table - Constructor

Construct table tool

Synopsis
table(tablename, tabledesc, nrow, readonly, lockoptions, ack, dminfo, endian, memorytable, tableserver, tablenote, handle)

Description
Use this constructor to construct a table tool inside Glish from the name of a disk file containing an AIPS++ Table. A new table may also be created from a table descriptor (see tablecreatedesc). When creating a new table, detailed data manager information can be given using the dminfo argument. This is a record as returned by the getdminfo function.

Most of the arguments are rarely used: most of the time, you'll just need to use the tablename, and perhaps readonly.

A table can be shared by multiple processes by using the appropriate locking options. The possible options are:
- auto: let the system take care of locking. At regular time intervals these autolocks are released to give other processes the opportunity to access the table. The aipsrc variable
table.relinquish.reqautolocks.interval defines the number of seconds between releasing autolocks on tables needed in another process.
table.relinquish.allautolocks.interval defines the number of seconds between releasing all autolocks.
- autonoread: as auto, but no read locking is needed. This must be used with care, because it means that reading can be done while the table tool is not synchronized with the table file (as is normally done when a lock is acquired). The function resync can be used to explicitly synchronize the table tool
- user: the user takes care by explicit calls to lock and unlock
- usernoread: as user and the no readlocking behaviour of autonoread.
- permanent: use a permanent lock; the constructor fails when the table is already in use in another process
- permanentwait: as above, but wait until the other process releases its lock
- default: this is the default option. If the given table is already open, the locking option in use is not changed. Otherwise it reverts to auto.
When auto locking is used, it is possible to give a record containing the fields option, interval, and/or maxwait. In this way advanced users have full control over the locking options. In practice this is hardly ever needed.

When creating a new table, the endian format in which the data should be stored, can be specified. The possible values are:
- big: big endian format (as used on e.g. SUN)
- little: little endian format (as used on e.g. PC)
- local: use the endian format of the machine being used
- aipsrc: use the endian format specified in aipsrc variable table.endianformat (which defaults to big).
The default is aipsrc.
Note that usually it is best to store data in local endian format, because that requires the least amount of byte swapping. However, if the table must be accessible with AIPS++ version 1.7 or before, big endian should be used.

When creating a new table, the table will normally reside on disk. It is, however, possible to specify that the table should be held in memory. In such a case the table is process specific, thus cannot be seen by other processes. Note that a memory table uses the MemoryStMan storage manager for all its stored columns, but it is still possible to use virtual columns as well.

Arguments

tablename	in	Name of table on disk
		Allowed:	String\|Bool
		Default:	F
tabledesc	in	Table descriptor
		Allowed:	Descriptor\|Bool
		Default:	F
nrow	in	Number of rows
		Allowed:	Int
		Default:	0
readonly	in	Open Read-only?
		Allowed:	Bool
		Default:	T
lockoptions	in	locking to be used
		Allowed:	String\|Record
		Default:	default
ack	in	Acknowledge creations, etc
		Allowed:	Bool
		Default:	T
dminfo	in	Data manager info for new table
		Allowed:	Record
		Default:	F
endian	in	Endian format of new table
		Allowed:	String
		Default:	aipsrc
memorytable	in	Hold new table in memory?
		Allowed:	Bool
		Default:	F
tableserver	in	Table handler to be used
		Allowed:	Any tableserver
		Default:	defaulttableserver
tablenote	in	note function to be used
		Allowed:	Any note function
		Default:	note
handle	in	attach to this table handle
		Allowed:	for internal use only
		Default:	F

Returns
table tool

Example

  table1:=table("3C273XC1.MS");
  table1.browse();

The first line opens an existing table 3C273XC1.MS, the second browses it using the browse tool function.

  table2:=table("name", readonly=F, lockoptions='user', endian='local');
  table2.lock();
  table2.addRows();
  table2.unlock();

In this example explicit user locking is used. The function lock is needed to acquire a (write) lock before the addRows is done. Thereafter the lock is released to give other processes the chance to operate on the table.
Note that releasing a lock implies flushing the table, so doing that very often can be quite expensive.

Next: tablefromfits - Constructor Up: table - Tool Previous: table - Tool Contents Index

	Package	utility
	Module	table
	Tool	table