EDOBE XDOM PMML Manual de usuario descargar pdf (Pagina 66)

immediately: it does not support "suspending" a CNKBuf data access

method, if the data is not currently available. To handle these

limitations, components accessing a

CNKBuf must follow these rules:

1. Before writing data to a

CNKBuf (using a CNKBufWriter), the

CNKProc must reserve space for the data, and wait for the

space to become available. Once the space is available, data

can be written into it, and then some or all of the written rows

must be released.

2. Before reading data from a

CNKBuf (using a CNKBufReader), the

CNKProc must request a certain number of data rows, and wait

for them to become available. Once the data is available, the

block of data can be read, and then some or all of the data

rows must be released.

The

CNKBuf is designed so that the CNKBuf's associated CNKBufWriter

has to wait until all of the associated CNKBufReader objects have

consumed the written data rows, before that storage can be used for

more data. Given this design, if a

CNKBuf is set up with no readers,

then the

CNKBuf will fill up with data and then stop, since no one will

ever read the data. It has been useful to make an exception to the

rules in this case: if a

CNKBuf has no readers, then it acts like there is

an attached reader that automatically reads all data rows as they are

written.

CNKBuf

Subclasses:

CNKMemoryBuf and

CNKBackingFileBu

As far as a proc object is concerned, all bufs (and buf readers and buf

writers) are the same, implementing the same methods. In actuality,

there are several different types of buf classes, implemented as

subclasses of

CNKBuf. CNKBuf does not have a public constructor, so

creating a buf involves creating an instance of one of these subclasses.

The

CNKMemoryBuf class implements a CNKBuf with a FIFO buffer of

rows in memory. Procs must write and read rows sequentially to a

CNKMemoryBuf, as described above. The only method specific to a

CNKMemoryBuf is the constructor:

CNKMemoryBuf::

CNKMemoryBuf();

The CNKBackingFileBuf class implements a CNKBuf with an associated

file that contains the data in the buffer. It can be used to support

procs that need to read their input data multiple times, or in random

access order. This class is described in more detail below.

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