[jira] Updated: (LUCY-58) FileHandle

["Marvin Humphrey (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LUCY-58?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Marvin Humphrey updated LUCY-58:
--------------------------------

    Attachment: FileHandle.pm
                FileHandle.c
                FileHandle.bp

FileHandle provides an interface for the limited range of low-level IO
functionality needed by Lucy.  Its role is roughly analogous to that of a
POSIX file descriptor, but with far fewer features.  

 * All FileHandles are either read-only or write-only.
 * There is no Seek().
 * All writing goes through FH_Write() and must be performed sequentially.  
 * FH_Read() functions similarly to POSIX pread(), reading from a specific
   file position.  The present implementation updates object state, but with a
   little work, true asynchronous IO is possible.
 * Memory mapping is supported via FH_Window() and FH_Release_Window().
   Systems with no memory mapping capabilities at all are not supported.

Adding a Seek() method is possible, but may not be necessary.  Lucene seeks
backwards during writing to write header data to certain files; however, in
Lucy, we will store such metadata in segmeta.json.


> FileHandle
> ----------
>
>                 Key: LUCY-58
>                 URL: https://issues.apache.org/jira/browse/LUCY-58
>             Project: Lucy
>          Issue Type: Sub-task
>          Components: Core
>            Reporter: Marvin Humphrey
>            Assignee: Marvin Humphrey
>            Priority: Blocker
>         Attachments: FileHandle.bp, FileHandle.c, FileHandle.pm
>
>
> Low-level IO abstraction.

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