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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (COMPRESS-388) Improve concurrent reads from ZipFile
Date Sun, 23 Apr 2017 16:14:04 GMT

    [ https://issues.apache.org/jira/browse/COMPRESS-388?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15980452#comment-15980452
] 

ASF GitHub Bot commented on COMPRESS-388:
-----------------------------------------

Github user sebbASF commented on a diff in the pull request:

    https://github.com/apache/commons-compress/pull/21#discussion_r112838358
  
    --- Diff: src/main/java/org/apache/commons/compress/archivers/zip/ZipFile.java ---
    @@ -1081,16 +1082,26 @@ private boolean startsWithLocalFileHeader() throws IOException
{
         }
     
         /**
    +     * Creates new BoundedInputStream, according to implementation of
    +     * underlying archive channel.
    +     */
    +    private BoundedInputStream createBoundedInputStream(long start, long remaining) {
    +        return archive instanceof FileChannel ?
    +            new BoundedFileChannelInputStream(start, remaining) :
    +            new BoundedInputStream(start, remaining);
    +    }
    +
    +    /**
          * InputStream that delegates requests to the underlying
          * SeekableByteChannel, making sure that only bytes from a certain
          * range can be read.
          */
         private class BoundedInputStream extends InputStream {
    -        private static final int MAX_BUF_LEN = 8192;
    -        private final ByteBuffer buffer;
    -        private long remaining;
    -        private long loc;
    -        private boolean addDummyByte = false;
    +        protected static final int MAX_BUF_LEN = 8192;
    +        protected final ByteBuffer buffer;
    +        protected long remaining;
    +        protected long loc;
    +        protected boolean addDummyByte = false;
     
    --- End diff --
    
    Do these really need to be protected rather than private or package-protected?


> Improve concurrent reads from ZipFile
> -------------------------------------
>
>                 Key: COMPRESS-388
>                 URL: https://issues.apache.org/jira/browse/COMPRESS-388
>             Project: Commons Compress
>          Issue Type: Improvement
>          Components: Archivers
>    Affects Versions: 1.13
>         Environment: Any
>            Reporter: Zbynek Vyskovsky
>              Labels: patch, performance
>             Fix For: 1.14
>
>   Original Estimate: 2h
>  Remaining Estimate: 2h
>
> Concurrent reads on the ZipFile archive is terribly slow on multiprocessor systems. On
my 4 CPU laptop it shows 26 reads/s vs 2 reads/s on 100MB samples for example.
> The cause is the use of synchronized blocks to access the underlying file channel. This
may be required for generic SeekableByteChannel but most commonly there is FileChannel implementation
which supports lock-free reading from any position (i.e. using pread/pwrite system calls or
their equivalent).
> With the fix the performance is about 10 times faster (on 4 CPU system, with more processor
the difference should grow significantly).



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