Globus XIO is an extensible input/output library written in C for the Globus Toolkit. It provides a single API (open/close/read/write) that supports multiple wire protocols, with protocol implementations encapsulated as drivers. The XIO drivers distributed with 4.2.0 include TCP, UDP, file, HTTP, GSI, GSSAPI_FTP, TELNET and queuing. In addition, Globus XIO provides a driver development interface for use by protocol developers. This interface allows the developer to concentrate on writing protocol code rather than infrastructure, as XIO provides a framework for error handling, asynchronous message delivery, timeouts, etc. The XIO driver-based approach maximizes the reuse of code by supporting the notion of a driver stack. XIO drivers can be written as atomic units and stacked on top of one another. This modularization provides maximum flexibility and simplifies the design and evaluation of individual protocols.

Features new in release 4.2.0

Other Supported Features

Deprecated Features

The only significant change to Globus XIO in this release is the addition of "string attributes". The previous method of handling attributes still works in an entirely backward compatible way, but the string attributes adds a much needed convenience. Drivers can now provide a list of key=value pairs. A user can then specify these options at the command line and at runtime. This makes run time configuration much more flexible.

A driver can choose to expose parameters in a string form. This feature makes dynamically setting driver-specific options much easier. A user can then load the driver by name and set specific options by name all at runtime with no object module references. For example, a TCP driver can be loaded with the string tcp and the options can be set with the string port=50668;keepalive=yes;nodelay=N.

This would set the port to 50668, keepalive to true and nodelay to false. The particular string definition is defined by the TCP driver. This is done by creating a globus_i_xio_attr_parse_table_t array within the driver's source code. See the TCP driver source code for an example. Each row of the array is 1 option. There are 3 sub-members of each row entry: key, cmd, and parse function. The key is a string that defines what option is to be set. In the above example, string port would be a key. cmd tells the driver what cntl is associated with the key. In other words, once the string is parsed out it converts the key into a driver-specific control enum. XIO then uses that enum as it would if a driver-specific option was set in the source code. For more information on controls, see globus_xio_attr_cntl.

The following problems and limitations are known to exist for XIO at the time of the 4.2.0 release:

XIO depends on the following GT components:

Tested Platforms for XIO:

Protocol changes since GT version 4.0.x

API changes since GT version 4.0.x

Adoption of standards in XIO is determined by the drivers. All drivers distributed by XIO are compliant with the protocol they implement.

See XIO for more information about this component.