. But, it seems intended behaviour of RI,
> because it requires additional check before invoke os sync. Following test
> reproduces the bug:
>
>     public void testSyncReadOnly() throws Exception {
>         String TESTFILE = "tempFile";
>         try {
>             FileOutputStream fos = new FileOutputStream(TESTFILE);
>             fos.write("something".getBytes());
>             fos.close();
>
>             RandomAccessFile raf = new RandomAccessFile(TESTFILE, "rw");
>             raf.getFD().sync();
>             raf.close();
>
>             FileInputStream fis = new FileInputStream(TESTFILE);
>             fis.getFD().sync();
>             fis.close();
>         } finally {
>             new File(TESTFILE).delete();
>         }
>     }
>
> I'll file a JIRA to record this bug soon!
> [1] "SyncFailedException - Thrown when the buffers cannot be flushed, or
> because the system cannot guarantee that all the buffers have been
> synchronized with physical media."
>
>
>  On 9/19/06, Richard Liang <richard.liangyx@gmail.com> wrote:
> >
> > On 9/18/06, Andrew Zhang <zhanghuangzhu@gmail.com> wrote:
> > > On 9/18/06, Richard Liang <richard.liangyx@gmail.com> wrote:
> > > >
> > > > Hello,
> > > >
> > > > One Apache Derby test[1] fails on Harmony. It seems that RI always
> > > > sync the FileOutputStream and FileChannel after each "write", which
> > is
> > > > different from Harmony. But there is no explicit description in Java
> > > > Spec. Shall we follow RI? Thanks a lot.
> > > >
> > > > The following test cases could demonstrate this issue.
> > > >
> > > >    public void testFile() {
> > > >        File derbyLog = new File("d:\\", "derby1.log");
> > > >
> > > >        try {
> > > >            FileOutputStream fos = new FileOutputStream(derbyLog);
> > > >            fos.write(0x41);
> > > >            assertEquals(1, derbyLog.length());
> > > >        } catch (Exception e) {
> > > >            e.printStackTrace();
> > > >        }
> > > >    }
> > > >
> > > >    public void testFileChannel() {
> > > >        File derbyLog = new File("d:\\", " derby2.log");
> > > >
> > > >        try {
> > > >            FileOutputStream fos = new FileOutputStream(derbyLog);
> > > >            FileChannel fc = fos.getChannel();
> > > >            fc.write (ByteBuffer.wrap(new byte[]{0x41, 0x42}));
> > > >            assertEquals(2, derbyLog.length());
> > > >        } catch (Exception e) {
> > > >            e.printStackTrace();
> > > >        }
> > > >    }
> > >
> > >
> > > Interesting. I think we'd better follow RI although it's
> > implementation
> > > dependent. Otherwise, it breaks existing application.
> > >
> > > To make test more interesting, I wrote a similar test:
> > >
> > >
> > >  public void testFile() throws Exception {
> > >         File derbyLog = File.createTempFile("test", "log");
> > >         derbyLog.deleteOnExit();
> > >         RandomAccessFile fos = new RandomAccessFile(derbyLog, "rws");
> > >         for (int i = 0; i < 1000; i++) {
> > >             fos.write(0x41);
> > >             assertEquals(1 + i, derbyLog.length());
> > >         }
> > >
> > >  }
> > >
> > > Run it and you'll be surprised. :-)
> >
> > Wow! It tooks RI 0.381 seconds, while 21.761 seconds for Harmony. We
> > shall improve our performance!
> >
> > Let's have a more further study about this issue.
> >
> > >
> > > [1]
> > > >
> > http://svn.apache.org/viewvc/db/derby/code/trunk/java/testing/org/apache/derbyTesting/functionTests/tests/lang/logStream.java?view=co
> > > > --
> > > > Richard Liang
> > > > China Development Lab, IBM
> > > >
> > > >
> > ---------------------------------------------------------------------
> > > > Terms of use : http://incubator.apache.org/harmony/mailing.html
> > > > To unsubscribe, e-mail: harmony-dev-unsubscribe@incubator.apache.org
> > > > For additional commands, e-mail:
> > harmony-dev-help@incubator.apache.org
> > > >
> > > >
> > >
> > >
> > > --
> > > Andrew Zhang
> > > China Software Development Lab, IBM
> > >
> > >
> >
> >
> > --
> > Richard Liang
> > China Development Lab, IBM
> >
> > ---------------------------------------------------------------------
> > Terms of use : http://incubator.apache.org/harmony/mailing.html
> > To unsubscribe, e-mail: harmony-dev-unsubscribe@incubator.apache.org
> > For additional commands, e-mail: harmony-dev-help@incubator.apache.org
> >
> >
>
>
> --
> Andrew Zhang
> China Software Development Lab, IBM
>



-- 
Best regards,
Andrew Zhang

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