EDOBE XDOM PMML Manual do Utilizador descarregar pdf (Página 72)

CNKBuf will call CNKBufReader::getEOF() to check whether there EOF

has been set.

CNKBuf::getEOF() gives the same information: it

returns true (non-zero) if the

EOF flag has been set for the CNKBuf.

CNKBuf::

virtual INT64 getTotalNumRows();

If the CNKBuf knows the total number of rows in its data set (it has

reached the

EOF of a sequential stream, or it has a backing file), then

this method returns the total number of rows. If it doesn't know this

information, it returns

-1.

CNKBuf::

virtual long getMinRowsToAvoidDeadlock();

virtual int isDeadlockPossible();

When a CNKProc is executed, it reads data rows from one or more

input

CNKBufReader objects, and writes data rows to one or more

CNKBufWriter objects. Before reading and writing these rows, it must

request a certain amount of rows, by calling

CNKBufReader::setRequestRows or CNKBufWriter::setRequestRows, as

described below.

When calling the

setRequestRows methods, a CNKProc should not ask

for more rows than the size of the

CNKBuf, since this request can never

be satisfied. This is not enough, though. There is another situation

where a problem can occur, even if the request is for fewer rows than

the size of the

CNKBuf.

Suppose that a

CNKBuf has 100 rows. Further suppose that this CNKBuf

has one

CNKProc that wants to write 60 rows at a time, and another

CNKProc that wants to read 80 rows at a time. When the pipeline is

executed, the writing

CNKProc requests space for writing 60 rows, the

request is satisfied (there are 100 free rows), and the 60 rows are

written. Now, there is a problem. The reading

CNKProc will request

80 rows, but this cannot be satisfied: there are only 60 rows available

to read. The writing

CNKProc will request space for writing an

additional 60 rows, but this cannot be satisfied: there are only 40

available rows. Therefore, both the reading and the writing

CNKProc

will wait forever for their row requests to be satisfied. This is a

deadlock.

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